ccna exp 2 - routing protocols and concepts

Introduction to Routing and Packet Forwardingg

Chapter 1: Routing Protocols and Concepts

Modified by Hasimi Sallehudin

1Institut Tadbiran Awam Negara© 2010 Cisco Systems, Inc. All rights reserved.

Objectives

Identify a router as a computer with an OS and de y a ou e as a co pu e a OS a dhardware designed for the routing process.

Demonstrate the ability to configure devices andDemonstrate the ability to configure devices and apply addresses.

Describe the structure of a routing tableDescribe the structure of a routing table.

Describe how a router determines a path and switches packetsswitches packets

2© 2010 Cisco Systems, Inc. All rights reserved. Institut Tadbiran Awam Negara

Router as a Computer

Describe the basic purpose of a routeresc be e bas c pu pose o a ou e-Computers that specialize in sending packets over the data network. They are responsible for interconnecting networks by selecting the best path for a packet to travel and forwarding packets to their destination

Routers have many of the same hardware and software components that are found in other computers p pincluding:

–CPU–RAM–ROM


–Operating System


Router components and their functions”pCPU - Executes operating system instructions

such as system initialization, routing functions, and switching functions.Random access memory (RAM) RAM stores the instructions and data neededRandom access memory (RAM) -RAM stores the instructions and data needed

to be executed by the CPU. RAM is used to store these components:–Operating System: The Cisco IOS (Internetwork Operating System) is copied into RAM during bootup.g p–Running Configuration File: This is the configuration file that stores the configuration commands that the router IOS is currently using.–IP Routing Table: This file stores information about directly connected and g yremote networks. It is used to determine the best path to forward the packet.–ARP Cache: This cache contains the IPv4 address to MAC address mappings, similar to the ARP cache on a PC. The ARP cache is used on

h h LAN i f h E h i frouters that have LAN interfaces such as Ethernet interfaces.–Packet Buffer: Packets are temporarily stored in a buffer when received on an interface or before they exit an interface.


RAM is volatile memory and loses its content when the router is powered down or restarted.


Router components and their functions”ou e co po e s a d e u c o sRead-only memory (ROM) - Holds diagnostic software used

when router is powered up. Stores the router’s bootstrap program.p g

–ROM is a form of permanent storage. Cisco devices use ROM to store:

–The bootstrap instructions–Basic diagnostic software–Scaled-down version of IOS–Scaled-down version of IOS

ROM uses firmware, which is software that is embedded inside the integrated circuit.

– Firmware includes the software that does not normally need to be modified or upgraded, such as the bootup instructions. – ROM does not lose its contents when the router loses power


or is restarted.

R t C tRouter as a ComputerRouter components and their functions”

Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP addresses (Routing protocol Hostname of router)addresses (Routing protocol, Hostname of router)

NVRAM (Nonvolatile RAM) does not lose its information when power is turned off. This is in contrast to the most common forms of RAM, such as DRAM, that requires continual power to maintain its information. NVRAM is used by the Cisco IOS as permanent storage for the startup configuration fileNVRAM is used by the Cisco IOS as permanent storage for the startup configuration file.

All configuration changes are stored in the running-config file in RAM, and with few exceptions, are implemented immediately by the IOS. To save those changes in case the router is restarted or loses power, the running-config

must be copied to NVRAM where it is stored as the startup-config file NVRAM retains itsmust be copied to NVRAM, where it is stored as the startup-config file. NVRAM retains its contents even when the router reloads or is powered off.

Flash memory - Contains the operating system (Cisco IOS)In most models of Cisco routers, the IOS is permanently stored in flash

memory and copied into RAM during the bootup process, where it is then executed by the CPU. Flash consists of SIMMs or PCMCIA cards, which can be upgraded to

increase the amount of flash memoryincrease the amount of flash memory.Interfaces - There exist multiple physical interfaces that are used to connect network.

Examples of interface types:-Ethernet / fast Ethernet interfaces


-Serial interfaces-Management interfaces


Router componentsou e co po e s


Internetwork Operating System

The operating system software used in Cisco routers is known as Cisco Internetwork Operating System (IOS)Internetwork Operating System (IOS).

– Cisco IOS is a multitasking operating system that is integrated with routing, switching, internetworking, and telecommunications functions.

Although the Cisco IOS may appear to be the same on many routers,Although the Cisco IOS may appear to be the same on many routers, there are many different IOS images.

– An IOS image is a file that contains the entire IOS for that router. Cisco creates many different types of IOS images, depending upon the model of the router and the features within the IOS.the router and the features within the IOS. – Typically the more features in the IOS, the larger the IOS image, and therefore, the more flash and RAM that is required to store and load the IOS.

Although some routers provide a graphical user interface (GUI), the d li i t f (CLI) i h th d fcommand line interface (CLI) is a much more common method of

configuring Cisco routers. – The CLI is used throughout this curriculum.

Upon bootup the startup config file in NVRAM is copied into RAM andUpon bootup, the startup-config file in NVRAM is copied into RAM and stored as the running-config file.

– IOS executes the configuration commands in the running-config. Any changes entered by the network administrator are stored in the running-config and are immediately implemented by the IOS


config and are immediately implemented by the IOS.

Overview - Managing Cisco IOS Software (cont)Overview Managing Cisco IOS Software (cont)



Major phases to the ajo p ases o erouter boot-up process

Test router hardwarePower-On Self Test (POST)Execute bootstrap loaderp

Locate & load Cisco IOS software

Locate IOS-Locate IOS-Load IOS

Locate & load startup configuration file or enter setup mode

-Bootstrap program looks


p p gfor configuration file

Stages of the router power-on boot sequence


R t C tRouter as a ComputerMajor phases to the router boot-up process

Step 1 and 2: Test router hardwareP O S lf T t (POST)•Power-On Self Test (POST)

–During this self-test, the router executes diagnostics from ROM on several hardware components including the CPU, RAM, and NVRAM

•Execute bootstrap loader–The main task of the bootstrap program is to locate the Cisco IOS and load it into RAM.–Note: At this point, if you have a console connection to the router, you will begin to see output on the screen.

Step 3 and 4: Locate & load Cisco IOS softwareLocate IOS and Load IOS-Locate IOS and Load IOS

–The IOS is typically stored in flash memory, but can also be stored in other places such as a TFTP server.–If a full IOS image can not be located, a g ,scaled-down version of the IOS is copied from ROM into RAM. This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM.


–Note: A TFTP server is usually used as a backup server for IOS but it can also be used as a central point for storing and loading the IOS.

R t C tRouter as a ComputerStep 5 and 6: Locate & load startup configuration file or enter setup

mode

-After the IOS is loaded, the bootstrap program searches for the startup configuration file, known as startup-config, in NVRAM. This parameters including:

•interface addressesinterface addresses•routing information•passwords•any other configurationsy g

–If the startup-config, is located in NVRAM, it is copied into RAM as the running-config.

•The IOS loads the commands in the file, one line at a timetime.

–If the startup configuration file does not exist in NVRAM, the router may search for a TFTP server.

• If the router detects that it has an active link to another configured router, it sends a broadcast searching for a configuration file across the active link. You will eventually see message like the following one:•%Error opening tftp://255.255.255.255/network-confg


%Error opening tftp://255.255.255.255/network confg (Timed out)•%Error opening tftp://255.255.255.255/cisconet.cfg (Timed out)

Router as a ComputerRouter as a ComputerLocate & load startup configuration file or enter setup mode

–Enter Setup Mode (Optional). If the startup configuration file can not be located the routerconfiguration file can not be located, the router prompts the user to enter setup mode.

•Setup mode is a series of questions prompting the user for basic configuration information. Setup mode is not intended to be used to enter complex router configurations and it is notcomplex router configurations, and it is not commonly used by network administrators.

–When booting a router that does not contain a startup configuration file, you will see the following question after the IOS has been loaded:

•Would you like to enter the initial configuration dialog? [yes/no]: no

–Setup mode will not be used in this course to configure the router. When prompted to enter setup mode, always answer no. If you e te setup ode, a ays a s e o youanswer yes and enter setup mode, you can press Ctrl-C at any time to terminate the setup process.

–When setup mode is not used, the IOS creates a default running-config.default running config.

•The default running-config is a basic configuration file that includes the router interfaces, management interfaces, and certain default information. Th d f lt i fi d t t i


•The default running-config does not contain any interface addresses, routing information, passwords, or other specific configuration information.


Verify the router boot-up process:

show version

-The show version command is used to view information about the router during the bootup process. Information includes:Information includes:

Image name & IOS versionIOS (tm) C2600 Software (C2600 I M) V i 12 2(28)(C2600-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5).

Bootstrap version stored in ROMO SROM: System Bootstrap,

Version 12.1(3r)T2, RELEASE SOFTWARE (fc1)

Image file name & where it wasImage file name & where it was loaded from

System image file is "flash:c2600-i-mz 122-28 bin"


flash:c2600 i mz.122 28.bin


Verify the router boot-up process:show version

Platform model number CPUAmount of RAMAmount of RAM

Some series of routers, like the 2600, use a fraction of DRAM as packet memory. Packet memory is

d f b ff i k tused for buffering packets.To determine the total amount of

DRAM on the router, add both numbers. In this example, the Cisconumbers. In this example, the Cisco 2621 router has 60,416 KB (kilobytes) of free DRAM used for temporarily storing the Cisco IOS and other system processes. The y pother 5,120 KB is dedicated for packet memory. The sum of these numbers is 65,536K, or 64 megabytes (MB) of total DRAM.



Verify the router boot-up process:show version

Number & type of interfaces2 FastEthernet/IEEE 802.3 interface(s)2 Low-speed serial(sync/async) network interface(s)

Amount of NVRAM32K bytes of non-volatile

configuration memory.NVRAM is used to store the

startup config filestartup-config file.Amount of flash

16384K bytes of processor board System flash (Read/Write)System flash (Read/Write)This is the amount of flash memory

on the router. Flash is used to permanently store the Cisco IOS.



Configuration register

show version

Configuration register is 0x2102–The last line of the show version command displays the current

fi d l f th ftconfigured value of the software configuration register in hexadecimal. If there is a second value displayed in parentheses, it denotes the configuration registerdenotes the configuration register value that will be used during the next reload.–The configuration register has

l i l di dg g

several uses, including password recovery. The factory default setting for the configuration register is 0x2102. This value indicates that th t ill tt t t l dthe router will attempt to load a Cisco IOS software image from flash memory and load the startup configuration file from NVRAM.


–Note: The configuration register is discussed in more detail in a later course.

C fi ti i tConfiguration register The order in which the router looks for system bootstrap depends on the boot field setting in the configuration register.g g

The default configuration register setting can be changed with the global configuration mode command config-register. Use a hexadecimal number as the argument for this command.command.

The configuration register is a 16-bit register in NVRAM.

The lowest four bits of the configuration register form the boot field. To ensure that the upper 12 bits are not changed, first retrieve the current values of the configuration register using the show version command. Then use the config-register command, changing only the value of the last hexadecimal digit.


Configuration register (cont )Configuration register (cont.)To enter the ROM monitor mode, set the configuration register value to 0xnnn0,

where nnn represents the previous value of the non-boot field di itdigits. This value sets the boot field bits to 0000 binary. From ROM monitor, boot the operating system manually by using the b command at the ROM monitor prompt.

To configure the system to boot automatically from ROMTo configure the system to boot automatically from ROM, set the configuration register to 0xnnn1,

This value sets the boot field bits to 0001 binary.

To configure the system to use the boot system commands in NVRAM set the configuration register tocommands in NVRAM, set the configuration register to any value from 0xnnn2 to 0xnnnF,

These values set the boot field bits to a value between 0010 and 1111 binary. Using boot system commands in NVRAM is the default.

Check Configuration Register value (NVRAM)

0 = ROM Monitor mode

1 = ROM IOS


1 ROM IOS

2 - 15 = Boot system from Flash

How a Cisco device locates and loads IOS The config-register can be Downloaded from:http:// lilligren com/cisco/do nloads htmDemo

config-register

http://www.lilligren.com/cisco/downloads.htm


Configuration register: 0, 1, and 2 and above


Configuration register: 2102 and 2142Configuration register: 2102 and 2142


Configuration registerConfiguration register Router(config)#config-register value1 2

3


Stages of the router power-on boot sequenceStages of the router power-on boot sequence 1. ROM

1. POST

2. Bootstrap code executed

1, 2

3. Check Configuration Register value (NVRAM)

0 = ROM Monitor mode

1 = ROM IOS

2 - 15 = Boot system from flash

3

42. Check for IOS boot system commands in startup-config file (NVRAM)

If boot system commands in startup-config

a. Run boot system commands in order they appear in startup-config to locate the IOS

4

b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)

3. Locate and load IOS, Default fallback sequence: No IOS boot system commands in startup-config

a. Flash (sequential)

b. TFTP server (netboot) - The router uses the configuration register value to form a filename from which to boot a default system image stored on a network server.

c. ROM (partial IOS) or keep retrying TFTP depending upon router model

- If no IOS located, get partial IOS version from ROM

4. Locate and load startup-configa. If startup-config found, copy to running-config

b. If startup-config not found, prompt for setup-mode

c If setup mode bypassed create a “skeleton” default running config (no startup config)


c. If setup-mode bypassed, create a skeleton default running-config (no startup-config)

How a Cisco device locates and loads IOSHow a Cisco device locates and loads IOS The router can use its own fallback sequence to load the software. q

The router looks to the boot system commands saved in NVRAM.(Tony) The router has its own default fallback sequence This default sequencefallback sequence. This default sequence can be interrupted by using the boot system command and/or config register.

The settings in the configuration register g g genable the following alternatives:

Global configuration mode boot system commands can be specified to enter fallback sources.fallback sources. If NVRAM lacks boot system commandsthe system by default uses the Cisco IOS software in flash memory.

(T ) N b t t d(Tony) No boot system commands(Tony) IOS specified in the boot system does not exist

If flash memory is empty, the router then


If flash memory is empty, the router then attempts to use TFTP to load an IOS image from the network.

How a Cisco device locates and loads IOS


U i th b t t dUsing the boot system command The three examples show boot system entries which specify that a Cisco IOS

ft i ill l dsoftware image will load First from flash memory,

Flash memory – A system image from flash memory can be loadedflash memory can be loaded.

Then from a network server, andNetwork server – In case flash memory becomes corrupted, a system i b l d d f TFTPimage can be loaded from a TFTP server.

Finally from ROM: ROM – If flash memory is corruptedROM If flash memory is corrupted and the network server fails to load the image, booting from ROM is the final bootstrap option in software. However the system image in ROM isHowever, the system image in ROM is a subset of the Cisco IOS that lacks the protocols, features of the full Cisco IOS.Also, if the software has been updated, the router may have an older version


the router may have an older version stored in ROM.•The command copy running-config startup-config saves the commands in NVRAM.

How a Cisco device locates and loads IOS

• What happen when both config-register and boot• What happen when both config-register and boot system both exist in the startup-config?

• Which one has the priority?p y


Management Ports

Routers have physical connectors that are d t th t Th tused to manage the router. These connectors

are known as management ports. –Unlike Ethernet and serial interfaces, management ports are not used for packet f diforwarding.

The most common management port is the console port.

The console port is used to connect a terminal–The console port is used to connect a terminal, or most often a PC running terminal emulator software, to configure the router without the need for network access to that router. –The console port must be used during initialThe console port must be used during initial configuration of the router.

Another management port is the auxiliary port. –Not all routers have auxiliary ports. y p–At times the auxiliary port can be used in ways similar to a console port. It can also be used to attach a modem. –Auxiliary ports will not be used in this


Auxiliary ports will not be used in this curriculum.

Routers determine the best path

Router Interface is a physical connector that enables a router to send or receive packets

–Each interface connects to a separate network•different IP network•different IP network

Typically, the interfaces connect to various types of networks, which means that different yptypes of media and connectors are required. Types of router interfaces:

-EthernetEthernet-Fastethernet-Serial-DSL-ISDNCable


-Cable

Two major groups of Router Interfaces: LAN & WANLAN Interfaces: such as Ethernet and FastEthernet

Are used to connect router to LAN networkHas a layer 2 MAC address

a router Ethernet interface participates in the ARP process for that LAN.

Can be assigned a Layer 3 IP addressCan be assigned a Layer 3 IP addressUsually consist of an RJ-45 jack

When a router is connected to a switch a straight-through cable isswitch, a straight through cable is used. When two routers are connected

directly through the Ethernet interfaces or when a PC NIC isinterfaces, or when a PC NIC is connected directly to a router Ethernet interface, a crossovercable is used.


f f &Two major groups of Router Interfaces: LAN & WANWAN Interfaces- such as serial, ISDN, and F R lFrame Relay

Are used to connect routers to external networks that interconnect LANs, usually over a larger geographical distance..Depending on the WAN technology, a p g gy,

layer 2 address may be used.Uses a layer 3 IP address

Similar to LAN interfaces each WANSimilar to LAN interfaces, each WAN interface has its own IP address and subnet mask, which identifies it as a member of a specific network.

The Layer 2 encapsulation can be of different types,

PPP, Frame Relay, and HDLC (High-


, y, ( gLevel Data Link Control).

f f &Two major groups of Router Interfaces: LAN & WANThe router in the figure has four i t finterfaces.

–Each interface has a Layer 3 IP address and subnet mask that configures it for a different network. –The Ethernet interfaces also have Layer 2 Ethernet MAC addresses.

The WAN interfaces are using different Layer 2 encapsulations.

S 0/0/0 C–Serial 0/0/0 is using HDLC –Serial 0/0/1 is using PPP. –Both of these serial point-to-pointBoth of these serial point to point protocols use a broadcast address for the Layer 2 destination address when encapsulating the IP packet into a data link


frame.


A router connects multiple networks. pThis means that it has multiple interfaces that each belong to a

different IP network. When a router receives an IP packet on one interface itWhen a router receives an IP packet on one interface, it

determines which interface to use to forward the packet onto its destination. The interface that the ro ter ses to for ard the packet ma beThe interface that the router uses to forward the packet may be

the network of the final destination of the packet (the network with the destination IP address of this packet), or it may be a network connected to another router that is used to reach the destinationconnected to another router that is used to reach the destination network.

Routers are the network center-Routers generally have 2 connections:

-WAN connection (Connection to ISP)


-LAN connection


Routers examine a packet’s destination IP address and ou e s e a e a pac e s des a o add ess a ddetermine the best path by enlisting the aid of a routing table



The primary responsibility of a router is to direct packets destined for local and remote networks by:and remote networks by:

–Determining the best path to send packets –Forwarding packets toward their destination

The router uses its routing table to determine the best path to forward theThe router uses its routing table to determine the best path to forward the packet.

–When the router receives a packet, it examines its destination IP address and searches for the best match with a network address in the router's routing table. –The routing table also includes the interface to be used to forward the packet. Once a match is found, the router encapsulates the IP packet into the data link frame of the outgoing or exit interface, and the packet is then forwarded toward its destination.

It is very likely that a router will receive a packet that is encapsulated in one type of data link frame, such as an Ethernet frame and when forwarding the packet, the router will encapsulate it in a different type of data link



Routers Operate at Layers 1, 2 & 3ou e s Ope a e a aye s , & 3–A router makes its primary forwarding decision at Layer 3, but as we saw earlier, it participates in Layer 1 and Layer 2participates in Layer 1 and Layer 2 processes as well. Router receives a stream of encoded bitsBits are decoded and passed to layer 2Router de-encapsulates the frameRemaining packet passed up to layer 3

-Routing decision made at this layer by examining destination IP addressexamining destination IP address

Packet is then re-encapsulated & sent out outbound interface



PC1 operates at all seven layers, encapsulating the data and sending the frame out as a stream of encoded bits to R1 its default gatewayof encoded bits to R1, its default gateway.

R1 receives the stream of encoded bits on its interface. The bits are decoded and passed up to Layer 2, where R1 decapsulates the frame. The router examines the destination address of the data link frame to determine if it matches the receiving interface, including a broadcast or multicast address. If there is a match with the data portion of the frame, the IP packet is passed up to Layer 3, where R1 makes its routing decision. R1 then re-encapsulates the packet into a new Layer 2 data link frame and forwards it out the outbound interface as a stream of encoded bits.

R2 receives the stream of bits, and the process repeats itself. R2 decapsulates the frame and passes the data portion of the frame, the IP packet, to Layer 3 where R2 makes its routing decision. R2 then re-encapsulates the packet into a new Layer 2 data link frame and forwards it out the outbound interface as a stream of encoded bits.

This process is repeated once again by router R3, which forwards the IP packet, encapsulated inside a data link frame and encoded as bits, to PC2.


Configure Devices and Apply Addresses

Implementing Basic Addressing Schemesp e e g as c dd ess g Sc e es

When designing a new network or mapping an existing network you must provide the following information innetwork you must provide the following information in the form of a document:

-Topology drawing that Illustrates physical connectivityp gy g p y y–Address table that provides the following information:

Device nameInterfaces usedIP addressesDefault gateway



Basic Router ConfigurationA basic router configuration should contain the following:

-Router name - Host name should be uniqueBanner At a minimum banner should warn against unauthorized use-Banner - At a minimum, banner should warn against unauthorized use

-Passwords - Use strong passwords-Interface configurations –

•Specify interface type, •IP address and subnet mask. •Describe purpose of interface. •Issue no shutdown command. •If DCE serial interface issue clock rate command.

After entering in the basic configuration the following tasks should beAfter entering in the basic configuration the following tasks should be completed

-Verify basic configuration and router operations. -Save the changes on a router


-Save the changes on a router


brief review from CCNA1Router>Router>enableRouter#Router#config t Router(config)#enable secret classRouter(config)#enable password ciscoRouter(config)#hostname R1R1(config)#R1( fi )#li l 0R1(config)#line console 0 R1(config-line)#password ciscoR1(config-line)#login R1(config-line)#exitR1(config-line)#exit R1(config)#line vty 0 4R1(config-line)#password ciscoR1(config-line)#login


( g ) gR1(config-line)#exit


brief review from CCNA1Configuring a Banner

From the global configuration mode, configure the

brief review from CCNA1

message-of-the-day (motd) banner. A delimiting character, such as a "#" is used at the beginning and at the end of the message. The delimiter allows you to configure a multiline banner, as shown here.

R1(config)#banner motd #

Enter TEXT message. End with the character '#'.

******************************************

WARNING!! Unauthorized Access Prohibited!!

******************************************

#

Configuring an appropriate banner is part of a good security plan. At a very minimum, a banner should warn against unauthorized access. Never configure a


banner that "welcomes" an unauthorized user.

Limiting Device Access Enable and Enable Secret PasswordsLimiting Device Access – Enable and Enable Secret Passwords To provide additional security, use enable passwordor enable secret command to establish

h i i b f i i il d EXECauthentication before accessing privileged EXEC (enable) mode.

Always use the enable secret command, not the older bl d d if iblenable password command, if possible.

The following commands are used to set the passwords:

Router(config)#enable password passwordRouter(config)#enable secret password

If no enable password or enable secret password isIf no enable password or enable secret password is set, the IOS prevents privileged EXEC access from a Telnet session.

Without an enable password having been set a TelnetWithout an enable password having been set, a Telnet session would appear this way:

Switch>enable% No password set


% No password setSwitch>

Limiting Device Access Enable and Enable Secret PasswordsLimiting Device Access – Enable and Enable Secret Passwords Example of enable password and enable secret:


Limiting Device Access – VTY PasswordLimiting Device Access VTY PasswordThe vty lines allow access to a router via Telnet.

By default, many Cisco devices support 5 VTY lines that are b d 0 t 4numbered 0 to 4.

A password needs to be set for all available vty lines. The same password can be set for all connections. However it is often desirable that a unique password be set forHowever, it is often desirable that a unique password be set for one line to provide a fall-back for administrative entry to the device if the other connections are in use.

The following commands are used to set a password: g pRouter(config)#line vty 0 4Router(config-line)#password passwordRouter(config-line)#login

By default, the IOS includes the login command on the VTY lines. This prevents Telnet access to the device without first requiring authentication.

If, by mistake, the no login command is set, which removes the requirement for authentication, unauthorized persons could connect to the line using Telnet. This would be a major security risk.


Encrypting Password DisplayEncrypting Password DisplayAnother useful command prevents passwords from showing up as plain text when viewing the

fi i filconfiguration files. This is the service password-encryption command. This command causes the encryption of passwords to occur when a password is configured.

The service password-encryption command applies weak encryption to all unencrypted passwords. yp yp p

This encryption does not apply to passwords as they are sent over media only in the configuration. The purpose of this command is to keep unauthorized p p pindividuals from viewing passwords in the configuration file.

Once the encryption has been applied, removing the yp pp , gencryption service does not reverse the encryption.


Configuring router passwords (cont )Configuring router passwords (cont.)

WARNINGservice password-encryption uses a Cisco Level 7 encryption which is very easy to decrypt.

For the GetPass! software www.boson.com

However, the enable secret <password> uses a stronger encryption method and cannot be easily hacked.


and !

Configuring router passwords (cont.)g g ( )

Doesn’t work for enable secret!



R1(config)#interface Serial0/0/0R1(config)#interface Serial0/0/0R1(config-if)#ip address 192.168.2.1 255.255.255.0R1(config-if)#description Ciruit#VBN32696-123 (help desk:1-800-555-1234)R1(config-if)#no shutdownR1(config-if)#clock rate 64000

Note: When cabling a point-to-point serial link in our lab environment, one end ofNote: When cabling a point to point serial link in our lab environment, one end of the cable is marked DTE and the other end is marked DCE. The router that has the DCE end of the cable connected to its serial interface will need the additional clock rate command configured on that serial interface.This step is only necessary in a lab environmentThis step is only necessary in a lab environment



th F tEth t i t f d t b fi dthe FastEthernet interface needs to be configuredR1(config)#interface FastEthernet0/0R1( fi if)#i dd 192 168 1 1 255 255 255 0R1(config-if)#ip address 192.168.1.1 255.255.255.0R1(config-if)#description R1 LANR1(config if)#no shutdownR1(config-if)#no shutdown



Each interface must belong to a different network. Alth h th IOS ll t fi IP dd–Although the IOS allows you to configure an IP address

from the same network on two different interfaces, the router will not activate the second interface. –For example, what if you attempt to configure the FastEthernet 0/1 interface on R1 with an IP address on the 192 168 1 0/24 t k? F tEth t 0/0 h l d b192.168.1.0/24 network? FastEthernet 0/0 has already been assigned an address on that same network. you will get the following message:

R1(config)#interface FastEthernet0/1R1(config-if)#ip address 192 168 1 2 255 255 255 0R1(config-if)#ip address 192.168.1.2 255.255.255.0192.168.1.0 overlaps with FastEthernet0/0

–If there is an attempt to enable the interface with the no shutdown command, the following message will appear:

R1(config-if)#no shutdownR1(config-if)#no shutdown192.168.1.0 overlaps with FastEthernet0/0FastEthernet0/1: incorrect IP address assignment

The output from the show ip interface brief command shows that the second interface configured for the 192.168.1.0/24 network, FastEthernet 0/1, is still down. R1#show ip interface brief


R1#show ip interface brief<output omitted>FastEthernet0/1 192.168.1.2 YES manual administratively down down


Verify Basic Router Configuratione y as c ou e Co gu a o-Issue the show running-config command

•displays the current running configuration that is stored in RAM.

-Issuing the copy running-config startup-config command •Save the basic router configuration

-Additional commands that will enable you to further verify router configuration are:

Show startup-config - Displays configuration file NVRAMShow startup config Displays configuration file NVRAMShow IP route - Displays routing tableShow interfaces - Displays all interface configurationsp y gShow IP int brief - Displays abbreviated interface

configuration information


SRouting Table StructureThe primary function of a router is to forward a packet toward its destination network which is the destination IP address of the packetdestination network, which is the destination IP address of the packet.

–To do this, a router needs to search the routing information stored in its routing table.

Routing Table is stored in ram and contains information:Routing Table is stored in ram and contains information:Directly connected networks - this occurs when a device is connected to

another router interfaceR t l t d t k thi i t k th t i t di tlRemotely connected networks - this is a network that is not directly

connected to a particular routernetwork/next hop associations - about the networks include source of

i f ti t k dd & b t k d I dd f t hinformation, network address & subnet mask, and Ip address of next-hop router

Show ip route command is used to view a routing tablep g


Routing Table StructureThe network/exit-interface association can also represent the destination network address of the IP packet.

This association occurs on the router's directly connected networks.

A directly connected network is a network that is directly attached to one of the router interfaces.

When a router interface is configured with an IP address and subnet mask, the interfaceWhen a router interface is configured with an IP address and subnet mask, the interface becomes a host on that attached network. The network address and subnet mask of the interface, along with the interface type and number, are entered into the routing table as a directly connected network. When a router forwards a packet to a host, such as a web server, that host is on the same network as a router's directly connected network.

A remote network is a network that is not directly connected to the routerA remote network is a network that is not directly connected to the router. In other words, a remote network is a network that can only be reached by sending the packet to another router. Remote networks are added to the routing table using either a dynamic routing protocol or by configuring static routes. Dynamic routes are routes to remote networks that were learned automatically by the router, using a dynamic routing

t l St ti t t t t k th t t k d i i t t llprotocol. Static routes are routes to networks that a network administrator manually configured.


Routing Table Structure

As shown in the figure the routing table is displayed with the show ip route d At thi i t th h t b t ti t fi dcommand. At this point, there have not been any static routes configured

nor any dynamic routing protocol enabled. Therefore, the routing table for R1 only shows the router's directly connected networks. For each network listed in the routing table, the following information is included:g , g

–C - The information in this column denotes the source of the route information, directly connected network, static route or a dynamic routing protocol. The C represents a directly connected route.192 168 1 0/24 Thi i th t k dd d b t k f th di tl–192.168.1.0/24 - This is the network address and subnet mask of the directly

connected or remote network. In this example, both entries in the routing table, 192.168.1./24 and 192.168.2.0/24, are directly connected networks.–FastEthernet 0/0 - The information at the end of the route entry represents the y pexit interface and/or the IP address of the next-hop router. In this example, both FastEthernet 0/0 and Serial0/0/0 are the exit interfaces used to reach these networks.



PCs also have a routing table. Cs a so a e a ou g ab eIn the figure, you can see the route print command output. The command reveals the configured or acquired default gateway, connected loopback multicast and broadcast networksconnected, loopback, multicast, and broadcast networks. The output from route print command will not be analyzed during this course. It is shown here to emphasize the point that g p pall IP configured devices should have a routing table.



The following analogies may help clarify the concept of connected static andthe concept of connected, static, and dynamic routes:Directly Connected Routes - To visit a neighbor, you only have to go down the

hi h l d li Thig y y g

street on which you already live. This path is similar to a directly-connected route because the "destination" is available directly through your " t d i t f " th t t"connected interface," the street.Static Routes - A train uses the same railroad tracks every time for a specified route This path is similar to a staticroute. This path is similar to a static route because the path to the destination is always the same.Dynamic Routes - When driving a car,

"d i ll " hyou can "dynamically" choose a different path based on traffic, weather, or other conditions. This path is similar to a dynamic route because you can choose a new path at many different


choose a new path at many different points on your way to the destination.

Routing Table StructureRouting Table StructureAdding a connected network to the routing table

-Router interfacesEach router interface is a member of a different networkActivated using the no shutdown commandIn order for static and dynamic routes to exist in routingIn order for static and dynamic routes to exist in routing

table you must have directly connected networks



Remote networks are added to the routing table either by configuring static routes or enabling a dynamic routing protocol. g p

Static routes in the routing table-Includes: network address and subnet mask and IP address of next hop router or exit interface-Denoted with the code S in the routing table-Routing tables must contain directly connected networks used to connect remote networks before static or dynamic routing can be used



When to use static routes-When network only consists of a few routers

•Using a dynamic routing protocol in such a case does not present any substantialcase does not present any substantial benefit.

-Network is connected to internet only through one ISP

There is no need to use a dynamic routing• There is no need to use a dynamic routing protocol across this link because the ISP represents the only exit point to the Internet.

-Hub & spoke topology is used on a large networknetwork

•A hub-and-spoke topology consists of a central location (the hub) and multiple branch locations (spokes), with each spoke having only one connection to the hubonly one connection to the hub. •Using dynamic routing would be unnecessary because each branch has only one path to a given destination-through the central location


central location.


Dynamic routing protocols-Are used to add remote networks to a routing table-Are used to discover networks-Are used to update and maintain routing tables

Automatic network discovery–-Network discovery is the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol. –Instead of configuring static routes to remote networks on every router, a dynamic routing protocol allows the routers to automatically learn about these networks from other routers.–These networks - and the best path to each network - are added to the router's prouting table and denoted as a network learned by a specific dynamic routing protocol.

Maintaining routing tablesDynamic routing protocols are used to share routing information with other router & to-Dynamic routing protocols are used to share routing information with other router & to

maintain and up date their own routing table.–Dynamic routing protocols not only make a best path determination to various networks, they will also determine a new best path if the initial path becomes unusable (or if the topology changes)



•R1 has learned about two remote•R1 has learned about two remote networks:

•A route that dynamically used RIP •In the figure R1 has automatically•In the figure, R1 has automatically learned about the 192.168.4.0/24 network from R2 through the dynamic routing protocol, RIP (Routing g p , ( gInformation Protocol).

•A static route that was configured manually.

•This is an example of how routing tables can contain routes learned dynamically and configureddynamically and configured statically and is not necessarily representative of the best

fi ti f thi t k


configuration for this network.


IP routing protocols. Example of routing protocols include:g p p g p–RIP (Routing Information Protocol) - - CCNA–IGRP (Interior Gateway Routing Protocol) - - ignore it–EIGRP (Enhanced Interior Gateway Routing Protocol) - - CCNA & NP–OSPF (Open Shortest Path First) - - CCNA & CCNP–IS-IS (Intermediate System-to-Intermediate System) - - CCNP–BGP (Border Gateway Protocol) - - CCNP

RIP (versions 1 and 2), EIGRP, and OSPF are discussed in this course. EIGRP d OSPF l l i d i d t il i CCNP l ith IS IS d BGPand OSPF are also explained in more detail in CCNP, along with IS-IS and BGP.

IGRP is a legacy routing protocol and has been replaced by EIGRP. Both IGRP and EIGRP are Cisco proprietary routing protocols, whereas all other routing protocols listed are standard, non-proprietary protocols.


protocols listed are standard, non proprietary protocols.

Routing Table StructureRouting Table Principles

-3 principles regarding routing tables: Every router makes its decisions alone, based on the

information it has in its routing tableinformation it has in its routing table.Different routing table may contain different informationA routing table can tell how to get to a destination but not g g

how to get back (Asymmetric Routing)Routing information about a path from one network to another

does not provide routing information about the reverse ordoes not provide routing information about the reverse, or return, path.


Router Paths and Packet Switching

Internet Protocol (IP) packet format contains fields that e e o oco ( ) pac e o a co a s e ds aprovide information about the packet and the sending and receiving hosts

Fields that are importance for CCNA students:-Version

L 3-IP header length-TTL

Layer 3

-Precedence & type of service-Packet lengthS-Source IP address

-Destination IP address


The Layer 2 data link frame usually contains header information with a data link source and destination address, trailer information, and the actual transmitted d t

Router Paths and Packet Switchingdata.

–The data link source address is the Layer 2 address of the interface that sent the data link frame.

MAC Layer Frame FormatA k t i f d d f t t t th L 3 d d ti ti IPAs a packet is forwarded from router to router, the Layer 3 source and destination IP addresses will not change; however, the Layer 2 source and destination data link addresses will change.

MAC Frames are also divided into fields. They include:y-Preamble

•Seven bytes of alternating 1s and 0s, used to synchronize signals

-Start of frame delimiter1 b te signaling the beginning of the frame

Layer 2

•1 byte signaling the beginning of the frame

-Destination MAC address•6 byte

-Source MAC address•6 byte

-Type/length•2 byte

-Data and pad


Data and pad•46 to 1500 bytes of data; zeros used to pad any data packet less than 46 bytes

-Frame check sequence•4 byte

Ethernet frame fields (cont.) The original Ethernet standards defined the

i i f i 64 b t d thminimum frame size as 64-bytes and the maximum as 1518-bytes.

These numbers include all bytes from the Destination MAC Address field through the 10101011

A Start Frame Delimiterg

Frame Check Sequence field. The Preamble and Start Frame Delimiter fields are not included when quoting the size of a frame. z

10101011.

frame. z

The IEEE 802.3ac standard released in 1998 extended the maximum allowable frame size to 1522-bytes to allow a "VLAN tag" to be i t d i t th Eth t f f tinserted into the Ethernet frame format.


http://www.techfest.com/networking/lan/ethernet2.htm

• Peer to Peer Communication is really communication between the headers at each layer. Layers 2 and 3 are best effort or connectionless


• Layers 2 and 3 are best effort or connectionless.• Layer 4 Transport is connection oriented. The ‘connection’ is in the header.

Router Paths: Best PathWhenever multiple paths to reach the same network exist, each path uses a different exit interface on the router to reach that network.

– The best path is selected by a routing protocol based on the value or metric it uses to determine the distance to reach a networkto reach a network.

•Metrics can be based on either a single characteristic or several characteristics of a path. •Some routing protocols can base route selection g pon multiple metrics, combining them into a single metric. •The smaller the value of the metric, the better the pathpath.

–Routing protocols, such as RIP, use simple hop-count, which the number of routers between a router and the destination network.

• For example, a router will prefer a path that is 5 hops away over a path that is 10 hops away.

–Other routing protocols, such as OSPF, determine the shortest path by examining the bandwidth of the


the shortest path by examining the bandwidth of the links, and using the links with the fastest bandwidth from a router to the destination network.


A Metric is a numerical value used by routing protocols help determine the best path to a destinationbest path to a destination

–The smaller the metric value the better the path2 types of metrics used by routing protocols are:

Hop count this is the number of routers a packet must travel through to-Hop count - this is the number of routers a packet must travel through to get to its destination

• Hop count of four indicates that a packet must pass through four routers to reach its destination. • If multiple paths are available to a destination, the routing protocol, such as RIP, picks the path with the least number of hops.

-Bandwidth - this is the “speed” of a link also known as the data capacity of a linka link

•OSPF routing protocol uses bandwidth as its metric. The best path to a network is determined by the path with an accumulation of links that have the highest bandwidth values, or the fastest links.


Router Paths: Equal Cost Load BalancingYou may be wondering what happens if a routing table has two or more paths with the same metric to the sametwo or more paths with the same metric to the same destination network.

–When a router has multiple paths to a destination network and the value of that metric (hop count, bandwidth, etc.) is the same, this is known as an equal cost

t i d th t ill f l t l d b l imetric, and the router will perform equal cost load balancing.

Equal cost metric is a condition where a router has multiple paths to the same destination that all have the same metric

–The router will forward packets using the multiple exit interfaces listed in the routing table.


CRouter Paths: Equal Cost Load BalancingTo solve this dilemma, a router will use Equal Cost Load Balancing This means the router sends packets over the multipleBalancing. This means the router sends packets over the multiple exit interfaces listed in the routing table.

–per-packet load balancing•( Process Switching)

–per-destination load balancing. •(Fast Switching)•(Fast Switching)

Router(config-if)# ip route-cache Router(config-if)#no ip route-cache

ping 10.0.0.1ping 10.0.0.2ping 10.0.0.1ping 10.0.0.2


Load balancing with RIPLoad balancing with RIPdebug ip packet

IP k t d b i i

per-packet load balancingIP packet debugging is on

GAD#

*Mar 1 19:10:29.646: IP: tableid=0, s=192.168.14.2 (FastEthernet0/0), d=192.168.16.2 (Serial0/1), routed via RIB

*Mar 1 19:10:29.646: IP: s=192.168.14.2 (FastEthernet0/0), d=192.168.16.2 (Serial0/1), g=192.168.13.2, len 60, forward





*Mar 1 19:10:32.218: IP: s=0.0.0.0 (FastEthernet0/0), d=255.255.255.255, len 604, rcvd 2









*Mar 1 19:10:35.974: IP: s=192.168.13.1 (local), d=255.255.255.255 (Serial0/1), len 72, sending broad/multicast




( ), ( ), g , ,

http://www.cisco.com/en/US/products/ps5763/products_configuration_guide_chapter09186a00802a1fae.html#wp1045020RIB:

Router(config-if)#no ip route-cache


IP k d b i i

per-destination load balancingIP packet debugging is on

GAD#



*Mar 1 19:14:36.026: IP: tableid=0, s=192.168.16.2 (Serial0/1), d=192.168.14.2 (FastEthernet0/0), routed via RIB

*Mar 1 19:14:36.026: IP: s=192.168.16.2 (Serial0/1), d=192.168.14.2 (FastEthernet0/0), g=192.168.14.2, len 60, forward



*Mar 1 19:14:46.562: IP: s=192.168.14.1 (local), d=255.255.255.255 (FastEthernet0/0), len 92, sending broad/multicast



*Mar 1 19:14:51.958: IP: s=192.168.13.2 (Serial0/1), d=255.255.255.255, len 72, rcvd 2

*Mar 1 19:14:51.962: IP: s=192.168.15.2 (Serial0/0), d=255.255.255.255

Router(config-if)# ip route-cache

79© 2010 Cisco Systems, Inc. All rights reserved. Institut Tadbiran Awam Negarahttp://www.cisco.com/en/US/products/ps5763/products_configuration_guide_chapter09186a00802a1fae.html#wp1045020RIB:

Router Paths: Un-Equal Cost Load BalancingJust in case you are wondering, a router can send packets over y g pmultiple networks even when the metric is not the same if it is using a routing protocol that has this capability. This is known as unequal cost load balancing. EIGRP (as well as IGRP) are the only q g ( ) yrouting protocols that can be configured for unequal cost load balancing.

Unequal cost load balancing in EIGRP is not discussed in thisUnequal cost load balancing in EIGRP is not discussed in this course but is covered in CCNP.


Unequal Cost Load Balancing with EIGRP

EIGRP Load Balancing E ti t l t l t

What is unequal cost load balancing?

Every routing protocol supports equal cost path load balancing. In addition to that, IGRP and EIGRP also support unequal cost path load balancing.

Use the variance command to instruct the router to include routes with a metric less than n times the minimum metric route for that destination, where n is the number specified by the variancecommand. Example: E-C-A: 20 * 2 = 40. Therefore, E-C-A and E-B-A will be used for load balancing. router eigrp 1

network x.x.x.x variance 2


variance 2

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml


Packet forwarding involves two functions:g–Path determination function–Switching function

Path determination is a process used by a router to pick the best path to a destinationOne of 3 path determinations results from searching f h b hfor the best path

–Directly connected network•The destination IP address of the packet is a host dd th t k thi t 'address on the same network as this router's

interface–Remote network

If th d ti ti IP dd f th k t b l• If the destination IP address of the packet belongs to a remote network, then the packet is forwarded to another router.

–No route determined


•the packet is discarded

R t P th d P k t S it hiRouter Paths and Packet SwitchingSwitching Function of Router is the process used by a router to switch a packet from an incoming interface to an outgoing interface on thea packet from an incoming interface to an outgoing interface on the same router.

What does a router do with a packet received from one network and destined for another network?

-A packet received by a router will do the following:Strips off layer 2 headersStrips off layer 2 headers. Examines destination IP address located in Layer 3 header to find

best route to destination.Re-encapsulates layer 3 packet into layer 2 frame. Forwards frame out exit interface.


Router Paths and Packet SwitchingAs a packet travels from one networking device to another

-The Source and Destination IP addresses NEVER change-The Source & Destination MAC addresses CHANGE as packet is forwarded from one router to the next.

•The Layer 2 data link source address represents the Layer 2 address of the outbound•The Layer 2 data link source address represents the Layer 2 address of the outbound interface. The Layer 2 destination address represents the Layer 2 address of the next-hop router. If the next hop is the final destination device, it will be the Layer 2 address of that device. •It is very likely that the packet will be encapsulated in a different type of Layer 2 frameIt is very likely that the packet will be encapsulated in a different type of Layer 2 frame than the one in which it was received. For example, the packet might be received by the router on a FastEthernet interface, encapsulated in an Ethernet frame, and forwarded out a serial interface encapsulated in a PPP frame.

-TTL field decrement by one until a value of zero is reached at which point router y pdiscards packet (prevents packets from endlessly traversing the network)

•Demo



Path determination and switching function details. PC1 a de e a o a d s c g u c o de a s CWants to send something to PC 2 here is part of what happens

Step 1 - PC1 encapsulates packet into a frame. Frame contains R1’s destination MAC address Ethertypes

The 13th and 14th octets of an Ethernet or IEEE802 3 packet (after theor IEEE802.3 packet (after the preamble) consist of the "Ethernet Type" or "IEEE802.3 Length" field. The "Ethernet Type" values are managed by XEROX. Some assignments are public (see + below), others private. ( ), p


http://www.cavebear.com/archive/cavebear/Ethernet/type.html

Router Paths and Packet SwitchingRouter Paths and Packet SwitchingStep 2 - R1 receives Ethernet frame.

R1 sees that destination MAC address matches its own MAC. R1 then strips off Ethernet frame. R1 Examines destination IP. R1 consults routing table looking for destination IP.

R1After finding destination IP in routing table, R1 now looks up next hop IP address.R1 re-encapsulates IP packet with a new Ethernet frame.

f the entry is not in the ARP cache, R1 sends an ARP request out its FastEthernet 0/1 interface. R2 sends back an ARP reply.

R1 forwards Ethernet packet out Fa0/1 interface.


Router Paths and Packet SwitchingRouter Paths and Packet SwitchingPath determination and switching function details. PC1 Wants to send something to PC 2 here is part of what happens

Step 3 - Packet arrives at R2Step 3 Packet arrives at R2R2 receives Ethernet frameR2 sees that destination MAC address matches its own MACR2 then strips off Ethernet frame

R2R2 then strips off Ethernet frameR2 Examines destination IPR2 consults routing table looking for destination IPAfter finding destination IP in routing table, R2 now looks up next hop IPAfter finding destination IP in routing table, R2 now looks up next hop IP

addressR2 re-encapsulates IP packet with a new data link frameR2 forwards Ethernet packet out S0/0 interface

When the interface is a point-to-point serial connection, R2 encapsulates the IP packet into the proper data link frame format used by the exit interface (HDLC, PPP, etc.). In this case, the Layer 2 encapsulation is PPP; therefore, the data link destination address is set to a broadcast. Remember, there are no MAC addresses on serial interfaces.


Router Paths and Packet SwitchingRouter Paths and Packet SwitchingPC1 Wants to send something to PC 2 here is part of what happens

Step 4 - Packet arrives at R3 fR3 receives PPP frame

R3 then strips off PPP frameR3 Examines destination IP R3 consults routing table looking for destination IPAfter finding destination IP in routing table, R3 is directly connected to

destination via its fast Ethernet interfaceIf the entry is not in the ARP cache R3 sends an ARP request out itsIf the entry is not in the ARP cache, R3 sends an ARP request out its

FastEthernet 0/0 interface. PC2 sends back an ARP reply with its MAC address. R3 re-encapsulates IP packet with a new Ethernet frameR3 forwards Ethernet packet out Fa0/0 interfacep

Step 5 - IP packet arrives at PC2. Frame is decapsulated & processed by upper layer protocols.


Packet propagation and switching within a routerPacket propagation and switching within a router 1


Packet propagation and switching within a router 2



44


Packet propagation and switching within a router

4


P k t ti d it hi ithi tPacket propagation and switching within a router 6

7


94

P k i d i hi i hiPacket propagation and switching within a router

77


Packet propagation and switching within a router

8


P k t ti d it hi ithi tPacket propagation and switching within a router

9


97

SummarySummaryRouters are computers that specialize in sending data over a network.Routers are composed of:

-Hardware i.e. CPU, Memory, System bus, Interfaces-Software used to direct the routing processSoftware used to direct the routing process

IOSConfiguration file

Routers need to be configured. Basic configuration consists of:-Router name-Router bannerRouter banner-Password(s)-Interface configurations i.e. IP address and subnet mask

Routing tables contain the following information-Directly connected networks-Remotely connected networks


Remotely connected networks-Network addresses and subnet masks-IP address of next hop address

Summary

Routers determine a packets path to its destination by doing the following

Receiving an encapsulated frame & examining destination MAC addressMAC address.If the MAC address matches then Frame is de-encapsulated

so that router can examine the destination IP address.If destination IP address is in routing table or there is a static

route then Router determines next hop IP address. Router will re-encapsulate packet with appropriate layer 2 frame and sendre encapsulate packet with appropriate layer 2 frame and send it out to next destination.Process continues until packet reaches destination.Note - only the MAC addresses will change the source and

destination IP addresses do not change.


Static Routing




Objectives

Define the general role a router plays in networks.e e e ge e a o e a ou e p ays e o s

Describe the directly connected networks, different router interfacesrouter interfaces

Examine directly connected networks in the routing table and use the CDP protocoltable and use the CDP protocol

Describe static routes with exit interfaces

Describe summary and default route

Examine how packets get forwarded when using static routes

Identify how to manage and troubleshoot static routes


General Role of the Router

Functions of a Routeru c o s o a ou eBest Path SelectionsForwarding packets to destination

Routers perform packet forwarding by learning about remote networks and maintaining routing information. g g

– The routers primary forwarding decision is based on Layer 3 information, the destination IP address. – The router's routing table is used to find the best match between the destination IP of a packet and a network address in the routing table. – The routing table will ultimately determine the exit interface to forward the packet and the router will encapsulate that packet in the appropriated data link frame for that outgoing interface


the appropriated data link frame for that outgoing interface.


Introducing the Topologyoduc g e opo ogy– The figure shows the topology used in this chapter. – 3 1800 series routers connected via WAN links– Each router connected to a LAN represented by a switch and a PC



Connections of a Router for WAN -A router has a DB-60 port that can support 5 different cabling standards–Newer routers support the smart serial ppinterface that allows for more data to be forwarded across fewer cable pins.

Connections of a Router for Ethernet-2 types of connectors can be used: Straight through and Cross-over Straight through used to connect:Straight through used to connect:

-Switch-to-Router, Switch-to-PC, Hub-to-PC, Hub-to-Server

Cross-over used to connect (pin 1 connectedCross-over used to connect (pin 1 connected to pin 3, and pin 2 connected to pin 6):

-Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hub-to-Hub, Router-to-Router, PC-


, , ,Router

General Role of the Router in COD

Smart Serial cables: DCE and DTE S a Se a cab es C a d-Use straight cable to connect between the DTE and DCE.. DCE and DTE Adapter

Ethernet cables:Cross-over cable: RED cableRoll-over cable: flat cables

Straight cable: all other cables

http://www.csdata.com/csdonline/customer/home.php


Serial Connectors

DTEDCEDCE

DTE DTEDCE

DTE DTEDCE

In our labs we will use serial DTE/DCE cables (no CSU/DSU) with a DTE cable connected to one router and

DCE bl t d t th th t


a DCE cable connected to the other router.

Interfaces

Examining Router Interfacesa g oute te aces-Show IP router command – used to view routing table-Show Interfaces command – used to show status of an interface-Show IP Interface brief command – used to show a portion of

the interface information on a condensed formatSh i fi d d t h fi ti-Show running-config command – used to show configuration

file in RAM


Interfaces

Configuring an Ethernet interfaceCo gu g a t e et te ace-By default all serial and Ethernet interfaces are down-To enable an interface use the No Shutdown command

•The show ip routecommand is used to display the routing table. •Initially, the routing table is empty if no interfaces have b fi dbeen configured.•Static routes and dynamic routes will not be added to th ti t bl til ththe routing table until the appropriate local interfaces have been configured on the router


the router.

Verifying Ethernet interfaceVerifying Ethernet interface- Show interfaces - command shows the status and gives a detailed description for all interfaces on the routerp– Show interfaces fastEthernet 0/0 – command used to show status of fast Ethernet port

R1#show interfaces fastethernet 0/0•R1#show interfaces fastethernet 0/0•FastEthernet0/0 is administratively down, line protocol is down• Administratively down means that the interface is currently in the shutdown mode, or turned off. •Line protocol is down means in this case that the interface is not receiving a carrier signal from•Line protocol is down means, in this case, that the interface is not receiving a carrier signal from a switch or the hub. This condition may also be due to the fact that the interface is in shutdown mode• You will notice that the show interfaces command does not show any IP addresses on R1's interfaces The reason for this is because we have not yet configured IP addresses on any of theinterfaces. The reason for this is because we have not yet configured IP addresses on any of the interfaces.


InterfacesInterfacesVerifying Ethernet interface

– Show run –Show run• command displays the current configuration file that the router is using. Configuration commands are temporarily stored in the running configuration file and implemented immediately by the routerand implemented immediately by the router. •However, using show running-config is not necessarily the best way to verify interface configurations.

-Show ip interface brief –-can be used to see a portion of the interface information in a condensed format.


Configuring an Ethernet interfaceConfiguring an Ethernet interfaceBy default, all router interfaces are shutdown. To enable this interface, use the no shutdown command, which changes the interface from administratively down to upinterface from administratively down to up.

R1(config)#interface fastethernet 0/0R1(config-if)#ip address 172.16.3.1 255.255.255.0R1(config-if)#no shutdown

The following message is returned from the IOS:

*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to upp , g p

–The first changed state to up message indicates that, physically, the connection is good. If you do not get this first message, be sure that the interface is properly connected to g , p p ya carrier signal from switch or a hub. –The second changed state to up message indicates that the Data Link layer is operational.

• However WAN interfaces in a lab environment require


• However, WAN interfaces in a lab environment require clocking on one side of the link. If you do correctly set the clock rate, then line protocol will not change to up.

Configuring an Ethernet interfaceConfiguring an Ethernet interfaceUnsolicited Messages from IOSgThe IOS often sends unsolicited messages.

As you can see in the figure, sometimes these messages will occur when you are in the middlemessages will occur when you are in the middle of typing a command, such as configuring a description for the interface.

–The IOS message does not affect the command, but it can cause you to lose your place when typing.

In order to keep the unsolicited output separateIn order to keep the unsolicited output separate from your input, enter line configuration mode for the consoled port and add the logging synchronous command, as shown. You will see that messages returned by IOS no longerthat messages returned by IOS no longer interfere with your typing.



-Show interfaces fastEthernet 0/0Reading the Routing Table

–Now look at routing table shown in the figure. Notice R1 now has a "directly connected" FastEthernet 0/0 interface a new network. –The interface was configured with the 172.16.3.1/24 IP address which makes it a member of the 172.16.3.0/24 network.

172.16.0.0/24 is subnetted, 1 subnetsC 172.16.3.0 is directly connected, FastEthernet0/0

–The C at the beginning of the route indicates that this is a directly connected network. In other words, R1 has an interface that belongs to this networknetwork.–The /24 subnet mask for this route is displayed in the line above the actual route.


InterfacesInterfacesReading the Routing Table172.16.0.0/24 is subnetted, 1 subnets172.16.0.0/24 is subnetted, 1 subnets

–Having a single route represent an entire network of host IP addresses makes thenetwork of host IP addresses makes the routing table smaller, with fewer routes, which results in faster routing table lookups.

•It means that this route matches all•It means that this route matches all packets with a destination address belonging to this network.

–The routing table could contain all 254 i di id l h t IP dd f thindividual host IP addresses for the 172.16.3.0/24 network, but that is an inefficient way of storing addresses.



show interfaces fastethernet 0/0show ip interface brief

The show interfaces fastethernet 0/0 command in the figure now showsin the figure now shows

–The interface is up, and the line protocol is up. The no shutdown command changed the interface from administratively down to up. –Notice that the IP address is now displayed.

The command show ip interface brief in the figure shows that the interface is up, and the li t l i (i d d f t)line protocol is up. (in a condensed format)Typically, the router's Ethernet or FastEthernet interface will be the default gateway IP address for any devices on that LANfor any devices on that LAN.

–For example, PC1 would be configured with a IP address belonging to the 172.16.3.0/24 network, with the default gateway IP address


g y172.16.3.1. –172.16.3.1 is router R1's FastEthernet IP address.

Ethernet Interfaces Participate in ARPEthernet Interfaces Participate in ARPA router's Ethernet interface participates in a LAN network just like any other device on that networkdevice on that network.

–This means that these interfaces have a Layer 2 MAC address, as shown in the figure. The show interfaces command displays the MAC dd f th Eth t i t fMAC address for the Ethernet interfaces.–If a router has a packet destined for a device on a directly connected Ethernet network, it checks the ARP table for an entry , ywith that destination IP address in order to map it to the MAC address.


Interfaces

Configuring a Serial interfaceConfiguring a Serial interface-Enter interface configuration mode-Enter in the ip address and subnet maskEnter in the ip address and subnet mask-Enter in the no shutdown command

Example:Example:-R1(config)#interface serial 0/0/0-R1(config-if)#ip address 172.16.2.1 255.255.255.0( g ) p-R1(config-if)#no shutdown


InterfacesR1(config)#interface serial 0/0/0R1(config if)#ip address 172 16 2 1 255 255 255 0R1(config-if)#ip address 172.16.2.1 255.255.255.0R1(config-if)#no shutdown

R2(config)#interface serial 0/0/0R2(config-if)#ip address 172.16.2.2 255.255.255.0R2(config-if)#no shutdown

–There is no requirement that both ends of the serial link use the same interface, (0/0/0, 0/0/1, 0/1/0, 0/1/1, ….)–in this case, Serial 0/0/0. However, because both interfaces are members of the same network, they both must have IP addresses that belong to the 172.16.2.0/24 network.If we now issue the show interfaces serial 0/0/0 command on either router we still see that–If we now issue the show interfaces serial 0/0/0 command on either router, we still see that

the link is up/down.

R2#show interfaces serial 0/0/0Serial0/0/0 is up, line protocol is downp, p

– The physical link between R1 and R2 is up because both ends of the serial link have been configured correctly with an IP address/mask and enabled with the no shutdown command. – However, the line protocol is still down. This is because the interface is not receiving a clock signal.


– There is still one more command that we need to enter, the clock rate command, on the router with the DCE cable. The clock rate command will set the clock signal for the link.

InterfacesStep 1 Step 3

Nothing is configured Setup “no shut”

Step 2 Step 4

Setup IP but not “no shut” Configured the clock rate


Examining Router InterfacesExamining Router Interfaces-Physically connecting a WAN Interface. A WAN Physical Layer connection has sides:-A WAN Physical Layer connection has sides:

Data Circuit-terminating Equipment (DCE) – This is the service provider. CSU/DSU is a DCE device.

The CSU/DSU (DCE device) is used to convert the data from the router (DTE device) into a form acceptable to the WAN service provider. a DCE device such as a CSU/DSU will provide the clock.

Data Terminal Equipment (DTE) – Typically the router is the DTE device.

Up-to-date technology

Cisco 1-Port T1/Fractional T1


Cisco 1 Port T1/Fractional T1 DSU/CSU WAN Interface Card (WIC-1DSU-T1-V2=)

Interfaces- What is the significant of the information 1?

For serial links that are directly interconnected, as in a lab environment, one side of a connection must be considered a DCE and provide a clocking signal.

You can also distinguish DTE from DCE –1) by looking at the connector between the two cables. The DTE cable has a male connector whereas the DCEThe DTE cable has a male connector, whereas the DCE cable has a female connector.–2) If a cable is connected between the two routers, you can use the show controllers command to determinecan use the show controllers command to determine which end of the cable is attached to that interface.

R1#show controllers serial 0/0/0Interface Serial0/0/0Hardware is PowerQUICC MPC860DCE V.35, no clock<output omitted>


Interfaces

Once the cable is attached, the clock can now be set with the clock rate commandthe clock rate command.

–The available clock rates, in bits per second, are 1200, 2400, 9600, 19200, 38400, 56000, 64000, 72000, 125000, 148000, 500000, 800000, 1000000 1300000 2000000 and 40000001000000, 1300000, 2000000, and 4000000. –Some bit rates might not be available on certain serial interfaces.

R1(config)#interface serial 0/0R1(config-if)#clock rate 6400001 10 28 %LINEPROTO 5 UPDOWN Li t l01:10:28: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up

Note: If a router's interface with a DTE cable is configuredNote: If a router s interface with a DTE cable is configured with the clock rate command, the IOS will disregard the command and there will be no ill effects.

–Use the “show controllers serial 0/0/0” to find out whether it is a DTE or DCE cable


find out whether it is a DTE or DCE cable.

TestingVerifying the Serial Interface ConfigurationR1#show interfacesR1#show ip interface briefR1#ping 172.16.2.2R1#show ip route


R ti T bl C tRouting Table ConceptsThe show ip route command reveals the content of the routing table.

Th i f ti t bl i t id th t ith th t–The main purpose of a routing table is to provide the router with paths to different destination networks.

The routing table consists of a list of "known" network addressesdi tl t d–directly connected,

–configured statically, –learned dynamically.

POP Quiz:– Can R1 ping R2?– Can PC1 ping PC2?p g


Routing Table ConceptsRouting Table ConceptsPurpose of the debug ip routing command

Allows you to view changes that the router performs when adding orAllows you to view changes that the router performs when adding or removing routes in real time

13

enable debugging with the debug ip routing command Configuring the IP address and Subnet Mask

disable interfaces with the shutdown command.

g g

4 Check the routing table

2 Check the routing table

5 Disable debug ip routing by using


5 routing by using either the “undebug ip routing” command or the “undebug all” command.

Never use the debug all command on the production router.

Routing Table and CDP Protocol

When a router only has its interfaces configured &no other routing protocols are configured then:

-The routing table contains only the directly connected networks-Only devices on the directly connected networks are reachable

POP Quiz: The output in this figure verifies that all Whypings failed?

p gconfigured interfaces are "up" and "up".



When a router only has its interfaces configured, and the ti t bl t i th di tl t d t k b trouting table contains the directly connected networks but

no other routes, only devices on those directly connected networks are reachable.

–R1 can communicate with any device on the 172 16 3 0/24R1 can communicate with any device on the 172.16.3.0/24 and 172.16.2.0/24 networks.–R2 can communicate with any device on the 172.16.1.0/24, 172.16.2.0/24, and 192.168.1.0/24 networks.

/–R3 can communicate with any device on the 192.168.1.0/24 and 192.168.2.0/24 networks.


Routing Table and CDP ProtocolRouting Table and CDP ProtocolChecking each route in turn

–The ping command is used to check end to end connectivity–Ping 172.16.3.1 failed

•Route does not match any route in the routing table

–Ping 192.168.1.1 succeed•192.168.1.0/24, matches the first 24 bits of the destination IP address


Routing Table and CDP ProtocolPurpose of CDP

–Cisco Discovery Protocol (CDP) is a powerful network monitoring and troubleshooting tool.

•CDP runs at the Data Link layer connecting the physical di t th l t l (ULP )media to the upper-layer protocols (ULPs).

•Because CDP operates at the Data Link layer, two or more Cisco network devices, such as routers that support different Network layer protocols (for example, IP and Novell IPX), can y p ( p , ),learn about each other.

–A layer 2 cisco proprietary tool used to gather information about other directly connected Cisco devices.

•enables you to access a summary of protocol and address information about Cisco devices that are directly connected.

–the types of devices that are connected, th i t f th t d t–the interfaces they are connected to,

–the interfaces used to make the connections, –the model numbers of the devices.


–……..

Routing Table and CDP ProtocolConcept of neighbors

-2 types of neighborsLayer 3 neighbors

At Layer 3, routing protocols consider neighbors to be d i th t h th t k dddevices that share the same network address space.

R1 and R2 are neighbors. Both are members of the 172.16.1.0/24 network.

R2 and R3 are also neighbors because they both shareR2 and R3 are also neighbors because they both share the 192.168.1.0/24 network.

But R1 and R3 are not neighbors because they do not share any network address space.

Layer 2 neighborsLayer 2 neighborsCDP operates at Layer 2 only. Therefore, CDP

neighbors are Cisco devices that are directly connected physically and share the same data link.

»R1 and S1 are CDP neighbors.»R1 and R2 are CDP neighbors.»R2 and S2 are CDP neighbors.R2 d R3 CDP i hb

Notice the difference between Layer 2 and Layer 3 neighbors. The switches are not neighbors to the routers at Layer 3, because the switches are operating at Layer 2 only


»R2 and R3 are CDP neighbors.»R3 and S3 are CDP neighbors.

the switches are operating at Layer 2 only. However, the switches are Layer 2 neighbors to their directly connected routers.

Routing Table and CDP ProtocolCDP is on by default.

–CDP exchanges hardware and software–CDP exchanges hardware and software device information with its directly connected CDP neighbors.

CDP show commandsShow cdp neighbors command

-Displays the following information:Neighbor device IDLocal interfaceLocal interfaceHoldtime value, in secondsNeighbor device capability codeNeighbor hardware platformNeighbor remote port ID

Show cdp neighbors detail command -It can also reveals the IP address of a neighboring device

–knowing the IP address of the CDP neighbor is often allows you to telnet into that device.

• and a lot more– IOS version


– Platform – …………


Disabling CDPsab g C– CDP be a security risk

• Because some IOS versions send out CDP advertisements by default, it is important to know how to disable CDP.

–If you need to disable CDP globally, for the entire device, use this command:this command:

• Router(config)#no cdp run

–If you want to use CDP but need to stop CDP advertisements on a particular interface, use this command:

• Router(config-if)#no cdp enable


Static Routes

A router can learn about remote networks in one of two ways:y–Manually, from configured static routes–Automatically, from a dynamic routing protocol

D i ti t l i t d d i th t h t•Dynamic routing protocols are introduced in the next chapter.

Purpose of a static routeA manually configured route used when routing from a network to a stub–A manually configured route used when routing from a network to a stub

network

•A stub network is a network accessed by a single route.•For an example, here we see that any network attached to R1 would only have one way to reach other destinations, whether to networks attached to R2 orwhether to networks attached to R2 or to destinations beyond R2. •Therefore, network 172.16.3.0 is a stub network and R1 is a stub router. Running a routing protocol between R1


•Running a routing protocol between R1 and R2 is a waste of resources

Static Routes

IP route commandoute co a dTo configure a static route use the following command: ip routeExample:

-Router(config)# ip route network-address subnet-mask {ip-address | exit-interface }


Static route operation Example: Fly from Chicago to LA

Chicago

O’Hare

Los Angeles

Chi O’H Ai L A lChicago O’Hare Airport Los Angeles

RTR(config)# ip route prefix mask {address | interface}


( g) p p f { | f }O’Hare

Los Angeles

Static Routes

Remember R1 knows about its directly yconnected networks.

–These are the routes currently in its routing table.

The remote networks that R1 does not know about are:

–172.16.1.0/124 - The LAN on R2–192.168.1.0/24 - The serial network between R2 and R3–192.168.2.0/24 - The LAN on R3


Static Routes

R1(config)#ip route 172 16 1 0 255 255 255 0 172 16 2 2Dissecting static route syntax

ip route - Static route command172 16 1 0 D ti ti t k dd

R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2

172.16.1.0 – Destination network address 255.255.255.0 - Subnet mask of destination

network172.16.2.2 - Serial 0/0/0 interface IP address

on R2, which is the "next-hop" to this network

show ip route output–S - Routing table code for static route172 16 1 0 N t k dd f th t–172.16.1.0 - Network address for the route

–/24 - Subnet mask for this route; this is displayed in the line above, known as the parent route, and discussed in Chapter 8–[1/0] - Administrative distance and metric for the static route (explained in a later chapter)–via 172.16.2.2 - IP address of the next-hop router, the IP address of R2's Serial 0/0/0 interface


interface

Static Routes

R1(config)#ip route 172 16 1 0 255 255 255 0 172 16 2 2show ip route output

–S - Routing table code for static route172 16 1 0 N t k dd f th t

R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2

–172.16.1.0 - Network address for the route–/24 - Subnet mask for this route; this is displayed in the line above, known as the parent route, and discussed in Chapter 8–[1/0] - Administrative distance and metric for the static route (explained in a later chapter)–via 172.16.2.2 - IP address of the next-hop router, the IP address of R2's Serial 0/0/0 interfaceinterface


Static Routes

Configuring routes to 2 or more remote networksCo gu g outes to o o e e ote et o sUse the following commands for R1

-R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2-R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2


Static Routes

Zinin’s 3 routing principlesfPrinciple 1: "Every router makes its decision alone, based on the information it has

in its own routing table.“R1 has three static routes in its routing table and makes forwarding decisions

based solely upon the information in the routing table. R1 does not consult the routing tables in any other routers. Making each router aware of remote networks is the responsibility of the

network administrator.Principle 2: "The fact that one router has certain information in its routing table doesPrinciple 2: The fact that one router has certain information in its routing table does

not mean that other routers have the same information.“The network administrator would be responsible for ensuring that the next-hop

router also has a route to this networkUsing Principle 2 we still need to configure the proper routing on the otherUsing Principle 2, we still need to configure the proper routing on the other

routers (R2 and R3) to make sure that they have routes to these three networks.Principle 3: "Routing information about a path from one network to another does not

provide routing information about the reverse, or return path.“M f h i i k i bidi i l Thi hMost of the communication over networks is bidirectional. This means that

packets must travel in both directions between the end devices involved. Using Principle 3 as guidance, we will configure proper static routes on the other

routers to make sure they have routes back to the 172.16.3.0/24 network.


Static Routes


Static Routes with next-hop IP address

Resolving to an Exit Interface-Recursive route lookup - Occurs when the router has to perform multiple lookups in the routing table before forwarding a packet. A static route that forwards all packets to the next-hop IP address goes through the following process (reclusive route lookup)

(Step 1) The router first must match static route’s destination IP address with the Next hop addressp

The packet's destination IP address is matched to the static route 192.168.2.0/24 with the next-hop IP address 172.16.2.2.

(Step 2) The next hop address is then matched to an exit interface(Step 2) The next hop address is then matched to an exit interfaceThe next-hop IP address of the static route, 172.16.2.2, is matched to the

directly connected network 172.16.2.0/24 with the exit interface of Serial 0/0/0.


Static Routes with Exit InterfacesStatic Routes with Exit InterfacesConfiguring a Static route with an Exit Interface

S i fi d i h i i f-Static routes configured with an exit interfaceare more efficient because the routing–The routing table can resolve the exit interface in a single search instead of 2 searchesin a single search instead of 2 searches

If the static route cannot be resolved to an exit interface, the static route is removed from th ti t blthe routing table

–Notice from the debug output that all three static routes were deleted when the Serial 0/0/0 interface was shut downinterface was shut down. –They were deleted because all three static routes were resolved to Serial 0/0/0. However the static routes are still in the R1's–However, the static routes are still in the R1 s

running configuration. If the interface comes back up (is enabled again with no shutdown), the IOS routing table process will reinstall these t ti t b k i t th ti t bl


static routes back into the routing table.

Static Routes with Exit InterfacesModifying Static routes

Existing static routes cannot be modified. The old static route must be deleted by placing no in front of the ip routeExample:Example:

-no ip route 192.168.2.0 255.255.255.0 172.16.2.2A new static route must be rewritten in the configurationA new static route must be rewritten in the configuration

R1(config)# no ip route 192.168.2.0 255.255.255.0 172.16.2.2R1(config)#ip route 192.168.2.0 255.255.255.0 serial 0/0/0


Static Routes with Exit Interfaces

Verifying the Static Route Configuration-Use the following commands

Step 1 show running-configStep 2 verify static route has been entered correctlyStep 2 verify static route has been entered correctlyStep 3 show ip routeStep 4 verify route was configured in routing tableSt 5 i i d t if k tStep 5 issue ping command to verify packets can

reach destination and that Return path is working


Static route operation

Both types of the routes all have distance of 1


all have distance of 1 and metric of 0.

Static Routes with Exit InterfacesStatic Routes with Exit InterfacesEthernet interfaces and ARP.

– If a static route is configured on an Ethernet linkIf a static route is configured on an Ethernet link•If the packet is sent to the next-hop router then…

–the destination MAC address will be the address of the next–the destination MAC address will be the address of the next hop’s Ethernet interface–This is found by the router consulting the ARP table.

»If an entry isn’t found then an ARP request will be sent out

R1(config)#ip route 192 168 2 0 255 255 255 0 fa 0/1R1(config)#ip route 192.168.2.0 255.255.255.0 fa 0/1


Static Routes with Exit InterfacesStatic Routes with Exit Interfaces

B t t t l it i t f ith Eth t i t fR1(config)#ip route 192.168.2.0 255.255.255.0 fastethernet 0/1

Best not to use only an exit interface with Ethernet interfaces.Router will have difficulty determining the destination MAC address.With Ethernet networks many different devices can be sharing theWith Ethernet networks, many different devices can be sharing the same multiaccess network, including hosts and even multiple routers. Router will not have sufficient information to determine which device is the next-hop deviceis the next hop device.Use both the next-hop interface and the exit interface for Ethernet exit interfaces.O l i l t l k d dOnly a single route lookup now needed.

R1(config)#ip route 192.168.2.0 255.255.255.0 fastethernet 0/1 172.16.2.2

The routing table entry for this route would be:

S 192.168.2.0/24 [1/0] via 172.16.2.2 FastEthernet0/1


Summary and Default Route

Summarizing routes reduces the size of the routing g gtable. Route summarization is the process of combining a

fnumber of static routes into a single static route.–For example, the networks 10.0.0.0/16, 10.1.0.0/16, 10.2.0.0/16, 10.3.0.0/16, 10.4.0.0/16, 10.5.0.0/16, all the way 0 0 0/ 6, 0 3 0 0/ 6, 0 0 0/ 6, 0 5 0 0/ 6, a e aythrough 10.255.0.0/16 can be represented by a single network address: 10.0.0.0/8.

Multiple static routes can be summarized into a singleMultiple static routes can be summarized into a single static route if:

–The destination networks can be summarized into a single gnetwork address, and –The multiple static routes all use the same exit-interface or next-hop IP address


e t op add ess

Calculating a summary route

Here's the process of creating the summary route 172 16 1 0/22 as sho n in the fig re172.16.1.0/22, as shown in the figure:

1. Write out the networks that you want to summarize in binary.

2. To find the subnet mask for summarization, start with the left-most bitthe left-most bit.

3. Work your way to the right, finding all the bits that match consecutively.

4. When you find a column of bits that do not match, stop. You are at the summary boundary.p y y

5. Now, count the number of left-most matching bits, which in our example is 22. This number becomes your subnet mask for the summarized route, /22 or 255.255.252.0

6 To find the network address for summarization copy6. To find the network address for summarization, copy the matching 22 bits and add all 0 bits to the end to make 32 bits.

By following these steps, we can discover that the 3 static routes on R3 can be summarized into a singlestatic routes on R3 can be summarized into a single static route, using the summary network address of 172.16.0.0 255.255.252.0:ip route 172.16.0.0 255.255.252.0 Serial0/0/1


Example: Calculating a summary route

Which address can be used toWhich address can be used to summarize networks 172.168.0.0 /24 through 172.168.7.0 /24?g

10101100 10101000 00000000 0000000010101100 10101000 00000001 0000000010101100 10101000 00000010 0000000010101100 10101000 00000011 0000000010101100 10101000 00000100 0000000010101100 10101000 00000100 0000000010101100 10101000 00000101 0000000010101100 10101000 00000110 0000000010101100 10101000 00000110 0000000010101100 10101000 00000111 00000000

Answer:52© 2010 Cisco Systems, Inc. All rights reserved. Institut Tadbiran Awam Negara

Answer:


Which address can beWhich address can be used to summarize networks 11000000 00000001 00000001 00000000• 192.1.1.0/27• 192.1.1.32/27• 192 1 1 64/28

11000000 00000001 00000001 0000000011000000 00000001 00000001 0010000011000000 00000001 00000001 01000000

• 192.1.1.64/28• 192.1.1.80/28• 192.1.1.96/29

11000000 00000001 00000001 0101000011000000 00000001 00000001 0110000011000000 00000001 00000001 01101000

• 192.1.1.104/29• 192.1.1.112/29• 192 1 1 120/29

11000000 00000001 00000001 0110100011000000 00000001 00000001 0111000011000000 00000001 00000001 01111000

192.1.1.120/29


Answer:

SSummary RouteConfiguring a summary route

–Step 1: Delete the current static routeR3(config)#no ip route 172.16.1.0 255.255.255.0 serial0/0/1R3(config)#no ip route 172.16.2.0 255.255.255.0 serial0/0/1R3(config)#no ip route 172.16.3.0 255.255.255.0 serial0/0/1

–Step 2: Configure the summary static route•R3(config)#ip route 172 16 0 0 255 255 252 0 serial0/0/1R3(config)#ip route 172.16.0.0 255.255.252.0 serial0/0/1

–Step 3: Verify the new static route •show ip route ping


Summary Route

Static routes and subnet masks–The routing table lookup process will use the most specific matchwhen comparing destination IP address and subnet mask

For example what if we had the following two static routes in the–For example, what if we had the following two static routes in the routing table

•172.16.0.0/24 is subnetted, 3 subnetsS 172 16 1 0 i di tl t d S i l0/0/0 d•S 172.16.1.0 is directly connected, Serial0/0/0 and

•S 172.16.0.0/16 is directly connected, Serial0/0/1

–Consider a packet with the destination IP address 172.16.1.10. This IP address matches both routes.

•The routing table lookup process will use the most-specific match. •Because 24 bits match the 172 16 1 0/24 route and only 16 bits ofBecause 24 bits match the 172.16.1.0/24 route, and only 16 bits of the 172.16.0.0/16 route match, the static route with the 24 bit match will be used. •This is the longest match


•This is the longest match.

Default Route

Default Static RouteThis is a route that will match all packets. Like route summarization this will help reduce

the size of the routing tableDefault static routes are used:

–When no other routes in the routing table match the packet's destination IP address. A common use is when connecting a company's edge router to the ISPwhen connecting a company s edge router to the ISP network.–When a router has only one other router to which it is connected. This condition is known as a stub router.

Configuring a default static routeSimilar to configuring a static route. Except

that destination IP address and subnet mask are all zerosExample:

-Router(config)#ip route 0.0.0.0 0.0.0.0 [ it i t f | i dd ]


[exit-interface | ip-address ]

Summary and Default RouteR1 is a stub router.

It i l t d t R2–It is only connected to R2. –Currently R1 has three static routes, which are used to reach all of the remote networks in our topology. –All three static routes have the exit interface Serial 0/0/0, forwarding packets , g pto the next-hop router R2.

R1 is an ideal candidate to have all f it t ti t l d bof its static routes replaced by a

single default route. –First, delete the three static routes,–Next, configure the single default static route using the same Serial 0/0/0 exit interface


interface R1(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0/0

Static Routes and Packet ForwardingStatic Routes and Packet ForwardingVerify the change to the routing table y g gwith the show ip route commandS* 0.0.0.0/0 is directly connected, Serial0/0/0

–Note the * or asterisk next to the S–Note the or asterisk next to the S. •As you can see from the Codes table in the figure, the asterisk indicates that this static route is a candidate default route.

–The key to this configuration is the /0 mask.

•We previously said that it is the subnet•We previously said that it is the subnet mask in the routing table that determines how many bits must match between the destination IP address of the packet and th t i th ti t blthe route in the routing table. •A /0 mask indicates that zero or no bits are needed to match.


S lf t t St ti d t ti d f lt tSelf test: Static and static default routeCan you use both static and Ca you use bo s a c a dstatic default route to configure the communication b t b th LANS d thbetween both LANS and the communication to the Internet.Internet.

-Only 3 statement of static route needed to setup the network.

1 t ti t-1 static route-2 default static route

WinterPark(config)# ip route 0.0.0.0 0.0.0.0 192.168.146.1Altamonte(config)# ip route 10.0.234.0 255.255.255.0 192.168.146.2Alt t ( fi )# i t 0 0 0 0 0 0 0 0 0/1


Altamonte(config)# ip route 0.0.0.0 0.0.0.0 s0/1

Static Routes and Packet Forwarding

Troubleshooting a Missing Route oub es oo g a ss g ou e

Tools that can be used to isolate routing problems include:include:

-Ping– tests end to end connectivity-Traceroute– used to discover all of the hops (routers) along the

Layer 3p ( ) g

path between 2 points-Show IP route– used to display routing table & ascertain forwarding processforwarding process-Show ip interface brief- used to show status of router interfaces-Show cdp neighbors detail– used to gather configuration

Layer 2Show cdp neighbors detail used to gather configuration

information about directly connected neighbors


Static Routes and Packet Forwarding

Solving a Missing Route So g a ss g ou e

Finding a missing or mis-configured route requires methodically using the correct toolsmethodically using the correct tools

-Start with PING. If ping fails then use traceroute to determine where packets are failing to arrive- Than trace route

Issue: show ip route to examine routing table.-If there is a problem with a mis-configured static route remove the static route then reconfigure the new static route


SummarySummaryRouters

-Operate at layer 3p y-Functions include best path selection & forwarding packets

Connecting NetworksWANs

Serial cables are connected to router serial ports. In the lab environment clock rates must be configured for DCEt e ab e o e t c oc ates ust be co gu ed o C

LANsStraight through cables or cross over cables are used to connect to fastethernet port (The type of cable used dependsconnect to fastethernet port. (The type of cable used depends on what devices are being connected)

Cisco Discovery ProtocolA layer 2 proprietary protocolA layer 2 proprietary protocolUsed to discover information about directly connected Cisco devices


SummarySummaryStatic Routes

-This is a manually configured path that specifies how the routerThis is a manually configured path that specifies how the router will get to a certain point using a certain path.

Summary static routes-This is several static routes that have been condensed into a-This is several static routes that have been condensed into a single static route.

Default routeIt is the route packets use if there is no other possible match for-It is the route packets use if there is no other possible match for

their destination in the routing table.Forwarding of packets when static route is used

Zi i ’ 3 ti i i l d ib h k t f d d-Zinin’s 3 routing principles describe how packets are forwardedTroubleshooting static routes may require some of the following commands:

-Ping -Traceroute-Show IP route


-Show ip interface brief -Show cdp neighbors detail

Introduction to Dynamic Routing Protocolg

Chapter 3: Routing Protocols and ConceptsModified by Hasimi Sallehudin


Objectives

Describe the role of dynamic routing protocols and esc be e o e o dy a c ou g p o oco s a dplace these protocols in the context of modern network design.

Identify several ways to classify routing protocols.

Describe how metrics are used by routing protocolsDescribe how metrics are used by routing protocols and identify the metric types used by dynamic routing protocols.

Determine the administrative distance of a route and describe its importance in the routing process.

Identify the different elements of the routing table.


Dynamic Routing Protocols

Dynamic routing protocols are usually y a c ou g p o oco s a e usua yused in larger networks to ease the administrative and operational overhead f i l t ti tof using only static routes.

Typically, a network uses a combination f b th d i ti t l dof both a dynamic routing protocol and

static routes.


The Evolution of Dynamic Routing Protocols

One of the earliest routing protocols was Routing Information Protocol (RIP).RIP h l d i t i RIP 2 H–RIP has evolved into a newer version RIPv2. However,

–The newer version of RIP still does not scale to larger network implementations.

To address the needs of larger networks, two advanced routing protocols were developed: Open Shortest Path First (OSPF) and Intermediate System-to-I t di t S t (IS IS)Intermediate System (IS-IS).Cisco developed Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP), which also scales well in larger network implementations.Additionally there was the need to interconnect different internetworks and provideAdditionally, there was the need to interconnect different internetworks and provide routing among them. Border Gateway Routing (BGP) protocol is now used between ISPs as well as between ISPs and their larger private clients to exchange routing information.With the advent of numerous consumer devices using IP the IPv4 addressing spaceWith the advent of numerous consumer devices using IP, the IPv4 addressing space is nearly exhausted. Thus IPv6 has emerged. To support the communication based on IPv6, newer versions of the IP routing protocols have been developed (see the IPv6 row in the table).



Function(s) of Dynamic Routing Protocols:-Dynamically share information between routers.-Automatically update routing table when topology changes.-Determine best path to a destinationDetermine best path to a destination.–Compared to static routing, dynamic routing protocols require less administrative overhead.

•However, the expense of using dynamic routing protocols is dedicating part of a router'sHowever, the expense of using dynamic routing protocols is dedicating part of a router s resources for protocol operation including CPU time and network link bandwidth.

– One of the primary benefits to using a dynamic routing protocol is that routers exchange routing information whenever there is a topology change. This exchange ll t t t ti ll l b t t k d l t fi d lt tallows routers to automatically learn about new networks and also to find alternate

paths when there is a link failure to a current network.



Despite the benefits of dynamic routing, static routing still esp e e be e s o dy a c ou g, s a c ou g shas its place.

There are times when static routing is more appropriate andThere are times when static routing is more appropriate and other times when dynamic routing is the better choice.

More often than not you will find a combination of bothMore often than not, you will find a combination of both types of routing in any network that has a moderate level of complexity.



A routing protocol g p–is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol's choice of best pathsg p p

The purpose of a dynamic routing protocol is to:-Discover remote networks-Maintaining up-to-date routing information-Choosing the best path to destination networksAbilit t fi d b t th if th t th i l il bl-Ability to find a new best path if the current path is no longer available


Dynamic Routing ProtocolsDynamic Routing ProtocolsComponents of a routing protocol

–Data structuresData structures•Some routing protocols use tables and/or databases for its operations. This information is kept in RAM

Al ith–Algorithm•Algorithm is a finite list of steps used in accomplishing a task•Algorithms are used for facilitating routing information and best pathAlgorithms are used for facilitating routing information and best path determination

–Routing protocol messagesTh f di i i hb d h f•These are messages for discovering neighbors and exchange of

routing information , and other tasks to learn and maintain accurate information about the network.


Dynamic Routing Protocol OperationDynamic Routing Protocol OperationAll routing protocols have the same purpose - to learn about remote networks and to quickly adapt whenever there is a change in the topology.

The method that a routing protocol uses to accomplish this depends upon the algorithm it uses and the operational characteristics of that protocol.

In general the operations of a dynamic routing protocol can be described asIn general, the operations of a dynamic routing protocol can be described as follows:

–The router sends and receives routing messages on its interfaces.–The router shares routing messages and routing information with other routers that are using the same routing protocol.–Routers exchange routing information to learn about remote networks. –When a router detects a topology change the routing protocol can advertise this change to other routers.



Advantages of static routingIt b k lti l

Advantages of dynamic routing-It can backup multiple interfaces/networks on a router-Minimal CPU processingEasier for administrator to

-Administrator has less work maintaining the configuration when adding or deleting networks.

-Easier for administrator to understand-Easy to configure-No extra resources are needed

-Protocols automatically react to the topology changes.-Configuration is less error-prone.No extra resources are needed

-More secureDisadvantages of static routing

g-More scalable, growing the network usually does not present a problem

Disadvantages of dynamic routing-Network changes require manual reconfiguration -Configuration and maintenance is time-consuming

Disadvantages of dynamic routing-Router resources are used (CPU cycles, memory and link bandwidth).

time consuming-Does not scale well in large topologies-Configuration is error-prone,

-More administrator knowledge is required for configuration, verification, and troubleshooting.


g p ,especially in large networks

Classifying Routing Protocols

Dynamic routing protocols are grouped according to y g p g p gcharacteristics. Examples include:

-RIPIGRP-IGRP

-EIGRPOSPF-OSPF

-IS-IS-BGPBGP

Autonomous System is a group of routers under the control of a single authority.


g y


Dynamic routing protocols:–RIP

•A distance vector interior routing protocol–IGRP

•The distance vector interior routing developed by Cisco (deprecated from 12.2 IOS and later)

–EIGRP•The advanced distance vector interior routing protocol developed by Cisco

OSPF–OSPF•A link-state interior routing protocol

–IS-IS•A link-state interior routing protocol

–BGP•A path vector exterior routing protocol


p g p

Classifying Routing ProtocolsClassifying Routing ProtocolsAn autonomous system (AS) - otherwise known as a routing domain - is a collection of routers under a common administration.common administration.Because the Internet is based on the ASs concept, two types of routing protocols are required: interior and exterior routing protocols.

Interior Gateway Protocols (IGP)-Interior Gateway Protocols (IGP)•are used for intra-autonomous system routing - routing inside an autonomous system•IGPs are used for routing within a routing domain, those networks within the control of a single organization. g g

–An autonomous system is commonly comprised of many individual networks belonging to companies, schools, and other institutions.

• IGPs for IP include RIP, IGRP, EIGRP, OSPF, and IS-ISExterior Gateway Protocols (EGP)-Exterior Gateway Protocols (EGP)

•are used for inter-autonomous system routing - routing between autonomous systems that are under the control of different administrations•At the ISP level, there are often more important issuesAt the ISP level, there are often more important issues than just choosing the fastest path. •BGP is typically used between ISPs and sometimes between a company and an ISP


A t tAutonomous systems An autonomous system (AS) is a collection of networks under a common administrationnetworks under a common administration sharing a common routing strategy.

To the outside world, an AS is viewed as a single entity. The AS may be run by one or more operators while presenting a consistent view of routing to the external world.

The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. This g y gautonomous system number is a 16 bit number.Routing protocols, such as Cisco’s IGRP, require assignment of a unique, autonomous system number.

American Registry for Internet Numbershttp://www.arin.net/registration/asn/index.html

A t S t b (ASN) id


Autonomous System number (ASN) resource guidehttp://www.apnic.net/services/asn_guide.html

IS-IS

Autonomous systemsAutonomous systems Cisco system AS number:

http://ws.arin.net/cgi-bin/whois.pl


Autonomous systemsAutonomous systems http://arin.net/education/asn_process/index.html

RFC 1930AS just like IP, it needs to apply from ARIN or the appropriate region and be unique on the i t tinternet.

The Internet Assigned Numbers Authority (IANA) has reserved the following block of AS numbers for private use (not to be advertised on the global Internet): 64512 through 65535


Classifying Routing ProtocolsClassifying Routing ProtocolsIGP: Comparison of Distance Vector & Link State Routing Protocols

Distance vector– routes are advertised as vectors of distance & direction.

•Distance is defined in terms of a metric such as hop count (RIP)•Direction is simply the next-hop router or exit interfaceinterface•Distance vector protocols typically use the Bellman-Ford algorithm for the best path route determination

– incomplete view of network topologyincomplete view of network topology.•Distance vector protocols use routers as sign posts along the path to the final destination. •Distance vector routing protocols do not have an g pactual map of the network topology

– Generally, periodic updates.•Some distance vector protocols periodically send


complete routing tables to all connected neighbors.

Classifying Routing ProtocolsClassifying Routing ProtocolsIGP: Comparison of Distance Vector & Link State Routing ProtocolsLink State Routing Protocols

Link state– complete view of network topology is created.p p gy

•The sign posts along the way from source to destination are not necessary, because all link-state routers are using an identical "map" of thestate routers are using an identical map of the network.

– updates are not periodic.•After the network has converged, a link-state update only sent when there is a change in the topology.


Classifying Routing ProtocolsClassifying Routing ProtocolsComparison of Distance Vector & Link State Routing Protocols

Di t t t l kDistance vector protocols work best in situations where:

–The network is simple and flat

Link-state protocols work best in situations where:

–The network design is hierarchical, pand does not require a special hierarchical design.–The administrators do not have

g ,usually occurring in large networks.–The administrators have a good knowledge of the implemented link-

enough knowledge to configure and troubleshoot link-state protocols.

knowledge of the implemented linkstate routing protocol.–Fast convergence of the network is crucial

–Specific types of networks, such as hub-and-spoke networks, are being implemented.

crucial.

–Worst-case convergence times in a network are not a concern.


Classifying Routing ProtocolsClassful routing protocols

–Do NOT send subnet mask in routing updatesDo NOT send subnet mask in routing updates, –Do NOT support VLSM, –Classful routing protocols cannot be used when a network is subnetted using more than one gsubnet mask,

• Tony: This does not mean you can not subnet the clasasfull network. You can still subnet it but can only do it once and allsubnet it, but can only do it once and all network needs to have the identical mask.

–Routing protocols such as RIPv1 and IGRP.

Classless routing protocolsg p–Do send subnet mask in routing updates.–support variable length subnet masks (VLSM).

•In the figure, the classless version of the network is g ,using both /30 and /27 masks in the same topology. •Tony: It means you can create the network with all different sizes of subnets. They don’t need to have the same mask.


need to have the same mask. •Classless routing protocols are RIPv2, EIGRP, OSPF, IS-IS, BGP.


Convergence is defined as when all routers’ routing Co e ge ce s de ed as e a ou e s ou gtables are at a state of consistency

– The network has converged when all routers have complete and faccurate information about the network

Convergence time is the time it takes routers to share i f ti l l t b t th d d t th i tiinformation, calculate best paths, and update their routing tables.R ti t l b t d b dRouting protocols can be rated based on the speed to convergence; the faster the convergence, the better the routing

t lprotocol. –RIP and IGRP are slow to converge–EIGRP and OSPF are faster to converge.


EIGRP and OSPF are faster to converge.

Routing Protocols Metrics

To select the best path, the routing l b bl l dprotocol must be able to evaluate and

differentiate between the available paths. For this purpose a metric is used.Metric

–A value used by a routing protocol to determine which routes are better than others.

Each routing protocol uses its own metric. –RIP uses hop count,

•The hop count refers to the number of routersThe hop count refers to the number of routers a packet must cross to reach the destination network. •For R3 in the figure, network 172.16.3.0 is two hops or two routers awayhops, or two routers away.

–EIGRP uses a combination of bandwidth and delay,–OSPF uses bandwidth (cost).


OSPF uses bandwidth (cost).


Metrics used in IP routing protocols–Bandwidth

•Influences path selection by preferring the path with the highest bandwidth

–CostCost•A value determined either by the IOS or by the network administrator to indicate preference for a route. Cost can represent a metric, a combination of metrics or a policy.

RIP

OSPFp y

–Delay•Considers the time a packet takes to traverse a path

Hop count

RIP

–Hop count•A simple metric that counts the number of routers a packet must traverse

–Load•Considers the traffic utilization of a certain link

–Reliability•Assesses the probability of a link failure, calculated from the interface error count or


calculated from the interface error count or previous link failures

Routing Protocols MetricsRouting Protocols MetricsThe Metric Field in the Routing Table

Metric used for each routing protocol-RIP - hop count-IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, ReliabilityReliability-IS-IS & OSPF – Cost, Bandwidth(Cisco’s implementation)

Refer to the example in the figure TheRefer to the example in the figure The routers are using the RIP routing protocol.

–The metric associated with a certain t b b t i d i throute can be best viewed using the

show ip route command. –The metric value is the second value in the brackets for a routing table entry. –In the figure, R2 has a route to the 192.168.8.0/24 network that is 2 hops away.

•R 192 168 8 0/24 [120/2] via


R 192.168.8.0/24 [120/2] via 192.168.4.1, 00:00:26, Serial0/0/1


Load balancingoad ba a c g–when two or more routes to the same destination have identical metric values–This is the ability of a router to distribute packets among multiple same cost pathsp

Load balancing does notLoad balancing does not automatically means the interfaces

will get use equally. R2 load balances traffic to PC5 over two equal cost paths.

??????



Load balancing can be done either oad ba a c g ca be do e e eper packet or per destination.

–How a router actually load balances packets between the equal-cost paths is governed by the switching process.

R2 load balances traffic to PC5 over two equal cost paths.

Example


CRouter Paths: Equal Cost Load BalancingTo solve this dilemma, a router will use Equal Cost Load Balancing This means the router sends packets over the multipleBalancing. This means the router sends packets over the multiple exit interfaces listed in the routing table.

–per-packet load balancing•( Process Switching)

–per-destination load balancing. •(Fast Switching)•(Fast Switching)

Router(config-if)# ip route-cache Router(config-if)#no ip route-cache

ping 10.0.0.1ping 10.0.0.2ping 10.0.0.1ping 10.0.0.2



IP k t d b i i

per-packet load balancingIP packet debugging is on

GAD#




















( ), ( ), g , ,

http://www.cisco.com/en/US/products/ps5763/products_configuration_guide_chapter09186a00802a1fae.html#wp1045020RIB:

Router(config-if)#no ip route-cache


IP k d b i i

per-destination load balancingIP packet debugging is on

GAD#



*Mar 1 19:14:36.026: IP: tableid=0, s=192.168.16.2 (Serial0/1), d=192.168.14.2 (FastEthernet0/0), routed via RIB

*Mar 1 19:14:36.026: IP: s=192.168.16.2 (Serial0/1), d=192.168.14.2 (FastEthernet0/0), g=192.168.14.2, len 60, forward



*Mar 1 19:14:46.562: IP: s=192.168.14.1 (local), d=255.255.255.255 (FastEthernet0/0), len 92, sending broad/multicast



*Mar 1 19:14:51.958: IP: s=192.168.13.2 (Serial0/1), d=255.255.255.255, len 72, rcvd 2

*Mar 1 19:14:51.962: IP: s=192.168.15.2 (Serial0/0), d=255.255.255.255

Router(config-if)# ip route-cache

30© 2010 Cisco Systems, Inc. All rights reserved. Institut Tadbiran Awam Negarahttp://www.cisco.com/en/US/products/ps5763/products_configuration_guide_chapter09186a00802a1fae.html#wp1045020RIB:

Unequal Cost Load Balancing with EIGRP

EIGRP Load Balancing E ti t l t l t

What is unequal cost load balancing?

Every routing protocol supports equal cost path load balancing. In addition to that, IGRP and EIGRP also support unequal cost path load balancing.

Use the variance command to instruct the router to include routes with a metric less than n times the minimum metric route for that destination, where n is the number specified by the variancecommand. Example: E-C-A: 20 * 2 = 40. Therefore, E-C-A and E-B-A will be used for load balancing. router eigrp 1

network x.x.x.x variance 2


variance 2

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

Administrative Distance of a Route

In fact, a router might learn of a , groute to the same network from more than one source.

For example a static route might have– For example, a static route might have been configured for the same network/subnet mask that was learned dynamically by a dynamic routingdynamically by a dynamic routing protocol, such as RIP. The router must choose which route to install.

P f t iPurpose of a metric–It’s a calculated value used to determine the best path to a destination

Purpose of Administrative Distance–It’s a numeric value that specifies the

For equal cost routes to be installed they both must be static routes or they both must be RIP


preference of a particular route source. routes or they both must be RIP routes.


Administrative distance is an integer value from 0 to 255. g

The lower the value the more preferred the route source. –An administrative distance of 0 is the most preferred. –Only a directly connected network has an administrative distance of 0, which cannot be changed–An administrative distance of 255 means the router will not believeAn administrative distance of 255 means the router will not believe the source of that route and it will not be installed in the routing table.


Administrative Distance of a RouteAdministrative Distance of a RouteIdentifying the Administrative Distance (AD) in a routing tabletable

It is the first number in the brackets in the routing table

•R2 is running both RIP and EIGRP routing protocols.•R2 has learned of the 192.168.6.0/24 route from R1 through EIGRP updates and from R3 throughR1 through EIGRP updates and from R3 through RIP updates. •RIP has an administrative distance of 120, but EIGRP has a lower administrative distance of 90. S R2 dd th t l d i EIGRP t

This show ip rip database command shows all RIP routes learned by R2,

h th t th RIP t i i t ll d i


•So, R2 adds the route learned using EIGRP to the routing table and forwards all packets for the 192.168.6.0/24 network to router R1.

whether or not the RIP route is installed in the routing table.

Administrative Distance of a RouteAdministrative Distance of a RouteThe AD value can also be verified with thebe verified with the show ip protocols command.



Directly connected routesect y co ected outes-Immediately appear in the routing table as soon as the interface is configured



Directly connected routesyHave a default AD of 0

Static RoutesAdministrative distance of a static route has a default value of 1

A static route using either a next-hop IP address or an exit interface has a default AD value of 1interface has a default AD value of 1.

–However, the AD value is not listed in show ip route when you configure a static route with the exit interface specified. When a static

t i fi d ith it i t f th t t h th t kroute is configured with an exit interface, the output shows the network as directly connected via that interface.


SummarySummaryDynamic routing protocols fulfill the following functions

-Dynamically share information between routers-Dynamically share information between routers-Automatically update routing table when topology changes-Determine best path to a destination

Routing protocols are grouped as either-Interior gateway protocols (IGP)Or-Exterior gateway protocols(EGP)

Types of IGPs includeCl l ti t l th t l i l d b t k-Classless routing protocols - these protocols include subnet mask

in routing updates-Classful routing protocols - these protocols do not include subnet

k i ti d tmask in routing update


SummarySummaryMetrics are used by dynamic routing protocols to calculate the best path to a destinationbest path to a destination.Administrative distance is an integer value that is used to indicate a router’s “trustworthiness”indicate a router s trustworthinessComponents of a routing table include:

-Route sourceRoute source-Administrative distance (The smaller the better)-Metric (The smaller the better)( )


Distance Vector Routing Protocols




Objectives

Identify the characteristics of distance vector routing protocols.y g p

Describe the network discovery process of distance vector routing protocols using Routing Information Protocol (RIP).

Describe the processes to maintain accurate routing tables used by distance vector routing protocols.

Id tif th diti l di t ti l d l i thIdentify the conditions leading to a routing loop and explain the implications for router performance.

Recognize that distance vector routing protocols are in use todayRecognize that distance vector routing protocols are in use today



Dynamic routing protocols help the network administrator overcome the time-consuming and exacting process of configuring and maintaining static routesconsuming and exacting process of configuring and maintaining static routes.Examples of Distance Vector routing protocols:

Routing Information Protocol (RIP) RFC 1058–RFC 1058.

–Hop count is used as the metric for path selection. –If the hop count for a network is greater than 15, RIP cannot supply a route to that network.R ti d t b d t lti t 30 d b d f lt–Routing updates are broadcast or multicast every 30 seconds, by default.

Interior Gateway Routing Protocol (IGRP) –proprietary protocol developed by Cisco. –Bandwidth, delay, load and reliability are used to create a composite metric.Bandwidth, delay, load and reliability are used to create a composite metric. –Routing updates are broadcast every 90 seconds, by default. –IGRP is the predecessor of EIGRP and is now obsolete.

Enhanced Interior Gateway Routing Protocol (EIGRP)y g ( )–Cisco proprietary distance vector routing protocol. –It can perform unequal cost load balancing. –It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path. –There are no periodic updates as with RIP and IGRP Routing updates are sent only


–There are no periodic updates as with RIP and IGRP. Routing updates are sent only when there is a change in the topology.


The Meaning of Distance Vector:The Meaning of Distance Vector:–A router using distance vector routing protocols knows 2 things:

Distance to final destinationDistance to final destinationThe distance or how far it is to the destination network

Vector or direction traffic should be directedVector, or direction, traffic should be directedThe direction or interface in which packets should be forwarded

For example, in the figure, R1 knows that the distance to reach network 172.16.3.0/24 is 1 hop and that the direction is out the i t f S0/0/0 t d R2


interface S0/0/0 toward R2.

Distance Vector Routing ProtocolsDistance Vector Routing ProtocolsCharacteristics of Distance Vector routing protocols:

Periodic updatesp•Periodic Updates sent at regular intervals (30 seconds for RIP). Even if the topology has not changed in several days,

NeighborsThe router is only aware of the network addresses of its

own interfaces and the remote network addresses it can reach through its neighbors. It has no broader knowledge of the network topology

Broadcast updatesBroadcast Updates are sent to 255.255.255.255. Some distance vector routing protocols use multicast

addresses instead of broadcast addressesaddresses instead of broadcast addresses.Entire routing table is included with routing update

Entire Routing Table Updates are sent, with some exceptions to be discussed later, periodically to all exceptions to be discussed later, periodically to all neighbors. Neighbors receiving these updates must process the entire

update to find pertinent information and discard the rest. Some distance vector routing protocols like EIGRP do not


Some distance vector routing protocols like EIGRP do not send periodic routing table updates.

Distance Vector Routing ProtocolsDistance Vector Routing ProtocolsRouting Protocol Algorithm:

Th l ith i d t l l t th b t th d th d–The algorithm is used to calculate the best paths and then send that information to the neighbors.–Different routing protocols use different algorithms to install routes g p gin the routing table, send updates to neighbors, and make path determination decisions.


Distance Vector Routing ProtocolsRouting Protocol Characteristics

Criteria used to compare routing protocols includes–Criteria used to compare routing protocols includesTime to convergence

Time to convergence defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence, the more preferable the protocol.

ScalabilityScalability defines how large a network can become based on the routing protocol that is

deployeddeployed. The larger the network is, the more scalable the routing protocol needs to be.

Resource usageResource usage includes the requirements of a routing protocol such as memory space, g q g p y p ,

CPU utilization, and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing

protocol operationClassless (Use of VLSM) or Classful( )

Classless routing protocols include the subnet mask in the updates. This feature supports the use of Variable Length Subnet Masking (VLSM) and better route

summarization.Implementation & maintenance


Implementation & maintenanceImplementation and maintenance describes the level of knowledge that is required for a

network administrator to implement and maintain the network based on the routing protocol deployed.

Distance Vector Routing ProtocolsDistance Vector Routing Protocols


Network Discovery

Router initial start up (Cold Starts)

Cold StartsRouter initial start up (Cold Starts)

When a router cold starts or powers up, it knows nothing about the network topology. It does not even know that there are devices on the other end of its links. The only information that a router has is from its own saved configuration file stored in NVRAM.

Initial network discovery-Initial network discoveryDirectly connected networks are initially placed in

routing tablerouting table


Network Discovery I iti l E hNetwork DiscoveryInitial Exchange of Routing Information

–If a routing protocol is configured then

Initial Exchange

If a routing protocol is configured then•Routers will exchange routing information•Initially, these updates only include information about their directly connected networks.

Routing updates received from other routers–Router checks update for new information

•If there is new information:–Metric is updated–New information is stored in routing table

After this first round of update exchanges, each t k b t th t d t k f th irouter knows about the connected networks of their

directly connected neighbors. However, did you notice that R1 does not yet know about 10 4 0 0 and that R3 does not yet know aboutabout 10.4.0.0 and that R3 does not yet know about 10.1.0.0?

–Full knowledge and a converged network will not take place until there is another exchange of routing information


information.

Network DiscoveryNetwork DiscoveryNext Update of Routing Information

At thi i t th t h k l d b t

Next Update

–At this point the routers have knowledge about their own directly connected networks and about the connected networks of their immediate neighborsimmediate neighbors. –Continuing the journey toward convergence, the routers exchange the next round of periodic updates Each router again checks the updatesupdates. Each router again checks the updates for new information.

Routing updates received from other routers–Router checks update for new information

•If there is new information:–Metric is updated–New information is stored in routing table


Network DiscoveryNetwork DiscoveryDistance vector routing protocols

Split horizon

typically implement a technique known as split horizon.

–Split horizon prevents information from being sent out the same interface from which it wasinterface from which it was received.

For example R2 would not send–For example, R2 would not send an update out Serial 0/0/0 containing the network 10.1.0.0 gbecause R2 learned about that network through Serial 0/0/0.


Network DiscoveryNetwork DiscoveryExchange of Routing Information Next Update

–Router convergence is reached when•All routing tables in the network contain the same network informationinformation,•[Tony]: The above statement is trying to tell you, the routing tables contains the same network information, BUT, each router has it’s own

i i f h i blvariation of the routing table.

–Routers continue to exchange routing information

-If no new information is found then Convergence is reached


Network Discovery and convergenceThe amount of time it takes for a network to converge isThe amount of time it takes for a network to converge is directly proportional to the size of that network.

Convergence must be reached before a network is considered completely operable

Speed of achieving convergence consists of 2 interdependent categoriescategories

–How quickly the routers propagate a change in the topology in a routing update to its neighbors–The speed of calculating best path routes using the new routing information collected

45

For example: It takes five rounds of periodic update intervals before most of the branch routers in Regions 1 2 and 3

2

3


routers in Regions 1, 2, and 3 learn about the new routes advertised by B2-R4.

1

Routing Table Maintenance

Periodic Updates: RIPv1 & RIPv2Periodic Updates: RIPv1 & RIPv2–These are time intervals in which a router sends out its entire routing table.

•RIPv1: updates are sent every 30 seconds as a broadcast (255.255.255.255) whether or not there has been a topology changechange•RIPv2: updates are sent every 30 seconds as a multicast (224.0.0.9) whether or not there has been a topology change



Periodic Updates: distance vector protocolsPeriodic Updates: distance vector protocols employ periodic updates to exchange routing information with their neighbors and to maintain up-information with their neighbors and to maintain up-to-date routing information in the routing table.

Failure of a link–Failure of a link–Introduction of a new link–Failure of a router–Change of link parameters


R ti T bl M i tRouting Table MaintenanceRIP uses 4 timers

–Update timerp• interval is a route sends an update

–Invalid timer•If an update has not been received after 180 seconds (the default) the route is marked asseconds (the default), the route is marked as invalid by setting the metric to 16. •The route is retained in the routing table until the flush timer expires.

–Holddown timer•This timer stabilizes routing information and helps prevent routing loops during periods when the topology is converging on new information. B d f lt th h ldd ti i t f 180•By default, the holddown timer is set for 180

seconds.–Flush timer

•By default, the flush timer is set for 240 seconds which is 60 seconds longer than theseconds, which is 60 seconds longer than the invalid timer. •When the flush timer expires, the route is removed from the routing table.



EIGRPEIGRP–Unlike other distance vector routing protocols, EIGRP does not send periodic updates. –Instead, EIGRP sends bounded updates about a , proute when a path changes or the metric for that route changes.

EIGRP routing updates are –Partial updates

•Updates sent only when there is a change in topology that influences routing information

T i d b t l h–Triggered by topology changes–Bounded

•Propagation of partial updates are automatically bounded so that only those routers that need thebounded so that only those routers that need the information are updated

–Non periodic•Updates are not sent out on a regular basis.


Updates are not sent out on a regular basis.

More details on how EIGRP operates will be presented in Chapter 9.

Routing Table MaintenanceRouting Table MaintenanceRIP Triggered Updates

–Routing table update that is sent immediately to adjacent routers in response to a routing change– The receiving routers in turn generate triggered updates– The receiving routers, in turn, generate triggered updates that notify their neighbors of the change.

Conditions in which triggered updates are sentConditions in which triggered updates are sent–Interface changes state–Route becomes unreachable–Route is placed in routing table


Routing Table MaintenanceRouting Table Maintenance

RIP Triggered Updates (problems)problems

RIP Triggered Updates (problems)–Using only triggered updates would be sufficient if there were a guarantee that the wave of updates would reach everywave of updates would reach every appropriate router immediately.

However, there are two problems with triggered updates:triggered updates:

–Packets containing the update message can be dropped or corrupted by some link in the networknetwork.–The triggered updates do not happen instantaneously. It is possible that a router that has not yet received the triggered update will y gg pissue a regular update at just the wrong time, causing the bad route to be reinserted in a neighbor that had already received the triggered update


triggered update.

Triggered Extensions to RIPTriggered Extensions to RIP

P i itProblems and PrerequisitesPrerequisites

–RIP must be enabled for this feature to function.function. –This feature runs on a point-to-point, serial interface only –Triggered extensions to IP RIP increase efficiency of RIP on point-to-point, serial interfaces.p ,

•interface serial 0 • ip rip triggered

http://cisco.com/en/US/docs/ios/12_0t/12_0t1/feature/guide/trigrip.html


Routing Table MaintenanceRouting Table MaintenanceRandom Jitter

Synchronized updatesSynchronized updatesA condition where multiple routers on multi access LAN segments transmit routing updates at the same time.P bl ith h i d d tProblems with synchronized updates

-Bandwidth consumption-Packet collisions (with hubs and not with switches)Packet collisions (with hubs and not with switches)

Solution to problems withsynchronized updates

- Used of random variable called RIP_JITTER

•A good reference is : Routing TCP/IP (Jeff Doyle) page 193-196. •Update timers : timer for periodic update


Update timers : timer for periodic update (default 30s) - RIP_JITTER (random to prevent colision - 15% of the update timers)

Routing Table MaintenanceRouting Table MaintenanceRandom Jitter

•Figure 5 1 RIP adds a small random variable to the update timer•Figure 5.1. RIP adds a small random variable to the update timer at each reset to help avoid routing table synchronization. The RIP updates from Cisco routers vary from 25.5 to 30 seconds, as h i th d lt ti f th d tshown in the delta times of these updates.

Routing TCP/IP, Volume I (CCIE ProfessionalProfessional Development)


http://www.ubookcase.com/book/Cisco/Routing.TCP.IP.Volume.I.CCIE.Professional.Development/source/1578700418/ch05lev1sec1.html#ch05fig1

R ti LRouting Loops

Routing loops are A condition in which a A condition in which a packet is continuously transmitted within a

i f tseries of routers without ever reaching its destination.its destination.


Routing Loops

Routing loops may be caused by:-Incorrectly configured static routes-Incorrectly configured route redistribution-Slow convergenceIncorrectl config red discard ro tes-Incorrectly configured discard routes

Routing loops can create the following issuesExcess use of bandwidth-Excess use of bandwidth

-CPU resources may be strained-Network convergence is degradedNetwork convergence is degraded-Routing updates may be lost or not processed in a timely manner


Routing Loops

Routing loops can eliminate–Defining a maximum metric to prevent count to infinityg p y–Holddown timers–Split horizon–Route poisoning or poison reverse–Triggered updates

Note: The IP protocol has its own mechanism to prevent the possibility of a packet traversing the

( ) fnetwork endlessly. IP has a Time-to-Live (TTL) field and its value is decremented by 1 at each router.

If the TTL is zero the router drops the packet


–If the TTL is zero, the router drops the packet.

Preventing loops with Count to Infinity

C t t I fi itCount to Infinity–It is a condition that exists when inaccurate routing

d t i th t i l t "i fi it " fupdates increase the metric value to "infinity" for a network that is no longer reachable.

This is a routing loop whereby packets bounce–This is a routing loop whereby packets bounce infinitely around a network.


Preventing loops by Setting a maximumSetting a maximumg

Distance Vector routing protocols set a specified metric value to indicate infinityy

Once a router “counts to infinity” it marks the route as unreachable

RIP defines infinity as 16 hops - an "unreachable" metric.metric.


P ti l ith h ldd tiPreventing loops with holddown timersHolddown timers are used to prevent regularHolddown timers are used to prevent regular update messages from inappropriately reinstating a route that may have gone bad.

H ldd ti ll t t t t h t-Holddown timers allow a router to not accept any changes to a route for a specified period of time.

- Do not appept the update when the route is flapping-Point of using holddown timers

Allows routing updates to propagate through network with the most current informationthe most current information.


fHolddown timers work in the following way1. A router receives an update from a neighbor indicating that a network that previously

ibl i l iblwas accessible is now no longer accessible.

2. The router marks the network as possibly down and starts the holddown timer.

3. If an update with a better metric for that network is received from any neighboring router during the holddown period the network is reinstated and the holddown timerrouter during the holddown period, the network is reinstated and the holddown timer is removed.

4. If an update from any other neighbor is received during the holddown period with the same or worse metric for that network, that update is ignored. Thus, more time is allowed for the information about the change to be propagated.

5. Routers still forward packets to destination networks that are marked as possibly down. This allows the router to overcome any issues associated with intermittent connectivity. If the destination network truly is unavailable and the packets areconnectivity. If the destination network truly is unavailable and the packets are forwarded, black hole routing is created and lasts until the holddown timer expires.


P ti l ith h ldd tiPreventing loops with holddown timers


P ti l ith Split HorizonPreventing loops with Split Horizon The Split Horizon Rule is used to prevent routing loops

Split Horizon rule:

A router should not advertise a network through theA router should not advertise a network through the interface from which the update came.

Because of split horizon, R1 also does not advertisedoes not advertise the information about network 10 4 0 0 back to


10.4.0.0 back to R2

Preventing loops with Route Poisoning

Split horizon with RouteSplit horizon with Route poisoning

–Route poisoning is used toRoute poisoning is used to mark the route as unreachable in a routing update that is sent to otherupdate that is sent to other routers. –Unreachable is interpreted

t i th t i t t th 1616as a metric that is set to the maximum. –For RIP, a poisoned route

1616

, phas a metric of 16.


Preventing loops with poison reverse

Split horizon with poisonSplit horizon with poison reverse

–The rule states that once aThe rule states that once a router learns of an unreachable route through an interface advertise it asinterface, advertise it as unreachable back through the same interface

P i i ifi–Poison reverse is a specific circumstance that overrides split horizon. It occurs to

th t R3 i tensure that R3 is not susceptible to incorrect updates about network 10 4 0 0


10.4.0.0.

Preventing loops with TTLPreventing loops with TTLIP & TTL

P f th TTL fi ld–Purpose of the TTL field

The TTL field is found in an IP header and i d t t k t f dl lis used to prevent packets from endlessly traveling on a network

H th TTL fi ld kHow the TTL field works

-TTL field contains a numeric value

The numeric value is decreased by one by every router on the route to the destination.

If numeric value reaches 0 then Packet is discarded.


Preventing loops with TTLPreventing loops with TTL


Routing Protocols TodayRouting Protocols TodayFactors used to determine whether to use RIP or EIGRP includeinclude

-Network size-Compatibility between models of routersCo pat b ty bet ee ode s o oute s-Administrative knowledge


Routing Protocols Today

RIPFeatures of RIP:Features of RIP:

-Supports split horizon & split horizon with poison reversepoison reverse

-Capable of load balancing

-Easy to configure

-Works in a multi vendor router environmentWorks in a multi vendor router environment



RIP V2F t f RIPFeatures of RIP:

•Includes the subnet mask in the routing updates, making it a classless routing protocol.•Has authentication mechanism to secure routing t bl d ttable updates.•Supports variable length subnet mask (VLSM).•Uses multicast addresses instead of broadcast.•Supports manual route summarization.



EIGRPFeatures of EIGRP:Features of EIGRP:

-Triggered updatesEIGRP h ll t l d t t bli h-EIGRP hello protocol used to establish

neighbor adjacenciesSupports VLSM & route summarization-Supports VLSM & route summarization

-Use of topology table to maintain all routes-Classless distance vector routing protocol-Cisco proprietary protocol


Summary

Characteristics of Distance Vector routingCharacteristics of Distance Vector routing protocols

–Periodic updatesp–RIP routing updates include the entire routing table–Neighbors are defined as routers that share a link and are configured to use the same protocolconfigured to use the same protocol

The network discovery process for D.V. routing protocolprotocol

–Directly connected routes are placed in routing table 1st

–If a routing protocol is configured then•Routers will exchange routing information

–Convergence is reached when all network routers have the t k i f ti


same network information

Summary

D.V. routing protocols maintains routing tables byg p g y–RIP sending out periodic updates–RIP using 4 different timers to ensure information is accurate and convergence is achieved in a timely manner–EIGRP sending out triggered updates

D.V. routing protocols may be prone to routing loops– routing loops are a condition in which packets continuously traverse a networktraverse a network–Mechanisms used to minimize routing loops include defining maximum hop count, holddown timers, split horizon, route poisoning and triggered updates


SSummaryConditions that can lead to routing loops includeg

–Incorrectly configured static routes–Incorrectly configured route redistribution–Slow convergence–Incorrectly configured discard routes

How routing loops can impact network performance includes:

–Excess use of bandwidth–CPU resources may be strained

N t k i d d d–Network convergence is degraded–Routing updates may be lost or not processed


Summary

Routing Information Protocol (RIP)A distance vector protocol that has 2 versions

RIPv1 – a classful routing protocolRIPv2 - a classless routing protocol

Enhanced Interior Gateway Routing Protocol (EIGRP)

–A distance vector routing protocols that has some features of link state routing protocols

A Cisco proprietary routing protocol–A Cisco proprietary routing protocol


RIP version 1




Objectives

Describe the functions, characteristics, and operation esc be e u c o s, c a ac e s cs, a d ope a oof the RIPv1 protocol.

Configure a device for using RIPv1.Configure a device for using RIPv1.

Verify proper RIPv1 operation.

fDescribe how RIPv1 performs automatic summarization.

Configure, verify, and troubleshoot default routes propagated in a routed network implementing RIPv1.

Use recommended techniques to solve problems related to RIPv1


RIP Historical Impact

RIP evolved from an earlier protocol pdeveloped at Xerox, called Gateway Information Protocol (GWINFO). With the development of Xerox Network System (XNS) GWINFO evolved intoSystem (XNS), GWINFO evolved into RIP. It later gained popularity because it was implemented in the Berkeley Software p yDistribution (BSD) as a daemon named routed (pronounced "route-dee", not "rout-ed"). Recognizing the need for standardizationRecognizing the need for standardization of the protocol, Charles Hedrick wrote RFC 1058 in 1988, in which he documented the existing protocol and specified some improvementsspecified some improvements. Since then, RIP has been improved with RIPv2 in 1994 and with RIPng in 1997. IPv6 form of RIP called

RIPng (next generation) is


RIPng (next generation) is now available

RIPv1

RIP Characteristics–A classful, Distance Vector (DV) routing protocol(DV) routing protocol–Metric = hop count–Routes with a hop count > 15 pare unreachable–Updates are broadcast every 30 seconds30 seconds–The data portion of a RIP message is encapsulated into a UDP segment with botha UDP segment, with both source and destination port numbers set to 520.


RIPv1RIPv1RIP Message FormatRIP header - divided into 3 fieldsRIP header divided into 3 fields

–Command field•REQUEST (1)- Request either a partial or full table update from another RIP router. •RESPONSE (2) - A response to a request.

–Version field•1 or 2•1 or 2

–Must be zero•Must be zero" fields provide room for future expansion of the pprotocol.

Route Entry - composed of 3 fields

–Address family identifier•CLNS, IPX, IP etc.

–IP address


–Metric

RIPv1

RIP Operation–RIP uses 2 message types:

Request message

-This is sent out on startup by each RIP-This is sent out on startup by each RIP enabled interface

Requests all RIP enabled neighbors to send-Requests all RIP enabled neighbors to send routing table

Response messageResponse message

-Message sent to requesting router containing routing table


containing routing table

RIP 1RIPv1IP addresses initially divided yinto classes

-Class AClass A

-Class B

C C-Class C

RIP is a classful routing protocol

-Does not send subnet masks in routing updates


Common RIP configuration issues g

RIP and IGRP:

Classful network statements only

IOS will take subnetted networks but will translate it into the classful network for the running-config.


RIPv1RIPv1Administrative Distance

–RIP’s default administrative distance is 120


Basic RIPv1 Configuration

A typical topology suitable forA typical topology suitable for use by RIPv1 includes:

-Three router set upThree router set up -No PCs attached to LANs

U f 5 diff t IP-Use of 5 different IP subnets


B i RIP 1 C fi tiBasic RIPv1 ConfigurationRouter RIP CommandRouter RIP Command

–To enable RIP enter:Router rip at the global configuration prompt-Router rip at the global configuration prompt-Prompt will look like R1(config-router)#


Basic RIPv1 ConfigurationBasic RIPv1 ConfigurationSpecifying Networksp y g

–Use the networkcommand to:

-Enable RIP on all interfaces that belong to this network-Advertise this network in RIP updatesupdates sent to other routers


every 30 seconds

Verification and Troubleshooting

Show ip Route

To verify andTo verify and troubleshoot routing

-Use the following

commands:

-show ip route

show ip protocols-show ip protocols

-debug ip rip


V ifi ti d T bl h tiVerification and Troubleshooting

show ip protocolsshow ip protocolscommand

-Displaysrouting

t lprotocol configured

ton router

POP QUIZ:POP QUIZ:What is the different

between the output of the command “show ip route”


pand “show ip protocol”?

Verification and TroubleshootingVerification and TroubleshootingDebug ip rip command

Used to display RIP routing updates as they are-Used to display RIP routing updates as they are happening



Passive interface command

-Used to prevent a router from sending updates throughUsed to prevent a router from sending updates through an interface

-Example:-Example:

Router(config-router)#passive-interface interface-type interface-number



Passive interfacesPassive interfaces


Preventing routing updates through an interface g g p gRoute filtering works by regulating the routes that are entered into or advertised out of a route table.

L bAs a result, a route filter influences which routes the router advertises to its neighbors.

On the other hand routers running link

Lab:

On the other hand, routers running link state protocols determine routes based on information in the link-state database. Route filters have no effect on link-state advertisements or the link state databaseadvertisements or the link-state database.

(Tony) Route filtering could have negative effect on the link-state routing protocol.

Using the passive interface commandUsing the passive interface command can prevent routers from sending routing updates through a router interface, but the router continues to listen and use routing updates from that neighborrouting updates from that neighbor.

Keeping routing update messages from being sent through a router interface prevents other systems on that network from learning about routes dynamically


from learning about routes dynamically.

Preventing routing updatesPreventing routing updates through an interface

Again this is only half the

It will break the rip update1

Again, this is only half the story.

When you use “passiveWhen you use “passive interface” on a distance vector routing protocol, you g p , yneed to complement it with “ip route” command.

You can use the “ip route” command to send route update

b k bli h h 22

back to establish the 2 way communication


Automatic SummarizationAutomatic Summarization Modified Topology

The original scenario has beenThe original scenario has been modified such that:

Three classful networks are used:

172.30.3.0

172.30.0.0/16192.168.4.0/24192 168 5 0/24

172.30.2.0

172.30.1.0

192.168.5.0/24The 172.30.0.0/16 network is subnetted into three subnets:

172.30.1.0/24172.30.2.0/24172.30.3.0/24

The following devices are part of the 172.30.0.0/16 classful network address:


All interfaces on R1S0/0/0 and Fa0/0 on R2

Automatic Summarization

C fi ti D t ilConfiguration Details

-To remove the RIP routing th f ll iprocess use the following

command

N t iNo router rip

-To check the configuration use the following command

Show run


Automatic SummarizationAutomatic SummarizationBoundary Routers

RIP automatically summarizes classful networks–RIP automatically summarizes classful networks–Boundary routers summarize RIP subnets from one major network to anothermajor network to another.


Automatic SummarizationAutomatic SummarizationProcessing RIP Updates

2 rules govern RIPv1 updates:-If a routing update and the interface it’s g preceived on belong to the samenetwork then

The subnet mask of theThe subnet mask of the interface is applied to the network in the routing update

If a routing update and the interface it’s-If a routing update and the interface it s received on belong to a differentnetwork then

Th l f l b k f hThe classful subnet mask of the network is applied to the network in the routing update.



Sending RIP UpdatesSending RIP Updates–RIP uses automatic summarization to reduce the size of a routing tablesize of a routing table.


A i S i iAutomatic SummarizationAdvantages of automaticAdvantages of automatic summarization:

-The size of-The size of routing updates is reduced

-Single routes are used to represent multiple routes which results in faster lookup in thefaster lookup in the routing table.


Automatic SummarizationAutomatic SummarizationDisadvantage of Automatic Summarization:

-Does not support discontiguous networks



Discontiguous Topologies do not

i h RIP 1converge with RIPv1

A router will onlyA router will only advertise major network addresses out interfaces that do not belong to the advertised route.


Default Route and RIPv1Default Route and RIPv1Modified Topology: Scenario Cp gy

Default routes P k h d fi d ifi ll i iPackets that are not defined specifically in a routing table will go to the specified interface for the default routeroute

Example: Customer routers use default routes to connect to an ISP router.connect to an ISP router.

Command used to configure a default route isip route 0 0 0 0 0 0 0 0 s0/0/1ip route 0.0.0.0 0.0.0.0 s0/0/1


Default Route and RIPv1Default Route and RIPv1


D f lt R t d RIP 1Default Route and RIPv1Propagating the Default Route in RIPv1Propagating the Default Route in RIPv1

Default-information originate command This command is used to specify that the router is to originate-This command is used to specify that the router is to originate

default information, by propagating the static default route in RIP update.


Default route with RIP

Centre#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,

Gateway of last resort is not set M bil # h i tGateway of last resort is not set

R 192.168.4.0/24 [120/1] via 192.168.2.1, 00:00:11, Serial0R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:11, Serial0C 192.168.2.0/24 is directly connected, Serial0

Mobile#sho ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,

Gateway of last resort is not set

R 192 168 4 0/24 [120/1] i 192 168 1 1 00 00 04 S i l0C 192.168.3.0/24 is directly connected, Ethernet0 R 192.168.4.0/24 [120/1] via 192.168.1.1, 00:00:04, Serial0

C 192.168.5.0/24 is directly connected, Ethernet0

C 192.168.1.0/24 is directly connected, Serial0

R 192.168.2.0/24 [120/1] via 192.168.1.1, 00:00:04, Serial0

R 192 168 3 0/24 [120/2] via 192 168 1 1 00:00:04 Serial0

Centre(config)#ip route 0.0.0.0 0.0.0.0 loopback0Setup up a default route on the Centre router

Centre(config)#router rip R 192.168.3.0/24 [120/2] via 192.168.1.1, 00:00:04, Serial0Centre(config)#router ripCentre(config-router)#default-information originate

Centre#sh ip route

Codes: C - connected, S - static, * - candidate default

Mobile#sho ip route

Codes: C - connected, S - static, * - candidate default - RIP, , ,

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

C 172.16.1.1 is directly connected, Loopback0

R 192.168.4.0/24 [100/8576] via 192.168.2.1, 00:00:22, Serial0

Gateway of last resort is 192.168.1.1 to network 0.0.0.0

R 192.168.4.0/24 [120/1] via 192.168.1.1, 00:00:09, Serial0

C 192.168.5.0/24 is directly connected, Ethernet0


9 68 0/ [ 00/85 6] a 9 68 , 00 00 , Se a 0

R 192.168.5.0/24 [120/2] via 192.168.2.1, 00:00:22, Serial0

S* 0.0.0.0/0 is directly connected, Loopback0

C 192.168.1.0/24 is directly connected, Serial0

R 192.168.2.0/24 [120/1] via 192.168.1.1, 00:00:04, Serial0

R 192.168.3.0/24 [120/2] via 192.168.1.1, 00:00:09, Serial0

R* 0.0.0.0/0 [120/2] via 192.168.1.1, 00:00:09, Serial0

Summary

RIP characteristics include:

Cl f l di t t ti t lClassful, distance vector routing protocol

Metric is Hop Count

Does not support VLSM or discontiguous subnets

Updates every 30 secondsUpdates every 30 seconds

Rip messages are encapsulated in a UDP segment with source and destination ports of 520with source and destination ports of 520


Summary: Commands used by RIPCommand Command’s purpose

Rtr(config)#router rip Enables RIP routing process

Rtr(config-router)#network Associates a network with a RIP routing process

Rtr#debug ip rip used to view real time RIP routing updates

Rtr(config-router)#passive-interface fa0/0 Prevent RIP updates from going out an interface

Rtr(config-router)#default-information originate Used by RIP to propagate default routes

Rtr#show ip protocols Used to display timers used by RIP


p p p y y

VLSM and CIDR




Objectives

Compare and contrast classful and classless IP Co pa e a d co as c ass u a d c ass essaddressing.

Review VLSM and explain the benefits of classless IPReview VLSM and explain the benefits of classless IP addressing.

Describe the role of the Classless Inter-DomainDescribe the role of the Classless Inter Domain Routing (CIDR) standard in making efficient use of scarce IPv4 addresses

In addition to subnetting, it became possible to summarize a large collection of classful networks into an aggregate route, or supernet.


IntroductionIntroductionPrior to 1981, IP addresses used only the first 8 bits to specify the network portion of the addressp

In 1981, RFC 791 modified the IPv4 32-bit address to allow for three different classes

•Class A addresses used 8 bits for the network portion of the address, •Class B used 16 bits, •Class C used 24 bits•Class C used 24 bits.

–This format became known as classful IP addressing.

IP address space was depleting rapidlyIP address space was depleting rapidlythe Internet Engineering Task Force (IETF) introduced Classless Inter-Domain Routing (CIDR)

–CIDR uses Variable Length Subnet Masking (VLSM) to help conserve address space.

-VLSM is simply subnetting a subnet


-VLSM is simply subnetting a subnet

IntroductionIntroductionWith the introduction of CIDR and VLSM, ISPs co ld no assign one part of a classf l net ork tocould now assign one part of a classful network to one customer and different part to another customercustomer.

This discontiguous address assignment by ISPs was paralleled by the development of classless routing protocols.

–Classless routing protocols do include the subnet mask in routing updates and are not required to perform

i tisummarization. –The classless routing protocols discussed in this course are RIPv2 EIGRP and OSPF


course are RIPv2, EIGRP and OSPF.

Classful and Classless IP AddressingClassful and Classless IP Addressing Classful IP addressing

When the ARPANET was commissioned in 1969 no one–When the ARPANET was commissioned in 1969, no one anticipated that the Internet would explode. –1989, ARPANET transformed into what we now call the Internet.

As of January 2007 there are over 433 million hosts on internet–As of January 2007, there are over 433 million hosts on internet

Initiatives to conserve IPv4 address space include:VLSM & CIDR notation (1993 RFC 1519)-VLSM & CIDR notation (1993, RFC 1519)

-Network Address Translation (1994, RFC 1631)Private Addressing (1996 RFC 1918)-Private Addressing (1996, RFC 1918)


Classful and Classless IP AddressingClassful and Classless IP AddressingClasses of IP addresses are identified by the decimal number of the 1st octet

Class A address begin with a 0 bit

Range of class A addresses = 0 0 0 0 to 127 255 255 255Range of class A addresses 0.0.0.0 to 127.255.255.255

Class B address begin with a 1 bit and a 0 bit

Range of class B addresses = 128 0 0 0 to 191 255 255 255Range of class B addresses = 128.0.0.0 to 191.255.255.255

Class C addresses begin with two 1 bits & a 0 bit

R f l C dd 192 0 0 0 t 223 255 255 255Range of class C addresses = 192.0.0.0 to 223.255.255.255.


Classful and Classless IP AddressingClassful and Classless IP AddressingMulticast addresses begin with three 1s and a 0 bit. gMulticast addresses are used to identify a group of hosts that are part of a multicast group. IP addresses that begin with four 1 bits were reserved for future use.


Classf l and Classless IP AddressingClassful and Classless IP AddressingThe IPv4 Classful Addressing Structure (RFC 790)

A IP dd h 2An IP address has 2 parts:

-The network portion

Found on the left side of an IP address

-The host portion

Found on the right side of an IP address


Classf l and Classless IP AddressingClassful and Classless IP AddressingAs shown in the figure, class A networks used the first octet for network assignment which translated to a 255 0 0 0for network assignment, which translated to a 255.0.0.0 classful subnet mask.

–Because only 7 bits were left in the first octet (remember the first bitBecause only 7 bits were left in the first octet (remember, the first bit is always 0), this made 2 to the 7th power or 128 networks. –With 24 bits in the host portion, each class A address had the

t ti l f 16 illi i di id l h t ddpotential for over 16 million individual host addresses.


Classf l and Classless IP AddressingClassful and Classless IP AddressingWith 24 bits in the host portion, each class A address had the potential for over 16 million individual host addressesthe potential for over 16 million individual host addresses. What was one organization going to do with 16 million addresses?addresses? Now you can understand the tremendous waste of address space that occurred in the beginning days of the Internet, p g g ywhen companies received class A addresses. Some companies and governmental organizations still have l A ddclass A addresses.

–General Electric owns 3.0.0.0/8, Apple Computer owns 17 0 0 0/8–Apple Computer owns 17.0.0.0/8,

–U.S. Postal Service owns 56.0.0.0/8.


Classf l and Classless IP AddressingClassful and Classless IP AddressingClass B: RFC 790 specified the first two octets as networknetwork.

–With the first two bits already established as 1 and 0, 14 bits remained in the first two octets for assigning networks, which resulted in 16 384 class B network addressesresulted in 16,384 class B network addresses. –Because each class B network address contained 16 bits in the host portion, it controlled 65,534 addresses. (Remember, 2 addresses were reserved for the network and broadcastaddresses were reserved for the network and broadcast addresses.)


Classf l and Classless IP AddressingClassful and Classless IP Addressingclass C: RFC 790 specified the first three octets as networkas network.

–With the first three bits established as 1 and 1 and 0, 21 bits remained for assigning networks for over 221 bits remained for assigning networks for over 2 million class C networks. –But, each class C network only had 8 bits in the host yportion, or 254 possible host addresses.


Classf l and Classless IP AddressingClassful and Classless IP AddressingClassful Routing Updates

–Recall that classful routing protocols (i.e. RIPv1) do not send subnet masks in their routing updates –This is because the router receiving the routing update could–This is because the router receiving the routing update could determine the subnet mask simply by examining the value of the first octet in the network address, or by applying its ingress interface mask for subnetted routes The subnet mask wasinterface mask for subnetted routes. The subnet mask was directly related to the network address.

/24 /16


/24

Classf l and Classless IP AddressingClassful and Classless IP AddressingIn the example,

R1 knows that subnet 172 16 1 0 belongs to the same major classful–R1 knows that subnet 172.16.1.0 belongs to the same major classful network as the outgoing interface. Therefore, it sends a RIP update to R2 containing subnet 172.16.1.0.

When R2 recei es the pdate it applies the recei ing interface s bnet•When R2 receives the update, it applies the receiving interface subnet mask (/24) to the update and adds 172.16.1.0 to the routing table

–When sending updates to R3, R2 summarizes subnets 172.16.1.0/24, 172 16 2 0/24 d 172 16 3 0/24 i t th j l f l t k 172 16 0 0172.16.2.0/24, and 172.16.3.0/24 into the major classful network 172.16.0.0.

•Because R3 does not have any subnets that belong to 172.16.0.0, it will apply the classful mask for a class B network, /16

/16


/24 /16

Classful and Classless IP AddressingClassless Inter-domain Routing (CIDR – RFC 1517)g ( )

Advantage of CIDR :More efficient use of IPv4 address spaceRoute summarization

( reduce routing table size) ( reduce routing update traffic)( reduce routing update traffic)

Requires subnet mask to be included in routing update because address class is meaningless

The network portion of the address is determined by the network subnet mask, also known as the network prefix, or prefix length (/8, /19, etc.). The network address is no longer determined by the class of the

addressBlocks of IP addresses could be assigned to a network based on the


Blocks of IP addresses could be assigned to a network based on the requirements of the customer, ranging from a few hosts to hundreds or thousands of hosts.

Classful and Classless IP AddressingClassful and Classless IP AddressingClassless IP Addressing

CIDR & Route Summarization–Variable Length Subnet Masking (VLSM)–Allows a subnet to be further sub-netted

•according to individual needs–Prefix Aggregation a.k.a. Route Summarization–CIDR allows for routes to be summarized as a single route


Classful and Classless IP AddressingClassful and Classless IP AddressingRoute Summarization

– In the figure, notice that ISP1 has four customers, each with a variable amount of IP address space.

However all of the customer address space can be summarized–However, all of the customer address space can be summarized into one advertisement to ISP2. –The 192.168.0.0/20 summarized or aggregated route includes all the networks belonging to Customers A, B, C, and D.

•This type of route is known as a supernet route. A t i lti l t k dd ith k•A supernet summarizes multiple network addresses with a mask

less than the classful mask.


Classful and Classless IP AddressingClassful and Classless IP AddressingRoute Summarization

– Propagating VLSM and supernet routes requires a classless routing protocol, because the subnet mask can no longer be determined by the value of the first octet.

•Classless routing protocols include the subnet mask ith th t k dd i th ti d twith the network address in the routing update.

•RIPv2, EIGRP, IS-IS, OSPF and BGP. I i•Interior:

•RIPv2•EIGRPEIGRP •IS-IS•OSPF

Exterior:


•Exterior: •BGP

Classful and Classless IP AddressingClassful and Classless IP Addressing

Is there any differenceIs there any difference between the terms CIDR and VLSM??


Classful and Classless IP Addressing

For example, the networks 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16 pand 172.19.0.0/16 can be summarized as 172.16.0.0/14.

–If R2 sends the 172.16.0.0 summary route without the /14 mask, R3 only knows to apply the default classful mask of /16. –In a classful routing protocol scenario, R3 is unaware of the 172.17.0.0/16, 172.18.0.0/16 and 172.19.0.0/16 networks–With a classless routing protocol, R2 will advertise the 172.16.0.0 g pnetwork along with the /14 mask to R3. R3 will then be able to install the supernet route 172.16.0.0/14 in its routing table giving it reachability to the 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16 and 172.19.0.0/16 networks.


172.16.0.0 /14

Classful and Classless IP Addressing

Classless Routing ProtocolClassless Routing Protocol

Routing Routing Supports Ability toRoutingProtocol

Routing updatesInclude

Supports VLSM

Ability to send

Supernet c udesubnet Mask

Supe eroutes

Classful

(RIPv1)No No No

(RIPv1)

Classless Yes Yes Yes


VLSMVLSMClassful routing

only allows for one-only allows for one subnet mask for all networks

VLSM & classless routing-This is the processThis is the process of subnetting a subnet-More than one subnet mask can be used

-More efficient use of IP addresses as compared to classful IP


to classful IP addressing

VLSMVLSMVLSM – the process of sub netting a subnet to fitsub-netting a subnet to fit your needs-Example:Example:Subnet 10.1.0.0/16, 8 more bits are borrowed o e b ts a e bo o edagain, to create 256 subnets with a /24 mask.

M k ll f 254 h t-Mask allows for 254 host addresses per subnet-Subnets range from: 10 1 0 0 / 24 t10.1.0.0 / 24 to 10.1.255.0 / 24

* Same process for Subnet


Same process for Subnet 10.2.0.0/16

VLSMVLSMSubnet 10.3.0.0/16, 12 more bits are borrowedmore bits are borrowed again, to create 4,096 subnets with a /28 mask.

–Mask allows for 14 host addresses per subnet–Subnets range from: 10.3.0.0Subnets range from: 10.3.0.0 / 28 to 10.3.255.240 / 28

Subnet 10.4.0.0/16, 4 more bit b d i tbits are borrowed again, to create 16 subnets with a /20 mask.

–Mask allows for 2,046 host addresses per subnetSubnets range from: 10 4 0 0


–Subnets range from: 10.4.0.0 / 20 to 10.4.240.0 / 20

Classless Inter Domain Routing (CIDR)Classless Inter-Domain Routing (CIDR)Route summarization done by CIDR

-Routes are summarized with masks that are less than that of the default classful mask (supernetting)

-Example:

172.16.0.0 / 13 is the summarized route for the 172.16.0.0 / 16 to 172.23.0.0 / 16 classful networks

Although 172.22.0.0/16 and 172.23.0.0/16 are not shown in the graphic, these are also included in the summary routeincluded in the summary route.


Classless Inter Domain Routing (CIDR)Classless Inter-Domain Routing (CIDR)Note: You may recall that a supernet is always a route summary, but a route summary is not always a supernet.a route summary is not always a supernet.

–It is possible that a router could have both a specific route entry and a summary route entry covering the same network.

L t th t t X h ifi t f 172 22 0 0/16 i–Let us assume that router X has a specific route for 172.22.0.0/16 using Serial 0/0/1 and a summary route of 172.16.0.0/13 using Serial0/0/0. –Packets with the IP address of 172.22.n.n match both route entries. –These packets destined for 172.22.0.0 would be sent out the Serial0/0/1 interface because there is a more specific match of 16 bits, than with the 13 bits of the 172.16.0.0/13 summary route.

ip route 172.22.0.0 255.255.0.0 s 0/0/1

Router X

255.255.0.0 s 0/0/1

s 0/0/1


Classless Inter-Domain Routing (CIDR)

Steps to calculate a route summary

1 Li t t k i bi1. List networks in binary format2 Count number of left2. Count number of left most matching bits to determine summary

t ’ kroute’s mask3. Copy the matching bits and add zero bitsbits and add zero bits to determine the summarized


network address


Which address can be usedWhich address can be used to summarize networks A:• 192.168.0.0/30• 192.168.0.4/30

192 168 0 8/30

11000000 10101000 00000000 0000000011000000 10101000 00000000 0000010011000000 10101000 00000000 00001000• 192.168.0.8/30

• 192.168.0.16/29• B

11000000 10101000 00000000 0000100011000000 10101000 00000000 00010000

• 192.168.4.0/30• 192.168.5.0/30• 192 168 6 0/30

11000000 10101000 00000100 0000000011000000 10101000 00000101 0000000011000000 10101000 00000110 00000000• 192.168.6.0/30

• 192.168.7.0/2911000000 10101000 00000110 0000000011000000 10101000 00000111 00000000


Answer:


Reverse process of summary route:Reverse process of summary route:Can you figure what networks are included in 192.168.32.0 /20

11000000 10101000 00100000 00000000

11000000 10101000 00100000 0000000011000000 10101000 00100000 0000000011000000 10101000 00100001 0000000011000000 10101000 00100010 00000000

…..…..

11000000 10101000 00101101 0000000011000000 10101000 00101101 0000000011000000 10101000 00101110 0000000011000000 10101000 00101111 00000000


Answer:

Designing VLSM Addressing 6.4.1

In this activity, you will use the network address 192 168 1 0/24address 192.168.1.0/24 to subnet and provide the IP addressing for a ggiven topology.



In this activity, you will use the network address 172 16 0 0/16address 172.16.0.0/16 to subnet and provide the IP addressing for a ggiven topology.



Th t k h th f ll i dd i i tThe network has the following addressing requirements: East Network Section

–The N-EAST (Northeast) LAN1 will require 4000 host IP addresses. –The N-EAST (Northeast) LAN2 will require 4000 host IP addresses. –The SE-BR1 (Southeast Branch1) LAN1 will require 1000 host IP addresses. –The SE-BR1 (Southeast Branch1) LAN2 will require 1000 host IP addresses. –The SE-BR2 (Southeast Branch2) LAN1 will require 500 host IP addresses. –The SE-BR2 (Southeast Branch2) LAN2 will require 500 host IP addresses. The SE ST1 (Southeast Satellite1) LAN1 will require 250 host IP addresses–The SE-ST1 (Southeast Satellite1) LAN1 will require 250 host IP addresses.

–The SE-ST1 (Southeast Satellite1) LAN2 will require 250 host IP addresses. –The SE-ST2 (Southeast Satellite2) LAN1 will require 125 host IP addresses. –The SE-ST2 (Southeast Satellite2) LAN2 will require 125 host IP addresses.

West Network SectionWest Network Section –The S-WEST (Southwest) LAN1 will require 4000 host IP addresses. –The S-WEST (Southwest) LAN2 will require 4000 host IP addresses. –The NW-BR1 (Northwest Branch1) LAN1 will require 2000 host IP addresses. –The NW-BR1 (Northwest Branch1) LAN2 will require 2000 host IP addressesThe NW BR1 (Northwest Branch1) LAN2 will require 2000 host IP addresses. –The NW-BR2 (Northwest Branch2) LAN1 will require 1000 host IP addresses. –The NW-BR2 (Northwest Branch2) LAN2 will require 1000 host IP addresses.

Central Network Section The Central LAN1 will require 8000 host IP addresses


–The Central LAN1 will require 8000 host IP addresses. –The Central LAN2 will require 4000 host IP addresses.

The WAN links between each of the routers will require an IP address for each end of the link.

Troubleshooting VLSM Addressing 6.4.3

In this activity, the network address 172.16.128.0/17 was used to provide the IP addressing for a network. VLSM has been used to subnet the address space pincorrectly.

You will need to troubleshoot the addressing that wasthe addressing that was assigned to each subnet to determine where errors are present and determine thepresent and determine the correct addressing assignments where needed.


Basic Route Summarization 6.4.4

In this activity, you are given a network with subnetting and addresssubnetting and address assignments already completed.

Your task is to determine summarized routes that can be used to reduce the number of entries in routing tablesentries in routing tables


Challenge Route Summarization 6.4.5

In this activity, you are given a network with subnetting and addresssubnetting and address assignments already completed.

Your task is to determine summarized routes that can be used to reduce the number of entries in routing tablesentries in routing tables


Challenge Route Summarization 6.4.5

Add i T blAddressing Table

Subnet Network Address S-WEST LAN1 192.168.7.0/27 S-WEST LAN2 192.168.7.32/27

Addressing Table Subnet Network Address N-EAST LAN1 192.168.5.0/27 N-EAST LAN2 192 168 5 32/27

Link from WEST to N-WEST 192.168.7.64/30 Link from WEST to S-WEST 192.168.7.68/30 Link from HQ to WEST 192.168.7.72/30 NW-BR1 LAN1 192.168.7.128/27

N EAST LAN2 192.168.5.32/27 Link from EAST to N-EAST 192.168.5.192/30 Link from EAST to S-EAST 192.168.5.196/30 Link from HQ to EAST 192.168.5.200/30 SE BR1 LAN1 192 168 4 0/26

NW-BR1 LAN2 192.168.7.160/27 NW-BR2 LAN1 192.168.7.192/28 NW-BR2 LAN2 192.168.7.208/28 Link from N-WEST to NW-BR1 192.168.7.224/30

SE-BR1 LAN1 192.168.4.0/26 SE-BR1 LAN2 192.168.4.64/26 SE-BR2 LAN1 192.168.4.128/27 SE-BR2 LAN2 192.168.4.160/27

Link from N WEST to NW BR1 192.168.7.224/30 Link from N-WEST to NW-BR2 192.168.7.228/30CENTRAL LAN1 192.168.6.0/25 CENTRAL LAN2 192.168.6.128/26 Link from HQ to CENTRAL 192 168 6 192/30

SE-ST1 LAN1 192.168.4.192/29 SE-ST1 LAN2 192.168.4.200/29 SE-ST2 LAN1 192.168.4.208/29 SE-ST2 LAN2 192.168.4.216/29

Link from HQ to CENTRAL 192.168.6.192/30 Link from SE-BR2 to SE-ST1 192.168.4.224/30 Link from SE-BR2 to SE-ST2 192.168.4.228/30 Link from S-EAST to SE-BR2 192.168.4.232/30 Link from S-EAST to SE-BR1 192 168 4 236/30


Link from S EAST to SE BR1 192.168.4.236/30

Troubleshooting Route Summarization 6.4.6

In this activity, the LAN IP addressing is already completed for the network. VLSM was used to subnet the address space. The summary routes are yincorrect.

You will need to troubleshoot the summary routes that

Addressing Table the summary routes that have been assigned to determine where errors are present and determine the

Router Summary Route Network Address

HQ WEST LANs 172.16.52.0/21

HQ EAST LANs 172.16.56.0/23

WEST HQ LAN 172 16 32 0/19present and determine the correct summary routes.

WEST HQ LANs 172.16.32.0/19

WEST EAST LANs 172.16.58.0/23

EAST HQ LANs 172.16.30.0/20

EAST WEST LANs 172 16 48 0/21


EAST WEST LANs 172.16.48.0/21

ISP HQ, WEST, and EAST LANs 172.16.32.0/18

SSummaryClassful IP addressing

IPv4 addresses have 2 parts:-Network portion found on left side of an IP addressaddress-Host portion found on right side of an IP addressaddress

Class A, B, & C addresses were designed to provide IP addresses for different sized organizationsThe class of an IP address is determined by the decimal

value found in the 1st octetIP addresses are running out so the use of Classless Inter

Domain Routing (CIDR) and Variable Length Subnet Mask (VLSM) are used to try and conserve address space


(VLSM) are used to try and conserve address space

SSummaryClassful Routing Updates

–Subnet masks are not sent in routing updates

Classless IP addressingClassless IP addressing–Benefit of classless IP addressing

Can create additional networkCan create additional network addresses using a subnet mask that fits your needsy

–Uses Classless Interdomain Routing (CIDR)


Summary

CIDRCIDRUses IP addresses more efficiently through use of VLSMuse of VLSM

-VLSM is the process of subnetting a subnetsubnetting a subnet

Allows for route summarizationRoute summarization is-Route summarization is representing multiple contiguous routes with a single routeg


Summary

Classless Routing UpdatesSubnet masks are included in updatesSubnet masks are included in updates


RIPv2



Objectives

Encounter and describe the limitations of RIPv1’s cou e a d desc be e a o s o slimitations.

Apply the basic Routing Information Protocol VersionApply the basic Routing Information Protocol Version 2 (RIPv2) configuration commands and evaluate RIPv2 classless routing updates.

Analyze router output to see RIPv2 support for VLSM and CIDR

Identify RIPv2 verification commands and common RIPv2 issues.

Configure, verify, and troubleshoot RIPv2 in “hands-on” labs


IntroductionIntroductionDifference between RIPv1 & RIPv2

RIPv1RIPv1•A classful distance vector routing protocol•Does not support discontiguous subnetsDoes not support discontiguous subnets•Does not support VLSM•Does not send subnet mask in routing update•Routing updates are broadcast

RIPv2•A classless distance vector routing protocol that is an enhancement of RIPv1’s featuresenhancement of RIPv1 s features.•Next hop address is included in updates•Routing updates are multicast (224.0.0.9 vs. 255.255.255.255)

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/rip.htm


•The use of authentication is an option

Introduction

Similarities between RIPv1 & RIPv2– Use of timers to prevent routing loopsUse of timers to prevent routing loops– Use of split horizon or split horizon with poison reverse to also help prevent routing loops.– Use of triggered updates when there is a change in the topology for faster convergence.

Maximum hop count of 15 with the hop count of 16 signifying– Maximum hop count of 15, with the hop count of 16 signifying an unreachable network.


RIP 1 Li it tiRIPv1 LimitationsLab Topology

3 t t3 router set upTopology is discontiguousThere exists a static summary routeStatic route information can be

injected into routing table updates using redistribution.Routers 1 & 3 contain VLSMRouters 1 & 3 contain VLSM

networksRemember that both the R1 and R3

routers have subnets that are part of the 172 30 0 0/16 major classfulthe 172.30.0.0/16 major classful network (class B). Also remember that R1 and R3 are

connected to R2 using subnets of the g209.165.200.0/24 major classful network (class C). This topology is discontiguous and

will not converge because


will not converge because 172.30.0.0/16 is divided by the 209.165.200.0/24.

RIP 1 Li it tiRIPv1 Limitations

The topology shows that R2 has a staticR2 has a static summary route to the 192.168.0.0/16 network. The configuration of this summary route will be


ydisplayed later in this section.

RIP 1 Li it tiRIPv1 LimitationsReview the VLSM addressing scheme in the figure As shownscheme in the figure. As shown in the top chart, both R1 and R3 have had the 172.30.0.0/16 network subnetted into /24 subnetssubnets.

–Four of these /24 subnets are assigned: –two to R1 (172.30.1.0/24 and (172.30.2.0/24)–two to R3 (172.30.100.0/24 and 172.30.110.0/24).

I th b tt h t hIn the bottom chart, we have taken the 172.30.200.0/24 subnet and subnetted it again, using the first four bits for gsubnets and the last four bits for hosts. The result is a 255.255.255.240 mask or /28. Subnet 1 and Subnet 2 are


Subnet 1 and Subnet 2 are assigned to R3.

RIP 1 LimitationsRIPv1 LimitationsScenario Continued

SVLSM-Recall this is sub netting the subnetPrivate IP addresses are on LAN linksPublic IP addresses are used on WAN links (through an ISP, or when inside users

d t t id itneed to access outside sites, a public IP address must be used.)Loopback interfaces -These are virtual interfaces that can be pinged and


that can be pinged and added to routing table

Cisco has set these addresses aside for educational purposes.

RIPv1 Limitations

Loopback interfacesNotice that R3 is using loopback interfaces (Lo0,

Lo1, and Lo2). A loopback interface is a software-only interface that

is used to emulate a physical interfaceis used to emulate a physical interface. Like other interfaces, it can be assigned an IP address.

Loopback interfaces are also used by other routing protocols, such as OSPF, for different purposes. p , , p p

These uses will be discussed in Chapter 11 OSPF.In a lab environment, loopback interfaces are useful

in creating additional networks without having to add more physical interfaces on the routermore physical interfaces on the router. A loopback interface can be pinged and the subnet

can be advertised in routing updates. Therefore, loopback interfaces are ideal forTherefore, loopback interfaces are ideal for

simulating multiple networks attached to the same router. In our example, R3 does not need four LAN

interfaces to demonstrate multiple subnets and


interfaces to demonstrate multiple subnets and VLSM. Instead, we use loopback interfaces.

RIPv1 LimitationsRIPv1 LimitationsRoute redistribution

Redistribution involves taking the routes from one routing– Redistribution involves taking the routes from one routing source and sending those routes to another routing source.

• In our example topology, we want the RIP process on R2 to redistribute our static route (192.168.0.0/16) by importing the route into RIP and then sending it to R1 and R3 using the RIP process.

R2( fi t )# di t ib t t ti-R2(config-router)#redistribute static


RIPv1 LimitationsRIPv1 LimitationsR2(config)#ip route 192.168.0.0 255.255.0.0 Null0

The address space represented by the static summary route–The address space represented by the static summary route 192.168.0.0/16 does not actually exist. –In order to simulate this static route, we use a null interface as the exit interface.– You do not need to enter any commands to create or configure the null interfaceconfigure the null interface. –It is always up but does not forward or receive traffic. Traffic sent to the null interface is discarded.


Static routes and null interfaces

Static routes and null interfacesStat c outes a d u te acesR2(config)#ip route 192.168.0.0 255.255.0.0 Null0

a static route must have an active exit interfacea static route must have an active exit interface before it will be installed in the routing table. Using the null interface will allow R2 to advertise the g

static route in RIP even though networks belonging to the summary 192.168.0.0/16 do not actually exist.


V if i d T ti C ti itVerifying and Testing Connectivityshow ip interfaces brief

T t t h th t th t l h f ll–To test whether or not the topology has full connectivity, we first verify that both serial links on R2 are up using the show ip interface brief

PingWhenever R2 pings any of the 172.30.0.0 subnets

on R1 or R3, only about 50% of the ICMP are successful.R1 is able to ping 10.1.0.1 but is unsuccessful

when attempting to ping the 172.30.100.1 on R3R3 is able to ping 10 1 0 1 but is unsuccessfulR3 is able to ping 10.1.0.1 but is unsuccessful

when attempting to ping the 172.30.1.1 on R1.


RIP 1 Li it tiRIPv1 LimitationsRIPv1 – a classful routing protocol

–Subnet mask are not sent in updatesSubnet mask are not sent in updates–Summarizes networks at major network boundaries–RIPv1 cannot support discontiguous networks, VLSM, or CIDR.

if t k i di ti d RIP 1 fi d ill t b–if network is discontiguous and RIPv1 configured convergence will not be reached–RIPv1 on both the R1 and R3 routers will summarize their 172.30.0.0 subnets to the classful major network address of 172 30 0 0 when sendingsubnets to the classful major network address of 172.30.0.0 when sending routing updates to R2. –From the perspective of R2, both updates have an equal cost of 1 hop to reach network 172 30 0 0/16 As you will see R2 installs both paths in thereach network 172.30.0.0/16. As you will see, R2 installs both paths in the routing table.


RIP 1 Li it tiRIPv1 LimitationsExamining the routing tables

-To examine the contents of routing updates use the debug ip rip command

R2 i i i t 172 30 0 0 l tR2 is receiving two 172.30.0.0 equal cost routes with a metric of 1 hop. R2 is receiving one route on Serial 0/0/0 from R1 and the other route on Serial 0/0/1 from R3.

R2 has two equal cost routes to the 172.30.0.0/16 network.


RIP 1 Li it tiRIPv1 Limitations

•R1 has its own 172 30 0 0 routes:•R1 has its own 172.30.0.0 routes: 172.30.2.0/24 and 172.30.1.0/24. •But R1 does not send R2 those subnets. •R3 has a similar routing table. B th R1 d R3 b d t d•Both R1 and R3 are boundary routers and

are only sending the summarized 172.30.0.0 network to R2 in their RIPv1 routing updates. A lt R2 l k b t th

•R2 that it is not including the 172.30.0.0 network in its updates to either R1 or R3. •Because the split horizon rule is in effect. •R2 learned about 172 30 0 0/16 on both the•As a result, R2 only knows about the

172.30.0.0/16 classful network and is unaware of any 172.30.0.0 subnets.

•R2 learned about 172.30.0.0/16 on both the Serial 0/0/0 and Serial 0/0/1 interfaces, it does not include that network in updates it sends out these same interfaces.


RIPv1 LimitationsRIPv1 LimitationsBecause RIPv1 does not send the subnet mask in routing updates, it R4 is added tog pcannot support VLSM. R3 router is configured with VLSM subnets all of which are members

R4 is added to the topology connected to R3

subnets, all of which are members of the class B network 172.30.0.0/16:

–172.30.100.0/24 (FastEthernet 0/0)172.30.100.0/24 (FastEthernet 0/0)–172.30.110.0/24 (Loopback 0)–172.30.200.16/28 (Loopback 1)

172 30 200 32/28 (L b k 2)–172.30.200.32/28 (Loopback 2)

As we saw with the 172.30.0.0/16 updates to R2 by R3, p y

–RIPv1 either summarizes the subnets to the classful boundary –or uses the subnet mask of the


o uses t e sub et as o t eoutgoing interface to determine which subnets to advertise.

RIPv1 LimitationsRIPv1 LimitationsWhy is RIPv1 on R3 not including the other subnets, 172 30 200 16/28 and R4 is added to172.30.200.16/28 and 172.30.200.32/28, in updates to R4?

– Those subnets do not have the

R4 is added to the topology connected to R3

Those subnets do not have the same subnet mask as FastEthernet 0/0.

– R3 will only include those 172 30 0 0 routes in its routing172.30.0.0 routes in its routing table with the same mask as the exit interface.

– Since the interface is 172.30.100.1 ith /24 k it ill l i l dwith a /24 mask, it will only include

172.30.0.0 subnets with a /24 mask. The only one that meets this condition is 172.30.110.0.

– The other 172.30.0.0 subnets, 172.30.200.16/28 and 172.30.200.32/28, are not included because the /28 masks


do not match the /24 mask of the outgoing interface.

RIP 1 Li it tiRIPv1 LimitationsNo CIDR Support

R2(config)#ip route 192 168 0 0R2(config)#ip route 192.168.0.0 255.255.0.0 Null0–the static route is included in R2's routing table, but R2 will not include the static route in itsnot include the static route in its update –R1 is not receiving this 192.168.0.0/16 route in its RIP updates from R2,

Reason: Classful routing protocols do not support p ppCIDR routes that are summarized with a smaller mask than the classful

b t ksubnet mask–If the 192.168.0.0 static route were configured with a /24 mask or greater, this route would be


g ,included in the RIP updates.

Config ring RIP 2Configuring RIPv2Comparing RIPv1 & RIPv2 Message Formats

–RIPv2 Message format is similar to RIPv1 but has 2 extensionsg1st extension is the subnet mask field

allows a 32 bit mask to be included in the RIP route entry.the receiving router no longer depends upon the subnet mask of thethe receiving router no longer depends upon the subnet mask of the

inbound interface or the classful mask when determining the subnet mask for a route

2nd extension is the addition of next hop addressThe Next Hop address is used to identify a better next-hop address - if

one exists - than the address of the sending router. If the field is set to all zeros (0.0.0.0), the address of the sending router

is the best next-hop addressis the best next-hop address.


Configuring RIPv2

Enabling and Verifying RIPv2Enabling and Verifying RIPv2

Configuring RIP on a Cisco router–By default it is running RIPv1–Even though the router only sends RIPv1 messages, it can interpret both RIPv1 and RIPv2 messagesinterpret both RIPv1 and RIPv2 messages. –A RIPv1 router will just ignore the RIPv2 fields in the route entry. RIPv1 RIPv2RIPv1 RIPv2


Configuring RIPv2Configuring RIPv2

Configuring RIPv2 on aConfiguring RIPv2 on a Cisco router

-Requires using the-Requires using the version 2 command

RIPv2 ignores RIPv1-RIPv2 ignores RIPv1 updates

To verify RIPv2 isTo verify RIPv2 is configured use the

show ip protocolsshow ip protocolscommand


Comparing RIP v1 and v2Comparing RIP v1 and v2RIP v2 send and receive v2

RIP v1 send v1 but can receive both v1 and v2RIP v1 send v1 but can receive both v1 and v2

No I can notI l dRIP network is broken

Version 1 Version 2

No. I can not take version 1

I can only send version 1

Version 1 Version 2

Yes. I can take version 1 or 2 I can only send

version 2


POP QuizPOP QuizHow do you make the RIPv2 back to the default “send 1” and receive 1 or 2”?

- Hint: Gad(config-router)#version 1 is not the answer.

Version 1 Version 2Version 1 Version 2


C fi i RIP 2Configuring RIPv2Auto-Summary & RIPv2Auto Summary & RIPv2

RIPv2 will automatically summarize routes at majorsummarize routes at major network boundaries andcan also summarize routes with a subnet mask that is smaller than the classful subnet masksubnet mask


Configuring RIPv2Configuring RIPv2

Disabling Auto-Summary in RIPv2

To disable automatic summarization issue th tthe no auto-summarycommand


Configuring RIPv2

Verifying RIPv2 Updates

When using RIPv2 with automatic summarization turned off

Each subnet and mask has its own specific entry, along with the exit interface and next-hop address to reach that subnet.

To verify information being sent by RIPv2 use they g y

debug ip rip command


VLSM & CIDRVLSM & CIDR

RIPv2 and VLSM

Networks using a VLSM IPNetworks using a VLSM IP addressing scheme

Use classlessUse classless routing protocols (i.e. RIPv2) to disseminate network addresses and their subnetand their subnet masks


VLSM & CIDR

CIDR uses Supernetting

S tti i b h f ti l f lSupernetting is a bunch of contiguous classful networks that is addressed as a single network.network.


VLSM & CIDR

To verify that supernets are being sent andbeing sent and received use the following commands

-Show ip route

Debug ip rip-Debug ip rip


Verifying & Troubleshooting RIPv2Verifying & Troubleshooting RIPv2Basic Troubleshooting steps

-Check the status of all links

-Check cablingCheck cabling

-Check IP address & subnet mask configuration

-Remove any unneeded configuration commands

Commands used to verify proper operation of RIPv2–Show ip interfaces brief–Show ip protocolsp p–Debug ip rip–Show ip route


–Show ip route

Verifying & Troubleshooting RIPv2

C RIP 2 ICommon RIPv2 Issues

When trouble shooting RIPv2 examine the following issues:Version

Check to make sure you are using version 2Network statements

Network statements may be incorrectly typed y y ypor missing

Automatic summarization

If summarized routes are not needed then disable automatic summarization


V if i & T bl h ti RIP 2Verifying & Troubleshooting RIPv2Reasons why it’s good to authenticate routing information y g g

-Prevent the possibility of accepting invalid routing updates

-Contents of routing updates are encryptedg p yp

Types of routing protocols that can use authentication

-RIPv2RIPv2

-EIGRP

-OSPFOSPF

-IS-IS

-BGP-BGP


Summary

RoutingProtocol

DistanceVector

ClasslessRoutingProtocol

UsesHold-Down

Use ofSplit

Horizon

MaxHop

count

AutoSummary

SupportCIDR

SupportsVLSM

Uses Authen-tication

Timers orSplit

Horizon w/

Poison

= 15

Poison Reverse

RIPv1 Yes No Yes Yes Yes Yes No No No

RIPv2 Yes Yes Yes Yes Yes Yes Yes Yes Yes


The Routing Table: A Closer Look




Objectives

Describe the various route types found in the routing esc be e a ous ou e ypes ou d e ou gtable structure

Describe the routing table lookup process.Describe the routing table lookup process.

Describe routing behavior in routed networks.


Introduction

Chapter Focus– Structure of the routing tableStructure of the routing table

•Will examine the format of the routing table and learn about level 1 and level 2 routes.

– Lookup process of the routing table– Classless and classful routing behaviors

Cisco IP Routing by Alex Zinin (ISBN 0-201-60473-6)Cisco IP Routing, by Alex Zinin (ISBN 0 201 60473 6).


Routing Table StructureRouting Table StructureLab Topology

3 router setup-R1 and R2 share a common 172.16.0.0/16 network with 172 16 2 0/24 subnets172.16.2.0/24 subnets.-R2 and R3 are connected by the 192.168.1.0/24 network.-R3 also has a 172 16 4 0/24 subnet which is disconnected orR3 also has a 172.16.4.0/24 subnet, which is disconnected, or discontiguous, from the 172.16.0.0 network that R1 and R2 share.


In a later section, we will configure the interfaces for R2


The figure shows routing table entries come from theThe figure shows routing table entries come from the following sources

-Directly connected networks-Directly connected networks-Static routesDynamic routing protocols-Dynamic routing protocols


Routing Table StructureRouting Table StructureThe figure shows what happens as the Serial 0/0/1 interface for R2 is configured with the 192.168.1.1/24 address.

– R1 and R3 already have their interfaces configured with the appropriate IP addresses and subnet masks.–We will now configure the interfaces for R2 and use debug ip routing to view the routing table process that is used to add these entries.

As soon as the “no shutdown” command is issued the route is added to routing table g

debug ip routingdebug ip routing



Ci IP ti t blCisco IP routing table is a hierarchical structurestructure

–The reason for this is to speed up lookupto speed up lookup process

The hierarchy–The hierarchy includes several levels.

•level 1 •level 2


level 2

Routing Table StructureRouting Table StructureLevel 1 Routes

–Have a subnet mask equal to or less than the classful qmask of the network address.–192.168.1.0/24 is a level 1 network route, because the subnet mask is equal to the network's classful mask. /24 f l C t k h th 192 168 1 0 t kfor class C networks, such as the 192.168.1.0 network.

Level 1 route can function as–Default route

•A default route is a static route with the address 0.0.0.0/0.

–Supernet routeSupe e ou e•A supernet route is a network address with a mask less than the classful mask.

–Network routeNetwork route•A network route is a route that has a subnet mask equal to that of the classful mask.

The source of the level 1 route can be a directly


The source of the level 1 route can be a directly connected network, static route, or a dynamic routing protocol.

Routing Table StructureRouting Table StructureThe level 1 route 192.168.1.0/24 can be further defined as an ultimate route.ultimate route.

ultimate route includes either:-A next-hop ip address (another path)

OROR-An exit interface

The directly connected network 192.168.1.0/24 It i l l 1 t k t b it h b t k th t i th–It is a level 1 network route because it has a subnet mask that is the same as

its classful mask.–This same route is also an ultimate route because it contains the exit interface Serial 0/0/1Serial 0/0/1.


Parent and Child RoutesA parent route is a level 1 route

Parent and Child Routes

–A parent route does not containany next-hop IP address or exit interface information

When the 172.16.3.0 subnet was added to the routing table, another route, 172.16.0.0, was also added. , ,

–The first entry, 172.16.0.0/24, does not contain any next-hop IP address or exit interface information.or exit interface information. –This route is known as a level 1 parent route.

A t t i t ll h di–A parent route is actually a heading that indicates the presence of level 2 routes, also known as child routes.


Routing Table StructureRouting Table StructureA level 1 parent route is automatically created any time a subnet is added tocreated any time a subnet is added to the routing table.

–In other words, a parent route is created whenever a route with a maskcreated whenever a route with a mask greater than the classful mask is entered into the routing table.

172 16 0 0/24 i b tt d 1 b t–172.16.0.0/24 is subnetted, 1 subnets

A level 2 route is a route that is a subnet of a classful network address.

– Child routes are level 2 routes– Child routes are a subnet of a l f l t k ddclassful network address

–C 172.16.3.0 is directly connected, FastEthernet0/0


Routing Table StructureRouting Table StructureThe parent route contains the 172.16.0.0 - The classful network address for our subnet.

Level 2 child routes contain 172.16.3.0, route source & the network address of the route

–Notice that the subnet mask is not included with the subnet the level–Notice that the subnet mask is not included with the subnet, the level 2 child route. The subnet mask for this child route (subnet) is the /24 mask included in its parent route, 172.16.0.0

Level 2 child routes are also considered ultimate routesLevel 2 child routes are also considered ultimate routes–Reason: they contain the next hop address &/or exit interface


Routing Table StructureRouting Table StructureThe figure shows the configuration of the Serialconfiguration of the Serial 0/0/0 interface on R2.

–The routing table showsThe routing table shows two child routes for the same 172.16.0.0/24 parent routeroute.

•Both 172.16.2.0 and 172.16.3.0 are members of the same parent route, •because they are both

b f thmembers of the 172.16.0.0/16 classful network



Both child routes have the same subnet mask

-This means the parent route maintains the /24 mask

Note: If there is only a single level 2 child route and that route isand that route is removed, the level 1 parent route will be automatically deleted. A level 1 parent route exists only when there is at least one level 2 child route


child route.

The role of the parent route will be examined when we discuss the route lookup process.

Routing Table StructureIn classless networks, child routes do not have to share the same subnet mask

–Whenever there are two or more child routes with different subnet masks belonging to the same classful network thesubnet masks belonging to the same classful network, the routing table presents a slightly different view, which states that this parent network is variably subnetted.


R ti T bl St tRouting Table Structure

Parent & Child Routes: Classless NetworksParent & Child Routes: Classless Networks



Parent & Child Routes: classful and classless NetworksParent & Child Routes: classful and classless Networks

NetworkType

Parent route’s

Term variably

Includes the # of

Subnet mask

classful

Classful mask is

Displayed

subnetted is seen in

parent route in routing

different masks of

child routes

included with each

child route entry

routing table

Class-ful

No No No No classless

Class-l

Yes Yes Yes Yesless


Routing Table Lookup ProcessRouting Table Lookup ProcessThe Route Lookup Process1. Examine level 1 routes

• If best match a level 1 ultimate route and is not a parent route this route is used to forward packet

• If the best match is a level 1 parent• If the best match is a level 1 parent route, proceed to Step 2

2. Router examines level 2 (child) routes• If there is a match with level 2 child

route then that subnet is used to forward packet

• If no match then proceed to Step 33 R t d t i l f l3. Router determines classful or

classless routing behavior• If classful then packet is dropped• If classless then router searches level• If classless then router searches level

one supernet and default routes4. If there exists a level 1 supernet or

default route match then Packet is f d d


forwarded5. If not packet is dropped

R ti T bl L k PRouting Table Lookup ProcessLongest Match: Level 1 Network Routes

Best match is also known as the longest match–Best match is also known as the longest match –The best match is the one that has the most number of left most bits matching between the destination IP address and the route in the routing table.

For example, in the figure we have a packet destined for 172 16 0 10 Many possible routes could match this packet Three172.16.0.10. Many possible routes could match this packet. Three possible routes are shown that do match this packet: 172.16.0.0/12, 172.16.0.0/18, and 172.16.0.0/26. Of the three routes, 172 16 0 0/26 has the longest match172.16.0.0/26 has the longest match.


Routing Table Lookup ProcessRouting Table Lookup ProcessFinding the subnet mask used to determine theused to determine the longest match

Scenario:Scenario:–PC1 pings 192.168.1.2–Router examines level 1

t f b t t hroute for best match–There exist a match between192.168.1.2 & 192.168.1.0 / 24–Router forwards packets out s0/0/0


Routing Table Lookup ProcessRouting Table Lookup ProcessThe process of matching

–1st there must be a match made between the parent route & destination IP

•If a match is made then an attempt at finding a match•If a match is made then an attempt at finding a match between the destination IP and the child route is made.•Do at least 16 of the left-most bits of the parent route match the pfirst 16 bits of the packet's destination IP address of 192.168.1.2?

–The answer, no,


Routing Table Lookup Process

Fi di t h b t k t’ d ti ti IP ddFinding a match between packet’s destination IP address and the next route in the routing table

The figure shows a match between the destination IP of 192 168 1 0–The figure shows a match between the destination IP of 192.168.1.0 and the level one IP of 192.168.1.0 / 24 then packet forwarded out s0/0/0–Not only does the minimum of 24 bits match, but a total of 30 bits match, as shown in the figure.


Routing Table Lookup ProcessIn the example in the figure, PC1 sends a ping to PC2 p g , p gat 172.16.3.10. What happens when there is a match with a level 1 parent route?B f l l 2 hild t i dBefore level 2 child routes are examined

-There must be a match between classful level one parent route and destination IP addressparent route and destination IP address.


Routing Table Lookup ProcessRouting Table Lookup ProcessAfter the match with parent route has been made Level 2 child routes will be examined for a matchroutes will be examined for a match

-Route lookup process searches for child routes with a match with destination IP


Routing Table Lookup ProcessRouting Table Lookup ProcessHow a router finds a match with one of the level 2 child routeschild routes

–First router examines parent routes for a match–If a match exists then:

Child routes are examined•Child routes are examined•Child route chosen is the one with the longest match

First, the router examines the parent route for a match.

The router checks the last child route forThe router checks the last child route for 172.16.3.0/24 and finds a match. The first 24 bits do match. The routing table process will use this route, 172.16.3.0/24, to forward the packet with the destination IP address of 172.16.3.10 out the exit interface of Serial 0/0/0.

R 172.16.3.0 [120/1] via 172.16.2.2, 00:00:25,


R 172.16.3.0 [120/1] via 172.16.2.2, 00:00:25, Serial0/0/0

Routing Table Lookup ProcessRouting Table Lookup Process

Example: Route LookupExample: Route Lookup Process with VLSM

The use of VLSM does not-The use of VLSM does not change the lookup process

-If there is a match betweenIf there is a match between destination IP address and the level 1 parent route then

-Level 2 child routes will be searched


Routing BehaviorRouting BehaviorClassful & classless routing protocols

Influence how routing table is populatedClassful & classless routing behaviors

Determines how routing table is searched after it is filled


Routing BehaviorRouting BehaviorClassful Routing Behavior: no ipBehavior: no ip classless

What happens if there is ppnot a match with any level 2 child routes of the parent?parent?-Router must determine if the routing behavior is gclassless or classful

-If router is utilizing classful routing behavior thenrouting behavior then

-Lookup process is terminated and ip classless and no ip classless


terminated and packet is dropped

ip classless and no ip classless

Using the ip classless command (cont.)g ( )

What is IP Classless?The "ip classless" command prevents the existence of a single "subnet" route from blocking access via the

http://www.networkking.net/out/IPClassless.htmp p g g

default route to other subnets of the same old-style network. Default only works with single-homed ISPs.RFC 1879

IP classless command is not easy to understand, we know that. But I bet, after you read the following lines, you will understand what it is all about.First, you must understand a very simple logic. Here is the logic: Me and you are on a journey. If you break my leg, then you must carry me all the way! If you understand this logic, you will understand "IP classless".RIP is telling you: I am classful, if you break my class, then you have to show me every route there is, or I will drop your packet. I will drop it even though there is a default route (0.0.0.0).What is classful? Classful means that a class A subnet should be shown as x 0 0 0 such as 10 0 0 0 255 0 0 0What is classful? Classful means that a class A subnet should be shown as x.0.0.0 such as 10.0.0.0 255.0.0.0If you show it as 10.44.0.0 255.255.0.0, you are breaking its class.Or, a class B subnet should be shown as x.x.0.0 255.255.0.0 such as 172.29.0.0 255.255.0.0If you show it as 172.29.26.0 255.255.255.0, you are breaking its class.Let’s assume RIP knows about 10.0.0.0If you break 10.0.0.0 into three, for example to 10.1.0.0 and 10.2.0.0 and 10.3.0.0, and then give RIP a packet with a destination of 10.4.0.1, RIP will drop it. Why? Why doesn’t RIP send the packet to the default route? Because RIP told you, if you break my class, then you have to show me every damn route, otherwise I will drop it. Here you broke RIP's class so you must show him the way to 10 4 0 1 and every other 10 x x x route in the universeHere, you broke RIP s class so you must show him the way to 10.4.0.1 and every other 10.x.x.x route in the universe. Otherwise RIP will drop the packet, even if there is a default route. RIP will not care about your default route or last resort gateway; it will drop your packet.How do you ask RIP not to drop your packet and send the unknown destinations to the default route, although you have been so mean to him and have broken its class? You tell him: please, please, ip classless!If i l l d th k t


If no ip classless, drop the packet

If ip classless, send the packet to the default.

Routing BehaviorRouting Behaviorip Classless

Beginning with IOS 11.3, “ip classless”was configured by default

–The command “no ip classless” means that the route lookup process uses classful routing tablelookups by defaultlookups by default.

Classless routing behavior works for Di ti t k-Discontiguous networks

AndCIDR t-CIDR supernets


Routing Behavior “no ip classless”Routing BehaviorClassful Routing Behavior – Search Process

–when classful routing behavior is in effect (no ip

no ip classless

g ( pclassless) the process will not continue searching level 1 routes in the routing table. If a packet doesn't match a child route for the parent network route, then the router drops the packetthe router drops the packet.

R2 receives a packet destined for PC3 at 172.16.4.10.

–Even with the default route configured. –The destination’s subnet mask is a /24 and none of the child routes left most bits match the first 24 bits. Thi k t i d dThis means packet is dropped


R ti B h iRouting BehaviorClassful Routing Behavior – Search P

“no ip classless”

Process The reason why the router will not search beyond the child routesy

At the beginning of the Internet's growth, networks were all classfulThis meant an organization couldThis meant an organization could

subnet a major network address and “enlighten” all the organization’s routers about the subnettingrouters about the subnettingTherefore, if the subnet was not in the

routing table, the subnet did not exist and packet was droppedand packet was dropped

The routing table process will not use the default route, 0.0.0.0/0, or any other route


route.

R ti B h iRouting BehaviorThe routing table process will not

“no ip classless”g p

use the default route, 0.0.0.0/0, or any other route.

A common error is to assume that a default route will always be used if the router does not have a better route. In our example, R2's default route is

not examined nor used, although it is a matchmatch.

This is often a very surprising result when a network administrator does not

d t d th diff b tunderstand the difference between classful and classless routing behavior.


Ro ting Beha iorRouting BehaviorClassless Routing Behavior-

“ip classless”g

ip lasslessStep 3: If classless routing behavior inStep 3: If classless routing behavior in effect then, continue searching level 1 supernet routes in the routing table for a match including the default route if there ismatch, including the default route, if there is one.

Step 4: Match with supernet or defaultSupernet routes Checked first

–If a match exists then forward packet

Default routes Checked second

Step 5: If there is no match or no default t th th Packet is dropped


route then the Packet is dropped

R ti B h iRouting BehaviorClassless Routing Behavior – Search Process

“ip classless”g

Router begins search process by finding a match between destination IP and parent route

After finding the above mentioned match, then there is a search of the child route

There is no match with the level 2 child routesThere is no match with the level 2 child routes.


Routing BehaviorRouting BehaviorIf no match is found in child routes of previous slide then

“ip classless”

previous slide then–Router continues to search the routing table for a match that may h f th 16 bit i th t hhave fewer than 16 bits in the match

The 192.168.1.0/24 route does not have 24 left-most bits that match thehave 24 left-most bits that match the destination IP address.

C 192.168.1.0/24 is directly connected, Serial0/0/1


Routing BehaviorRouting BehaviorS* 0.0.0.0/0 is directly connected, Serial0/0/1

“ip classless”

The mask is /0, which means that zero or no bits need to match.

A default route will be the lowest-bit match. In classless routing behavior, if no other route matches the default routeroute matches, the default route will match.

–In this case the router will use theIn this case the router will use the default route, because it is the best match. The packet will be forwarded out the Serial 0/0/1 interface.


out the Serial 0/0/1 interface.

Routing Behavior

What does R3 do with return traffic back to PC2 at 172 16 2 10?172.16.2.10?

In this case, R3 uses the 172.16.0.0/16 child route and f d th t ffi t S i lforwards the traffic out Serial 0/0/1 back to R2.


R ti B h iRouting BehaviorClassful vs. Classless Routing Behavior

-It is recommended to use classless routing behavior

Reason: so supernet and default routes can be used whenever needed


O QLongest Match http://www.cisco.com/warp/public/105/21.html

POP QUIZp p p

Let's look at the three routes we just installed in the routing table, and see how they look on the router.

router# show ip route.... D 192.168.32.0/26 [90/25789217] via 10.1.1.1 ---- (192.168.32.0 to 192.168.32.63)[ ] ( )R 192.168.32.0/24 [120/4] via 10.1.1.2 ---- (192.168.32.0 to 192.168.32.255)O 192.168.32.0/19 [110/229840] via 10.1.1.3 ---- (192.168.32.0 to 192.168.63.255)....

If a packet arrives on a router interface destined for 192.168.32.1, which route would the router choose?

If a packet arrives on a router interface destined for 192.168.32.100,which route would the router choose?


Answers are on the next page

Longest MatchLongest Matchhttp://www.cisco.com/warp/public/105/21.html

Let's look at the three routes we just installed in the routing table, and see how j g ,they look on the router. router# show ip route

.... D 192.168.32.0/26 [90/25789217] via 10.1.1.1 ---- (192.168.32.0 to 192.168.32.63)R 192.168.32.0/24 [120/4] via 10.1.1.2 ---- (192.168.32.0 to 192.168.32.255)O 192.168.32.0/19 [110/229840] via 10.1.1.3 ---- (192.168.32.0 to 192.168.63.255)....

If a packet destined to 192.168.32.1 is directed toward 10.1.1.1, because 192.168.32.1 falls within the 192.168.32.0/26 network (192.168.32.0 to 192 168 32 63) It also falls within the other two routes available but the192.168.32.63). It also falls within the other two routes available, but the 192.168.32.0/26 has the longest prefix within the routing table (26 bits verses 24 or 19 bits). if a packet destined for 192.168.32.100 arrives on one of the router's interfaces,

f fp

it's forwarded to 10.1.1.2, because 192.168.32.100 doesn't fall within 192.168.32.0/26 (192.168.32.0 through 192.168.32.63), but it does fall within the 192.168.32.0/24 destination (192.168.32.0 through 192.168.32.255). Again, it also falls into the range covered by 192.168.32.0/19, but 192.168.32.0/24 has a longer

fi l th


prefix length

Summary

Content/str ct re of a ro ting tableContent/structure of a routing tableRouting table entries

Directly connected networks-Directly connected networks-Static route-Dynamic routing protocolsDynamic routing protocols

Routing tables are hierarchical-Level 1 route

Have a subnet mask that is less than or equal to classful subnet mask for the network address

L l 2 t-Level 2 routeThese are subnets of a network address


SummarySummaryRouting table lookup process

Begins with examining level 1 routes for best match with packet’s destination IPBegins with examining level 1 routes for best match with packet s destination IPIf the best match = an ultimate route then

-Packet is forwarded -Else--Parent route is examined-Parent route is examined

If parent route & destination IP match then Level 2 (child) routes are examined

Level 2 route examinationLevel 2 route examinationIf a match between destination IP and child route found then Packet forwarded -Else If Router is using classful routing behavior then g gPacket is dropped -Else

If router is using classless routing behavior thenRouter searches Level 1 supernet & default routes for a matchIf a match is found then Packet if forwarded -ElsePacket is dropped


Packet is dropped

Summary

Routing behaviors

-This refers to how a routing table is searched

Classful routing behavior

-Indicated by the use of the no ip classless commandy p

-Router will not look beyond child routes for a lesser match

Classless routing behavior

-Indicated by the use of the ip classless commandIndicated by the use of the ip classless command

-Router will look beyond child routes for a lesser match


EIGRP




IntroductionIntroduction


EIGRP

Roots of EIGRP: IGRP-Developed in 1985 to overcome RIPv1’s limited hop count-Distance vector routing protocolM t i d b IGRP-Metrics used by IGRP

bandwidth (used by default)Delay (used by default)Delay (used by default)Reliability (not used by default)Load (not used by default)Load (not used by default)

-Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S


EIGRP

EIGRP is a distance vector, classless routing protocol that was released in 1992 with IOS 9 21released in 1992 with IOS 9.21. As its name suggests, EIGRP is an enhancement of Cisco IGRP (Interior Gateway Routing Protocol). Both are Cisco proprietary protocols and only operate on CiscoBoth are Cisco proprietary protocols and only operate on Cisco routers.The main purpose in Cisco's development of EIGRP was to create a classless version of IGRP. EIGRP includes several features that are not commonly found in other distance vectorfeatures that are not commonly found in other distance vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP. These features include:

–Reliable Transport Protocol (RTP)–Bounded Updatesp–Diffusing Update Algorithm (DUAL)–Establishing Adjacencies–Neighbor and Topology Tables

Alth h EIGRP t lik li k t t ti t l it iAlthough EIGRP may act like a link-state routing protocol, it is still a distance vector routing protocol.

–Note: The term hybrid routing protocol is sometimes used to define EIGRP. However, this term is misleading because EIGRP is not a hybrid between distance vector and link-state routing protocols - it is


hybrid between distance vector and link state routing protocols it is solely a distance vector routing protocol. Therefore, Cisco is no longer using this term to refer to EIGRP.

EIGRP

The AlgorithmThe Algorithm–EIGRP uses the Diffusing Update Algorithm (DUAL).–EIGRP does not send periodic updates and route entries do not age outout. –Only changes in the routing information, such as a new link or a li k b i il bllink becoming unavailable cause a routing update to occur. –EIGRP routing updates are still g pvectors of distances transmitted to directly connected neighbors.


EIGRPPath Determination

G–EIGRP's DUAL maintains a topology table separate from the routing table, which includes both the best path to a destination network and any backupdestination network and any backup paths that DUAL has determined to be loop-free.

If a route becomes unavailable DUAL–If a route becomes unavailable, DUAL will search its topology table for a valid backup path.

If i t th t t i•If one exists, that route is immediately entered into the routing table. If d t i t DUAL f•If one does not exist, DUAL performs

a network discovery process to see if there happens to be a backup path that did not meet the requirement of


that did not meet the requirement of the feasibility condition.

EIGRPConvergence

–EIGRP does not use holddown timers.

Instead loop free paths are–Instead, loop-free paths are achieved through a system of route calculations (diffusing computations) that are performed in a coordinatedthat are performed in a coordinated fashion among the routers. –The detail of how this is done is beyond the scope of this course, but the result is faster convergence than traditional distance vector routing protocols.


EIGRPEIGRPEIGRP Message Format

EIGRP HeaderEIGRP HeaderData link frame header - contains

source and destination MAC addressIP packet header - contains source

& destination IP addressEIGRP packet header - contains

AS numberAS numberType/Length/Field - data portion of

EIGRP messageIn the IP packet header, p ,

the protocol field is set to 88 to indicate EIGRPthe destination address is set to

th lti t 224 0 0 10the multicast 224.0.0.10. If the EIGRP packet is

encapsulated in an Ethernet frame, the destination MAC address is


the destination MAC address is also a multicast address: 01-00-5E-00-00-0A.

EIGRPEIGRPAll fields are shown to provide an accurate picture of the EIGRP message format. However, only the fields relevant to the CCNA candidate are discussed.

EIGRP packet header containsEIGRP packet header contains–Opcode field

•Update•QueryQuery•Reply•Hello

–Autonomous System numberS• The AS number is used to track multiple

instances of EIGRP.

EIGRP Parameters contains–WeightsWeights

•EIGRP uses for its composite metric. •By default, only bandwidth and delay are weighted. Both are set to 1. •The other K values are set to zero.

–Hold time•The amount of time the EIGRP neighbor receiving this message


neighbor receiving this message should wait before considering the advertising router to be down.

EIGRPEIGRPTLV: IP internal contains (EIGRP routes within an autonomous system)

–Metric field (Delay and Bandwidth)–Metric field (Delay and Bandwidth)•Delay is calculated as the sum of delays from source to destination in units of 10 microseconds. •Bandwidth is the lowest configured bandwidth gof any interface along the route.

–Subnet mask field•The subnet mask is specified as the prefix length or the number of network bits in the

b t ksubnet mask.•255.255.255.0 is 24

–Destination field•the address of the destination network.t e add ess o t e dest at o et o•Although only 24 bits are shown in this figure. •If a network address is longer than 24 bits, then the Destination field is extended for another 32 bits

TLV: IP external contains–Fields used when external

routes are imported into


EIGRP routing process– import or redistribute a route into EIGRP.

EIGRPEIGRPProtocol Dependent Modules (PDM)

EIGRP PDM t t lEIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalkPDMs are responsible for the specific routing task for each network layerrouting task for each network layer protocol

–As you can see in the figure, EIGRP uses different EIGRP packets and

i t i t i hb t lmaintains separate neighbor, topology, and routing tables for each Network layer protocol.

•The IP-EIGRP module is responsibleThe IP EIGRP module is responsible for sending and receiving EIGRP packets that are encapsulated in IP and for using DUAL to build and maintain the IP routing table. How do people routeg•The IPX EIGRP module is responsible for exchanging routing information about IPX networks with other IPX EIGRP routers

How do people route IPX or Appletalk today if they still get either IPX A l t lk?


other IPX EIGRP routers. •Apple-Talk EIGRP is for Apple-talk

IPX or Appletalk?

EIGRPEIGRPReliable Transport Protocol (RTP)

P rpose of RTPPurpose of RTP–Used by EIGRP to transmit and receive EIGRP packets– EIGRP was designed as a Network layer g yindependent routing protocol; therefore, it cannot use the services of UDP or TCP because IPX and Appletalk do not use protocols from the TCP/IP protocol suite.

Characteristics of RTP–Involves both reliable & unreliable delivery of EIGRP packet

Reliable delivery requires acknowledgmentReliable delivery requires acknowledgment from destinationUnreliable delivery does not require an

acknowledgement from destinationP k t b t–Packets can be sent

UnicastMulticast

–Using address 224 0 0 10


–Using address 224.0.0.10

EIGRPEIGRPEIGRP’s 5 Packet Types

•Hello•Update•ACK

Hello packets–Used to discover & form adjacencies with neighbors

ACK•Query•ReplyUsed to discover & form adjacencies with neighbors

–EIGRP hello packets are multicasts and use unreliabledelivery.


EIGRPEIGRPUpdate packets

–Update packets are used to propagate

•Hello•Update•ACKUpdate packets are used to propagate

routing information–Update packets are sent only when necessary.

G

ACK•Query•Reply

–EIGRP updates are sent only to those routers that require it. –When a new neighbor is discovered, unicast update packets are sent so that the p pneighbor can build up its topology table. –In other cases, such as a link-cost change, updates are multicast. U d t l t itt d li bl–Updates always are transmitted reliably

Acknowledgement packets–Used to acknowledge receipt of update, query & reply packets–An acknowledgment packet is a hello packet that has no data. EIGRP acknowledgement packets are

•R2 has lost connectivity to the LAN attached to its FastEthernet interface. •R2 immediately sends an unicast Update to R1 and R3 noting the downed route.


–EIGRP acknowledgement packets are always sent as an unreliable unicast

g•R1 and R3 respond with an unicast acknowledgement.

EIGRP

Q & R l k t

•Hello•Update•ACKQuery & Reply packets

Used by DUAL for searching for networks

ACK•Query•Replynetworks

Queries and replies use reliable delivery.Query packets can use

MulticastR l k t lReply packet use only

unicast•R2 has lost connectivity to the LAN•R2 has lost connectivity to the LAN and it sends out queries to all EIGRP neighbors. •All neighbors must send a reply


regardless of whether or not they have a route to the downed network.

EIGRP

Query Update Reply Hello Acknowledge

Reliable Reliable Reliable Unreliable Unreliable(not require acknowledgment )

(a hello packet that has no data )

multicast Multicast & unicast

unicast multicast unicast


EIGRPEIGRPPurpose of Hello Protocol

To discover neighbors & establish adjacencies with neighbor routers–To discover neighbors & establish adjacencies with neighbor routers

Characteristics of hello protocolTime interval for sending hello packet–Time interval for sending hello packet

5 seconds - high bandwidth (greater than T1) 60 seconds - multipoint circuits T1 bandwidth or slower p

-HoldtimeThis is the maximum time

router should wait before declaring a neighbor downDefault holdtime

–3 times hello interval


»15 seconds»180 seconds

EIGRPEIGRPEIGRP Bounded Updates

EIGRP only sends update when there is a change in route status

Partial update–A partial update includes only the route information that has changed – the whole routing table is NOT sent

Bounded updateBounded update–When a route changes, only those devices that are impacted will be notified of the change

EIGRP’s use of partial bounded updates minimizes use of bandwidth


EIGRPEIGRPDiffusing Update Algorithm (DUAL)Diffusing Update Algorithm (DUAL)

–Purpose•EIGRP’s primary method for preventing routing loops•And also hold-down timers and split horizon, too.

–Advantage of using DUALP id f f t ti b k i li t f l•Provides for fast convergence time by keeping a list of loop-

free backup routes–DUAL maintains a list of backup routes it has already determined to be loop-free. If the primary route in the routing table fails, the best backup route is immediately added to the routing table.


EIGRP

Administrative Distance (AD)–Defined as the trustworthiness of the source route

EIGRP default administrative distances–Summary routes = 5Summary routes 5–Internal routes = 90–Imported routes = 170


EIGRP

A th ti tiAuthentication

EIGRP canEncrypt routing information– Encrypt routing information

– Authenticate routing information

It is good practice to authenticateIt is good practice to authenticate transmitted routing information. – This practice ensures that routers will

only accept routing information fromonly accept routing information from other routers that have been configured with the same password or authentication information.authentication information.

Note: Authentication does not encrypt the router's routing table.


http://www.ciscopress.com/articles/article.asp?p=1171169&seqNum=3

EIGRPEIGRPNetwork Topology

Topology used is the same as previous chapters with the addition of an ISP router

–ISP router does not physically exist

EIGRP will automaticallyEIGRP will automatically summarizes at classful boundaries, similar to RIP.


Basic EIGRP ConfigurationBasic EIGRP Configuration Autonomous System (AS) & Process IDs

–This is a collection of networks under the control of a–This is a collection of networks under the control of a single authority (reference RFC 1930)–AS Numbers are assigned by IANA

ARIN not IANA–Entities needing AS numbers

ISPInternet Backbone prodiersInternet Backbone prodiersInstitutions connecting to other institutions using

AS numbersThese ISPs and large institutions use the exterior

gateway routing protocol or BGP, to propagate routing information.

16-bit and 32-bit AS NumbersCommencing 1 January 2007,"16-bit only AS Numbers" refers to AS numbers in the range 0 - 65535


16 bit only AS Numbers refers to AS numbers in the range 0 65535"32-bit only AS Numbers" refers to AS Numbers in the range 65,536 - 4,294,967,295"32-bit AS Numbers" refers to AS Numbers in the range 0 - 4,294,967,295

Basic EIGRP ConfigurationBasic EIGRP ConfigurationEIGRP autonomous system number actually functions as anumber actually functions as a process ID

–The vast majority of companies and institutions with IP networksand institutions with IP networks do not need an AS number–The ISP is responsible for the

ti f k t ithi itrouting of packets within its autonomous system and between other autonomous systems.

Process ID represents an instance of the routing protocol running on a router

ExampleRouter(config)#router eigrp autonomous-system


Basic EIGRP Configuration

The router eigrp commandThe router eigrp command

The global command that enables eigrp ist i t trouter eigrp autonomous-system

-All routers in the EIGRP routing domain must use th ID b (the same process ID number (autonomous-system number)


B i EIGRP C fi tiBasic EIGRP ConfigurationThe Network Command

Functions of the network command–Enables interfaces to transmit & receive EIGRP updates–Includes network or subnet in EIGRP updates

Examplep–Router(config-router)#network network-address

The network-address is the classful network address for this interface.

a single classful network statement is used on R1 to include both 172.16.1.0/24 and 172.16.3.0/30 subnets:172.16.1.0/24 and 172.16.3.0/30 subnets:


When EIGRP is configured on R2, DUAL sends a notification message to the console stating that a neighbor relationship with another EIGRP router has been established.

Basic EIGRP ConfigurationBasic EIGRP ConfigurationThe network Command with a Wildcard Mask

-This option is used when you want to configure EIGRP to advertise specific subnets-Example

Router(config-router)#network network-address [wildcard-mask]

192.168.10.8 – 192.168.10.11


Basic EIGRP ConfigurationBasic EIGRP ConfigurationRouter(config-router)#network network-address [wildcard-mask]

Think of a wildcard mask as the inverse of a subnet mask.

The inverse of subnet mask 255.255.255.252 is 0.0.0.3.

To calculate the inverse of the subnet mask, subtract the subnet mask from 255.255.255.255:

255.255.255.255

- 255.255.255.252

---------------

0. 0. 0. 3

Wildcard mask


B i EIGRP C fi tiBasic EIGRP ConfigurationVerifying EIGRP

EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or receivedg y p

Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors isj g

show ip eigrp neighborsH column Lists SRTT (S th R d T i Ti )H column - Lists the neighbors in the order they were learned.

SRTT (Smooth Round Trip Timer)

Queue Count - Should always be zero.

RTO (Retransmit Interval) - Used by RTP to manage reliableby RTP to manage reliable EIGRP packets.

Sequence Number - Used to track updates, queries, and reply packets.


EIGRP

The show ip protocols command is also used to verify that EIGRP is enabledenabled

Remember, the process ID must be , pthe same on all routers for EIGRP to establish neighbor adjacencies and share routing information.

EIGRP's internal and external administrative distances are also displayed:

–Distance: internal 90 external 170


Basic EIGRP Configuration We willBasic EIGRP ConfigurationExamining the Routing

We will configure the bandwidth later.

g gTableThe show ip routecommand is also used to verify EIGRPverify EIGRP

–EIGRP routes are denoted in a routing table by the letter “D”–EIGRP is a classless

ti t l (i l d throuting protocol (includes the subnet mask in the routing update), it supports VLSM and CIDR.

By default EIGRPBy default , EIGRP automatically summarizes routes at major network boundary

–We can disable the automatic summarization with the no auto-summary command. We will examine this in more detail in a later


detail in a later.

EIGRP Null0 Summary RouteEIGRP Null0 Summary RouteEIGRP has automatically included a summary route to Null0(192 168 10 0/24 and 172 16 0 0/16)(192.168.10.0/24 and 172.16.0.0/16)

–Null0 is not a physical interface–In the routing table summary routes are sourced from Null0

Reason: routes are used for advertisement purposes–EIGRP will automatically include a null0 summary route as child route when 2 conditions are met2 conditions are met

At least one subnet is learned via EIGRPAutomatic summarization is enabledIf the packet matches the level 1 parent - the classful network

address - but none of the subnets, the packet is discarded.


Basic EIGRP Configuration

R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by y yR1 & R3

–R1 and R2 are not propagating the individualpropagating the individual subnets because of automatic summarization.

[Tony] We will configure the bandwidth later. Once the ba d dt ate O ce t ebandwidth is reconfigured, you will not see the equal-cost route on R3.


route on R3.

EIGRP Metric CalculationEIGRP Metric CalculationEIGRP Composite Metric & the K Values

EIGRP th f ll i l i it it t iEIGRP uses the following values in its composite metric-Bandwidth, delay, reliability, and load (reliability and load are not used)

The composite metric used by EIGRPThe composite metric used by EIGRP– formula used has values K1 K5

K1 & K3 = 1K2, K4, K5 = 0


EIGRP Metric Calculation

U th h i t l d t if th KUse the sh ip protocols command to verify the K values

Again, changing these values to other than the default is not recommended unless the networkunless the network administrator has a very good reason to do so.


EIGRP Metric CalculationEIGRP Metric CalculationEIGRP Metrics

U th h i t fUse the show interfacescommand to view metricsEIGRP Metrics

–Bandwidth – EIGRP uses a static bandwidth to calculate metric

Most serial interfaces use–Most serial interfaces use a default bandwidth value of 1.544Mbos (T1)–The value of the b d idthbandwidth may or may not reflect the actual SPEED of the interface. –If actual SPEED of the link differs from the default bandwidth value, then you should modify the bandwidth value,


The default bandwidth for ethernet is 10,000 Kbits. The default bandwidth for fastethernet is 100,000 Kbits.


EIGRP MetricsEIGRP Metrics

Delay is the defined as the measure of time it takes for ameasure of time it takes for a packet to traverse a route

–it is a static value based onit is a static value based on link type to which interface is connected–The delay value, much like the bandwidth value, is a default value that can be changed by thethat can be changed by the network administrator manually.


EIGRP M t i C l l tiEIGRP Metric CalculationReliability (not a default EIGRP metric)

–A measure of the likelihood that a link will fail or how often the link has experienced errors. –Measure dynamically & expressed as a fraction of 255

•the higher the fraction the better the reliability•the higher the fraction the better the reliability–Reliability is calculated on a 5-minute weighted average to avoid the sudden impact of high (or low) error rates.

Load (not a default EIGRP metric)( )– A number that reflects how much traffic is using a link– Number is determined dynamically and is expressed as a fraction of 255

The lower the fraction the less the load on the linkThis value is calculated on a 5-minute weighted average to avoid the sudden

impact of high (or low) channel usage.


EIGRP Metric CalculationEIGRP Metric CalculationUsing the Bandwidth Commandg

Modifying the interface bandwidth-Router(config-if)#bandwidth kilobits-Router(config-if)#bandwidth kilobits

Verifying bandwidth U th h i t f d–Use the show interface command

Note – bandwidth command does not change the link’s physicalnot change the link s physical bandwidth

–The bandwidth command only modifies the bandwidth metric used by yrouting protocols such as EIGRP and OSPF.


EIGRP Metric CalculationEIGRP Metric CalculationThe EIGRP metric can be determined by examining they g

bandwidth delay

The value before changebefore change the bandwidth is

2172416



EIGRP uses the lowest bandwidth (BW)in its metric calculation

Calculated BW = reference BW / lowest BW(kbps)

Delay – EIGRP uses the cumulative sum of all outgoingDelay – EIGRP uses the cumulative sum of all outgoing interfaces

Calculated Delay = the sum of outgoing interface delaysCalculated Delay the sum of outgoing interface delays

EIGRP Metric = calculated BW + calculated delay



10,000,000 is divided by 1024. If the result is not a whole number, then the value is rounded down. In this case, 10,000,000 divided by 1024 equals 9765.625. The .625 is dropped before multiplying by 256. The bandwidth portion of the composite metric is 2 499 840bandwidth portion of the composite metric is 2,499,840.


DUAL Concepts

The Diffusing Update Algorithm (DUAL) is used to prevent loopingp p g

–Successor–Feasible Distance (FD)–Feasible Successor (FS)–Reported Distance (RD) or Advertised Distance (AD)–Feasible Condition or Feasibility Condition (FC)


DUAL ConceptsDUAL ConceptsSuccessor

The best least cost routeto a destination found in the routing tablethe routing table

Feasible distanceThe lowest calculatedThe lowest calculated metric along a path to a destination network

2 commands can be used to find the “successor” and “feasiblesuccessor and feasible distance”:

–show ip route


–show ip eigrp topology

DUAL ConceptsDUAL Concepts

EIGRPEIGRP Topology TableTable dissected


DUAL ConceptsDUAL ConceptsFeasible Successors, Feasibility Condition & Reported

DistanceFeasible Successor

–This is a loop free backup route to the same destination as successor route–If the link between R2 and–If the link between R2 and R3 failed, the R1 will become the successor for sending traffic to 192 168 1 0traffic to 192.168.1.0


EIGRP technologies (cont )EIGRP technologies (cont.)Feasible Successor, FC: RD30 < FD31

172 30 1 0172.30.1.0

FD to 172.30.1.0 is 31 via Router Y

Ad i d

Current Successor = 31 RD of RTY= 21

RTZ is NOT Feasible Successor, FC: RD220 not< FD31

Advertised or Destination Feasible Dist. Reported. Dist. Neighbor172.30.1.0 40 30 X In Topology Table


172.30.1.0 31 21 Y In Routing Table172.30.1.0 230 220 Z Not in Topology Table

Verifying basic EIGRPVerifying basic EIGRP


What if the successor fails?1) If feasible successor exists:

What if the successor fails?

If current successor route fails, feasible successor becomes the current successor, i.e. the current route.

Routing of packets continue with little delay.g p y

2) If no feasible successor exists:

This may be because the Reported Distance is greater than the Feasible Distance.

B f thi t b i t ll d it t b l d i th ti t t dBefore this route can be installed, it must be placed in the active state and recomputed.

Routing of packets continue but with more of a delay.


DUAL Concepts

Feasibility Condition (FC)–Met when a neighbor’s reported distance (RD) is less than the local router’sthan the local router s FD to the same destination network

Th t d di t i–The reported distance is simply an EIGRP neighbor's feasible distance to the same destination networksame destination network. –The reported distance is the metric that a router reports to a neighbor about


reports to a neighbor about its own cost to that network.

DUAL ConceptsDUAL ConceptsReported distance (RD)

The metric that a router–The metric that a router reports to a neighbor about its own cost to that network–R2 examines the reportedR2 examines the reported distance (RD) of 2172416 from R1. Because the reported distance (RD) of R1 is less than R2's own feasible distance (FD) ( )of 3014400, R1 meets the feasibility condition. R1 is now a feasible successor for R2 to the 192.168.1.0/24 network.

Why isn't R1 the successor if its reported distance (RD) is less than R2's feasible distance (FD) t 192 168 1 0/24?to 192.168.1.0/24?

–Because the total cost for R2, its feasible distance (FD), to reach 192 168 1 0/24 is greater


reach 192.168.1.0/24 is greater through R1 than it is through R3.


EIGRP Topology tableEIGRP Topology table–Viewed using the show ip

eigrp topology commandContents of table include:

– all successor routes– all feasible successor

routes



EIGRP TopologyEIGRP Topology Table dissected

P - This route is in theP This route is in the passive state. When DUAL is not performing its diffusing computations to d t i th fdetermine a path for a network, the route will be in a stable mode, known as the passive state.the passive state. A - If DUAL is recalculating or searching for a new path, the route will be in an

ti t tactive state.

All routes in the topology table should be in the


table should be in the passive state for a stable routing domain.

if there is not a second entry, then there are no feasible successors


To view detailedTo view detailed information about the metrics of a specific entry in the topology table, add the optional parameter [network] toparameter [network] to the show ip eigrp topology command

Remember that EIGRP is a distance vector routing protocol.


DUAL ConceptsDUAL ConceptsTopology Table: No Feasible

SuccessorSuccessor

The topology table for R1 to the network 192.168.1.0 only shows the et o 9 68 0 o y s o s t esuccessor 192.168.10.6. There are no feasible successors.

By looking at the actual physical–By looking at the actual physical topology or network diagram, it is obvious that there is a backup route to 192.168.1.0/24 through R2.to 192.168.1.0/24 through R2.

Why isn't R2 listed as a feasible successor?

–R2 is not a feasible successor because it does not meet the feasibility condition.


DUAL ConceptsDUAL ConceptsNo Feasible Successor

show ip eigrp topology all-links

Looking at the topology it is obvious that R2 is a backup routeR2 is a backup route,

–The command shows all possible paths to a network including successors, feasible successors and even thosefeasible successors, and even those routes that are not feasible successors.–For R2 to be considered a feasible successor it must meet the feasibilitysuccessor, it must meet the feasibility condition. R2's feasible distance to reach 192.168.1.0/24 must be less the R1's current feasible distance (FD) As we cancurrent feasible distance (FD). As we can see in the figure, R2's feasible distance is 3014400, which is higher than R1's feasible distance of 2172416.


DUAL ConceptsDUAL ConceptsDoes this mean R2 cannot be used if the successor fails?

–No, R3 can be used, but there will be a longer delay before adding it tobe a longer delay before adding it to the routing table. –Before this can happen, DUAL will need to do some further processing.


DUAL Concepts

The centerpiece of EIGRP is DUAL d it EIGRP t l l tiand its EIGRP route-calculation

engine. The actual name of this technology is DUAL Finite State Machine (FSM). Machine (FSM). Finite Sate Machine (FSM)

–An abstract machine that defines a set of possible states somethinga set of possible states something can go through, what event causes those states and what events result form those states–FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input eventsof input events–Selects a best loop-free path to a destination

Selects alternate routes by using


–Selects alternate routes by using information in EIGRP tables

DUAL ConceptsFinite State Machines (FSM)Finite State Machines (FSM)

To examine output from EIGRP’s finite state machine us the debug eigrp fsm commandus the debug eigrp fsm command


More EIGRP ConfigurationsThe Null0 Summary Route

By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes

EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist

–One or subnets exists that was learned via EIGRPOne or subnets exists that was learned via EIGRP–Automatic summarization is enabled


More EIGRP ConfigurationsMore EIGRP ConfigurationsRegardless of whether classful or classless routing behavior is being used the null0routing behavior is being used, the null0 summary will potentially be used and denying the use of any supernet or default routeroute.

Disabling Automatic Summarization–The no auto-summary command is usedThe no auto-summary command is used to disable automatic summarization

•This causes all EIGRP neighbors to send updates that will not besend updates that will not be automatically summarized

this will cause changes in both g-routing tables -topology tables


More EIGRP ConfigurationsMore EIGRP ConfigurationsThe no auto-summary command


More EIGRP ConfigurationsMore EIGRP ConfigurationsThe no auto-summary commandWitho t a tomatic s mmari ation R3'sWithout automatic summarization, R3's routing table now includes the three subnets, 172.16.1.0/24, 172.16.2.0/24, and 172.16.3.0/24. Why does R3's routing table y gnow have two equal cost paths to 172.16.3.0/24? Shouldn't the best path only be through R1 with the 1544 Mbps link?

Remember that EIGRP only uses the link with–Remember that EIGRP only uses the link with the slowest bandwidth when calculating the composite metric. –The slowest link is the 64 Kbps link that contains the 192.168.3.0/24 network. In this example, the 1544 Mbps link and the 1024 Kbps link are irrelevant in the calculation as far as the bandwidth metric is concerned. –Because both paths have the same number and types of outgoing interfaces, the delay values end up being the same. As a result the EIGRP metric for both paths is


–As a result, the EIGRP metric for both paths is the same, even though the path through R1 would actually be the "faster" path.

M l S i iManual SummarizationEIGRP can be configured to summarize routes, whether or not automatic summarization (auto-summary) is enabled.

–EIGRP is a classless routing protocol & include subnet mask in updatep

Command used to configure manual summarization

–Router(config-if)#ip summary-address eigrp as-number network-address

b t ksubnet-mask


More EIGRP Configurations

EIGRP Default RoutesEIGRP Default Routes

“quad zero” static default routeCan be used with any currently-Can be used with any currently

supported routing protocol-Is usually configured on a router that is connected a network outside the EIGRP domain (for example, to an ISP. )

EIGRP & the “Quad zero” static default routeEIGRP & the Quad zero static default route–Requires the use of the redistribute static command to include the static default route in EIGRP routing updates to other routers.


More EIGRP Configurations

In the routing tables for R1In the routing tables for R1 and R3, notice the routing source and administrative distance for the new static default route. The entry for the static default route on R1the static default route on R1 is the following:

D*EX 0.0.0.0/0 [170/3651840] [ ]via 192.168.10.6, 00:01:08, Serial0/1

–D: This static route was learned from an EIGRP routing updaterouting update.–*: The route is a candidate for a default route.–EX: The route is an external EIGRP route in this case aEIGRP route, in this case a static route outside of the EIGRP routing domain.–170: This is the administrative distance of an external EIGRP route


external EIGRP route.

Fi T i EIGRPFine-Tuning EIGRPEIGRP bandwidth utilization

–By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information

Thi t th EIGRP f tili i li k d t•This prevents the EIGRP process from over-utilizing a link and not allowing enough bandwidth for the routing of normal traffic.

–The command to change the percentage of bandwidth used by EIGRP is

Router(config-if)#ip bandwidth-percent eigrp as-number percentnumber percent

In our example, we are limiting EIGRP to no more than 50

t f th li k' b d idthpercent of the link's bandwidth. Therefore, EIGRP will never use more the 32kbps of the link's bandwidth for EIGRP packet


bandwidth for EIGRP packet traffic.

More EIGRP ConfigurationsMore EIGRP ConfigurationsConfiguring Hello Intervals and Hold Times

Hello inter als and hold times are config rable on a per interface-Hello intervals and hold times are configurable on a per-interface basis-The command to configure hello interval is

Router(config-if)#ip hello-interval eigrp as-number seconds

Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval

-The command to configure hold time value isRouter(config-if)#ip hold-time eigrp as-number seconds

Defaults For low-speed, NBMA networks: 60 seconds F ll th t k 5 dFor all other networks: 5 seconds

Defaults


For low-speed, NBMA networks: 180 seconds For all other networks: 15 seconds

SummarySummaryBackground & History

EIGRP is a derivative of IGRP–EIGRP is a derivative of IGRPEIGRP is a Cisco proprietary distance vector routing

protocol released in 1994

EIGRP terms and characteristics–EIGPR uses RTP to transmit & receive EIGRP packets& p–EIGRP has 5 packet type:

Hello packetsUpdate packetsAcknowledgement packetsQuery packetsReply packets


–Supports VLSM & CIDR

Summary

EIGRP terms and characteristicsEIGRP uses a hello protocol–EIGRP uses a hello protocol

Purpose of hello protocol is to discover & establish adjacenciesj

–EIGRP routing updatesAperiodicAperiodicPartial and boundedFast convergenceFast convergence


Summary

EIGRP commands–The following commands are used for EIGRPThe following commands are used for EIGRP configuration

RtrA(config)#router eigrp [autonomous-system #]RtrA(config-router)#network network-number

–The following commands can be used to verify EIGRPSh i lShow ip protocolsShow ip eigrp neighborsSho ip ro teShow ip route


Summary

EIGRP metrics includeBandwidth (default)–Bandwidth (default)

–Delay (default)R li bili–Reliability

–Load


SummarySummaryDUAL

P f DUAL–Purpose of DUALTo prevent routing loops

–SuccessorPrimary route to a destination

–Feasible successorBackup route to a destination

–Feasible distanceLowest calculated metric to a destination

–Reported distanceThe distance towards a destination as advertised

b t i hb


by an upstream neighbor

SummarySummaryChoosing the best route

Aft t h i d ll d t f di tl–After router has received all updates from directly connected neighbors, it can calculate its DUAL

1st metric is calculated for each route1st metric is calculated for each route2nd route with lowest metric is designated

successor & is placed in routing tablesuccessor & is placed in routing table3rd feasible successor is found

C i i f f ibl i h–Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distancethe installed route s feasible distance–Feasible routes are maintained in topology table


table

Summary

Automatic summarizationOn by default–On by default

–Summarizes routes on classful boundaryS i i b di bl d i h f ll i–Summarization can be disabled using the following

commandRt A( fi if)# tRtrA(config-if)#no auto-summary


Link-State Routing Protocols



Objectives

Describe the basic features & concepts of link-state prouting protocols.– Distance vector routing protocols are like road signs

because routers must make preferred path decisions basedbecause routers must make preferred path decisions based on a distance or metric to a network.

– Link-state routing protocols are more like a road map because they create a topological map of the network andbecause they create a topological map of the network and each router uses this map to determine the shortest path to each network.The ultimate objective is that every router receives all of the– The ultimate objective is that every router receives all of the link-state information about all other routers in the routing area. With this link-state information, each router can create its own topological map of the network and independentlyits own topological map of the network and independently calculate the shortest path to every network.

List the benefits and requirements of link-state routing


protocols.

Link-State Routing

Link state routing protocolsLink state routing protocols-Also known as shortest path first algorithms

-These protocols built around Dijkstra’s SPF

OSPF ill b di d i Ch t 11 d IS IS ill b di d i CCNP


OSPF will be discussed in Chapter 11, and IS-IS will be discussed in CCNP.

Link-State Routing

Dikjstra’s algorithm also known as the shortest path first (SPF) algorithm

Thi l ith l t t l h th f–This algorithm accumulates costs along each path, from source to destination.


Link-State Routing

The shortest path to a destination is not necessarily the path with the least number of hops


Link-State Routing ProcessHow routers using Link State Routing Protocols reach convergence1 Each routers learns about its own directly connected networks1. Each routers learns about its own directly connected networks

– interface is in the up state2. Each router is responsible for meeting its neighbors on directly

t d t kconnected networks– exchange hello packet to other directly connected link state routers.

3. Each router builds a Link-State Packet (LSP) containing the state of ( ) geach directly connected link – recording all the pertinent information about each neighbor, including

neighbor ID, link type, and bandwidth.4. Each router floods the LSP to all neighbors, who then store all LSPs

received in a database.– Each router stores a copy of each LSP received from its neighbors in

a local databasea local database.5. Each router uses the database to construct a complete map of the

topology and computes the best path to each destination network.Th SPF l ith i d t t t th f th t l d


– The SPF algorithm is used to construct the map of the topology and to determine the best path to each network.

Link-State Routing: Step 1 – Learn about directly connected Networks

Link

This is an interface on a s s a te ace o arouter

Link stateLink state

This is the information about the state of theabout the state of the links


Link-State Routing: step 2 - Sending Hello Packets to Neighbors

Link state routing protocols use a hello protocolLink state routing protocols use a hello protocolPurpose of a hello protocol:

T di i hb (th t th-To discover neighbors (that use the same link state routing protocol) on its link


Link-State Routing:

Connected interfaces that are

Link-State Routing: step 2 - Sending Hello Packets to NeighborsConnected interfaces that are using the same link state routing protocols will exchangerouting protocols will exchange hello packets.

Once routers learn it hasOnce routers learn it has neighbors they form an adjacencyadjace cy

– 2 adjacent neighbors will exchange hello packets – These packets will serve as a keep alive function


Link-State Routing:

Contents of LSP:

Link-State Routing: step 3 - Building the Link State Packet (LSP)

Contents of LSP:– State of each directly connected link– Includes information about neighbors such as neighbor ID linkneighbors such as neighbor ID, link type, & bandwidth.

A simplified version of the LSPs from R1 is:

1. R1; Ethernet network 10.1.0.0/16; Cost 22. R1 -> R2; Serial point-to-point network; 10.2.0.0/16; Cost 203. R1 -> R3; Serial point-to-point network; 10.3.0.0/16; Cost 54. R1 -> R4; Serial point-to-point

/ C


network; 10.4.0.0/16; Cost 20

Link-State Routing:

Once LSP are created they are

Link-State Routing: step 4 - Flooding LSPs to Neighbors

Once LSP are created they are forwarded out to neighbors.

–Each router floods its link-state ac ou e oods s s a einformation to all other link-state routers in the routing area.

Whenever a router receives an LSP–Whenever a router receives an LSP from a neighboring router, it immediately sends that LSP out all other interfaces except the interfaceother interfaces except the interface that received the LSP. –This process creates a flooding effect p gof LSPs from all routers throughout the routing area.


Link-State Routing:

LSP t t d th f ll i diti

Link-State Routing: step 4 - Flooding LSPs to Neighbors

LSPs are sent out under the following conditions– Initial router start up or routing process

Wh th i h i t l– When there is a change in topology• including a link going down or coming up, or a neighbor adjacency being established or brokenj y g


Link-State Routing:

Routers use a database to

Link-State Routing: step 5 - Constructing a link state data base

Routers use a database to construct a topology map of the network

–After each router has propagated its own LSPs using the link-state flooding process each router willflooding process, each router will then have an LSP from every link-state router in the routing area. –These LSPs are stored in the link-state database. –Each router in the routing area canEach router in the routing area can now use the SPF algorithm to construct the SPF trees that you saw earlier


earlier.

Link-State Routing:Link-State Routing: step 5 - Constructing a link state data base

router R1 has learned the link-state information for each router in its routing area. routing area.

With a complete link-state database, R1 pcan now use the database and the shortest path first (SPF) algorithm to calculate the preferred path or shortest path to each network.p


Link-State Routing:

Process begins by examining R2’s LSP information

Link-State Routing: Example - How R1 constructs its SPF tree.

Process begins by examining R2 s LSP information–R1 can ignore the first LSP, because R1 already knows that it is connected to R2 on network 10.2.0.0/16 with a cost of 20.

R1 th d LSP d t li k f R2 t th–R1 can use the second LSP and create a link from R2 to another router, R5, with the network 10.9.0.0/16 and a cost of 10. This information is added to the SPF tree.

Using the third LSP R1 has learned that R2 has a network–Using the third LSP, R1 has learned that R2 has a network 10.5.0.0/16 with a cost of 2 and with no neighbors. This link is added to R1's SPF tree.


Link-State Routing:



Process begins by examining R3 s LSP information–R1 can ignore the first LSP, because R1 already knows that it is connected to R3 on network 10.3.0.0/16 with a cost of 5.

R1 th d LSP d t li k f R3 t th–R1 can use the second LSP and create a link from R3 to the router R4, with the network 10.7.0.0/16 and a cost of 10. This information is added to the SPF tree.

Using the third LSP R1 has learned that R3 has a network–Using the third LSP, R1 has learned that R3 has a network 10.6.0.0/16 with a cost of 2 and with no neighbors. This link is added to R1's SPF tree.


Link-State Routing:



Process begins by examining R4 s LSP information–R1 can ignore the first LSP because R1 already knows that it is connected to R4 on network 10.4.0.0/16 with a cost of 20. –R1 can also ignore the second LSP because SPF has already learnedR1 can also ignore the second LSP because SPF has already learned about the network 10.6.0.0/16 with a cost of 10 from R3. –However, R1 can use the third LSP to create a link from R4 to the router R5, with the network 10.10.0.0/16 and a cost of 10. This information is

dd d t th SPF tadded to the SPF tree. –Using the fourth LSP, R1 learns that R4 has a network 10.8.0.0/16 with a cost of 2 and with no neighbors. This link is added to R1's SPF tree.


Link-State Routing:



Process begins by examining R5 s LSP information–R1 can ignore the first two LSPs (for the networks 10.9.0.0/16 and 10.10.0.0/16), because SPF has already learned about these links and added them to the SPF tree. –R1 can process the third LSP learning that R5 has a network 10.11.0.0/16 with a cost of 2 and with no neighbors. This link is added to the SPF tree for R1.


Link-State Routing

Determining the shortest pathDetermining the shortest path–The shortest path to a destination determined by adding the costs & finding the lowest cost

•Network 10.5.0.0/16 via R2 serial 0/0/0 at a cost of 22•Network 10.6.0.0/16 via R3 serial 0/0/1 at a cost of 7at a cost of 7•Network 10.7.0.0/16 via R3 serial 0/0/1 at a cost of 15•Network 10.8.0.0/16 via R3 serial 0/0/1 at a cost of 17•Network 10.9.0.0/16 via R2 serial 0/0/0 at a cost of 30N t k 10 10 0 0/16 i R3 i l 0/0/1•Network 10.10.0.0/16 via R3 serial 0/0/1

at a cost of 25•Network 10.11.0.0/16 via R3 serial 0/0/1 at a cost of 27

Only the LANs are shown in the table, but SPF can also be used to determine the


used to determine the shortest path to each WAN link network.

Link-State Routing

O th SPF l ith hOnce the SPF algorithm has determined the shortest path routes, these routes are placed inroutes, these routes are placed in the routing table.

The routing table will also includeThe routing table will also include all directly connected networks and routes from any other sources, such as static routes. Packets will now be forwarded according to these entries in theaccording to these entries in the routing table.



Advantages of a Link State Routing ProtocolAdvantages of a Link-State Routing Protocol

Routingprotocol

BuildsTopological

map

Router can independently determine the shortest path

ConvergenceEvent driven

routing updates

Useof

LSP

to every network.

Distance No No Slow Generally No NoDistance vector

No No Slow Generally No No

Link State Yes Yes Fast Generally Yes Yes



There are several advantages of link-state routing protocols compared to distance vector routing t lprotocols.

Builds a Topological Map• Link-state routing protocols create a topological map, or SPF tree of the network topology.

•Using the SPF tree each router can independently determine the shortest path to every networkUsing the SPF tree, each router can independently determine the shortest path to every network.• Distance vector routing protocols do not have a topological map of the network.

•Routers implementing a distance vector routing protocol only have a list of networks, which includes the cost (distance) and next-hop routers (direction) to those networks.

Fast Convergence• When receiving a Link-state Packet (LSP), link-state routing protocols immediately flood the LSP out all

interfaces except for the interface from which the LSP was received. • A router using a distance vector routing protocol needs to process each routing update and update its

ti t bl b f fl di th t th i t f ith t i d d trouting table before flooding them out other interfaces, even with triggered updates.

Event-driven Updates• After the initial flooding of LSPs, link-state routing protocols only send out an LSP when there is a change

in the topology. The LSP contains only the information regarding the affected link. • Unlike some distance vector routing protocols, link-state routing protocols do not send periodic updates.

Hierarchical Design• Link-state routing protocols such as OSPF and IS-IS use the concept of areas. Multiple areas create a

hierarchical design to networks allowing for better route aggregation (summarization) and the isolation of


hierarchical design to networks, allowing for better route aggregation (summarization) and the isolation of routing issues within an area.


R i t f i li k t t ti t lRequirements for using a link state routing protocolMemory requirements

T i ll li k t t ti t l– Typically link state routing protocols use more memory

Processing RequirementsM CPU i i i d f li k t t ti– More CPU processing is required of link state routing

protocols

Bandwidth Requirementsq– Initial startup of link state routing protocols can consume lots of bandwidth

This should only occur during initial startup of routers but can– This should only occur during initial startup of routers, but can also be an issue on unstable networks.


Link-State Routing ProtocolsModern link-state routing protocols are designed to

i i i h ff CPU dminimize the effects on memory, CPU, and bandwidth.

• The use and configuration of multiple areas can reduce the size of the link-state databases. Multiple areas canthe size of the link state databases. Multiple areas can also limit the amount of link-state information flooding in a routing domain and send LSPs only to those routers that need them.

• For example when there is a change in the topologyFor example, when there is a change in the topology, only those routers in the affected area receive the LSP and run the SPF algorithm.

• This can help isolate an unstable link to a specific area in the routing domainin the routing domain.

In the figure, If a network in Area 51 goes down, the LSP with the information about this downed link is only flooded to other routers in that area.only flooded to other routers in that area.

• Routers in other areas will learn that this route is down, but this will be done with a type of link-state packet that does not cause them to rerun their SPF algorithm.

Note: Multiple areas with OSPF and IS-IS


are discussed in CCNP


2 link state routing protocols used for routing IP2 link state routing protocols used for routing IP -Open Shortest Path First (OSPF)-Intermediate System-Intermediate System (IS-IS)


Summary

Link State Routing protocols are also known as Shortest Path First protocolsSummarizing the link state process

-Routers 1ST learn of directly connected networksRouters 1ST learn of directly connected networks-Routers then say “hello” to neighbors-Routers then build link state packets-Routers then build link state packets-Routers then flood LSPs to all neighborsRouters use LSP database to build a network topology-Routers use LSP database to build a network topology

map & calculate the best path to each destination


Summary

LinkAn interface on the routerAn interface on the router

Link StateInformation about an interface such asInformation about an interface such as

-IP addressSubnet mask-Subnet mask

-Type of networkC t i t d ith li k-Cost associated with link

-Neighboring routers on the link


Summary

Link State Packets

Aft i iti l fl di dditi l LSP t tAfter initial flooding, additional LSP are sent out when a change in topology occurs

Examples of link state routing protocols

-Open shortest path first

-IS-IS-IS-IS


OSPF (Single Area OSPF)




Introduction

•In this chapter, you will learn basic, single-area OSPF implementations and configurations


and configurations. •More complex OSPF configurations and concepts (multi-areas OSPF) are reserved for CCNP-level courses.

Introduction to OSPFIntroduction to OSPFBackground of OSPF

Began in 19871989 OSPFv1 released in RFC 1131

This version was experimental & never deployed1991 OSPFv2 released in RFC 12471998 OSPFv2 updated in RFC 23281999 OSPFv3 published in RFC 2740 p


Introduction to OSPFIntroduction to OSPFOSPF Message Encapsulation

OSPF packet typeOSPF packet type– There exist 5 types (next slide)

OSPF packet header –Contains - Router ID an area IDand Type code for OSPF packet type

IP packet header– Contains - Source IP address, Destination IP address, & Protocol es a o add ess, & o ocofield set to 89. the destination address is set to one of two multicast addresses: 224.0.0.5 or 224 0 0 6224.0.0.6.

Data Link Frame Header –Contains - destination MAC address is


also a multicast address: 01-00-5E-00-00-05 or 01-00-5E-00-00-06.

I t d ti t OSPFIntroduction to OSPF5 OSPF Packet Types:

1. Hello - Hello packets are used to establish and maintain adjacency with other OSPF routers.

2. DBD - The Database Description (DBD) packet contains an abbre iated list of the sending ro ter'scontains an abbreviated list of the sending router's link-state database and is used by receiving routers to check against the local link-state database.

3. LSR - Receiving routers can then request more information about any entry in the DBD by sending a Link-State Request (LSR).

4. LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information.

–LSUs contain 7 different types of Link-State Advertisements (LSAs).–LSUs and LSAs are discussed in a later topic.

5 LSA k Wh LSU i i d th t


5. LSAck - When an LSU is received, the router sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU.

OSPF: Hello ProtocolOSPF: Hello ProtocolPurpose of Hello Packet

Discover OSPF neighbors & establish adjacenciesDiscover OSPF neighbors & establish adjacenciesAdvertise parameters on which routers must agree to become

neighborsUsed by multi-access networks to elect a Designated Router and

a Backup Designated RouterType: OSPF Packet Type: Hello (1), DD (2), LS Request (3), LS Update (4), LS ACK (5)

Router ID: ID of the originating router

Area ID: area from which the packet originated

Network Mask: Subnet mask associated with the sending interfacesending interface

Hello Interval: number of seconds between the sending router's hellos

Router Priority: Used in DR/BDR election (discussed l t )later)

Designated Router (DR): Router ID of the DR, if any

Backup Designated Router (BDR): Router ID of the BDR, if any


List of Neighbors: lists the OSPF Router ID of the neighboring router(s)

OSPF: Hello ProtocolOSPF: Hello ProtocolEstablish adjacencies:

– They must agree on three values: Hello Why 10 second hello interval

Also need to have the same Area ID.

y ginterval, Dead interval, and network type.

OSPF Hello Intervals–Hello interval indicates how often an OSPF router transmits its Hello packets

Why 10 second hello interval communications consider better than the 30 second routing update for RIP?

router transmits its Hello packets–Usually multicast (224.0.0.5) for ALLSPFRouters–sent every 10 seconds on multiaccess and ypoint-to-point segments–Sent every 30 seconds for NBMA segments

OSPF Dead Intervals–This is the time that must transpire before the neighbor is considered down–Default time is 4 times the hello interval–For multiaccess and point-to-point segmentsFor multiaccess and point to point segments, this period is 40 seconds. –For NBMA networks, the Dead interval is 120 seconds. If the Dead interval expires before the routers


–If the Dead interval expires before the routers receive a Hello packet, OSPF will remove that neighbor from its link-state database.

OSPF: Hello Protocol

To reduce the amount of OSPF traffic onTo reduce the amount of OSPF traffic on multiaccess networks, OSPF elects a Designated Router (DR) and Backup Designated Router (BDR). g ( )Hello protocol packets contain information that is used in electing DR and BDR

The DR is responsible for updating all other–The DR is responsible for updating all other OSPF routers (called DROthers) when a change occurs in the multiaccess network. –The BDR monitors the DR and takes over asThe BDR monitors the DR and takes over as DR if the current DR fails.

In the figure, R1, R2, and R3 are connected through point to point links Therefore no More detail discussionthrough point-to-point links. Therefore, no DR/BDR election occurs.

–The DR/BDR election and processes will be discussed in a later topic and the topology will

More detail discussion on the DR, BDR, DROther later. You need to know this for


discussed in a later topic and the topology will be changed to a multiaccess network.

need to know this for CCNA exam.

Introduction to OSPFIntroduction to OSPFOSPF Link-state Updates

Purpose of a Link State Update (LSU)Purpose of a Link State Update (LSU)–Used to deliver link state advertisements

Purpose of a Link State Advertisement (LSA)–Contains information about neighbors & path costs–An LSU packet can contain 11 different types of LSAs,


Introduction to OSPFIntroduction to OSPFOSPF Algorithm

OSPF routers build & maintain link-state d t b t i i LSAdatabase containing LSA received from other routersrouters1. Information found in

database is utilized upon e ec tion of Dijkstra SPFexecution of Dijkstra SPF algorithm

2. SPF algorithm used to gcreate SPF tree

3. SPF tree used to populate routing table


routing table

Introduction to OSPFIntroduction to OSPFAdministrative DistanceAdministrative Distance

Default Administrative Distance for OSPF is 110


Introduction to OSPFIntroduction to OSPFOSPF Authentication

–It is good practice to authenticate transmittedIt is good practice to authenticate transmitted routing information. –This is an interface specific configurationp g–This practice ensures that routers will only accept routing information from other routers that have been configured with the same password or authenticationconfigured with the same password or authentication information

MD5 authentication k ID th t

Note: Authentication does not encrypt the router's routing table

uses a key ID that allows the router to reference multiple passwords, making

?router s routing table. p , g

password migration easier and more secure.


?

Basic OSPF Configuration

Lab TopologyLab Topology

Topology used for this chapter –Discontiguous IP addressing scheme–Since OSPF is a classless routing protocol the subnet mask is will be configured as part of ouris will be configured as part of our OSPF configuration.


Basic OSPF ConfigurationBasic OSPF ConfigurationThe router ospf commandThe router ospf command

To enable OSPF on a router use the following command

R1(config)#router ospf process-idProcess id

ID cannot be 0

A locally significant number between 1 and 65535


Basic OSPF ConfigurationBasic OSPF ConfigurationOSPF network command

–Requires entering: q g•network address•wildcard mask - the inverse of the subnet mask•area-id - area-id refers to the OSPF area OSPF area•area-id - area-id refers to the OSPF area. OSPF area is a group of routers that share link state information

Router(config-router)#network network-address wildcard-ask area area-idRouter(config router)#network network address wildcard ask area area id

255.255.255.255- 255.255.255.240 --------------------

0 0 0 15

Subtract the subnet mask

Wildcard mask0. 0. 0. 15

255.255.255.255- 255.255.255.252

Subtract the subnet mask


--------------------0. 0. 0. 03 Wildcard mask

Basic OSPF ConfigurationBasic OSPF ConfigurationCisco IOS now properly handles overlapping network ... area configuration commands.

Consider the following example: g pfw#conf tEnter configuration commands, one per line. End with CNTL/Z.fw(config)#router ospf 100fw(config router)#network 0 0 0 0 255 255 255 255 area 0fw(config-router)#network 0.0.0.0 255.255.255.255 area 0fw(config-router)#network 10.0.0.0 0.0.3.255 area 113:06:57: %OSPF-6-AREACHG: 10.0.0.0 255.255.252.0 changed from area 0 to area 1fw(config-router)#network 10.0.0.0 0.0.0.7 area 213:07:10: %OSPF-6-AREACHG: 10.0.0.0 255.255.255.248 changed from area 1 to area 2fw(config-router)#^Z

I've entered overlapping network statements, each one with a smaller address range. Not l d IOS d t t th t th l it l i t i l d donly does IOS detect that they overlap, it also prints nice syslog messages and reorders

the commands in the running configuration. Well done !fw#show run | begin router ospfrouter ospf 100plog-adjacency-changesnetwork 10.0.0.0 0.0.0.7 area 2network 10.0.0.0 0.0.3.255 area 1network 0 0 0 0 255 255 255 255 area 0

http://blog.ioshints.info/2006/11/network-statements-in-ospf-

ht l


network 0.0.0.0 255.255.255.255 area 0 process-are.html

Basic OSPF ConfigurationBasic OSPF Configurationospf network definition for adding all interfaces / default route

What’s the difference?router ospf 1network 0.0.0.0 0.0.0.0 area 0

vsvs.router ospf 1network 0.0.0.0 255.255.255.255 area 0

Both add all existing interfaces into area 0 and all later added interfaces also. Both statements are valid.

http://blog.sazza.de/?p=427


B i OSPF C fi tiBasic OSPF Configuration

Area area idArea area-idAn OSPF area is a group of routers that share link-state

information.In this chapter, we will configure all of the OSPF routers within a

single area. This is known as single-area OSPF. Multi-area OSPF is covered in CCNP.


B i OSPF C fi tiBasic OSPF ConfigurationRouter ID– This is an IP address used to identify a router– 3 criteria for deriving the router ID

1 U IP dd fi d ith OSPF t id d1. Use IP address configured with OSPF router-id command-Takes precedence over loopback and physical interface

addresses2. If router-id command not used then router chooses highest

IP address of any loopback interfaces3 If no loopback interfaces are configured then the highest IP3. If no loopback interfaces are configured then the highest IP

address on any active physical interface is usedThe interface does not need to be enabled for OSPF, meaning that it does not need to be included in one of themeaning that it does not need to be included in one of the OSPF network commands. However, the interface must be active - it must be in the up state


up state.

However!!!!!!

B i OSPF C fi tiBasic OSPF Configuration

R t IDRouter IDIf th ki h th– If you are the king when the kingdom is built, you are thekingdom is built, you are the KING for life

– It means when ID is elected, it i th ID f th t lis the ID for the router, unless …………..


Basic OSPF ConfigurationBasic OSPF ConfigurationOSPF Router ID

Commands used to verify current router ID–Show ip protocols–Show ip ospf–Show ip ospf interface


Basic OSPF ConfigurationBasic OSPF ConfigurationOSPF Router ID

Router ID (not configured) & Loopback addresses (configured)

–Highest loopback address will be used as router IDHighest loopback address will be used as router ID–Advantage of using loopback address the loopback interface cannot fail OSPF stability

The OSPF router-id commandThe OSPF router id command–Introduced in IOS 12.0–OSPF router-id command, which is a fairly recent addition to IOS, it is more common to find loopback , paddresses used for configuring OSPF router IDs.–Command syntax

Router(config)#router ospf process-idRouter(config-router)#router-id ip-address

Modifying the Router ID–Use the command Router#clear ip ospf process


Use the command Router#clear ip ospf process

This command does not work in PT.

Basic OSPF ConfigurationBasic OSPF ConfigurationModifying the Router IDy g

The router ID is selected when OSPF is configured with its first OSPF network command.

– If the OSPF router-id command or the loopbackIf the OSPF router id command or the loopback address is configured after the OSPF network command, the router ID will be derived from the interface with the highest active IP address.

fModifying the Router IDThe router ID can be modified with 1. the IP address from a subsequent OSPF router-id

command b reloading the ro ter orcommand by reloading the router or 2. by using the following command:

Router#clear ip ospf process

3. Modifying a router ID with a new loopback or physical interface IP address may require reloading the router


reloading the router

Basic OSPF ConfigurationBasic OSPF ConfigurationDuplicate Router IDsDuplicate Router IDs

When two routers have the same router ID in an OSPF domain, routing may not function properly.properly.

– If the router ID is the same on two neighboring routers, the neighbor establishment may not occur.

When duplicate OSPF router IDs occur, IOS will display a message similar to:

– %OSPF-4-DUP_RTRID1: Detected router ith d li t t IDwith duplicate router ID

To correct this problem, configure all routers so that they have unique OSPF router IDs.Because some IOS versions do not support the router-id command, we will use the loopback address method for assigning router IDs


router IDs.

Quick ReviewQuick Review

We just went over 3 different types of IDWe just went over 3 different types of IDospf process-id.

OSPF process– OSPF process. – Cannot be 0

Area ID:Area ID:– OFPS area– If it is the first, and the backbone area, it is 0, ,

Router ID– Router ID– 1 IP address is elected per router,

• Highest physical address (or)


• Highest logical address (loopback)

Basic OSPF ConfigurationBasic OSPF ConfigurationVerifying OSPF

U th h i f d t if &Use the show ip ospf command to verify & trouble shoot OSPF networks:

Neighbor adjacencyAdjacency indicated by

The OSPF state of the interface is “full state”full state

No adjacency indicated by -Neighboring router’s Router ID is not

displayedA state of full is not displayed

-Consequence of no adjacency-•Neighbor ID - The router ID of the neighboring router.•Pri - The OSPF priority of the interface..St t Th OSPF t t f th i t f FULL t tConsequence of no adjacency

No link state information exchangedInaccurate SPF trees & routing tables

•State - The OSPF state of the interface. FULL state means that the router and its neighbor have identical OSPF link-state databases.•Dead Time - The amount of time remaining that the router will wait to receive an OSPF Hello packet from the neighbor before declaring the neighbor down. This value is reset when the interface receives a Hello packet


is reset when the interface receives a Hello packet.•Address - The IP address of the neighbor's interface to which this router is directly connected.•Interface - The interface on which this router has formed adjacency with the neighbor.

Basic OSPF ConfigurationBasic OSPF ConfigurationNote:

On multiaccess networks such as Ethernet, two routers that are adjacent may have their states displayed as 2WAYstates displayed as 2WAY.

–This will be discussed in a DR and BDR section.

Two routers may not form an OSPF dj ifadjacency if:

–The subnet masks do not match, causing the routers to be on separate networks. •Neighbor ID - The router ID of the neighboring router.

•Pri - The OSPF priority of the interface..St t Th OSPF t t f th i t f FULL t t

–OSPF Hello or Dead Timers do not match.–OSPF Network Types do not match.

Th i i i i t OSPF

•State - The OSPF state of the interface. FULL state means that the router and its neighbor have identical OSPF link-state databases.•Dead Time - The amount of time remaining that the router will wait to receive an OSPF Hello packet from the neighbor before declaring the neighbor down. This value is reset when the interface receives a Hello packet


–There is a missing or incorrect OSPF network command.

is reset when the interface receives a Hello packet.•Address - The IP address of the neighbor's interface to which this router is directly connected.•Interface - The interface on which this router has formed adjacency with the neighbor.

Verifying OSPFVerifying OSPFShow ip protocols

–OSPF process ID, p ,–the router ID, –networks the router is advertising, –the default administrative distance, 110 for OSPF.

Show ip ospf–OSPF process ID –router IDrouter ID. –OSPF area information –the last time the SPF algorithm was calculated.

•R1 has participated in during the past 11 and a half hours is to send small Hello packets to its neighbors.

–SPF schedule delay •The router waits 5000 msecs after receiving an LSU before running the SPF algorithm. •There is an additional Hold Time of 10000 msecs between 2 SPF calculations.

Show ip ospf interface


–The quickest way to verify Hello and Dead intervals• for OSPF routers to become neighbors, their OSPF Hello and Dead intervals must be identical.

Configuring OSPF loopback address and router priorityConfiguring OSPF loopback address and router priority The command show ip ospf interface will display the interface priority value as well as other key information.p y y


Basic OSPF ConfigurationBasic OSPF ConfigurationExamining the routing table

Use the show ip route command to display the routing table-An “O’ at the beginning of a route indicates that the router source is OSPFOSPF-OSPF does not automatically summarize at major network boundaries

•Loopback interface countsinterface counts as a network. •These loopback interfaces are not advertised in OSPF.•They function as

t ID


router ID.

OSPF M t iOSPF MetricOSPF uses cost as the metric for determining the best routebest route

–A cost is associated with the output side of each router interface.

Th l th t th lik l th i t f i–The lower the cost, the more likely the interface is to be used to forward data traffic

The Cisco IOS uses the cumulative b d idth f th t i i t f fbandwidths of the outgoing interfaces from the router to the destination network as the cost value.

C i b d b d id h f i f-Cost is based on bandwidth of an interfaceCost is calculated using the formula

108 / bandwidth-Reference bandwidth

The 100Mbps (FastEthernet) and higher will have the same OSPF cost of 1.


This reference bandwidth can be modified usingauto-cost reference-bandwidth command

OSPF MetricOSPF MetricCOST of an OSPF route is the accumulated value from one router to the destination networkone router to the destination network

•For example, in the figure, the routing table on R1 shows 64 + 1 65the routing table on R1 shows a cost of 65 to reach the 10.10.10.0/24 network on R2.

•Because 10.10.10.0/24

64 + 1 = 65

is attached to a FastEthernet interface, R2 assigns the value 1 as the cost for 10.10.10.0/24. •R1 then adds the additional cost value of 64

d d hto send data across the default T1 link between R1 and R2.


OSPF MetricOSPF MetricSometimes the actual speed of a link is different than the default bandwidth

Thi k it i ti th t th b d idth l fl t–This makes it imperative that the bandwidth value reflects link’s actual speed

Reason: so routing table has best path information

The show interface command will display interface’sThe show interface command will display interface s bandwidth

–Most serial link default to 1.544Mbps–However, some serial interfaces may default to 128 kbps.However, some serial interfaces may default to 128 kbps.


M dif i OSPF t t iModifying OSPF cost metric OSPF uses cost as the metric for determining the best route.

Cost is calculated using the formula 108/bandwidth, where bandwidth is expressed in bps. (Cost = 100,000,000/Bandwidth)

The Cisco IOS automatically determines cost basedThe Cisco IOS automatically determines cost based on the bandwidth of the interface. It is essential for proper OSPF operation that the correct interface bandwidth is set.

Router(config)#interface serial 0/0Router(config-if)#bandwidth 64

The default bandwidth for Cisco serial interfaces is 1 544 Mbps or 1544 kbps1.544 Mbps, or 1544 kbps.

2A/S 2TCOD has these 2 types of serial cards in the lab


OSPF Metric: BandwidthOSPF Metric: BandwidthRemember, this bandwidth value does not actually affect the speed of the link; it is used by some routingthe link; it is used by some routing protocols to compute the routing metric.

–It is important that the bandwidth l fl t th t l d f thvalue reflect the actual speed of the

link so that the routing table has accurate best path information.

The figure displays the routing table g p y gfor R1.

–R1 believes that both of its serial interfaces are connected to T1 links,

f th li k i 64 kb li k•one of the links is a 64 kbps link •the other one is a 256 kbps link.

–This results in R1's routing table having two equal-cost paths to thehaving two equal cost paths to the 192.168.8.0/30 network, when Serial 0/0/1 is actually the better path.


How to modify the cost of all the links?

Basic OSPF ConfigurationBasic OSPF ConfigurationModifying the Cost of a link

B th id f i l li k h ld bBoth sides of a serial link should be configured with the same bandwidth

–Commands used to modify bandwidth valueCommands used to modify bandwidth valueBandwidth command

–Example: Router(config-if)#bandwidthbandwidth-kbpsip ospf cost command – allows you to directly specify

interface cost-Example:R1(config)#interface serial 0/0/0

R1(config-if)#ip ospf cost 1562


M dif i th C t f th li kModifying the Cost of the linkDifference between bandwidth command & the ip ospf

t dcost command–Ip ospf cost command

Sets cost to a specific valueSets cost to a specific value–Bandwidth command

Link cost is calculated


OSPF d M lti N t kOSPF and Multiaccess NetworksChallenges in Multiaccess Networks

OSPF defines five network types:OSPF defines five network types:–Point-to-point

•network there are only two devices on the network, one at each end. ,

–Broadcast Multiaccess•a network with more than two devices on the same shared media. •all devices on the network see all broadcast frames.

–Nonbroadcast Multiaccess (NBMA)•networks include Frame Relay ATM•networks include Frame Relay, ATM, and X.25 networks.

–Point-to-multipoint •networks include Frame Relay, ATM,

d X 25 t kand X.25 networks. –Virtual links

•Virtual links are a special type of link that can be used in multi-area OSPF


can be used in multi area OSPF.

OSPF in Multiaccess Networks2 challenges presented by multiaccess networks

–Multiple adjacencies–Extensive LSA floodingExtensive LSA flooding

The creation of an adjacency between every pair of routers in a network would create an unnecessary numberwould create an unnecessary number of adjacencies.

–This would lead to an excessive number of LSAs passing betweennumber of LSAs passing between routers on the same network.

•5 routers in the figure will need 10 adjacencies, j ,•10 routers would require 45 adjacencies. •20 routers would require 190


20 routers would require 190 adjacencies

OSPF i M lti N t kOSPF in Multiaccess NetworksExtensive flooding of LSAsg

For every LSA sent out there must be an acknowledgement of receipt sent back to transmitting router.

consequence: lots of bandwidth consumed and chaotic traffic


Solution:

Steps in the operation of OSPF OSPF routers send Hello packets on OSPF enabled interfaces. On multi-access networks the routers elect a DR and BDR On these networks other routersOn multi access networks, the routers elect a DR and BDR. On these networks other routers become adjacent to the DR.

To reduce the number of adjacencies trafficsTo reduce the number of adjacencies each router must form, OSPF calls one of the routers the designated router. A designated router is elected as

f i dj i d h ll h bli hrouters are forming adjacencies, and then all other routers establish adjacencies only with the designated router. This simplifies the routing table update procedure and reduces the number of link-state records in the database. The designated router plays other important roles as well to reduce the overhead of a OSPF link-state procedures. For example, other routers send link-state advertisements it to the designated router only by g y yusing the all-designated-routers multicast address of 224.0.0.6.


http://www.chebucto.ns.ca/Chebucto/Technical/Manuals/Max/max6000/isptele/maxospf.htm

Steps in the operation of OSPF

OSPF routers send HelloOSPF routers send Hello packets on OSPF enabled interfaces.

On multi-access networks, the routers elect a DR and BDR. On these networks other routers become adjacent to the DR.


Steps in the operation of OSPFSteps in the operation of OSPF To reduce the number of adjacencies traffics


http://www.cisco.com/warp/public/104/11.html

OSPF i M lti N t kOSPF in Multiaccess NetworksSolution to LSA flooding issue is the use of

–Designated router (DR)–Backup designated router (BDR)

•this solution is analogous to electing i th t d d lsomeone in the room to go around and learn

everyone's names and then announce these names to everyone in the room at once.

–DROther• All other routers become DROthers (this indicates a router that is neither the DR or the BDR).DROth l f f ll dj i ith th•DROthers only form full adjacencies with the

DR and BDR in the network.

DR & BDRO lti t k OSPF l t–On multiaccess networks, OSPF elects a

Designated Router (DR) to be the collection and distribution point for LSAs sent and received. –A Backup Designated Router (BDR) is also


p g ( )elected in case the Designated Router fails. –DR & BDR are elected to send & receive LSA

OSPF i M lti N t kOSPF in Multiaccess NetworksDR & BDR & DROther

–Routers on a multiaccess network elect a DR and BDR.

DR & BDR are elected to send &–DR & BDR are elected to send & receive LSA–DROthers only form full adjacencies with the DR and BDR inadjacencies with the DR and BDR in the network.

Sending & Receiving LSASending & Receiving LSA–DRothers send LSAs via multicast 224.0.0.6 to DR & BDR (ALLDRouters - All DR routers)(ALLDRouters All DR routers)–DR forward LSA via multicast address 224.0.0.5 to all other routers (AllSPFRouters - All OSPF routers)


(AllSPFRouters - All OSPF routers).

OSPF in Multiaccess Networks

DR/BDR Election ProcessDR/BDR Election Process

DR/BDR elections DO NOT occur in point to

DR/BDR elections will take place on multiaccessNOT occur in point-to-

point networksplace on multiaccess networks as shown below


OSPF in Multiaccess NetworksOSPF in Multiaccess Networks

Criteria for getting elected DR/BDRg g1. DR: Router with the highest OSPF

interface priority.2 BDR: Router with the second highest2. BDR: Router with the second highest

OSPF interface priority. 3. If OSPF interface priorities are equal, the

highest router ID is used to break the tie.


Criteria for getting elected DR/BDR1. DR: Router with the highest OSPF interface

priority.p y2. BDR: Router with the second highest OSPF

interface priority. 3. If OSPF interface priorities are equal, the

highest router ID is used to break the tie.Example:

– The OSPF for all interface priority is 1The OSPF for all interface priority is 1. – The OSPF router ID is used to elect the DR

and BDR. • RouterC with the highest router ID, g ,

becomes the DR• RouterB, with the second highest router

ID, becomes the BDR. B R t A i t l t d• Because RouterA is not elected as either the DR or BDR, it becomes the DROther.


DROthers only form FULL adjacencies with the DR and BDR, but will still form a neighbor adjacency with any DROthers that join the network. When two DROther routers form a neighbor adjacency, the neighbor state is displayed as 2WAY.

You need 4 routers topology to see this “2way” adjacency.

OSPF network types (cont.)

Real DR and BDR election processThe first router up on the network is the DRDR. The second router up on the network is the BDR. If the DR fails then the BDR becomes DRIf the DR fails then the BDR becomes DR and another router is elected the BDR. The DR does not change just because another router comes on line with a higher gpriority or a higher router id. If both the existing DR and BDR fail and a new DR must be elected, the router with the highest priority is elected DRthe highest priority is elected DR. If there's a tie, the router with the highest router id is elected DR.


Timing of DR/BDR Election (This is really of how the election works)

Election occurs as soon as 1st router has its OSPFElection occurs as soon as 1 router has its OSPF enabled on multiaccess network. This can happen when

1 When the routers are powered on1. When the routers are powered-on • it is possible that a router with a lower router ID will become the DR. This could be a lower-end router that took less time to bootrouter that took less time to boot.

2. when the OSPF network command for that interface is configured.

When a DR is elected it remains as the DR until one of the following occurs

The DR fails-The DR fails.-The OSPF process on the DR fails.-The multiaccess interface on the DR fails.



DR FailsDR Fails–If the DR fails, the BDR assumes the role of DR and an election is held to choose a new BDRBDR. –In the figure, RouterC fails and the former BDR, RouterB, becomes DR. The only otherBDR, RouterB, becomes DR. The only other router available to be BDR is RouterA.



New RouterNew Router–If a new router enters the network after the DR and BDR have been elected, it will

t b th DR th BDR if itnot become the DR or the BDR even if it has a higher OSPF interface priority or router ID than the current DR or BDR.

•If the current DR fails, the BDR will become the DR, and the new router can be elected the new BDR.can be elected the new BDR. •After the new router becomes the BDR, if the DR fails, then the new

t ill b th DRrouter will become the DR. •The current DR and BDR must both fail before the new router can be


elected DR or BDR.


Old DR ReturnsOld DR Returns–A previous DR does not regain DR status if it returns to the network.

•In the figure, RouterC has finished a reboot and becomes a DROther even though its router ID, 192.168.31.33, isthough its router ID, 192.168.31.33, is higher than the current DR and BDR.



BDR FailsBDR Fails–If the BDR fails, an election is held among the DRothers to see which router

ill b th BDRwill be the new BDR.•In the figure, the BDR router fails. •An election is held between RouterC•An election is held between RouterC and RouterD. •RouterD wins the election with the higher router ID.



New DR FailsNew DR Fails–In the figure, RouterB fails. Because RouterD is the current BDR, it is promoted to DR RouterC becomes the BDRto DR. RouterC becomes the BDR.

So, how do you make sure that the routers you want to be DR and BDR ywin the election? Without further configurations, the solution is to either:either:

–Boot up the DR first, followed by the BDR, and then boot all other routers, or–Shut down the interface on all routers, followed by a no shutdown on the DR, then the BDR, and then all other routers.


OR: use the priority command set not desired DR and BDR to 0

OSPF in Multiaccess NetworksOSPF in Multiaccess NetworksOSPF Interface Priority

Manipulating the DR/BDR election process continuedManipulating the DR/BDR election process continued–Use the ip ospf priority interface command.–Example:Router(config-if)#ip ospf priority {0 - 255}

Priority number range 0 to 255–0 means the router cannot become the DR or BDR–1 is the default priority value–1 is the default priority value

»router ID determined the DR and BDR


OSPF in Multiaccess NetworksOSPF in Multiaccess NetworksOSPF Interface Priority

Modify PriorityModify Priority–Router(config-if)#ip ospf priority {0 - 255}

Force ElectionAft d i h td d h td–After doing a shutdown and a no shutdown

on the FastEthernet 0/0 interfaces of all three routers, we see the result of the change of OSPF interface priorities. –The show ip ospf neighbor command on RouterC now shows that RouterA (Router ID 192.168.31.11) is the DR with the highest OSPF interface priority of 200 DRp y–RouterB (Router ID 192.168.31.22) is still the BDR with the next highest OSPF interface priority of 100.

N ti f R t A' t t f h i BDR–Notice from RouterA's output of show ip ospf neighbor that it does not show a DR, because RouterA is the actual DR on this network.

BDR


More OSPF ConfigurationRedistrib ting an OSPF Defa lt Ro teRedistributing an OSPF Default Route

Topology includes a link to ISPR t t d t ISP–Router connected to ISP

Called an autonomous system border routerUsed to propagate a default route

In this topology, the Loopback1 (Lo1) simulate the connection to another Used to propagate a default route

–Example of static default routeR1(config)#ip route 0.0.0.0 0.0.0.0 loopback 1

router.

–Requires the use of the default-information originatecommandcommand–Example of default-information originate command

R1(config-router)#default-information originate


Redistributing an OSPF Default Route

The default route in R2 and R3 with the routing source OSPF, but with the additional code, E2. For R2, the route is:

O*E2 0.0.0.0/0 [110/1] via 192.168.10.10, 00:05:34, Serial0/0/1

E2 denotes that this route is an OSPF ExternalE2 denotes that this route is an OSPF External Type 2 route. the cost of an E2 route is always the external cost, irrespective of the interior cost to reach that route. (CCNP)


More OSPF ConfigurationMore OSPF ConfigurationFine-Tuning OSPF

Since link speeds are getting faster it may be necessary to

fchange reference bandwidth values

Do this using the auto cost–Do this using the auto-cost reference-bandwidth command–Example:

R1(config-router)#auto-cost reference-bandwidth 10000

•the default value is equivalent to 100. To increase it to 10GigE speeds, you would need


g p , yto change the reference bandwidth to 10000.•Again, make sure you configure this command on all routers in the OSPF routing domain.

More OSPF ConfigurationMore OSPF ConfigurationFine-Tuning OSPF

R1(config-router)#auto-cost reference-bandwidth 1000010000

•the default value is equivalent to 100. To increase it to 10GigE speeds you would needincrease it to 10GigE speeds, you would need to change the reference bandwidth to 10000.

R1 Before, the cost to 10.10.10.0/24 is 1172. Aft fi i f b d idth


After configuring a new reference bandwidth, the cost for the same route is now 117287.

More OSPF ConfigurationMore OSPF Configuration

Fine-Tuning OSPFModifying OSPF timers

–Reason to modify timersFaster detection of network failures

–Manually modifying Hello & Dead intervalsRouter(config-if)#ip ospf hello-interval secondsR t ( fi if)#i f d d i t l dRouter(config-if)#ip ospf dead-interval seconds

–Point to be madeHello & Dead intervals must be the same betweenHello & Dead intervals must be the same between

neighbors


The End

Questions?Questions?

What will be the result of the DR and BDR elections for this single areaWhat will be the result of the DR and BDR elections for this single area OSPF network? (Choose three.)

HQ ill b DR f 10 4 0 0/16

*. Decision process:

1. Which segment will have election?HQ will be DR for 10.4.0.0/16.

Router A will be DR for 10.4.0.0/16.

HQ will be BDR for 10 4 0 0/16

2. Priority?

3. Router ID (each router will only has 1 ID)?HQ will be BDR for 10.4.0.0/16.


Remote will be DR for 10 5 0 0/16

ID)?

1. Set using “router-ID” command

2. Highest Loopback IP address?


Remote will be DR for 10.5.0.0/16.

Remote will be BDR for 10.5.0.0/16.3. Highest physical IP address

(include serial interface)?

The End


The routers in the diagram are configured as shown The loopback interface onThe routers in the diagram are configured as shown. The loopback interface on router R1 is labeled as lo0. All OSPF priorities are set to the default except for Ethernet0 of router R2, which has an OSPF priority of 2. What will be the result of the OSPF DR/BDR elections on the 192.1.1.0 network? (Choose two.)the OSPF DR/BDR elections on the 192.1.1.0 network? (Choose two.)

R1 will be the DR *. Decision process:

1 Which segment will have election?R1 will be the BDR

R2 will be the DR

1. Which segment will have election?

2. Priority?

3. Router ID (each router will only has 1 ID)?R2 will be the BDR

R3 will be the DR1. Set using “router-ID” command



R3 will be the BDR 3. Highest physical IP address (include serial interface)?



1 Which segment will have election?1. Which segment will have election?

2. Priority?

3. Router ID (each router will only has 1 ID)?




3. Highest physical IP address (include serial interface)?

Questions?

Answer?????Answer?????



2 i i ?2. Priority?

3. Router ID (each router will only has 1 ID)?

1. Set using “router-ID” command1. Set using router ID command


3. Highest physical IP address (include i l i f )?


serial interface)?

Questions?

Answer?????HQ will be DR for 10.4.0.0/16

Answer?????


HQ ill b BDR fHQ will be BDR for 10.4.0.0/16.

Router A will be DR for*. Decision process:

1 Which segment will have election?Router A will be DR for 10.5.0.0/16

Remote will be DR for


2. Priority?

3. Router ID (each router will only has 1 ID)?10.5.0.0/16.

Remote will be BDR for 10 5 0 0/16




10.5.0.0/16 3. Highest physical IP address (include serial interface)?

SummarySummaryRFC 2328 describes OSPF link state concepts and operationsoperations

OSPF Characteristics–A commonly deployed link state routing protocol–Employs DRs & BDRs on multi-access networks

DRs & BDRs are electedDRs & BDRs are electedDR & BDRs are used to transmit and receive LSAs

–Uses 5 packet types:Uses 5 packet types:1: HELLO2: DATABASE DESCRIPTION3: LINK STATE REQUEST4: LINK STATE UPDATE 5: LINK STATE ACKNOWLEDGEMENT


5: LINK STATE ACKNOWLEDGEMENT

Summary

OSPF CharacteristicsOSPF Characteristics–Metric = cost

Lowest cost = best pathLowest cost = best path

ConfigurationE bl OSPF t i th f ll i d–Enable OSPF on a router using the following command

R1(config)#router ospf process-iduse the network command to define which interfaces will–use the network command to define which interfaces will

participate in a given OSPF processR1(config-router)#network network-address

wildcard-mask area area-id


Summary

Verifying OSPF configuration–Use the following commands

show ip protocolshow ip routeh i f i t fshow ip ospf interface

show ip ospf neighbor


ccna exp 2 - routing protocols and concepts

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