exploration routing semester 2

8/14/2019 Exploration Routing Semester 2

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2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

Introduction to Routingand Packet Forwarding

Routing Protocols andConcepts Chapter 1


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ITE PC v4.0Chapter 1 2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Objectives Identify a router as a computer with an OS and

hardware designed for the routing process.

Demonstrate the ability to configure devices andapply addresses.

Describe the structure of a routing table.

Describe how a router determines a path andswitches packets


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Router as a Computer Describe the basic purpose of a router

-Computers that specialize in sending packets over the data

network. They are responsible for interconnecting networks byselecting the best path for a packet to travel and forwardingpackets to their destination

Routers are the network center

-Routers generally have 2 connections:

-WAN connection (Connection to ISP)

-LAN connection


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Router as a Computer Data is sent in form of packets between 2 end devices

Routers are used to direct packet to its destination

(routing table)


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Router as a Computer Routers examine a packets destination IP address and

determine the best path by enlisting the aid of a routing

table


6/336ITE PC v4.0Chapter 1 6 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Router as a Computer Router components and their functions:

CPU - Executes operating system instructions

Random access memory (RAM) - Contains the running copy ofconfiguration file. Stores routing table. RAM contents lost when poweris off

Read-only memory (ROM) - Holds diagnostic software used whenrouter is powered up. Stores the routers bootstrap program.

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

Flash memory - Contains the operating system (Cisco IOS)

Interfaces - There exist multiple physical interfaces that are used toconnect network. Examples of interface types:

-Ethernet / fast Ethernet interfaces

-Serial interfaces

-Management interfaces



Router as a Computer Router components



Router as a Computer Major phases to the

router boot-up process

Test router hardwarePower-On Self Test(POST)

Execute bootstrap loader

Locate & load Cisco IOSsoftware

-Locate IOS

-Load IOS

Locate & load startupconfiguration file or entersetup mode

-Bootstrap program looksfor configuration file



Router as a Computer Verify the router boot-up process:

-The show version command is used to view information about

the router during the bootup process. Information includes:Platform model number

Image name & IOS version

Bootstrap version stored in ROMImage file name & where it was loaded from

Number & type of interfaces

Amount of NVRAMAmount of flash

Configuration register



Router as a Computer



Router as a Computer Router Interface is a physical connector that enables a

router to send or receive packets

Each interface connects to a separate network

Consist of socket or jack found on the outside of a router

Types of router interfaces:-Ethernet

-Fastethernet

-Serial-DSL

-ISDN

-Cable



Router as a Computer Two major groups of Router InterfacesLAN Interfaces:

Are used to connect router to LANnetwork

Has a layer 2 MAC address

Can be assigned a Layer 3 IP

addressUsually consist of an RJ-45 jack

WAN Interfaces

Are used to connect routers to external networks thatinterconnect LANs.

Depending on the WAN technology, a layer 2 addressmay be used.

Uses a layer 3 IP address


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Router as a Computer Routers and the Network Layer

Routers use destination IP address to forward packets

The path a packet takes is determined after a routerconsults information in the routing table.

After router determines the best path

Packet is encapsulated into a frame

Frame is then placed on network medium in form of Bits


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Router as a Computer Routers Operate at Layers 1, 2 & 3

Router receives a stream of encoded bits

Bits are decoded and passed to layer 2Router de-encapsulates the frame

Remaining packet passed up to layer 3

-Routing decision made at this layer by examiningdestination IP address

Packet is then re-encapsulated & sent out outbound interface


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Configure Devices and Apply Addresses Implementing Basic Addressing Schemes

When designing a new network or mapping an existing

network you must provide the following information inthe form of a document:

-Topology drawing that Illustrates physical connectivity

Address table that provides the following information:

Device name

Interfaces used

IP addresses

Default gateway

Ex. 1.2.1.1


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Configure Devices and Apply Addresses Basic Router Configuration

A basic router configuration should contain the following:

-Router name - Host name should be unique-Banner - At a minimum, banner should warn againstunauthorized use

-Passwords - Use strong passwords

-Interface configurations - Specify interface type, IP addressand subnet mask. Describe purpose of interface. Issue noshutdown command. If DCE serial interface issue clock ratecommand.

After entering in the basic configuration the following tasks shouldbe completed

-Verify basic configuration and router operations.

-Save the changes on a router


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Configure Devices and Apply Addresses


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Configure Devices and Apply Addresses Verify Basic Router Configuration

-Issue the show running-configcommand

-Save the basic router configuration by Issuing the copyrunning-config startup-configcommand

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

Show running-config - Displays configuration currently inRAM

Show startup-config - Displays configuration file NVRAM

Show IP route - Displays routing table

Show interfaces - Displays all interface configurations

Show IP int brief - Displays abbreviated interface

configuration information


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Routing Table Structure Routing Table is stored in ram and contains information

about:

Directly connected networks - this occurs when a device is

connected to another router interface

Remotely connected networks - this is a network that is notdirectly connected to a particular router

Detailed information about the networks include source ofinformation, network address & subnet mask, and Ip address ofnext-hop router

Show ip route command is used to view a routing table


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Routing Table Structure

Adding a connected network to the routing table-Router interfaces

Each router interface is a member of a different network

Activated using the no shutdowncommand

In order for static and dynamic routes to exist in routingtable you must have directly connected networks


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Routing Table Structure 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 usedto connect remote networks before static or dynamic routing

can be used

When to use static routes

-When network only consists of a few routers

-Network is connected to internet only through one ISP

-Hub & spoke topology is used on a large network


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Routing Table Structure Connected and Static routes


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Routing Table Structure Dynamic routing protocols

-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

-Routers are able discover new networks by sharing routingtable information


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Routing Table Structure Maintaining routing tables

-Dynamic routing protocols are used to share routing information withother router & to maintain and up date their own routing table.

IP routing protocols. Example of routing protocols include:

-RIP

-IGRP

-EIGRP

-OSPF

-IS-IS

-BGP


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Routing Table Structure Routing Table Principles

-3 principles regarding routing tables:

Every router makes its decisions alone, based on theinformation it has in its routing table.

Different routing table may contain different information

A routing table can tell how to get to a destination but nothow to get back


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Routing Table Structure Effects of the 3 Routing Table Principles

-Packets are forwarded through the network from one router

to another, on a hop by hop basis.-Packets can take path X to a destination but return viapath Y (Asymmetric routing).


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Router Paths and Packet Switching Internet Protocol (IP) packet format contains fields that

provide information about the packet and the sending

and receiving hosts Fields that are important for CCNA students:

-Destination IP address

-Source IP address-Version & TTL

-IP header length

-Precedence & type of service-Packet length


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Router Paths and Packet Switching A Metric is a numerical value used by routing protocols helpdetermine the best path to a destination

The smaller the metric value the better the path

2 types of metrics used by routing protocols are:-Hop count - this is the number of routers a packet must travelthrough to get to its destination

-Bandwidth - this is the speed of a link also known as the data

capacity of a link


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Router Paths and Packet Switching Path determination is a process used by a router to pick the best

path to a destination

One of 3 path determinations results from searching for the best

pathDirectly connected network

Remote network

No route determined->ICMP unreachable


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Router Paths and Packet Switching Switching Function of Router is the process used by a

router to switch a packet from an incoming interface to

an outgoing interface on the same router.-A packet received by a router will do the following:

Strips off layer 2 headers.

Examines destination IP address located in Layer 3header to find best route to destination.

Re-encapsulates layer 3 packet into layer 2 frame.

Forwards frame out exit interface.


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

-The Source and Destination IP addresses NEVER change

-The Source & Destination MAC addresses CHANGE as packetis forwarded from one router to the next.

-TTL field decrement by one until a value of zero is reached atwhich point router discards packet (prevents packets from

endlessly traversing the network)


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Router Paths and Packet Switching Path determination and switching function details. PC1

Wants to send something to PC 2 here is part of what

happensStep 1 - PC1 encapsulates packet into a frame. Framecontains R1s destination MAC address


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Router Paths and Packet Switching

Step 2 - R1 receives Ethernet frame.

R1 sees that destination MAC address matches its ownMAC.

R1 then strips off Ethernet frame.

R1 Examines destination IP.

R1 consults routing table looking for destination IP.

After finding destination IP in routing table, R1 now looks upnext hop IP address.

R1 re-encapsulates IP packet with a new Ethernet frame.

R1 forwards Ethernet packet out Fa0/1 interface.


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Router Paths and Packet Switching Path determination and switching function details. PC1 Wants to

send something to PC 2 here is part of what happens

Step 3 - Packet arrives at R2

R2 receives Ethernet frame

R2 sees that destination MAC address matches its ownMAC

R2 then strips off Ethernet frame

R2 Examines destination IP

R2 consults routing table looking for destination IPAfter finding destination IP in routing table, R2 now looks upnext hop IP address

R2 re-encapsulates IP packet with a new data link frame

R2 forwards Ethernet packet out S0/0 interface


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Router Paths and Packet Switching

Path determination and switching function details. PC1 Wants tosend something to PC 2 here is part of what happens

Step 4 - Packet arrives at R3

R3 receives PPP frame

R3 then strips off PPP frameR3 Examines destination IP

R3 consults routing table looking for destination IP

After finding destination IP in routing table, R3 is directly

connected to destination via its fast Ethernet interfaceR3 re-encapsulates IP packet with a new Ethernet frame

R3 forwards Ethernet packet out Fa0/0 interface

Step 5 - IP packet arrives at PC2. Frame is decapsulated &

processed by upper layer protocols.


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Summary

Routers 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 processIOS

Configuration file

Routers need to be configured. Basic configuration consists of:-Router name

-Router banner

-Password(s)

-Interface configurations i.e. IP address and subnet mask Routing tables contain the following information

-Directly connected networks

-Remotely connected networks-Network addresses and subnet masks

-IP address of next hop address


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Summary Routers determine a packets path to its destination bydoing the following

Receiving an encapsulated frame & examining destinationMAC address.

If the MAC address matches then Frame is de-encapsulatedso that router can examine the destination IP address.

If destination IP address is in routing table or there is a staticroute then Router determines next hop IP address. Router willre-encapsulate packet with appropriate layer 2 frame and sendit out to next destination.

Process continues until packet reaches destination.

Note - only the MAC addresses will change the source anddestination IP addresses do not change.


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Static Routing



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Objectives Define the general role a router plays in networks.

Describe the directly connected networks, different

router interfaces

Examine directly connected networks in the routingtable and use the CDP protocol

Describe static routes with exit interfaces

Describe summary and default route

Examine how packets get forwarded when usingstatic routes

Identify how to manage and troubleshoot static routes


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General Role of the Router Functions of a Router

-Best Path Selections

-Forwarding packets to destination

Introducing the Topology

-3 x 1800 series routers connected via WAN links

-Each router connected to a LAN represented by a switch and aPC


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Interfaces Examining Router Interfaces

-Show IP router command used to view routing table

-Show Interfaces command used to show status of aninterface

-Show IP Interface brief command used to show a portion ofthe interface information

-Show running-config command used to show configurationfile in RAM


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Interfaces Configuring an Ethernet interface

-By default all serial and Ethernet interfaces are down

-To enable an interface use the No Shutdown command


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Interfaces Configuring a Serial interface

-Enter interface configuration mode

-Enter in the ip address and subnet mask

-Enter in the no shutdown command

Example:

-R1(config)#interface serial 0/0

-R1(config-if)#ip address 172.16.2.1 255.255.255.0

-R1(config-if)#no shutdown


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Interfaces Examining Router Interfaces

-Physically connecting a WAN Interface.

-A WAN Physical Layer connection has sides:Data Circuit-terminating Equipment (DCE) This is theservice provider. CSU/DSU is a DCE device.

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


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Interfaces Configuring serial links in a lab environment

One side of a serial connection must be considered a DCE

This requires placing a clocking signal use the clock rate

command.

Example:

-R1(config)#interface serial 0/0

-R1(config-if)#clockrate 64000

Serial Interfaces require a clock signal to control the timing ofthe communcations.


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Routing Table and CDP Protocol Purpose of the debug ip routing command

Allows you to view changes that the router performs whenadding or removing routes

Example:

-R2#debug ip routing

-IP routing debugging is on


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Routing Table and CDP Protocol To configure an Ethernet interface

Example:

-R2(config)#interface fastethernet 0/0-R2(config-if)#ip address 172.16.1.1 255.255.255.0

-R2(config-if)#no shutdown


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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


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Routing Table and CDP Protocol


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Routing Table and CDP Protocol Purpose of CDP

A layer 2 cisco proprietary tool used to gather information aboutother directly connected Cisco devices.

Concept of neighbors

-2 types of neighbors

Layer 3 neighborsLayer 2 neighbors


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Routing Table and CDP Protocol CDP show commands

Show cdp neighbors command

-Displays the following information:Neighbor device ID

Local interface

Holdtime value, in secondsNeighbor device capability code

Neighbor hardware platform

Neighbor remote port IDShow cdp neighbors detail command

-Useful in determining if an IP address configuration error


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Routing Table and CDP Protocol

Disabling CDP

To disable CDP globally usethe following command

Router(config)#no cdp run


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Static Routes with Exit Interfaces Purpose of a static route

A manually configured route used when routing from a networkto a stub network (a network accessed by a single route)


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Static Routes with Exit Interfaces IP route command

To configure a static route use the following command: ip route

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


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Static Routes with Exit Interfaces Dissecting static route syntax

ip route - Static route command

172.16.1.0 Destination network address255.255.255.0 - Subnet mask of destination network

172.16.2.2 - Serial 0/0/0 interface IP address on R2, which isthe "next-hop" to this network


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Static Routes with Exit Interfaces Configuring routes to 2 or more remote networks

Use 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


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Static Routes with Exit Interfaces Zinins 3 routing principles

Principle 1: "Every router makes its decision alone, based onthe information it has in its own routing table.

Principle 2: "The fact that one router has certain information inits routing table does not mean that other routers have the sameinformation.

Principle 3: "Routing information about a path from onenetwork to another does not provide routing information aboutthe reverse, or return path."


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Static Routes with Exit Interfaces Using Zinins 3 routing principles, how would you

answer the following?

-Would packets from PC1 reach their destination?Yes, packets destined for 172.16.1.0/24 and 192.168.1.0/24

networks would reach their destination.

-Does this mean that any packets from these networks destined

for 172.16.3.0/24 network will reach their destination?

No, because neither R2 nor R3 router has a route to the172.16.3.0/24 network.


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Static Routes with Exit Interfaces Resolving to an Exit Interface

-Recursive route lookup - Occurs when the router has to perform multiplelookups in the routing table before forwarding a packet. A static route that

forwards all packets to the next-hop IP address goes through the followingprocess (reclusive route lookup)

The router first must match static routes destination IP address with theNext hop address

The next hop address is then matched to an exit interface


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Static Routes with Exit Interfaces Configuring a Static route with an Exit Interface

-Static routes configured with an exit interface are more efficient

The routing table can resolve the exit interface in a single search insteadof 2 searches

-Example of syntax require to configure a static route with an exit interface


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Static Routes with Exit Interfaces Modifying Static routes

Existing static routes cannot be modified. The old static routemust be deleted by placing no in front of the ip route

Example:

-no ip route 192.168.2.0 255.255.255.0 172.16.2.2

A new static route must be rewritten in the configuration


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Static Routes with Exit Interfaces Verifying the Static Route Configuration

-Use the following commands

Step 1 show running-configStep 2 verify if static route has been entered correctly

Step 3 show ip route

Step 4 verify if route was configured in routing tableStep 5 issue ping command to verify packets can reachdestination and that Return path is working


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Static Routes with Exit Interfaces

Ethernet interfaces and ARP.If 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 theaddress of the next hops Ethernet interface

This is found by the router consulting the

ARP table.

If an entry isnt found then an ARPrequest will be sent out


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Summary and Default Route Configuring a summary route

Step 1: Delete the current static route

Step 2: Configure the summary static routeStep 3: Verify the new static route


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Summary and Default Route Static routes and subnet masks

The routing table lookup process will use the most specificmatch when comparing destination IP address and subnetmask

Default static routes and subnet masks

Since the subnet mask used on a default static route is 0.0.0.0all packets will match.


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Static Routes and Packet Forwarding

Packet forwarding withstatic routes. (recallZinins 3 routingprinciples)

Router 1

Packet arrives on R1sFastethernet 0/0interface

-R1 does not have a

route to the destinationnetwork,192.168.2.0/24

-R1 uses the default

static route.


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Static Routes and Packet Forwarding

Packet forwarding with static routes. (recall Zinins 3routing principles)

Router 2

-The packet arrives on the Serial 0/0/0 interface on R2.-R2 has a static route to 192.168.2.0/24 out Serial0/0/1.


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Static Routes and Packet Forwarding Packet forwarding with static routes. (recall Zinins 3

routing principles)

Router 3-The packet arrives on the Serial0/0/1 interface on R3.

-R3 has a connected route to 192.168.2.0/24 out Fastethernet

0/1.


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Static Routes and Packet Forwarding Troubleshooting a Missing Route

Tools that can be used to isolate routing problems

include:-Ping tests end to end connectivity

-Traceroute used to discover all of the hops (routers) along the

path between 2 points-Show IP route used to display routing table & ascertainforwarding process

-Show ip interface brief- used to show status of router interfaces

-Show cdp neighbors detail used to gather configurationinformation about directly connected neighbors


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Static Routes and Packet Forwarding Solving a Missing Route

Finding a missing or mis-configured route requires

methodically using the correct tools-Start with PING. If ping fails then use traceroute to determinewhere packets are failing to arrive

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


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S


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Summary Static Routes

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

Summary static routes

-This is several static routes that have been condensed into asingle static route.

Default route

-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

-Zinins 3 routing principles describe how packets are forwarded

Troubleshooting static routes may require some of the following

commands:-Ping

-Traceroute

-Show IP route

-Show ip interface brief-Show cdp neighbors detail


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Introduction to DynamicRouting Protocol



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Objectives Describe the role of dynamic routing protocols and

place these protocols in the context of modernnetwork design.

Identify several ways to classify routing protocols.

Describe how metrics are used by routing protocols

and identify the metric types used by dynamic routingprotocols.

Determine the administrative distance of a route and

describe its importance in the routing process.

Identify the different elements of the routing table.


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Dynamic Routing Protocols - History


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Dynamic Routing Protocols Function(s) of Dynamic Routing Protocols:-Dynamically share information between routers.

-Automatically update routing table when topology changes.-Determine best path to a destination.


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Static Routing Protocols Advantages of static routing-It can backup multiple interfaces/networks on a router

-Easy to configure-No extra resources are needed

-More secure

Disadvantages of static routing-Network changes require manual reconfiguration

-Does not scale well in large topologies


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Static vs Dynamic Routing Protocols


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Classifying Routing Protocols Dynamic routing protocols are grouped accordingto characteristics. Examples include:

-RIP-IGRP

-EIGRP

-OSPF

-IS-IS

-BGP

Autonomous System is a group of routers under

the control of a single authority.


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Classifying Routing Protocols Types of routing protocols:-Interior Gateway Protocols (IGP)

-Exterior Gateway Protocols (EGP)


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Classifying Routing Protocols Interior Gateway Routing Protocols (IGP)-Used for routing inside an autonomous system & used to routewithin the individual networks themselves.

-Examples: RIP, EIGRP, OSPF

Exterior Routing Protocols (EGP)

-Used for routing between autonomous systems-Example: BGPv4

Classifying Routing Protocols


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Classifying Routing Protocols

IGP: Comparison of Distance Vector & Link StateRouting Protocols

Distance vector

routes are advertised as vectors

of distance & direction.

incomplete view of network

topology.

Generally, periodic

updates.

Link state

complete view of networktopology is created.

updates are not

periodic.


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Classifying Routing Protocols Classful routing

protocols

Do NOT send subnet maskin routing updates

Classless routingprotocols

Do send subnet mask in

routing updates.


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Classifying Routing Protocols Convergence is defined as when all routers routingtables are at a state of consistency


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Routing Protocols Metrics Metrics used in IP routing protocols-Bandwidth

-Cost-Delay

-Hop count

-Load

-Reliability

Routing Protocols Metrics


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Routing Protocols Metrics

The Metric Field in theRouting Table

Metric used for each

routing protocol-RIP - hop count

-IGRP & EIGRP -

Bandwidth (used bydefault), Delay (used bydefault), Load, Reliability

-IS-IS & OSPFCost,

Bandwidth (Ciscosimplementation)


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Routing Protocols Metrics Load balancingThis is the ability of a router to distribute packets amongmultiple same cost paths


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Administrative Distance of a Route Purpose of a metricIts a calculated value used to determine the best path to adestination

Purpose of Administrative Distance

Its a numeric value that specifies the preference of a particularroute


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Administrative Distance of a Route Identifying the Administrative Distance (AD) in arouting table

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


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Administrative Distance of a Route Dynamic Routing Protocols


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Administrative Distance of a Route Directly connected routesHave a default AD of 0

Static RoutesAdministrative distance of a static route has a default value of1


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Summary


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Summary

Dynamic routing protocols fulfill the following functions-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 include

-Classless routing protocols - these protocols include subnet maskin routing updates

-Classful routing protocols - these protocols do not include subnetmask in routing update

Summary


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Summary

Metrics are used by dynamic routing protocols to calculate thebest path to a destination.

Administrative distance is an integer value that is used to

indicate a routers trustworthiness Components of a routing table include:

-Route source

-Administrative distance-Metric

Excercise 3.5.1


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Distance Vector RoutingProtocols

Routing Protocols and Concepts Chapter 4


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Static routes VS scalability


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Distance Vector Routing Protocols Distance Vector TechnologyThe Meaning of Distance Vector:

A router using distance vector routing protocols knows 2things:

Distance to final destination

Vector, or direction, traffic should be directed

Distance Vector Routing Protocols


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Characteristics of Distance Vector routing protocols:

Periodic updates

Neighbors

Broadcast updates

Entire routing table is included with routing update



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Routing Protocol Algorithm:

-Defined as a procedure for accomplishing a certain task


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Distance Vector Routing ProtocolsRouting Protocol CharacteristicsCriteria used to compare routing protocols includes

Time to convergenceScalability

Classless or VLSMResource usage

Implementation & maintenance


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Network Discovery Router initial start up (Cold Starts)

-Initial network discovery

Directly connected networks are initially placed inrouting table

Network Discovery


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Network Discovery Initial Exchange of Routing Information

If a routing protocol is configured then

-Routers will exchange routing 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 Discovery


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y

Exchange of Routing InformationRouter convergence is reached when

-All routing tables in the network contain the samenetwork information

Routers continue to exchange routing information

-If no new information is found then Convergence isreached


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Routing Table Maintenance Periodic Updates: RIPv1 & RIPv2

These are time intervals in which a router sends

out its entire routing table.


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Routing Table Maintenance Bounded Updates: EIGRP

EIRPG routing updates are

-Partial updates

-Triggered by topology changes

-Bounded

-Non periodic

Routing Table Maintenance


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g

Triggered Updates

Conditions in which triggered updates are sent

-Interface changes state

-Route becomes unreachable

-Route is placed in routing table

Routing Table Maintenance


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g

Random Jitter

Synchronized updates

A condition where multiple routers on multi access LAN

segments transmit routing updates at the same time.

Problems with synchronized updates

-Bandwidth consumption

-Packet collisionsSolution to problems with

synchronized updates

- Used of random variablecalled RIP_JITTER 0-25% of

default interval

Routing Loops


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Routing Loops

Routing loops are

A condition inwhich a packet iscontinuouslytransmitted within

a series of routerswithout everreaching its

destination.


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Routing Loops Routing loops may be caused by:

-Incorrectly configured static routes

-Incorrectly configured route redistribution

-Slow convergence

-Incorrectly configured discard routes

Routing loops can create the following issues

-Excess use of bandwidth

-CPU resources may be strained

-Network convergence is degraded

-Routing updates may be lost or not processed in a timelymanner


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Routing Loops

Count to Infinity

This is a routing loop whereby packets bounceinfinitely around a network.


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Routing Loops Setting a maximum (RIP = 15)

Distance Vector routing protocols set a specified

metric value to indicate infinity

Once a router counts to infinity it marks the routeas unreachable

Routing Loops


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g p

Preventing loops with holddown timers

-Holddown timers allow a router to not accept any changes to aroute for a specified period of time.

-Point of using holddown timersAllows routing updates to propagate through network withthe most current information.

Routing Loops


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g p

The Split Horizon Rule is used to prevent routingloops

Split Horizon rule:

A router should not advertise a network through theinterface from which the update came.


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Routing Loops Split horizon with poison

reverse

The rule states thatonce a router learns ofan unreachable route

through an interface,advertise it asunreachable

Routing Loops


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IP & TTLPurpose of the TTL field

The TTL field is found in an IP header and is

used to prevent packets from endlesslytraveling on a network

How 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 Packetis discarded.

Routing Protocols Today


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Factors used to determine whether to use RIP or EIGRPinclude

-Network size

-Compatibility between models of routers-Administrative knowledge


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Routing Protocols Today EIGRP

Features of EIGRP:-Triggered updates

-EIGRP hello protocol used to establish

neighbor adjacencies

-Supports VLSM & route summarization

-Use of topology table to maintain all routes

-Classless distance vector routing protocol

-Cisco proprietary protocol


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Summary D.V. routing protocols maintains routing tables byRIP sending out periodic updates

RIP using 4 different timers to ensure information is accurateand 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 continuouslytraverse a network

Mechanisms used to minimize routing loops include defining

maximum hop count, holddown timers, split horizon, routepoisoning and triggered updates

Summary


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Conditions that can lead to routing loops include

Incorrectly configured static routes

Incorrectly configured route redistribution

Slow convergence

Incorrectly configured discard routes

How routing loops can impact network performanceincludes:

Excess use of bandwidth

CPU resources may be strained

Network convergence is degraded

Routing updates may be lost or not processed


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Summary Routing Information Protocol (RIP)

A distance vector protocol that has 2 versions

RIPv1 a classful routing protocol

RIPv2 - a classless routing protocol

Enhanced Interior Gateway Routing Protocol(EIGRP)

A distance vector routing protocols that has some features oflink state routing protocols

A Cisco proprietary routing protocol


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RIP version 1



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Objectives Describe the functions, characteristics, and operationof the RIPv1 protocol.

Configure a device for using RIPv1. Verify proper RIPv1 operation.

Describe how RIPv1 performs automatic

summarization.

Configure, verify, and troubleshoot default routespropagated in a routed network implementing RIPv1.

Use recommended techniques to solve problemsrelated to RIPv1


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RIPv1 RIP Characteristics

-A classful, Distance Vector (DV) routing protocol-Metric = hop count

-Routes with a hop count > 15 are unreachable

-Updates are broadcast every 30 seconds

RIPv1


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RIP Message Format RIP header - divided into

3 fields

-Command field-Version field

-Must be zero

Route Entry - composedof 3 fields

-Address familyidentifier

-IP address

-Metric


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RIPv1 RIP Operation

RIP uses 2 message types:

Request message

-This is sent out on startup by each RIP

enabled interface-Requests all RIP enabled neighbors to sendrouting table

Response message

-Message sent to requesting routercontaining routing table

RIPv1


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IP addresses initially dividedinto classes

-Class A-Class B

-Class C

RIP is a classful routingprotocol

-Does not send subnetmasks in routing updates

RIPv1


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Administrative DistanceRIPs default administrative distance is 120

Basic RIPv1 Configuration


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Basic RIPv1 Configuration A typical topology suitable for

use by RIPv1 includes:

-Three router set up-No PCs attached to LANs

-Use of 5 different IP

subnets



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Router RIP Command

To enable RIP enter:

-Router ripat the global configuration prompt-Prompt will look like R1(config-router)#



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Specifying Networks

Use the networkcommand to:

-Enable RIP on allinterfaces thatbelong to this

network

-Advertise thisnetwork in RIP

updatessent to otherrouters

every 30 seconds

Verification and Troubleshooting


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Show ip Route

To verify andtroubleshoot routing

-Use the following

commands:

-show ip route

-show ip protocols

-debug ip rip



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show ipprotocols

command-Displaysrouting

protocolconfiguredon router

Verification and Troubleshooting Debug ip rip command


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ebug p p co a d

-Used to display RIP routing updates as they arehappening



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e cat o a d oub es oot g

Passive interface command

-Used to prevent a router from sending updates throughan interface

-Example:

Router(config-router)#passive-interface interface-type interface-number



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g Passive interfaces

Automatic SummarizationModified Topology


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p gy

The original scenario has beenmodified such that:

Three classful networks are used:

172.30.0.0/16

192.168.4.0/24

192.168.5.0/24

The 172.30.0.0/16 network issubnetted into three subnets:

172.30.1.0/24

172.30.2.0/24

172.30.3.0/24

The following devices are part of the172.30.0.0/16 classful network address:

All interfaces on R1S0/0/0 and Fa0/0 on R2

Automatic Summarization


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Configuration Details

-To remove the RIP routing

process use the followingcommand

No router rip

-To check the configurationuse the following command

Show run

Automatic Summarization Boundary Routers


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y

RIP automatically summarizes classful networks

Boundary routers summarize RIP subnets from one

major network to another.



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Processing RIP Updates

2 rules govern RIPv1 updates:

-If a routing update and the interface itsreceived on belong to the samenetwork then

The subnet mask of theinterface is applied to the

network in the routing update

-If a routing update and the interface itsreceived on belong to a differentnetwork then

The classful subnet mask of thenetwork is applied to thenetwork in the routing update.



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Sending RIPUpdates

RIP usesautomaticsummarization to reduce

the size of arouting table.



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Advantages of automaticsummarization:

-The size ofrouting updates isreduced

-Single routes areused to representmultiple routeswhich results in

faster lookup in therouting table.



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Disadvantage of Automatic Summarization:

-Does not support discontiguous networks



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DiscontiguousTopologies do not

converge with RIPv1

A router will only

advertise majornetwork addressesout interfaces that do

not belong to theadvertised route.

Default Route and RIPv1


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Modified Topology: Scenario C

Default routes

Packets that are not defined specifically in a routingtable will go to the specified interface for the defaultroute

Example: Customer routers use default routes toconnect to an ISP router.

Command used to configure a default route is

ip route 0.0.0.0 0.0.0.0 s0/0/1



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Propagating the DefaultRoute in RIPv1

Default-informationoriginate command

-This command is used to specify that therouter is to originate default information,

by propagating the static default route inRIP update.


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Summary: Commands used by RIP


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Command Commands 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


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VLSM and CIDR

Routing Protocols and

Concepts Chapter 6

ObjectivesC d l f l d l l IP


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Compare and contrast classful and classless IPaddressing.

Review VLSM and explain the benefits of classless IPaddressing.

Describe the role of the Classless Inter-Domain

Routing (CIDR) standard in making efficient use ofscarce IPv4 addresses

Introduction

P i t 1981 IP dd d l th fi t 8 bit t


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Prior to 1981, IP addresses used only the first 8 bits tospecify the network portion of the address

In 1981, RFC 791 modified the IPv4 32-bit address to

allow for three different classes IP address space was depleting rapidly

the 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

Classful and Classless IP Addressing

Cl f l IP dd i


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Classful IP addressing As of January 2007, there

are over 433 million hostson Internet

Initiatives to conserve IPv4address space include:

-VLSM & CIDR notation(1993, RFC 1519)

-Network AddressTranslation (1994, RFC1631)

-Private Addressing(1996, RFC 1918)


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Classful and Classless IP Addressing Classes of IP addresses are identified by the decimal number of

th 1 t t t


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the 1st octet

Class A address begin with a 0 bit

Range of class A addresses = 0.0.0.0 to 127.255.255.255Class B address begin with a 1 bit and a 0 bit

Range of class B addresses = 128.0.0.0 to 191.255.255.255

Class C addresses begin with two 1 bits & a 0 bit

Range of class C addresses = 192.0.0.0 to 223.255.255.255.


Th IP Cl f l Add i S (RFC )


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The IPv4 Classful Addressing Structure (RFC 790)

An IP address has 2 parts:

-The network portion

Found on the left side of an IP address

-The host portionFound on the right side of an IP address



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Purpose of a subnet mask

It is used to determine the network portion of an IPaddress


Classful Routing Updates


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Classful Routing Updates-Recall that classful routing protocols (i.e. RIPv1)do not send subnet masks in their routing updates

The reason is that the Subnet mask isdirectly related to the network address



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Classless Inter-domain Routing (CIDR RFC 1517)

Advantage of CIDR :

-More efficient use of IPv4 addressspace

-Route summarization

Requires subnet mask to be included in routing updatebecause address class is meaningless

Recall purpose of a subnet mask:

-To determine the network and host portionof an IP address


Classless IP Addressing


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Classless 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 asingle route



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Classless Routing Protocol

Characteristics of classless routing protocols:

-Routing updates include the subnet mask

-Supports VLSM

Supports Route Summarization



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RoutingProtocol

Routingupdates

Include

subnetMask

SupportsVLSM

Ability to sendSupernet routes

Classful No No No

Classless Yes Yes Yes

Classless Routing Protocol

VLSM

Classful routing


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Classful routing-only allows for onesubnet mask for allnetworks

VLSM & classless routing

-This is the processof subnetting a subnet

-More than onesubnet mask can beused

-More efficient use of IPaddresses as comparedto classful IP

addressing BACKBONE

VLSM

VLSM the process of


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VLSM the process ofsub-netting a subnet to fityour needs

-Example:

Subnet 10.1.0.0/16, 8more bits are borrowed

again, to create 256subnets with a /24 mask.

-Mask allows for 254 host

addresses per subnet

-Subnets range from:10.1.0.0 / 24 to

10.1.255.0 / 24

Classless Inter-Domain Routing (CIDR)

Route summarization done by CIDR


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Route summarization done by CIDR-Routes are summarized with masks that are lessthan that of the default classful mask

-Example:

172.16.0.0 /13 is the summarizedroute for the 172.16.0.0 /16 to172.23.0.0 /16 classful networks

Classless Inter-Domain Routing (CIDR)


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Steps to calculate a routesummary

-List networks in binaryformat

-Count number of left

most matching bits todetermine summaryroutes mask

-Copy the matchingbits and add zero bitsto determine thesummarizednetwork address

Summary

Classful IP addressing


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Classful IP addressingIPv4 addresses have 2 parts:

-Network portion found on left side of an IP

address-Host portion found on right side of an IPaddress

Class A, B, & C addresses were designed to provide IPaddresses for different sized organizations

The class of an IP address is determined by the decimalvalue found in the 1st octet

IP addresses are running out so the use of Classless InterDomain Routing (CIDR) and Variable Length Subnet Mask(VLSM) are used to try and conserve address space

Summary

Classful Routing Updates


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Classful Routing UpdatesSubnet masks are not sent in routing updates

Classless IP addressing

Benefit of classless IP addressing

Can create additional network

addresses using a subnet maskthat fits your needs

Uses Classless Interdomain Routing (CIDR)

Summary CIDR


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CIDR

Uses IP addresses more efficiently through

use of VLSM-VLSM is the process ofsubnetting a subnet

Allows for route summarization-Route summarization isrepresenting multiple contiguous

routes with a single route


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RIPv2


Concepts Chapter 7

Objectives Encounter and describe the limitations of RIPv1s


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Encounter and describe the limitations of RIPv1 slimitations.

Apply the basic Routing Information Protocol Version2 (RIPv2) configuration commands and evaluateRIPv2 classless routing updates.

Analyze router output to see RIPv2 support for VLSMand CIDR

Identify RIPv2 verification commands and commonRIPv2 issues.

Configure, verify, and troubleshoot RIPv2 in hands-on labs

Introduction

Chapter focus


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Chapter focus-Difference between RIPv1 & RIPv2

RIPv1

-A classful distance vector routing protocol-Does not support discontiguous subnets

-Does not support VLSM

-Does not send subnet mask in routing update

-Routing updates are broadcastRIPv2

-A classless distance vector routing protocol that is anenhancement of RIPv1s features.

-Next hop address is included in updates

-Routing updates are multicast

-The use of authentication is an option

Introduction


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Similarities between RIPv1 & RIPv2

-Use of timers to prevent routing loops-Use of split horizon or split horizon with poisonreverse

-Use of triggered updates

-Maximum hop count of 15

RIPv1 Limitations

Lab Topology


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ab opo ogy

Scenario:

3 router set up

Topology is discontiguous

There exists a static summaryroute

Static route information can beinjected into routing table updatesusing redistribution.

Routers 1 & 3 contain VLSMnetworks


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RIPv1 Limitations Null Interfaces


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This is a virtual interface that does not need to becreated or configured

-Traffic sent to a null interface is discarded

-Null interfaces do not send or receive traffic

Static routes and null interfaces

null interfaces will serve as the exit interface forstatic route

-Example of configuring a static supernet route with anull interface

-R2(config)#ip route 192.168.0.0 255.255.0.0 Null0


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RIPv1 Limitations


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Verifying and Testing Connectivity

Use the following commands: show ip interfaces brief

ping

traceroute

RIPv1 Limitations



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-Subnet mask are not sent in updates

-Summarizes networks at major network boundaries

-if network is discontiguous and RIPv1 configured

convergencewill not be reached

RIPv1 Limitations

Examining the routing tables


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g g

-To examine the contents ofrouting updates use the

debug ip ripcommand

-If RIPv1 is

configured thenSubnet masks will not beincluded with the

network address

RIPv1 Limitations

RIPv1 does not supportVLSM


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ppVLSM

Reason: RIPv1 does not

send subnet maskin routing updates

RIPv1 does summarize

routes to the Classfulboundary

Or uses the Subnet mask

of the outgoing interfaceto determine whichsubnets to advertise

RIPv1 Limitations


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No CIDR Support

In the diagram R2 will not

include the static route in itsupdate

Reason: Classful routingprotocols do not supportCIDR routes that aresummarized with a smallermask than the classfulsubnet mask


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Configuring RIPv2


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Enabling and Verifying RIPv2

Configuring RIP on a Cisco routerBy default it is running RIPv1


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Di bli A t

Configuring RIPv2


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Disabling Auto-Summary in RIPv2

To disable automaticsummarization issuethe no auto-summary

command


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VLSM & CIDR


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CIDR uses Supernetting

Supernetting is a bunch of contiguous classfulnetworks that is addressed as a singlenetwork.

VLSM & CIDR

To verify that


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To verify thatsupernets arebeing sent andreceived use thefollowing commands

-Show ip route

-Debug ip rip

Verifying & Troubleshooting RIPv2

Basic Troubleshooting stepsCh k th t t f ll li k


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-Check the status of all links

-Check 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 protocolsDebug ip rip

Show ip route


Common RIPv2 Issues


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Common RIPv2 Issues

When trouble shooting RIPv2 examine the following issues:

Version

Check to make sure you are using version 2

Network statements

Network statements may be incorrectly typedor missing

Automatic summarization

If summarized routes are not needed then disableautomatic summarization


Reasons why its good to authenticate routing information


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-Prevent the possibility of accepting invalid routingupdates

-Contents of routing updates are encrypted

Types of routing protocols that can use authentication

-RIPv2

-EIGRP

-OSPF

-IS-IS

-BGP


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The Routing Table: ACloser Look


Concepts Chapter 8

Objectives Describe the various route types found in the routing

table structure


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table structure

Describe the routing table lookup process.

Describe routing behavior in routed networks.

Introduction


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ITE PC v4.0Chapter 1 3 2007 Cisco Systems, Inc. Al

exploration routing semester 2

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