ccna exploration v4.0 routing protocols …blackhawk.cs.mercer.edu/courses/david cozart/ist...

CCNA EXPLORATION V4.0 ROUTING PROTOCOLS AND CONCEPTS

ACCESSIBLE INSTRUCTOR MATERIALS POWERPOINT OBJECTIVES

Prepared by Cisco Learning Institute

June 23, 2008

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June 23, 2008 Page 1

Chapter 1 – Introduction to Routing and Packet Forwarding Objectives • Identify a router as a computer with an OS and hardware designed for the routing

process. • Demonstrate the ability to configure devices and apply addresses. • Describe the structure of a routing table. • Describe how a router determines a path and switches packets. Router as a Computer • Describe the basic purpose of a router

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

WAN connection (Connection to ISP) LAN connection

• Data is sent in form of packets between 2 end devices • Routers are used to direct packet to its destination • Routers examine a packet’s destination IP address and determine the best path by

enlisting the aid of a routing table • Router components and their functions

o CPU - Executes operating system instructions o Random access memory (RAM) - Contains the running copy of configuration file.

Stores routing table. RAM contents lost when power is off o Read-only memory (ROM) - Holds diagnostic software used when router is

powered up. Stores the router’s bootstrap program. o Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP

addresses (Routing protocol, Hostname of router) o Flash memory - Contains the operating system (Cisco IOS) o Interfaces - There exist multiple physical interfaces that are used to connect

network. o Examples of interface types:

Ethernet / fast Ethernet interfaces Serial interfaces Management interfaces

• Router components • Major phases to the router boot-up process

o Test router hardware Power-On Self Test (POST) Execute bootstrap loader




o Locate & load Cisco IOS software Locate IOS Load IOS

o Locate & load startup configuration file or enter setup mode Bootstrap program looks for configuration file

• Verify the router boot-up process: o 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 ROM Image file name & where it was loaded from Number & type of interfaces Amount of NVRAM Amount of flash Configuration register

• 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:

o Ethernet o Fastethernet o Serial o DSL o ISDN o Cable

• Two major groups of Router Interfaces o LAN Interfaces:

Are used to connect router to LAN network Has a layer 2 MAC address Can be assigned a Layer 3 IP address Usually consist of an RJ-45 jack

o WAN Interfaces Are used to connect routers to external networks that interconnect LANs. Depending on the WAN technology, a layer 2 address may be used. Uses a layer 3 IP address

• Routers and the Network Layer o Routers use destination IP address to forward packets

The path a packet takes is determined after a router consults 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




o Routers Operate at Layers 1, 2 & 3 o Router receives a stream of encoded bits o Bits are decoded and passed to layer 2 o Router de-encapsulates the frame o Remaining packet passed up to layer 3

Routing decision made at this layer by examining destination IP address o Packet is then re-encapsulated & sent out outbound interface

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 in the form of a document: o Topology drawing that Illustrates physical connectivity o Address table that provides the following information:

Device name Interfaces used IP addresses Default gateway

• Basic Router Configuration • A basic router configuration should contain the following:

o Router name - Host name should be unique o Banner - At a minimum, banner should warn against unauthorized use o Passwords - Use strong passwords o 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 be completed o Verify basic configuration and router operations. o Save the changes on a router

• Verify Basic Router Configuration o Issue the show running-config command o Save the basic router configuration by Issuing the copy running-config startup-

config command o Additional commands that will enable you to further verify router configuration

are: Show running-config - Displays configuration currently in RAM 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

Routing Table Structure • Routing Table is stored in ram and contains information about:




o Directly connected networks - this occurs when a device is connected to another router interface

o Remotely connected networks - this is a network that is not directly connected to a particular router

o Detailed information about the networks include source of information, network address & subnet mask, and Ip address of next-hop router

• Show ip route command is used to view a routing table • Adding a connected network to the routing table

o Router interfaces Each router interface is a member of a different network Activated using the no shutdown command In order for static and dynamic routes to exist in routing table you must have

directly connected networks • Static routes in the routing table

o Includes: network address and subnet mask and IP address of next hop router or exit interface

o Denoted with the code S in the routing table o 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

o When network only consists of a few routers o Network is connected to internet only through one ISP o Hub & spoke topology is used on a large network

• Connected and Static routes • Dynamic routing protocols

o Used to add remote networks to a routing table o Are used to discover networks o Are used to update and maintain routing tables

• Automatic network discovery o Routers are able discover new networks by sharing routing table information

• Maintaining routing tables o Dynamic routing protocols are used to share routing information with other router

& to maintain and up date their own routing table • IP routing protocols. Example of routing protocols include:

o RIP o IGRP o EIGRP o OSPF

• Routing Table Principles o 3 principles regarding routing tables:

Every router makes its decisions alone, based on the information 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 not how to get back




• Effects of the 3 Routing Table Principles o Packets are forwarded through the network from one router to another, on a hop

by hop basis o Packets can take path “X” to a destination but return via path “Y” (Asymmetric

routing) 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 importance for CCNA students:

o Destination IP address o Source IP address o Version & TTL o IP header length o Precedence & type of service o Packet length

• MAC Layer Frame Format • MAC Frames are also divided into fields. They include:

o Preamble o Start of frame delimiter o Destination MAC address o Source MAC address o Type/length o Data and pad o Frame check sequence

• A Metric is a numerical value used by routing protocols help determine the best path to a destination o The smaller the metric value the better the path

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

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

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

• To solve this dilemma, a router will use Equal Cost Load Balancing. This means the router sends packets over the multiple exit interfaces listed in the routing table

• 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 path o Directly connected network o Remote network o No route determined

• 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




o A packet received by a router will do the following: Strips 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

• As a packet travels from one networking device to another o The Source and Destination IP addresses NEVER change o The Source & Destination MAC addresses CHANGE as packet is forwarded from

one router to the next o TTL field decrement by one until a value of zero is reached at which point router

discards packet (prevents packets from endlessly traversing the network) • Path determination and switching function details. PC1 Wants to send something to

PC 2 here is part of what happens o Step 1 - PC1 encapsulates packet into a frame. Frame contains R1’s destination

MAC address o Step 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 After finding destination IP in routing table, R1 now looks up next hop IP

address R1 re-encapsulates IP packet with a new Ethernet frame R1 forwards Ethernet packet out Fa0/1 interface

• Path determination and switching function details. PC1 Wants to send something to PC 2 here is part of what happens o Step 3 - Packet arrives at R2

R2 receives Ethernet frame R2 sees that destination MAC address matches its own MAC R2 then strips off Ethernet frame R2 Examines destination IP R2 consults routing table looking for destination IP After finding destination IP in routing table, R2 now looks up next hop IP

address R2 re-encapsulates IP packet with a new data link frame R2 forwards Ethernet packet out S0/0 interface

• Path determination and switching function details. PC1 Wants to send something to PC 2 here is part of what happens o Step 4 - Packet arrives at R3

R3 receives PPP frame R3 then strips off PPP frame R3 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 interface

R3 re-encapsulates IP packet with a new Ethernet frame R3 forwards Ethernet packet out Fa0/0 interface

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

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

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

IOS Configuration file

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

• Routing tables contain the following information o Directly connected networks o Remotely connected networks o Network addresses and subnet masks o IP address of next hop address

• Routers determine a packets path to its destination by doing the following o Receiving an encapsulated frame & examining destination MAC address. o If the MAC address matches then Frame is de-encapsulated so that router can

examine the destination IP address. o 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 send it out to next destination.

o Process continues until packet reaches destination. o Note - only the MAC addresses will change the source and destination IP

addresses do not change.

Chapter 2 – Static Routing Objectives • Define the general role a router plays in networks. • Describe the directly connected networks, different router interfaces. • Examine directly connected networks in the routing table 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 Router

o Best Path Selections o Forwarding packets to destination

• Introducing the Topology o 3 1800 series routers connected via WAN links o Each router connected to a LAN represented by a switch and a PC

• Connections of a Router for WAN o A router has a DB-60 port that can support 5 different cabling standards

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

Straight through used to connect: Switch-to-Router, Switch-to-PC, Router-to-Server, Hub-to-PC, Hub-to-Server Cross-over used to connect: Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hub-to-Hub, Router-to-Router

Interfaces • Examining Router Interfaces

o Show IP router command – used to view routing table o Show Interfaces command – used to show status of an interface o Show IP Interface brief command – used to show a portion of the interface

information o Show running-config command – used to show configuration file in RAM

• Configuring an Ethernet interface o By default all serial and Ethernet interfaces are down o To enable an interface use the No Shutdown command

• Verifying Ethernet interface o Show interfaces for fastEthernet 0/0 – command used to show status of fast

Ethernet port o Show ip interface brief o Show running-config

Ethernet interfaces participate in ARP • Configuring a Serial interface

o Enter interface configuration mode o Enter in the ip address and subnet mask o Enter in the no shutdown command

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




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

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

Data Terminal Equipment (DTE) – Typically the router is the DTE device • Configuring serial links in a lab environment

o One side of a serial connection must be considered a DCE o This requires placing a clocking signal – use the clock rate command. o Example:

R1(config)#interface serial 0/0 R1(config-if)#clockrate 64000

o Serial Interfaces require a clock signal to control the timing of the communications

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

o Allows you to view changes that the router performs when adding or removing routes

o Example: R2#debug ip routing IP routing debugging is on

• To configure an Ethernet interface o 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

• When a router only has its interfaces configured & no other routing protocols are configured then: o The routing table contains only the directly connected networks o Only devices on the directly connected networks are reachable

• Checking each route in turn o The ping command is used to check end to end connectivity

• Purpose of CDP o A layer 2 cisco proprietary tool used to gather information about other directly

connected Cisco devices • Concept of neighbors

o 2 types of neighbors Layer 3 neighbors Layer 2 neighbors

• CDP show commands o Show cdp neighbors command

Displays the following information: - Neighbor device ID



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- Local interface - Holdtime value, in seconds - Neighbor device capability code - Neighbor hardware platform - Neighbor remote port ID

o Show cdp neighbors detail command Useful in determining if an IP address configuration error

• Disabling CDP o To disable CDP globally use the following command

Router(config)#no cdp run Static Routes with Exit Interfaces • Purpose of a static route

o A manually configured route used when routing from a network to a stub network • IP route command

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

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

• Dissecting static route syntax o ip route - Static route command o 172.16.1.0 – Destination network address o 255.255.255.0 - Subnet mask of destination network o 172.16.2.2 - Serial 0/0/0 interface IP address on R2, which is the "next-hop" to

this network • Configuring routes to 2 or more remote networks

o 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

• Zinin’s 3 routing principles o Principle 1: "Every router makes its decision alone, based on the information it

has in its own routing table.“ o Principle 2: "The fact that one router has certain information in its routing table

does not mean that other routers have the same information.“ o Principle 3: "Routing information about a path from one network to another does

not provide routing information about the reverse, or return path." • Using Zinin’s 3 routing principles, how would you answer the following?

o 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. o 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 the 172.16.3.0/24

network.



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• Resolving to an Exit Interface o 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) The router first must match static route’s destination IP address with the Next

hop address The next hop address is then matched to an exit interface

• Configuring a Static route with an Exit Interface o Static routes configured with an exit interface are more efficient because the

routing o The routing table can resolve the exit interface in a single search instead of 2

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

• Modifying Static routes o Existing static routes cannot be modified. The old static route must be deleted by

placing no in front of the ip route o Example:

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

• Verifying the Static Route Configuration o Use the following commands

Step 1 show running-config Step 2 verify static route has been entered correctly Step 3 show ip route Step 4 verify route was configured in routing table Step 5 issue ping command to verify packets can reach destination and that

Return path is working • Ethernet interfaces and ARP

o If a static route is configured on an Ethernet link o If the packet is sent to the next-hop router then

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

Summary and Default Route • Summarizing routes reduces the size of the routing table. • Route summarization is the process of combining a number of static routes into a

single static route. • Configuring a summary route

o Step 1: Delete the current static route o Step 2: Configure the summary static route o Step 3: Verify the new static route



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• Default Static Route o This is a route that will match all packets. Stub routers that have a number of

static routes all exiting the same interface are good candidates for a default route. Like route summarization this will help reduce the size of the routing table

• Configuring a default static route o Similar to configuring a static route. Except that destination IP address and

subnet mask are all zeros o Example:

Router(config)#ip route 0.0.0.0 0.0.0.0 [exit-interface | ip-address ] • Static routes and subnet masks

o The routing table lookup process will use the most specific match when comparing destination IP address and subnet mask

• Default static routes and subnet masks o Since the subnet mask used on a default static route is 0.0.0.0 all packets will

match • Packet forwarding with static routes. (recall Zinin’s 3 routing principles) • Router 1

o Packet arrives on R1’s Fastethernet 0/0 interface R1 does not have a route to the destination network, 192.168.2.0/24 R1 uses the default static route

• Packet forwarding with static routes. (recall Zinin’s 3 routing principles) • Router 2

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

• Packet forwarding with static routes. (recall Zinin’s 3 routing principles) • Router 3

o The packet arrives on the Serial0/0/1 interface on R3. o R3 has a connected route to 192.168.2.0/24 out Fastethernet 0/1

• Troubleshooting a Missing Route • Tools that can be used to isolate routing problems include:

o Ping– tests end to end connectivity o Traceroute– used to discover all of the hops (routers) along the path between 2

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

directly connected neighbors • Solving a Missing Route • Finding a missing or mis-configured route requires methodically using the correct

tools o Start with PING. If ping fails then use traceroute to determine where packets are

failing to arrive • Issue: show ip route to examine routing table



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o If there is a problem with a mis-configured static route remove the static route then reconfigure the new static route

• Solving a Missing Route Summary • Routers

o Operate at layer 3 o Functions include best path selection & forwarding packets

• Connecting Networks o WANs

Serial cables are connected to router serial ports. In the lab environment clock rates must be configured for DCE.

o LANs Straight through cables or cross over cables are used to connect to

fastethernet port. (The type of cable used depends on what devices are being connected).

• Cisco Discovery Protocol o A layer 2 proprietary protocol o Used to discover information about directly connected Cisco devices

• Static Routes o This is a manually configured path that specifies how the router will get to a

certain point using a certain path. • Summary static routes

o This is several static routes that have been condensed into a single static route. • Default route

o 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 o Zinin’s 3 routing principles describe how packets are forwarded.

• Troubleshooting static routes may require some of the following commands: o Ping o Traceroute o Show IP route o Show ip interface brief o Show cdp neighbors detail

Chapter 3 – Introduction to Dynamic Routing Protocol Objectives • Describe the role of dynamic routing protocols and place these protocols in the

context of modern network design. • Identify several ways to classify routing protocols.



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• Describe 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 • Function(s) of Dynamic Routing Protocols:

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

• The purpose of a dynamic routing protocol is to: o Discover remote networks o Maintaining up-to-date routing information o Choosing the best path to destination networks o Ability to find a new best path if the current path is no longer available

• Components of a routing protocol o Algorithm

In the case of a routing protocol algorithms are used for facilitating routing information and best path determination

o Routing protocol messages These are messages for discovering neighbors and exchange of routing

information • Advantages of static routing

o It can backup multiple interfaces/networks on a router o Easy to configure o No extra resources are needed o More secure

• Disadvantages of static routing o Network changes require manual reconfiguration o Does not scale well in large topologies

Classifying Routing Protocols • Dynamic routing protocols are grouped according to characteristics. Examples

include: o RIP o IGRP o EIGRP o OSPF o IS-IS o BGP

• Autonomous System is a group of routers under the control of a single authority • Types of routing protocols:

o Interior Gateway Protocols (IGP)



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o Exterior Gateway Protocols (EGP) • Interior Gateway Routing Protocols (IGP)

o Used for routing inside an autonomous system & used to route within the individual networks themselves.

o Examples: RIP, EIGRP, OSPF • Exterior Routing Protocols (EGP)

o Used for routing between autonomous systems o Example: BGPv4

• IGP: Comparison of Distance Vector & Link State Routing Protocols o Distance vector

routes are advertised as vectors of distance & direction incomplete view of network topology Generally, periodic updates

o Link state complete view of network topology is created updates are not periodic

• Classful routing protocols o Do NOT send subnet mask in routing updates

• Classless routing protocols o Do send subnet mask in routing updates

• Convergence is defined as when all routers’ routing tables are at a state of consistency

Routing Protocols Metrics • Metric

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

• Metrics used in IP routing protocols o Bandwidth o Cost o Delay o Hop count o Load o Reliability

• The Metric Field in the Routing Table • Metric used for each routing protocol

o RIP - hop count o IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load,

Reliability o IS-IS & OSPF – Cost, Bandwidth (Cisco’s implementation)

• Load balancing o This is the ability of a router to distribute packets among multiple same cost

paths



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Administrative Distance of a Route • Purpose of a metric

o It’s a calculated value used to determine the best path to a destination • Purpose of Administrative Distance

o It’s a numeric value that specifies the preference of a particular route • Identifying the Administrative Distance (AD) in a routing table

o It is the first number in the brackets in the routing table • Dynamic Routing Protocols • Directly connected routes

o Have a default AD of 0 • Static Routes

o Administrative distance of a static route has a default value of 1 • Directly connected routes

o Immediately appear in the routing table as soon as the interface is configured Summary • Dynamic routing protocols fulfill the following functions

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

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

• Types of IGPs include o Classless routing protocols - these protocols include subnet mask in routing

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

update • Metrics are used by dynamic routing protocols to calculate the best path to a

destination. • Administrative distance is an integer value that is used to indicate a router’s

“trustworthiness” • Components of a routing table include:

o Route source o Administrative distance o Metric

Chapter 4 – Distance Vector Routing Protocols Objectives • Identify the characteristics of distance vector routing protocols.



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• 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.

• Identify the conditions leading to a routing loop and explain the implications for router performance.

• Recognize that distance vector routing protocols are in use today. Distance Vector Routing Protocols • Examples of Distance Vector routing protocols:

o Routing Information Protocol (RIP) o Interior Gateway Routing Protocol (IGRP) o Enhanced Interior Gateway Routing Protocol (EIGRP)

• Distance Vector Technology o The Meaning of Distance Vector:

A router using distance vector routing protocols knows 2 things: - Distance to final destination - Vector, or direction, traffic should be directed

• Characteristics of Distance Vector routing protocols: o Periodic updates o Neighbors o Broadcast updates o Entire routing table is included with routing update

• Routing Protocol Algorithm: o Defined as a procedure for accomplishing a certain task

• Routing Protocol Characteristics o Criteria used to compare routing protocols includes

Time to convergence Scalability Resource usage Implementation & maintenance

Network Discovery • Router initial start up (Cold Starts)

o Initial network discovery Directly connected networks are initially placed in routing table

• Initial Exchange of Routing Information o If a routing protocol is configured then

Routers will exchange routing information • Routing updates received from other routers

o Router checks update for new information If there is new information:

- Metric is updated - New information is stored in routing table



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• Exchange of Routing Information o Router convergence is reached when

All routing tables in the network contain the same network information o Routers continue to exchange routing information

If no new information is found then Convergence is reached • Convergence must be reached before a network is considered completely operable • Speed of achieving convergence consists of 2 interdependent categories

o Speed of broadcasting routing information o Speed of calculating routes

Routing Table Maintenance • Periodic Updates: RIPv1 & RIPv2

o These are time intervals in which a router sends out its entire routing table • RIP uses 4 timers

o Update timer o Invalid timer o Holddown timer o Flush timer

• Bounded Updates: EIGRP • EIRPG routing updates are

o Partial updates o Triggered by topology changes o Bounded o Non periodic

• Triggered Updates o Conditions in which triggered updates are sent

Interface changes state Route becomes unreachable Route is placed in routing table

• Random Jitter o 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 collisions

Solution to problems with synchronized updates - Used of random variable called RIP_JITTER

Routing Loops • Routing loops are

o A condition in which a packet is continuously transmitted within a series of routers without ever reaching its destination.

• Routing loops may be caused by:



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o Incorrectly configured static routes o Incorrectly configured route redistribution o Slow convergence o Incorrectly configured discard routes

• Routing loops can create the following issues o Excess use of bandwidth o CPU resources may be strained o Network convergence is degraded o Routing updates may be lost or not processed in a timely manner.

• Count to Infinity o This is a routing loop whereby packets bounce infinitely around a network.

• Setting a maximum • Distance Vector routing protocols set a specified metric value to indicate infinity.

o Once a router “counts to infinity” it marks the route as unreachable. • Preventing loops with holddown timers

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

o Point of using holddown timers Allows routing updates to propagate through network with the most current

information. • The Split Horizon Rule is used to prevent routing loops • Split Horizon rule:

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

• Split horizon with poison reverse o The rule states that once a router learns of an unreachable route through an

interface, advertise it as unreachable back through the same interface. • IP & TTL

o Purpose of the TTL field The TTL field is found in an IP header and is used to prevent packets from

endlessly traveling on a network. o 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 Packet is discarded.

Routing Protocols Today • Factors used to determine whether to use RIP or EIGRP include

o Network size o Compatibility between models of routers o Administrative knowledge

• RIP o Features of RIP:



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Supports split horizon & split horizon with poison reverse Capable of load balancing Easy to configure Works in a multi vendor router environment

• EIGRP o 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

Summary • Characteristics of Distance Vector routing protocols

o Periodic updates o RIP routing updates include the entire routing table o Neighbors are defined as routers that share a link and are configured to use the

same protocol • The network discovery process for D.V. routing protocol

o Directly connected routes are placed in routing table 1st o If a routing protocol is configured then

Routers will exchange routing information o Convergence is reached when all network routers have the same network

information • D.V. routing protocols maintains routing tables by

o RIP sending out periodic updates o RIP using 4 different timers to ensure information is accurate and convergence

is achieved in a timely manner o EIGRP sending out triggered updates

• D.V. routing protocols may be prone to routing loops o Routing loops are a condition in which packets continuously traverse a network o Mechanisms used to minimize routing loops include defining maximum hop

count, holddown timers, split horizon, route poisoning and triggered updates • Conditions that can lead to routing loops include

o Incorrectly configured static routes o Incorrectly configured route redistribution o Slow convergence o Incorrectly configured discard routes

• How routing loops can impact network performance includes: o Excess use of bandwidth o CPU resources may be strained o Network convergence is degraded o Routing updates may be lost or not processed



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• Routing Information Protocol (RIP) o A distance vector protocol that has 2 versions

RIPv1 – a classful routing protocol RIPv2 - a classless routing protocol

o 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

Chapter 5 – RIP version 1 Objectives • Describe the functions, characteristics, and operation of the RIPv1 protocol. • Configure a device for using RIPv1. • Verify proper RIPv1 operation. • Describe 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. RIPv1 • RIP Characteristics

o A classful, Distance Vector (DV) routing protocol o Metric = hop count o Routes with a hop count > 15 are unreachable o Updates are broadcast every 30 seconds

• RIP Message Format • RIP header - divided into 3 fields

o Command field o Version field o Must be zero

• Route Entry - composed of 3 fields o Address family identifier o IP address o Metric RIP Operation

• RIP uses 2 message types: o Request message

This is sent out on startup by each RIP enabled interface Requests all RIP enabled neighbors to send routing table

o Response message Message sent to requesting router containing routing table



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• IP addresses initially divided into classes o Class A o Class B o Class C

• RIP is a classful routing protocol o Does not send subnet masks in routing updates

• Administrative Distance o RIP’s default administrative distance is 120

Basic RIPv1 Configuration • A typical topology suitable for use by RIPv1 includes:

o Three router set up o No PCs attached to LANs o Use of 5 different IP subnets

• Router RIP Command o To enable RIP enter:

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

• Specifying Networks o Use the network command to:

Enable RIP on all interfaces that belong to this network Advertise this network in RIP updates sent to other routers every 30 seconds

Verification and Troubleshooting • Show ip Route • To verify and troubleshoot routing

o Use the following commands: show ip route show ip protocols debug ip rip

• show ip protocols command o Displays routing protocol configured on router

• Debug ip rip command o Used to display RIP routing updates as they are happening

• Passive interface command o Used to prevent a router from sending updates through an interface o Example:

Router(config-router)#passive-interface interface-type interface-number • Passive interfaces Automatic Summarization • Modified Topology

o The original scenario has been modified such that: Three classful networks are used:



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- 172.30.0.0/16 - 192.168.4.0/24 - 192.168.5.0/24

The 172.30.0.0/16 network is subnetted into three subnets: - 172.30.1.0/24 - 172.30.2.0/24 - 172.30.3.0/24

The following devices are part of the 172.30.0.0/16 classful network address: - All interfaces on R1 - S0/0/0 and Fa0/0 on R2

• Configuration Details o To remove the RIP routing process use the following command

No router rip o To check the configuration use the following command

Show run • Boundary Routers

o RIP automatically summarizes classful networks o Boundary routers summarize RIP subnets from one major network to another

• Processing RIP Updates o 2 rules govern RIPv1 updates:

If a routing update and the interface it’s received on belong to the same network then - The subnet mask of the interface is applied to the network in the routing

update If a routing update and the interface it’s received on belong to a different

network then - The classful subnet mask of the network is applied to the network in the

routing update. • Sending RIP Updates

o RIP uses automatic summarization to reduce the size of a routing table. • Advantages of automatic summarization:

o The size of routing updates is reduced o Single routes are used to represent multiple routes which results in faster

lookup in the routing table. • Disadvantage of Automatic Summarization:

o Does not support discontiguous networks • Discontiguous Topologies do not converge with RIPv1 • A router will only advertise major network addresses out interfaces that do not

belong to the advertised route. Default Route and RIPv1 • Modified Topology: Scenario C • Default routes



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o Packets that are not defined specifically in a routing table will go to the specified interface for the default route

o Example: Customer routers use default routes to connect 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

• Propagating the Default Route in RIPv1 • Default-information originate command

o This command is used to specify that the router is to originate default information, by propagating the static default route in RIP update.

Summary • RIP characteristics include:

o Classful, distance vector routing protocol o Metric is Hop Count o Does not support VLSM or discontiguous subnets o Updates every 30 seconds

• Rip messages are encapsulated in a UDP segment with source and destination ports of 520

• Commands Used by RIP o Rtr(config)#router rip

Enables RIP routing process o Rtr(config-router)#network

Associates a network with a RIP routing process o Rtr#debug ip rip

used to view real time RIP routing updates o Rtr(config-router)#passive-interface fa0/0

Prevent RIP updates from going out an interface o Rtr(config-router)#default-information originate

Used by RIP to propagate default routes o Rtr#show ip protocols

Used to display timers used by RIP

Chapter 6 – VLSM and CIDR Objectives • Compare and contrast classful and classless IP addressing. • Review VLSM and explain the benefits of classless IP addressing. • Describe the role of the Classless Inter-Domain Routing (CIDR) standard in making

efficient use of scarce IPv4 addresses. Introduction • Prior to 1981, IP addresses used only the first 8 bits to specify the network portion of

the address



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• 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) o CIDR uses Variable Length Subnet Masking (VLSM) to help conserve address

space. VLSM is simply subnetting a subnet

Classful and Classless IP Addressing • Classful IP addressing • As of January 2007, there are over 433 million hosts on internet • Initiatives to conserve IPv4 address space include:

o VLSM & CIDR notation (1993, RFC 1519) o Network Address Translation (1994, RFC 1631) o Private Addressing (1996, RFC 1918)

• The High Order Bits o These are the leftmost bits in a 32 bit address

• Classes of IP addresses are identified by the decimal number of the 1st octet o Class A address begin with a 0 bit

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

Range of class B addresses = 128.0.0.0 to 191.255.255.255 o 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. • The IPv4 Classful Addressing Structure (RFC 790)

o An 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 • Purpose of a subnet mask

o It is used to determine the network portion of an IP address • Classful Routing Updates

o Recall that classful routing protocols (i.e. RIPv1) do not send subnet masks in their routing updates. The reason is that the Subnet mask is directly related to the network address

• Classless Inter-domain Routing (CIDR – RFC 1517) o Advantage of CIDR:

More efficient use of IPv4 address space Route summarization

o Requires subnet mask to be included in routing update because address class is meaningless Recall purpose of a subnet mask:



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- To determine the network and host portion of an IP address • Classless IP Addressing • CIDR & Route Summarization

o Variable Length Subnet Masking (VLSM) o Allows a subnet to be further sub-netted according to individual needs o Prefix Aggregation a.k.a. Route Summarization o CIDR allows for routes to be summarized as a single route

• Classless Routing Protocol • Characteristics of classless routing protocols:

o Routing updates include the subnet mask o Supports VLSM o Supports Route Summarization

Routing Protocol Routing Updates Include Subnet

Mask

Supports VLSM Ability to Send Supernet Routes

Classful No No No Classless Yes Yes Yes

VLSM • Classful routing

o Only allows for one subnet mask for all networks • VLSM & classless routing

o This is the process of subnetting a subnet o More than one subnet mask can be used o More efficient use of IP addresses as compared to classful IP addressing

• VLSM – the process of sub-netting a subnet to fit your needs o Example:

Subnet 10.1.0.0/16, 8 more bits are borrowed again, to create 256 subnets 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 Routes are summarized with masks that are less than that of the default classful mask

o 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 • Steps to calculate a route summary

o List networks in binary format o Count number of left most matching bits to determine summary route’s mask o Copy the matching bits and add zero bits to determine the summarized network

address



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Summary • Classful IP addressing

o IPv4 addresses have 2 parts: Network portion found on left side of an IP address Host portion found on right side of an IP address

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

o The class of an IP address is determined by the decimal value found in the 1st octet

o IP 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

o Classful Routing Updates Subnet masks are not sent in routing updates

o Classless IP addressing Benefit of classless IP addressing

- Can create additional network addresses using a subnet mask that fits your needs

Uses Classless Interdomain Routing (CIDR) • CIDR

o Uses IP addresses more efficiently through use of VLSM VLSM is the process of subnetting a subnet

o Allows for route summarization Route summarization is representing multiple contiguous routes with a single

route • Classless Routing Updates

o Subnet masks are included in updates

Chapter 7 – RIPv2 Objectives • Encounter and describe the limitations of RIPv1’s limitations. • Apply 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. Introduction • Chapter focus

o Difference between RIPv1 & RIPv2 RIPv1



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- 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 broadcast

RIPv2 - A classless distance vector routing protocol that is an enhancement of

RIPv1’s features. - Next hop address is included in updates - Routing updates are multicast - The use of authentication is an option

o Similarities between RIPv1 & RIPv2 Use of timers to prevent routing loops Use of split horizon or split horizon with poison reverse Use of triggered updates Maximum hop count of 15

RIPv1 Limitations • Lab Topology

o Scenario: 3 router set up Topology is discontiguous There exists a static summary route Static route information can be injected into routing table updates using

redistribution. Routers 1 & 3 contain VLSM networks

o Scenario Continued VLSM

- Recall this is sub netting the subnet Private IP addresses are on LAN links Public IP addresses are used on WAN links Loopback interfaces

- These are virtual interfaces that can be pinged and added to routing table • Null Interfaces

o This is a virtual interface that does not need to be created or configured Traffic sent to a null interface is discarded Null interfaces do not send or receive traffic

• Static routes and null interfaces o null interfaces will serve as the exit interface for static route

Example of configuring a static supernet route with a null interface R2(config)#ip route 192.168.0.0 255.255.0.0 Null0

• Route redistribution o Redistribution command is way to disseminate a static route from one router to

another via a routing protocol



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o Example R2(config-router)#redistribute static

• Verifying and Testing Connectivity o Use the following commands:

show ip interfaces brief ping traceroute

• RIPv1 – a classful routing protocol o Subnet mask are not sent in updates o Summarizes networks at major network boundaries o if network is discontiguous and RIPv1 configured convergence will not be

reached • Examining the routing tables

o To examine the contents of routing updates use the debug ip rip command o If RIPv1 is configured then

Subnet masks will not be included with the network address • RIPv1 does not support VLSM

o Reason: RIPv1 does not send subnet mask in routing updates • RIPv1 does summarize routes to the Classful boundary

o Or uses the Subnet mask of the outgoing interface to determine which subnets to advertise

• No CIDR Support • In the diagram R2 will not include the static route in its update

o Reason: Classful routing protocols do not support CIDR routes that are summarized with a smaller mask than the classful subnet mask

Configuring RIPv2 • Comparing RIPv1 & RIPv2 Message Formats

o RIPv2 Message format is similar to RIPv1 but has 2 extensions 1st extension is the subnet mask field 2nd extension is the addition of next hop address

• Enabling and Verifying RIPv2 • Configuring RIP on a Cisco router

o By default it is running RIPv1 Configuring RIPv2 on a Cisco router

- Requires using the version 2 command - RIPv2 ignores RIPv1 updates

To verify RIPv2 is configured use the show ip protocols command • Auto-Summary & RIPv2 • RIPv2 will automatically summarize routes at major network boundaries and can

also summarize routes with a subnet mask that is smaller than the classful subnet mask

• Disabling Auto-Summary in RIPv2 • To disable automatic summarization issue the no auto-summary command



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• Verifying RIPv2 Updates • When using RIPv2 with automatic summarization turned off

o 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 the debug ip rip command VLSM & CIDR • RIPv2 and VLSM • Networks using a VLSM IP addressing scheme

o Use classless routing protocols (i.e. RIPv2) to disseminate network addresses and their subnet masks

• CIDR uses Supernetting o Supernetting is a bunch of contiguous classful networks that is addressed as a

single network. o To verify that supernets are being sent and received use the following commands

Show ip route Debug ip rip

Verifying & Troubleshooting RIPv2 • Basic Troubleshooting steps

o Check the status of all links o Check cabling o Check IP address & subnet mask configuration o Remove any unneeded configuration commands

• Commands used to verify proper operation of RIPv2 o Show ip interfaces brief o Show ip protocols o Debug ip rip o Show ip route

• Common RIPv2 Issues • When trouble shooting RIPv2 examine the following issues:

o Version Check to make sure you are using version 2

o Network statements Network statements may be incorrectly typed or missing

o Automatic summarization If summarized routes are not needed then disable automatic summarization

• Reasons why it’s good to authenticate routing information o Prevent the possibility of accepting invalid routing updates o Contents of routing updates are encrypted

• Types of routing protocols that can use authentication o RIPv2 o EIGRP o OSPF



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o IS-IS o BGP

Summary

Routing Protocol

Distance Vector

Classless Routing Protocol

Uses Hold- Down Timers

Use of Split Horizon or Split Horizon w/ Poison Reverse

RIPv1 Yes No Yes Yes RIPv2 Yes Yes Yes Yes

Routing Protocol

Max Hop Count = 15

Auto Summary

Supports CIDR

Supports VLSM

Uses Authentication

RIPv1 Yes Yes No No No RIPv2 Yes Yes Yes Yes Yes

Chapter 8 – The Routing Table: A Closer Look Objectives • Describe the various route types found in the routing table structure. • Describe the routing table lookup process. • Describe routing behavior in routed networks. Introduction • Chapter Focus

o Structure of the routing table o Lookup process of the routing table o Classless and classful routing behaviors



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Routing Table Structure • Lab Topology • 3 router setup

o R1 and R2 share a common 172.16.0.0/16 network with 172.16.0.0/24 subnets. o R2 and R3 are connected by the 192.168.1.0/24 network. o R3 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. • Routing table entries come from the following sources

o Directly connected networks o Static routes o Dynamic routing protocols

• Level 1 Routes • As soon as the no shutdown command is issued the route is added to routing table • Cisco IP routing table is a hierarchical structure

o The reason for this is to speed up lookup process • Level 1 Routes • Have a subnet mask equal to or less than the classful mask of the network address. • Level 1 route can function as

o Default route o Supernet route o Network route

• Level 1 Routes o Ultimate Route

Includes either: - A next-hop address

OR - An exit interface

• Parent and Child Routes o A parent route is a level 1 route o A parent route does not contain any next-hop IP address or exit interface

information • Automatic creation of parent routes

o Occurs any time a subnet is added to the routing table Child routes

- Child routes are level 2 routes - Child routes are a subnet of a classful network address

• Level 2 child routes contain route source & the network address of the route • Level 2 child routes are also considered ultimate routes

o Reason: they contain the next hop address &/or exit interface • Both child routes have the same subnet mask

o This means the parent route maintains the /24 mask • Diagram illustrates 2 child networks belonging to the parent route 172.16.0.0 / 24 • In classless networks, child routes do not have to share the same subnet mask



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Network Type

Parent Route’s Classful Mask is Displayed

Term Variably Subnetted is seen in Parent Route in Routing Table

Includes the # of Different Masks of Child Routes

Subnet Mask Included with each Child Route Entry

Classful No No No No Classless Yes Yes Yes Yes • Parent & Child Routes: Classless Networks Routing Table Lookup Process • The Route Lookup Process

o 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 o 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 determine routing behavior type o Router determines classful or classless routing behavior

If classful then packet is dropped If classless then router searches level one supernet and default routes If there exists a level 1 supernet or default route match then Packet is

forwarded. If not packet is dropped • Longest Match: Level 1 Network Routes

o Best match is also known as the longest match o 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. • Finding the subnet mask used to determine the longest match

o Scenario: PC1 pings 192.168.1.2 Router examines level 1 route for best match There exist a match between192.168.1.2 & 192.168.1.0 / 24 Router forwards packets out s0/0/0

• The process of matching o 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 between the destination IP and the child route is made.

• Finding a match between packet’s destination IP address and the next route in the routing table o 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 • Level 1 Parent & Level 2 Child Routes • Before level 2 child routes are examined



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o There must be a match between classful level one parent route and destination IP address.

• After the match with parent route has been made Level 2 child routes will be examined for a match o Route lookup process searches for child routes with a match with destination IP

• How a router finds a match with one of the level 2 child routes o First router examines parent routes for a match o If a match exists then:

Child routes are examined Child route chosen is the one with the longest match

• Example: Route Lookup Process with VLSM o The use of VLSM does not change the lookup process o If there is a match between destination IP address and the level 1 parent route

then o Level 2 child routes will be searched

Routing Behavior • Classful & classless routing protocols

o Influence how routing table is populated • Classful & classless routing behaviors

o Determines how routing table is searched after it is filled • Classful Routing Behavior: no ip classless • What happens if there is not a match with any level 2 child routes of the parent?

o Router must determine if the routing behavior is classless or classful o If router is utilizing classful routing behavior then

Lookup process is terminated and packet is dropped • Classful Routing Behavior – Search Process • An example of when classful routing behavior is in effect and why the router drops

the Packet o The destination’s subnet mask is a /24 and none of the child routes left most bits

match the first 24 bits. This means packet is dropped • Classful Routing Behavior – Search Process • The reason why the router will not search beyond the child routes

o Originally networks were all classful o This meant an organization could subnet a major network address and

“enlighten” all the organization’s routers about the subnetting o Therefore, if the subnet was not in the routing table, the subnet did not exist and

packet was dropped • ip Classless • Beginning with IOS 11.3, ip classless was configured by default • Classless routing behavior works for

o Discontiguous networks, AND o CIDR supernets

• Classless Routing Behavior: ip classless



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• Route lookup process when ip classless is in use o If classless routing behavior in effect then

Search level 1 routes Supernet routes Checked first

o If a match exists then forward packet Default routes Checked second

o If there is no match or no default route then the Packet is dropped

• Classless Routing Behavior – Search Process • Router begins search process by finding a match between destination IP and parent

route o After finding the above mentioned match, then there is a search of the child route

• Classless Routing Behavior – Search Process • If no match is found in child routes of previous slide then

o Router continues to search the routing table for a match that may have fewer bits in the match

• Classful vs. Classless Routing Behavior o It is recommended to use classless routing behavior

Reason: so supernet and default routes can be used whenever needed Summary • Content/structure of a routing table

o Routing table entries Directly connected networks Static route Dynamic routing protocols

o 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

Level 2 route - These are subnets of a network address

• Routing table lookup process o Begins with examining level 1 routes for best match with packet’s destination IP

If the best match = an ultimate route then Packet is forwarded Parent route is examined

- If parent route & destination IP match then Level 2 (child) routes are examined

o Level 2 route examination If a match between destination IP and child route found then Packet

forwarded -Else If Router is using classful routing behavior then Packet is dropped -Else If router is using classless routing behavior then



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Router searches Level 1 supernet & default routes for a match If a match is found then Packet if forwarded -Else Packet is dropped

• Routing behaviors o This refers to how a routing table is searched

• Classful routing behavior o Indicated by the use of the no ip classless command o Router will not look beyond child routes for a lesser match

• Classless routing behavior o Indicated by the use of the ip classless command o Router will look beyond child routes for a lesser match

Chapter 9 – EIGRP Objectives • Describe the background and history of Enhanced Interior Gateway Routing Protocol

(EIGRP). • Examine the basic EIGRP configuration commands and identify their purposes. • Calculate the composite metric used by EIGRP. • Describe the concepts and operation of DUAL. • Describe the uses of additional configuration commands in EIGRP. EIGRP • Roots of EIGRP: IGRP

o Developed in 1985 to overcome RIPv1’s limited hop count o Distance vector routing protocol o Metrics used by IGRP

bandwidth (used by default) Delay (used by default) reliability load

o Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S • EIGRP Message Format

o EIGRP Header Data link frame header - contains source and destination MAC address IP packet header - contains source & destination IP address EIGRP packet header - contains AS number Type/Length/Field - data portion of EIGRP message

o EIGRP packet header contains Opcode field Autonomous System number

o EIGRP Parameters contains



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Weights Hold time

• TLV: IP internal contains o Metric field o Subnet mask field o Destination field

• TLV: IP external contains o Fields used when external routes are imported into EIGRP routing process

• Protocol Dependent Modules (PDM) o EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalk o PDMs are responsible for the specific routing task for each network layer protocol

• Reliable Transport Protocol (RTP) o Purpose of RTP

Used by EIGRP to transmit and receive EIGRP packets o Characteristics of RTP

Involves both reliable & unreliable delivery of EIGRP packet - Reliable delivery requires acknowledgment from destination - Unreliable delivery does not require an acknowledgement from destination

Packets can be sent - Unicast - Multicast

Using address 224.0.0.10 • EIGRP’s 5 Packet Types

o Hello packets Used to discover & form adjacencies with neighbors

o Update packets Used to propagate routing information

o Acknowledgement packets Used to acknowledge receipt of update, query & reply packets

o Query & Reply packets Used by DUAL for searching for networks Query packets

- Can use Unicast Multicast

Reply packet - Use only

Unicast • Purpose of Hello Protocol

o To discover & establish adjacencies with neighbor routers • Characteristics of hello protocol

o Time interval for sending hello packet Most networks it is every 5 seconds Multipoint non broadcast multi-access networks



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- Unicast every 60 seconds o Holdtime

This is the maximum time router should wait before declaring a neighbor down

Default holdtime - 3 times hello interval

• EIGRP Bounded Updates o EIGRP only sends update when there is a change in route status o Partial update

A partial update includes only the route information that has changed – the whole routing table is NOT sent

o Bounded update When a route changes, only those devices that are impacted will be notified

of the change o EIGRP’s use of partial bounded updates minimizes use of bandwidth

• Diffusing Update Algorithm (DUAL) o Purpose

EIGRP’s primary method for preventing routing loops o Advantage of using DUAL

Provides for fast convergence time by keeping a list of loop-free backup routes

• Administrative Distance (AD) o Defined as the trustworthiness of the source route

• EIGRP default administrative distances o Summary routes = 5 o Internal routes = 90 o Imported routes = 170

• Authentication o EIGRP can

Encrypt routing information Authenticate routing information

• Network Topology o Topology used is the same as previous chapters with the addition of an ISP

router • EIGRP will automatically summarize routes at classful boundaries Basic EIGRP Configuration • Autonomous System (AS) & Process IDs

o This is a collection of networks under the control of a single authority (reference RFC 1930)

o AS Numbers are assigned by IANA o Entities needing AS numbers

ISP Internet Backbone providers



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Institutions connecting to other institutions using AS numbers • EIGRP autonomous system number actually functions as a process ID • Process ID represents an instance of the routing protocol running on a router • Example

o Router(config)#router eigrp autonomous-system • The router eigrp command

o The global command that enables eigrp is router eigrp autonomous-system All routers in the EIGRP routing domain must use the same process ID

number (autonomous-system number) • The Network Command

o Functions of the network command Enables interfaces to transmit & receive EIGRP updates Includes network or subnet in EIGRP updates

o Example Router(config-router)#network network-address

• The network Command with a Wildcard Mask o This option is used when you want to configure EIGRP to advertise specific

subnets o Example

Router(config-router)#network network-address [wildcard-mask] • Verifying EIGRP

o EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received

o Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is show ip eigrp neighbors

• The show ip protocols command is also used to verify that EIGRP is enabled • Examining the Routing Table

o The show ip route command is also used to verify EIGRP o EIGRP routes are denoted in a routing table by the letter “D” o By default , EIGRP automatically summarizes routes at major network boundary

• Introducing the Null0 Summary Route o Null0 is not a physical interface o In the routing table summary routes are sourced from Null0

Reason: routes are used for advertisement purposes o EIGRP will automatically include a null0 summary route as child route when 2

conditions are met At least one subnet is learned via EIGRP Automatic summarization is enabled

• R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3

EIGRP Metric Calculation • EIGRP Composite Metric & the K Values



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o EIGRP uses the following values in its composite metric Bandwidth, delay, reliability, and load

o The composite metric used by EIGRP formula used has values K1 K5

- K1 & K3 = 1 - all other K values = 0

• Use the sh ip protocols command to verify the K values • EIGRP Metrics

o Use the show interfaces command to view metrics o EIGRP Metrics

Bandwidth – EIGRP uses a static bandwidth to calculate metric Most serial interfaces use a default bandwidth value of 1.544Mbos (T1)

• EIGRP Metrics o Delay is the defined as the measure of time it takes for a packet to traverse a

route It is a static value based on link type to which interface is connected

• Reliability (not a default EIGRP metric) o A measure of the likelihood that a link will fail o Measure dynamically & expressed as a fraction of 255 the higher the fraction the

better the reliability • Load (not a default EIGRP metric)

o A number that reflects how much traffic is using a link o Number is determined dynamically and is expressed as a fraction of 255

The lower the fraction the less the load on the link • Using the Bandwidth Command

o Modifying the interface bandwidth Use the bandwidth command Example

- Router(config-if)#bandwidth kilobits o Verifying bandwidth

Use the show interface command o Note – bandwidth command does not change the link’s physical bandwidth

• The EIGRP metric can be determined by examining the bandwidth delay • EIGRP uses the lowest bandwidth (BW) in its metric calculation

o Calculated BW = reference BW / lowest BW(kbps) • Delay – EIGRP uses the cumulative sum of all outgoing interfaces

o Calculated Delay = the sum of outgoing interface delays • EIGRP Metric = calculated BW + calculated delay DUAL Concepts • The Diffusing Update Algorithm (DUAL) is used to prevent looping • Successor

o The best least cost route to a destination found in the routing table • Feasible distance



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o The lowest calculated metric along a path to a destination network • Feasible Successors, Feasibility Condition & Reported Distance • Feasible Successor

o This is a loop free backup route to same destination as successor route • Reported distance (RD)

o The metric that a router reports to a neighbor about its own cost to that network • Feasibility Condition (FC)

o Met when a neighbor’s RD is less than the local router’s FD to the same destination network

• Topology Table: Successor & Feasible Successor • EIGRP Topology table

o Viewed using the show ip eigrp topology command Contents of table include:

- all successor routes - all feasible successor routes

• EIGRP Topology Table dissected • Topology Table: No Feasible Successor

o A feasible successor may not be present because the feasibility condition may not be met In other words, the reported distance of the neighbor is greater than or equal

to the current feasible distance • Finite Sate Machine (FSM)

o An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those states

o FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events

• DUAL FSM o Selects a best loop-free path to a destination o Selects alternate routes by using information in EIGRP tables

• Finite State Machines (FSM) o To examine output from EIGRP’s finite state machine us the debug eigrp fsm

command More EIGRP Configurations • The Null0 Summary Route

o 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

o 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 EIGRP Automatic summarization is enabled

• Disabling Automatic Summarization



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o The auto-summary command permits EIGRP to automatically summarize at major network boundaries

o The no auto-summary command is used to disable automatic summarization This causes all EIGRP neighbors to send updates that will not be

automatically summarized - This will cause changes to appear in both routing tables topology tables

• Manual Summarization o Manual summarization can include supernets

Reason: EIGRP is a classless routing protocol & include subnet mask in update

o Command used to configure manual summarization Router(config-if)#ip summary-address eigrp as-number network-address

subnet-mask • Configuring a summary route in EIGRP • EIGRP Default Routes

o “quad zero” static default route Can be used with any currently supported routing protocol Is usually configured on a router that is connected a network outside the

EIGRP domain o EIGRP & the “Quad zero” static default route

Requires the use of the redistribute static command to disseminate default route in EIGRP updates

• Fine-Tuning EIGRP o EIGRP bandwidth utilization

By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information

The command to change the percentage of bandwidth used by EIGRP is - Router(config-if)#ip bandwidth-percent eigrp as- number percent

• Configuring Hello Intervals and Hold Times o Hello intervals and hold times are configurable on a per-interface basis o 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 o The command to configure hold time value is

Router(config-if)#ip hold-time eigrp as-number seconds Summary • Background & History

o EIGRP is a derivative of IGRP EIGRP is a Cisco proprietary distance vector routing protocol released in

1994



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• EIGRP terms and characteristics o EIGPR uses RTP to transmit & receive EIGRP packets o EIGRP has 5 packet type:

Hello packets Update packets Acknowledgement packets Query packets Reply packets

o Supports VLSM & CIDR • EIGRP terms and characteristics

o EIGRP uses a hello protocol Purpose of hello protocol is to discover & establish adjacencies

o EIGRP routing updates Aperiodic Partial and bounded Fast convergence

• EIGRP commands o The following commands are used for EIGRP configuration

RtrA(config)#router eigrp [autonomous-system #] RtrA(config-router)#network network-number

o The following commands can be used to verify EIGRP Show ip protocols Show ip eigrp neighbors Show ip route

• EIGRP metrics include o Bandwidth (default) o Delay (default) o Reliability o Load

• DUAL o Purpose of DUAL

To prevent routing loops o Successor

Primary route to a destination o Feasible successor

Backup route to a destination o Feasible distance

Lowest calculated metric to a destination o Reported distance

The distance towards a destination as advertised by an upstream neighbor • Choosing the best route

o After router has received all updates from directly connected neighbors, it can calculate its DUAL 1st metric is calculated for each route



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2nd route with lowest metric is designated successor & is placed in routing table

3rd feasible successor is found - Criteria for feasible successor: it must have lower reported distance to the

destination than the installed route’s feasible distance - Feasible routes are maintained in topology table

• Automatic summarization o On by default o Summarizes routes on classful boundary o Summarization can be disabled using the following command

RtrA(config-if)#no auto-summary

Chapter 10 – Link-State Routing Protocols Objectives • Describe the basic features & concepts of link-state routing protocols. • List the benefits and requirements of link-state routing protocols. Link-State Routing • Link state routing protocols

o Also known as shortest path first algorithms o These protocols built around Dijkstra’s SPF

• Dijkstra’s algorithm also known as the shortest path first (SPF) algorithm • The shortest path to a destination is not necessarily the path with the least number

of hops • Link-State Routing Process

o How routers using Link State Routing Protocols reach convergence Each routers learns about its own directly connected networks Link state routers exchange hello packet to “meet” other directly connected link state routers. Each router builds its own Link State Packet (LSP) which includes information

about neighbors such as neighbor ID, link type, & bandwidth. After the LSP is created the router floods it to all neighbors who then store the

information and then forward it until all routers have the same information. Once all the routers have received all the LSPs, the routers then construct a

topological map of the network which is used to determine the best routes to a destination

• Directly Connected Networks o Link

This is an interface on a router o Link state

This is the information about the state of the links • Sending Hello Packets to Neighbors



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o Link state routing protocols use a hello protocol Purpose of a hello protocol:

- To discover neighbors (that use the same link state routing protocol) on its link

• Sending Hello Packets to Neighbors o Connected interfaces that are using the same link state routing protocols will

exchange hello packets. o Once routers learn it has neighbors they form an adjacency

2 adjacent neighbors will exchange hello packets These packets will serve as a keep alive function

• Building the Link State Packet o Each router builds its own Link State Packet (LSP)

Contents of LSP: - State of each directly connected link - Includes information about neighbors such as neighbor ID, link type, &

bandwidth. • Flooding LSPs to Neighbors

o Once LSP are created they are forwarded out to neighbors. After receiving the LSP the neighbor continues to forward it throughout

routing area. • LSPs are sent out under the following conditions

o Initial router start up or routing process o When there is a change in topology

• Constructing a link state data base o Routers use a database to construct a topology map of the network

• Shortest Path First (SPF) Tree o Building a portion of the SPF tree

Process begins by examining R2’s LSP information - R1 ignores 1st LSP

Reason: R1 already knows it’s connected to R2 - R1 uses 2nd LSP

Reason: R1 can create a link from R2 to R5. This information is added to R1’s SPF tree

- R1 uses 3rd LSP Reason: R1 learns that R2 is connected to 10.5.0.0/16. This link is added to R1’s SPF tree.

• Determining the shortest path o The shortest path to a destination determined by adding the costs & finding the

lowest cost • Once the SPF algorithm has determined the shortest path routes, these routes are

placed in the routing table. Link-State Routing Protocols • Advantages of a Link-State Routing Protocol



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Routing Protocol

Builds Topological Map

Router can Independently Determine the Shortest Path to Every Network

Convergence A Periodic/ Event Driven Routing Updates

Use of LSP

Distance Vector

No No Slow Generally No

No

Link State Yes Yes Fast Generally Yes

Yes

• Requirements for using a link state routing protocol

o Memory requirements Typically link state routing protocols use more memory

o Processing Requirements More CPU processing is required of link state routing protocols

o Bandwidth Requirements Initial startup of link state routing protocols can consume lots of bandwidth

• 2 link state routing protocols used for routing IP o Open Shortest Path First (OSPF) o Intermediate System-Intermediate System (IS-IS)

Summary • Link State Routing protocols are also known as Shortest Path First protocols • Summarizing the link state process

o Routers 1ST learn of directly connected networks o Routers then say “hello” to neighbors o Routers then build link state packets o Routers then flood LSPs to all neighbors o Routers use LSP database to build a network topology map & calculate the best

path to each destination • Link

o An interface on the router • Link State

o Information about an interface such as IP address Subnet mask Type of network Cost associated with link Neighboring routers on the link

• Link State Packets o After initial flooding, additional LSP are sent out when a change in topology

occurs



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Examples of link state routing protocols - Open shortest path first - IS-IS

Chapter 11 – OSPF Objectives • Describe the background and basic features of OSPF. • Identify and apply the basic OSPF configuration commands. • Describe, modify and calculate the metric used by OSPF. • Describe the Designated Router/Backup Designated Router (DR/BDR) election

process in multi-access networks. • Describe the uses of additional configuration commands in OSPF. Introduction to OSPF • Background of OSPF

o Began in 1987 o 1989 OSPFv1 released in RFC 1131

This version was experimental & never deployed o 1991 OSPFv2 released in RFC 1247 o 1998 OSPFv2 updated in RFC 2328 o 1999 OSPFv3 published in RFC 2740

• OSPF Message Encapsulation o OSPF packet type

There exist 5 types o OSPF packet header

Contains - Router ID and area ID and Type code for OSPF packet type o IP packet header

Contains - Source IP address, Destination IP address, & Protocol field set to 89

• OSPF Message Encapsulation o Data link frame header

Contains - Source MAC address and Destination MAC address • OSPF Packet Types

o Hello Protocol OSPF Hello Packet

– Purpose of Hello Packet Discover OSPF neighbors & establish adjacencies Advertise guidelines on which routers must agree to become

neighbors Used by multi-access networks to elect a designated router and a

backup designated router o Hello Packets continued



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Contents of a Hello Packet – router ID of transmitting router

o OSPF Hello Intervals Usually multicast (224.0.0.5) Sent every 30 seconds for NBMA segments

o OSPF Dead Intervals This is the time that must transpire before the neighbor is considered down Default time is 4 times the hello interval

• Hello protocol packets contain information that is used in electing o Designated Router (DR)

DR is responsible for updating all other OSPF routers o Backup Designated Router (BDR)

This router takes over DR’s responsibilities if DR fails • OSPF Link-state Updates

o Purpose of a Link State Update (LSU) Used to deliver link state advertisements

o Purpose of a Link State Advertisement (LSA) Contains information about neighbors & path costs

• OSPF Algorithm o OSPF routers build & maintain link-state database containing LSA received from

other routers Information found in database is utilized upon execution of Dijkstra SPF

algorithm SPF algorithm used to create SPF tree SPF tree used to populate routing table

• Administrative Distance o Default Administrative Distance for OSPF is 110

• OSPF Authentication o Purpose is to encrypt & authenticate routing information o This is an interface specific configuration o Routers will only accept routing information from other routers that have been

configured with the same password or authentication information Basic OSPF Configuration • Lab Topology

o Topology used for this chapter Discontiguous IP addressing scheme Since OSPF is a classless routing protocol the subnet mask is configured in

• The router ospf command o To enable OSPF on a router use the following command

R1(config)#router ospf process-id Process id

- A locally significant number between 1 and 65535 this means it does not have to match other OSPF routers



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• OSPF network command o Requires entering: network address

wildcard mask - the inverse of the subnet mask area-id - area-id refers to the OSPF area. OSPF area is a group of routers

that share link state information o Example: Router(config-router)#network network-address wildcard-ask area

area-id • Router ID

o This is an IP address used to identify a router o 3 criteria for deriving the router ID

Use IP address configured with OSPF router-id command - Takes precedence over loopback and physical interface addresses

If router-id command not used then router chooses highest IP address of any loopback interfaces

If no loopback interfaces are configured then the highest IP address on any active interface is used

• OSPF Router ID o Commands used to verify current router ID

Show ip protocols Show ip ospf Show ip ospf interface

o Router ID & Loopback addresses Highest loopback address will be used as router ID if router-id command isn’t

used Advantage of using loopback address the loopback interface cannot fail

OSPF stability o The OSPF router-id command

Introduced in IOS 12.0 Command syntax

– Router(config)#router ospfprocess-id – Router(config-router)#router-idip-address

o Modifying the Router ID Use the command Router#clear ip ospf process

• Verifying OSPF o Use the show ip ospf command to verify & trouble shoot OSPF networks

Command will display the following: – Neighbor adjacency

No adjacency indicated by - – Neighboring router’s Router ID is not displayed – A state of full is not displayed

Consequence of no adjacency - – No link state information exchanged – Inaccurate SPF trees & routing tables

• Verifying OSPF - Additional Commands



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Command Description Show ip protocols Displays OSPF process ID, router ID, networks

router is advertising & administrative distance Show ip ospf Displays OSPF process ID, router ID, OSPF area

information & the last time SPF algorithm calculated Show ip ospf interface Displays hello interval and dead interval • Examining the routing table

o 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 OSPF Note OSPF does not automatically summarize at major network boundaries

OSPF Metric • OSPF uses cost as the metric for determining the best route

o The best route will have the lowest cost o Cost is based on bandwidth of an interface

Cost is calculated using the formula - 108 / bandwidth

o Reference bandwidth defaults to 100Mbps can be modified using auto-cost reference-bandwidth command

• COST of an OSPF route o Is the accumulated value from one router to the next

• Usually the actual speed of a link is different than the default bandwidth o 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’s bandwidth

o Most serial link default to 1.544Mbps Basic OSPF Configuration • Modifying the Cost of a link

o Both sides of a serial link should be configured with the same bandwidth Commands used to modify bandwidth value

- Bandwidth command Example: Router(config-if)#bandwidthbandwidth-kbps

- ip 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 • Modifying the Cost of the link

o Difference between bandwidth command & the ip ospf cost command Ip ospf cost command

- Sets cost to a specific value



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Bandwidth command - Link cost is calculated

OSPF and Multi-access Networks • Challenges in Multi-access Networks

o OSPF defines five network types: Point-to-point Broadcast Multi-access Nonbroadcast Multi-access (NBMA) Point-to-multipoint Virtual links

• 2 challenges presented by multi-access networks o Multiple adjacencies o Extensive LSA flooding

• Extensive flooding of LSAs o 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 to LSA flooding issue is the use of o Designated router (DR) o Backup designated router (BDR)

DR & BDR selection - Routers are elected to send & receive LSA

Sending & Receiving LSA - DRothers send LSAs via multicast 224.0.0.6 to DR & BDR - DR forward LSA via multicast address 224.0.0.5 to all other routers

• DR/BDR Election Process o DR/BDR elections DO NOT occur in point to point networks

• DR/BDR elections will take place on multi-access networks as shown below • Criteria for getting elected DR/BDR

o DR: Router with the highest OSPF interface priority. o BDR: Router with the second highest OSPF interface priority. o If OSPF interface priorities are equal, the highest router ID is used to break the

tie. • Timing of DR/BDR Election

o Occurs as soon as 1st router has its interface enabled on multi-access network When a DR is elected it remains as the DR until one of the following occurs

- The DR fails. - The OSPF process on the DR fails. - The multi-access interface on the DR fails.

• Manipulating the election process o If you want to influence the election of DR & BDR then do one of the following

Boot up the DR first, followed by the BDR, and then boot all other routers, OR



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Shut down the interface on all routers, followed by a no shutdown on the DR, then the BDR, and then all other routers.

• OSPF Interface Priority o Manipulating 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

More OSPF Configuration • Redistributing an OSPF Default Route

o Topology includes a link to ISP Router connected to ISP

- Called an autonomous system border router - Used to propagate a default route

Example of static default route R1(config)#ip route 0.0.0.0 0.0.0.0 loopback 1

Requires the use of the default-information originate command Example of default-information originate command

R1(config-router)#default-information originate • Fine-Tuning OSPF

o Since link speeds are getting faster it may be necessary to change reference bandwidth values Do this using the auto-cost reference-bandwidth command Example:

- R1(config-router)#auto-cost reference-bandwidth 10000 • Fine-Tuning OSPF

o Modifying OSPF timers Reason to modify timers

- Faster detection of network failures Manually modifying Hello & Dead intervals

- Router(config-if)#ip ospf hello-interval seconds - Router(config-if)#ip ospf dead-interval seconds

Point to be made - Hello & Dead intervals must be the same between neighbors

Summary • RFC 2328 describes OSPF link state concepts and operations • OSPF Characteristics

o A commonly deployed link state routing protocol o Employs DRs & BDRs on multi-access networks

DRs & BDRs are elected DR & BDRs are used to transmit and receive LSAs



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o Uses 5 packet types: 1: HELLO

2: DATABASE DESCRIPTION 3: LINK STATE REQUEST 4: LINK STATE UPDATE 5: LINK STATE ACKNOWLEDGEMENT

• OSPF Characteristics o Metric = cost

Lowest cost = best path o Configuration

Enable OSPF on a router using the following command - R1(config)#router ospf process-id

use the network command to define which interfaces will participate in a given OSPF process - Router(config-router)#network network-address wildcard-mask area area-

id • Verifying OSPF configuration

o Use the following commands show ip protocol show ip route show ip ospf interface show ip ospf neighbor

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