Routing, Switching & Virtual LANs

 Chapter 1 - Introduction to Classless Routing

RIP v1 and v2

These notes explain the major differences between the RIPv1 and RIPv2 routing protocols. Some useful commands for configuring, viewing and troubleshooting RIP are also described briefly.

Introduction

RIP v1 Compared to RIP v2

Example Network Running RIP v1

Example Network Running RIP v2

Commands for Configuring RIP

Commands for Viewing RIP Information

Commands for Troubleshooting RIP

Summary

Introduction

These notes discuss the differences between the RIPv1 and RIPv2 routing protocols.

On completion of these notes you should...

• Understand the major differences between RIPv1 and RIPv2
• Understand that RIPv2 allows for VLSM and CIDR
• Configure RIPv2 on a router

RIPv1 Compared to RIPv2

RIP is a distance-vector interior routing protocol. As a distance-vector routing protocol, routing updates are periodically sent and received from neighbouring routers. The hop count metric is used to determine the best route to a destination.

RIPv1 is a classful protocol. Only network address information is enclosed inside routing updates. Subnet information is not sent. Although RIP is a popular routing protocol because it is easy to implement, version 1 has many limitations:-

• RIPv1 does not include subnet mask information in its updates which means that VLSM and CIDR cannot be supported.
    
• RIPv1 updates are sent and received on port 520 using UDP inside IP datagrams. These updates are broadcast which means all devices on a network (not just routers) will check to see if the information is relevant to them.
    
• RIPv1 does not support authentication - information is sent in plain-text and the source of the update cannot be authenticated.

In the late 1980's, RIPv2 was developed to overcome the limitations of RIPv1. RIPv2 is a classless protocol which allows subnet information to be sent in routing updates. RIPv2 has the following features:-

• RIP v2 includes subnet mask information in its updates which means that VLSM and CIDR can now be supported.
    
• RIPv2 updates are sent as multicasts instead of broadcasts using the multicast address of 224.0.0.9. This allows for devices not listening for RIPv2 multicasts to ignore the updates.
    
• RIPv2 supports both plain-text and MD5 authentication which allows the source of the information to be authenticated.

The table below shows the main differences between RIPv1 and RIPv2.

Example Network Running RIP v1

Examine the network shown in the diagram below:-

Upon receiving an RIP update packet, a router uses one of the following methods to determine an address's network prefix:-

• By Association - When a router receives a network address, it checks to see if the receiving interface belongs to the same network, but on a different subnet. If it does, the router applies the same subnet mask belonging to the interface to the network address.
  
• By Class - When a router receives a network address that is not in the same subnet as the receiving interface, it applies the default class subnet mask.

Example Network Running RIP v2

Examine the network shown in the diagram below:-

Commands used for Configuring RIP

Here are some useful commands used for configuring RIP

~~ router rip ~~

The router rip command turns the RIP routing process on.

Examples:-

The following example starts the routing process and switches the router to config-router mode.

Router(config)#router rip

This takes you to config-router mode. e.g.

Router(config-router)#

Use the no form of this command to turn the routing process off.

Router(config)#no router rip

To view commands that can be used within the config-router mode use the ? command. Some of the useful commands that can be used in this mode are listed below:

Router(config-router)#?

~~ network ~~

The network command is used to specify a list of networks to be advertised in routing updates. If the network address of an interface does not match an entry in the list of networks to be advertised, then that interface will not be advertised in any RIP update.

Examples:-

The following example specifies that any directly commected networks falling within the 100.9.4.0 or 172.16.0.0 address classes should be included in routing updates:

Router(config)#router rip

Router(config-router)#network 100.9.4.0

Router(config-router)#network 172.16.0.0

To remove an entry from the network list, use the no form of this command.

Router(config-router)#no network 172.16.0.0

~~ version ~~

The version command is used to specify the RIP version to use.

Examples:-

The following example sets RIPv1 as the routing protocol to be used on all interfaces:

Router(config)#router rip

Router(config-router)#version 1

The following example sets RIPv2 as the routing protocol to be used:

Router(config-router)#version 2

Commands for Viewing RIP Information

Here are some useful commands used for viewing RIP routing information

~~ sh ip route ~~

The sh ip route command displays the contents of the routing table.

Example:-

The following example displays a routing table:

~~ sh ip protocol ~~

The sh ip protocol command is useful for checking the version of RIP used, networks that are included in the routing updates, update intervals and other information.

Example:-

The following example shows typical output from the command:

~~ sh ip rip database ~~

The sh ip rip database command is useful for checking the summary route and routing table entries.

Example:-

The following example shows typical output from the command:

Commands for Troubleshooting RIP

Here are two of the most common commands used for troubleshooting RIP

~~ debug ip rip ~~

The debug ip rip command is useful for troubleshooting RIP. The command displays RIP routing updates as they are sent and received. The no form of the command or undebug all switches off the debugging.

Example:-

The following example shows typical output from the command:

~~ clear ip route * ~~

The clear ip route * command is useful for clearing all routing table entries. This is useful when routing table entries are confusing and you wish for the routing table to be rebuilt.

Example:-

The following example shows routing table entries before the command is used:

After the clear ip route * command is used, the routing table entries only show the directly connected networks. Additional networks will be added using information from any new routing updates received:

Summary

On completing these notes you should have learnt:-

• RIPv1 and RIPv2 are distance-vector routing protocols that use hop count as the routing metric. RIPv2 was developed to overcome the limitations of RIPv1.
    
• RIPv1 is a classful routing protocol and so does not support VLSM and CIDR. Moreover, it has other limitations such as the broadcasting of updates and the lack of an authentication method.
    
• RIPv2 is a classless routing protocol and so can support VLSM and CIDR. Moreover, it multicasts it's updates on 224.0.0.9 and also allows for plain-text or MD5 authentication.
    
• Useful commands for configuring, viewing and troubleshooting RIP include:- network, sh ip route, sh ip protocol, sh ip rip database, debug ip rip, clear ip route *.