RIPv2 - Routing Protocols and Concepts - page 317

RIPv2 and CIDR

CIDR stands for classless interdomain routing . Defined in RFC 1519 , CIDR uses the concept of
supernetting . A supernet is a block of contiguous classful networks represented as a single network
address with a smaller mask than the classful mask.

For example, given the route 172.16.0.0/12, how many classful network addresses are included in the
route and what are they?

16 Class B routes from 172.16.0.0/16 through 172.31.0.0/16

Verifying and Troubleshooting RIPv2

There are several ways to verify and troubleshoot RIPv2. Many of the same commands used for
RIPv2 can be used to verify and troubleshoot other routing protocols.

It is always best to begin with the basics:

Make sure that all the links (interfaces) are up and operational.

1.

Check the cabling. 2.

Check to make sure that you have the correct IP address and subnet mask on each interface. 3.

Remove any configuration commands that are no longer necessary or have been replaced by
other commands.

4.

Verification and Troubleshooting Commands

The show ip route command is the first command to use to check for network convergence. This
command displays the routing table so that you can verify that all routes are listed.

The show ip interface brief command can be used to verify that directly connected networks are
appropriately configured.

If all the interfaces are properly configured, check the routing protocol configuration with the show ip
protocols command. This command verifies many critical items, including RIP version, networks
configured, and RIP neighbors.

If these three commands do not provide enough information to solve a RIP routing problem, use the
debug ip rip command to watch RIP updates as they are sent and received. Many times, a route is
received but not added to the routing table. List at least one reason why this might happen:

RIP is operating as a classful protocol because automatic summarization is in effect.

A static route is configured for the network. Static routes have a lower AD and will be preferred over
a RIP route to the same destination.

The ping command is a quick way to test round-trip connectivity between a source and a destination.

The show running-config command is the last command you should use to verify and troubleshoot
your configuration. Usually, other commands are more efficient and provide more information than a
simple listing of the current configuration.