Cisco Systems 78-11741-02 Running Igrp and RIP Concurrently, Disables automatic summarization

Configuring Routing Information Protocol

RIP Configuration Task List

Invalid after 180 seconds, hold down 180, flushed after 240

Outgoing update	filter list for all interfaces is
Incoming update	filter list for all interfaces is
Redistributing:	rip
Default version	control: send version 2, receive version 2
Interface		Send	Recv Triggered RIP Key-chain
Ethernet2		2	2
Ethernet3		2	2
Ethernet4		2	2
Ethernet5		2	2

Automatic network summarization is not in effect Address Summarization:

10.11.0.0/16 for Ethernet2

You can check summary address entries in the RIP database. These entries will appear in the database only if relevant child routes are being summarized. When the last child route for a summary address becomes invalid, the summary address is also removed from the routing table. The following example shows a summary address entry for route 10.11.0.0/16, with three child routes active:

router# show ip rip database

10.0.0.0/8	auto-summary
10.11.11.0/24	directly connected, Ethernet2
10.1.0.0/8	auto-summary
10.11.0.0/16	int-summary
^^^^^^^^^^^^^^^^^^^^^^^^^^^
10.11.10.0/24	directly connected, Ethernet3
10.11.11.0/24	directly connected, Ethernet4
10.11.12.0/24	directly connected, Ethernet5

Disabling Automatic Route Summarization

RIP Version 2 supports automatic route summarization by default. The software summarizes subprefixes to the classful network boundary when crossing classful network boundaries.

If you have disconnected subnets, disable automatic route summarization to advertise the subnets. When route summarization is disabled, the software sends subnet and host routing information across classful network boundaries. To disable automatic summarization, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# no auto-summary	Disables automatic summarization.

Running IGRP and RIP Concurrently

It is possible to run Interior Gateway Routing Protocol (IGRP) and RIP concurrently. The IGRP information will override the RIP information by default because of the administrative distance of IGRP.

However, running IGRP and RIP concurrently does not work well when the network topology changes. Because IGRP and RIP have different update timers, and because they require different amounts of time to propagate routing updates, one part of the network will accept and use IGRP routes and another part will accept and use RIP routes. Running IGRP and RIP concurrently will result in routing loops. Even though these loops do not exist for very long, the time-to-live (TTL) value will quickly reach zero, and Internet Control Message Protocol (ICMP) will send a “TTL exceeded” message. This message will cause most applications to stop attempting network connections.

Cisco IOS IP Configuration Guide

IPC-206