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Chapter 8: AI2524 Protocol Configuration Steps
August 1997 Page 8-19
2524UM
Run IGRP and RIP Concurrently
It is possible to run IGRP and RIP concurrently. The IGRP informa-
tion will override the RIP information by default because of IGRP's
administrative distance.
Running IGRP and RIP concurrently does not work well when the net-
work topology changes. Because IGRP and RIP have different update
timers, and because they require different amounts of time to propa-
gate routing updates, one part of the network will follow IGRP routes
and another part will follow RIP routes. This results in routing loops.
Although these loops do not exist for long, the Time To Live (TTL)
will quickly reach zero, and ICMP will send a TTL exceeded message.
This message will cause most applications to stop attempting network
connections.
Disable the Validation of Source IP Addresses
By default, the software validates the source IP address of incoming
RIP routing updates. If that source address is not valid, the software
discards the routing update.
Consider disabling this feature if you have a router that is off network
and you want to receive its updates. Disabling this feature is not rec
ommended under normal circumstances. To disable the default func
tion that validates the source IP addresses of incoming routing updates,
perform this task in router configuration mode:
z
Disable the validation of the source IP address of incoming RIP
routing updates.
no validate-update-source ion
In addition to running multiple routing protocols simultaneously, the
Cisco IOS software can redistribute information from one routing pro-
tocol to another. For example, you can instruct the software to readver-
tise IP Enhanced IGRP-derived routes using the RIP protocol or to
readvertise static routes using the IP Enhanced IGRP protocol. This
capability applies to all the IP-based routing protocols.
You may also conditionally control the redistribution of routes be
tween routing domains by defining a method known as route maps be-
tween the two domains.
z
To redistribute routes from one protocol into another, type this
command in router configuration mode:
redistribute protocol
autonomous-system-
number
[route-map
map-tag
]