Understanding the network.pdf - Back to Home

To verify that the adjusted route metric is being announced, enable RIP debugging
with the privileged EXEC command and examine the RIP update
message.
RIP: sending v2 update to 224.0.0.9 via Ethernet0 (192.168.191.19)
192.168.10.0/24 -> 0.0.0.0, metric 1, tag 0
192.168.12.0/24 -> 0.0.0.0, metric 1, tag 0
192.168.20.0/24 -> 0.0.0.0, metric 16, tag 0
192.168.192.64/26 -> 0.0.0.0, metric 3, tag 0
192.168.181.0/24 -> 0.0.0.0, metric 1, tag 0
Adjusting RIP Process Timers
RIP's default is to send a message update every 30 seconds (the router's entire
routing table) whether there is a change or not. The IOS RIP updates can have up to
a 4.5 second variation in frequency; this is to prevent all of the routing tables from
sending updates at the same time.
In addition to the [update] timer, there is the [invalid] timer, which sets how
long a route can remain in the routing table without being updated. If the [invalid]
timer expires, the route is set to a metric of 16 and the [flush] is started. Upon
expiration, the route is purged from the table.
IOS also supports a [hold down] timer, which is triggered when an update has a
different metric than one previously recorded. These timers can be adjusted with
the RIP routing subprocess command to reduce message update times. In our present example,
because the RIP process is only used for advertising routes to the ISP and changes
in the topology are rare, setting the timers for updates that are more infrequent is
preferable over the default timers. All values are set in seconds:
asbr-a1(config-router)#timers basic 120 240 180 300
NOTE
This option is also available with IGRP.