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Apply Offsets to Routing Metrics
An offset list is the mechanism for increasing incoming and outgoing metrics to routes learned via RIP. You
can limit the offset list with an access list. To increase the value of routing metrics, perform the following task
in router configuration mode.
Command Purpose
offset-list access-list-name { in | out}
Apply an offset to routing metrics.
5.4.9 Adjust Timers
Routing protocols use several timers that determine such variables as the frequency of routing updates, the
length of time before a route becomes invalid, and other parameters. These timers can be adjusted to fine-
tune the routing protocol performance to better suit the inter-network needs.
The default settings for the various timers are as follows:
• The update timer is 30 seconds. During every update, the RIP process sends an unsolicited
response message containing the complete routing table to all neighboring RIP routers
• The timeout timer is 180 seconds. Upon expiration of the timeout, an unresponsive route becomes
invalid; however, it is retained in the routing table for a short time so that neighbors can be notified
that the route has been dropped
• The garbage collect timer is 120 seconds. Upon expiration of the garbage-collection timer, the
unresponsive route is finally removed from the routing table
To adjust the timers, use the following command in router configuration mode.
Command Purpose
timers basic
update timeout garbage
Adjust routing protocol timers.
5.4.10 Enable or Disable Split-horizon
Normally, routers that are connected to broadcast-type IP networks, and that use distance-vector routing
protocols, employ split horizon with poison reverse to reduce the possibility of routing loops.
The split horizon with poison reverse mechanism blocks information about routes from being advertised by a
router out any interface from which that information originated. This behavior usually optimizes
communications among multiple routers, particularly when links are broken. However, with non-broadcast
networks, such as Frame Relay, situations can arise for which this behavior is less than ideal. For these
situations, a user might want to disable split horizon. If an interface is configured with secondary IP
addresses and split horizon is enabled, updates might not be sourced by every secondary address. Only
one routing update is sourced per network numbe, unless split horizon is disabled.
To enable or disable split horizon, perform the following tasks in interface configuration mode.
Command Purpose
ip rip poison reverse
Enable split horizon with
poison reverse.
no ip rip poison reverse
Disable split horizon with
poison reverse.
5.4.11 Manage Authentication Keys
If you are sending and receiving RIP Version 2 packets, you can enable RIP authentication on an interface.
RIP Version 1 does not support authentication.
The IC35516 software supports two modes of authentication on an interface for which RIP authentication is
enabled: plain text authentication and MD5 authentication. The default authentication in every RIP Version 2
packet is plain text authentication.