Configuring Split Horizon - Cisco Catalyst 3750 Software Configuration Manual

Chapter 28 Configuring IP Unicast Routing
This example shows how to configure a router for IGRP and assign it autonomous system 109. The
network router configuration commands show the networks directly connected to the router.
Switch(config)# router igrp 109
Switch(config-router)# network 131.108.0.0
Switch(config-router)# network 192.31.7.0

Configuring Split Horizon

Routers connected to broadcast-type IP networks and using distance-vector routing protocols normally
use the split-horizon mechanism to reduce the possibility of routing loops. Split horizon blocks
information about routes from being advertised by a router on any interface from which that information
originated. This feature can optimize communication among multiple routers, especially when links are
broken.
In general, we do not recommend disabling split horizon unless you are certain that your application
Note
requires it to properly advertise routes.
Beginning in privileged EXEC mode, follow these steps to disable split horizon on the interface:
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 ip address ip-address subnet-mask
Step 4
no ip split-horizon
Step 5
end
Step 6 show ip interface interface-id
Step 7
copy running-config startup-config
To enable the split horizon mechanism, use the ip split-horizon interface configuration command.
78-15870-01
Purpose
Enter global configuration mode.
Enter interface configuration mode, and specify the interface to
configure.
Configure the IP address and IP subnet.
Disable split horizon on the interface.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring IGRP
28-27