Split Horizon - Cisco WS-C3550-12G Software Configuration Manual

Configuring IGRP
This is an example of output from the show ip protocols privileged EXEC command that verifies the
IGRP configuration.
Switch# show ip protocols
<output truncated>
Routing Protocol is "igrp 109"
Sending updates every 90 seconds, next due in 52 seconds
Invalid after 270 seconds, hold down 280, flushed after 630
Outgoing update filter list for all interfaces is
Incoming update filter list for all interfaces is
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
IGRP maximum hopcount 100
IGRP maximum metric variance 1
Redistributing: igrp 109
Maximum path: 4
Routing for Networks:
Routing Information Sources:
Distance: (default is 100)

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.
Note In general, we do not recommend disabling split horizon unless you are certain that your application
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.
Catalyst 3550 Multilayer Switch Software Configuration Guide
22-34
131.108.0.0
183.31.0.0
Gateway Distance Last Update
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.
Chapter 22 Configuring IP Unicast Routing
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