Cisco Systems 3750E Configuring Split Horizon, Ip summary-address rip ip address ip-network mask

Chapter 38 Configuring IP Unicast Routing

Configuring RIP

Beginning in privileged EXEC mode, follow these steps to set an interface to advertise a summarized local IP address and to disable split horizon on the interface:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	interface interface-id	Enter interface configuration mode, and specify the Layer 3
		interface to configure.
Step 3
	ip address ip-address subnet-mask	Configure the IP address and IP subnet.
Step 4
	ip summary-address rip ip address ip-network mask	Configure the IP address to be summarized and the IP
		network mask.
Step 5
	no ip split horizon	Disable split horizon on the interface.
Step 6
	end	Return to privileged EXEC mode.
Step 7
	show ip interface interface-id	Verify your entries.
Step 8
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

To disable IP summarization, use the no ip summary-address rip router configuration command.

In this example, the major net is 10.0.0.0. The summary address 10.2.0.0 overrides the autosummary address of 10.0.0.0 so that 10.2.0.0 is advertised out interface Gigabit Ethernet port 2, and 10.0.0.0 is not advertised. In the example, if the interface is still in Layer 2 mode (the default), you must enter a no switchport interface configuration command before entering the ip address interface configuration command.

Note If split horizon is enabled, neither autosummary nor interface summary addresses (those configured with the ip summary-address rip router configuration command) are advertised.

Switch(config)# router rip

Switch(config-router)# interface gi1/0/2

Switch(config-if)#ip address 10.1.5.1 255.255.255.0

Switch(config-if)#ip summary-address rip 10.2.0.0 255.255.0.0

Switch(config-if)# no ip split-horizon

Switch(config-if)# exit

Switch(config)# router rip

Switch(config-router)# network 10.0.0.0

Switch(config-router)#neighbor 2.2.2.2 peer-group mygroup

Switch(config-router)# end

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.

Note In general, we do not recommend disabling split horizon unless you are certain that your application requires it to properly advertise routes.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
38-24	OL-9775-02