Cisco Systems 3560 Manual De Usuario

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.

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 gi0/2

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

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 
requires it to properly advertise routes.

Beginning in privileged EXEC mode, follow these steps to disable split horizon on the interface:

To enable the split horizon mechanism, use the ip split-horizon interface configuration command.

Enter global configuration mode.

interface interface-id

Enter interface configuration mode, and specify the interface to 
configure.

ip address ip-address subnet-mask 

Configure the IP address and IP subnet.

Disable split horizon on the interface.

end 

Return to privileged EXEC mode.

show ip interface interface-id

Verify your entries.

copy running-config startup-config 

(Optional) Save your entries in the configuration file.