Configuring IGRP
IGRP Configuration Examples
IPC-221
Cisco IOS IP Configuration Guide

Figure38 Disabled Split Horizon Example

In this example, split horizon must be disabled in order for network 128.125.0.0 to be advertised into network 131.108.0.0, and vice versa. These subnets overlap at Router C, serial interface 0. If split horizon were enabled on serial interface 0, it would not advertise a route back into the Frame Relay network for either of these networks. The configurations for routers A, B, and C follow.

Router Configuration A

interface ethernet 1
ip address 12.13.50.1
!
interface serial 1
ip address 128.125.1.2
encapsulation frame-relay

Router Configuration B

interface ethernet 2
ip address 20.155.120.1
!
interface serial 2
ip address 131.108.1.2
encapsulation frame-relay

Router Configuration C

interface ethernet 0
ip address 10.20.40.1
!
interface serial 0
ip address 128.124.1.1
ip address 131.108.1.1 secondary
encapsulation frame-relay
Router B
Router C
Router A
E1
E0
S1
Interface address:
131.108.1.2
Interface address:
128.125.1.2
Secondary
interface address:
131.108.1.1
Interface address:
128.125.1.1
S0
E2
S2
Network address:
12.13.50.0
Interface address:
12.13.50.1
Network address:
10.20.40.0
Interface address:
10.20.40.1
Network address:
20.155.120.0
Interface address:
20.155.120.1
S1069a
Frame Relay
network
Network
address:
128.125.1.0
Network
address:
131.108.1.0