Cisco Systems 78-11741-02 Router Configuration a, Router Configuration B, Router Configuration C

Configuring IGRP

IGRP Configuration Examples

Figure 38 Disabled Split Horizon Example

Network address:			Network address:
	10.20.40.0			20.155.120.0
		Interface address:			Interface address:
		10.20.40.1			20.155.120.1
	E0			E2
		S0		Router B S2
	Router C

Network address:

12.13.50.0

				Secondary
	Interface address:					Interface address:
	12.13.50.1	Interface address:		interface address:
						131.108.1.2
			128.125.1.1	131.108.1.1
E1
					Network
	S1		Network		address:
					131.108.1.0
Router A		Interface address:	address:
			128.125.1.0
		128.125.1.2
					Frame Relay
					network	S1069a

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

Cisco IOS IP Configuration Guide

IPC-221