Split Horizon Examples

The following sample configuration illustrates a simple example of disabling split horizon on a serial
link. In this example, the serial link is connected to an X.25 network.
interface serial 0
encapsulation x25
no ip split-horizon
In the next example, Figure 19 illustrates a typical situation in which the no ip split-horizon
interface configuration command would be useful. This figure depicts two IP subnets that are both
accessible via a serial interface on Router C (connected to Frame Relay network). In this example,
the serial interface on Router C accommodates one of the subnets via the assignment of a secondary
IP address.
The Ethernet interfaces for Router A, Router B, and Router C (connected to IP networks 12.13.50.0,
10.20.40.0, and 20.155.120.0) all have split horizon enabled by default, while the serial interfaces
connected to networks 128.125.1.0 and 131.108.1.0 all have split horizon disabled by default. The
partial interface configuration specifications for each router that follow Figure 19 illustrate that the
ip split-horizon command is not explicitly configured under normal conditions for any of the

interfaces.