The rip split-horizon command enables split horizon.
The undo rip split-horizon command disables split horizon.
By default, split horizon is enabled.
If a route is advertised through the interface from which the route is learned, the route is blocked by split horizon. Split horizon is used to avoid routing loops between neighboring devices.
Generally, it is not recommended that you disable split horizon.
If split horizon is enabled on the interface that is configured with secondary IP addresses, RIP Update packets may not be sent by each secondary address. An Update packet does not regard every network as the source unless split horizon is disabled.
If an interface is connected to a Non Broadcast Multiple Access (NBMA) network, split horizon on the interface is disabled by default.
If both poison reverse and split horizon are configured, simple split horizon (the route is suppressed by the interface through which the route is learned) is substituted by poison reverse. Here, simple split horizon means that the route is suppressed when it is advertised through the interface from which it is learned.