Split Horizon

Split Horizon

Split horizon is a network routing technique used in distance-vector routing protocols to prevent the advertisement of certain routes back out the same interface from which they were received. This technique improves network stability by avoiding routing loops and ensuring that routing information is propagated correctly.

How Split Horizon Works

In a network using split horizon, a router implements a simple rule: it does not advertise routes back out the same interface from which it received them. This rule prevents incorrect routing information from being sent back to the original sender, which can lead to routing loops. Routing loops occur when routers continuously exchange incorrect routing information, causing network performance to degrade.

To illustrate how split horizon works, consider the following scenario:

In the diagram, Router A receives route information for Network B through Interface 1. Since Router A is using split horizon, it will not advertise this route back out Interface 1. This prevents Router B from receiving its own route information back from Router A, eliminating the possibility of a routing loop.

Benefits and Significance of Split Horizon

The use of split horizon in distance-vector routing protocols offers several benefits that contribute to network stability and performance:

1. Loop Prevention: By not advertising routes back out the same interface, split horizon prevents routing loops. Routing loops can cause excessive traffic and prolonged network instability.

2. Improved Network Convergence: Split horizon reduces the time it takes for a network to converge to an optimal routing state. By avoiding the propagation of incorrect routing information, the network can converge more quickly and efficiently.

3. Bandwidth Conservation: Split horizon reduces unnecessary network traffic by preventing the dissemination of redundant routing information. This conserves bandwidth and improves network efficiency.

Implementing Split Horizon

To implement split horizon in a network, follow these steps:

1. Enable Split Horizon: Activate split horizon on the routers in the network that use distance-vector routing protocols. This can typically be done through router configuration settings.

2. Monitor Network Routing Tables: Regularly monitor the network routing tables to ensure the effectiveness of split horizon. As the network topology changes, update configurations and routing tables accordingly.

3. Consider Split Horizon Variants: In some cases, the basic split horizon technique may not be sufficient. Variants like split horizon with poison reverse or split horizon with route poisoning can be used to further enhance loop prevention and network stability.

Related Terms

• Distance-Vector Routing Protocols: Network protocols that use distance and direction to determine the best path to a destination.
• Routing Loop: A situation in which routers continuously exchange incorrect routing information, causing network instability.