Split-Horizon is another mechanism of RIP that tries to avoid the count-to-infinity problem. By default, split-horizon is enabled on RIP routers. Explain why split-horizon cannot solve the count-to- infinity problem in this exercise.

What will be an ideal response?

Split-Horizon cannot perfectly solve the count-to-infinity problem in multi-path environment. Split-Horizon with poisoned reverse will prevent any routing loops between only two gateways. However, for more three gateways, it is possible to have a loop in a routing path. For example, in this experiment, Router2 believes it has a route through Router4, Router4 though Router3, Router3 through Router1. Split-Horizon cannot stop such a loop. This loop will only be resolved when the metric reaches infinity and the network involved is then declared unreachable. In this experiment, there is ANOTHER path to reach 10.0.1.0 network, therefore, instead of reaching infinity, the metric value would be increased to the adequate value. (Here, on Router3, it’s 12 hops) In this experiment, Router4 and Router2 are on the race condition. If the Router4 sends RIP response packet which contains the metric value of three to the network 10.0.1.0 to Router3 before
Router2 sends RIP response packet of the inaccessibility information to 10.0.1.0, Then Router3 gets wrong information regarding network 10.0.1.0. In this case, Router 2, Router3 and Router4 have an empirical routing loop Router4 -> Router3 -> Router2 -> Router4 which causes the count-to-infinity problem. The metric values to reach 10.0.1.0 will keep increasing one by one through each router until the proper converged value is obtained.