Routing Loop

A routing loop may be caused by the actual failure of a router or when notification of such failures have not been forwarded to other routers. It may also occur over time as a network expands or merges with other networks. There are many strategies that can be applied to reduce the occurrence of routing loops. In many instances, these techniques may be used in conjunction with others. One method is placing a limit on the number of hops a packet takes between routers, the case found in RIP (Routing Information Protocol). Another strategy works by using a hold-down timer. A hold-down timer is a routing function that prevents a route from being updated for a given amount of time. This period is typically calculated to slightly exceed the amount of time required to update each router regarding failures and network changes. A poison reverse is another method used to prevent routing loops. This functions by establishing a single route in which destinations may be reached by blocking the reverse direction.