Routing loops

A routing loop is formed in a network when an error occurs in the operation of the routing algorithm, and as a result, in a group of nodes, the path to a particular destination forms a loop.

In the simplest version, a routing loop of size two, node A thinks that the path to some destination (call it D) is through its neighbouring node, node B. At the same time, node B thinks that the path to D starts at node A.

Thus, whenever traffic for D arrives at either A or B, it will loop endlessly between A and B, unless some mechanism exists to prevent that behaviour.