Avoiding counting to infinity in distance vector routing

Abstract

The Routing Information Protocol (RIP) may occasionally introduce misleading routing information into the routing table, due to network topology changes such as link or router failures. This is known as the “counting to infinity" problem. In the past, the distance metric had to be below 16 hops, in order to keep this counting within reasonable limits. In this paper a more elaborate approach is presented in order to recognize those router interfaces, which might have received misleading routing messages. This is accomplished by evaluating routing updates more carefully than is done by the well known split horizon approach. In contrast to other approaches, the router interfaces are examined in pairs to determine if a loop exists between them. The algorithm locally extracts all the information it needs from the normal update messages that are exchanged between RIP neighbors and is thus executed in constant time. Only some minor calculations have to be carried out to gain the knowledge that is necessary to recognize those interfaces which may have received misleading routing information. Hence, this distance vector routing without “counting to infinity" can be used in complex networking environments.