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Thursday, March 25, 2010

Routing Information Protocol (RIP)

Characteristics of RIP

- RIP (Routing Information Protocol) is a standard for exchange of routing information among gateways and hosts.
- RIP is most useful as an "interior gateway protocol".
- All RIP routing protocols are based on a distance vector algorithm called the Bellman-Ford algorithm, after Bellman's development of the equation used as the basis of dynamic programming, and Ford's early work in the area.
- RIP is considered an effective solution for small homogeneous networks.
- For larger, more complicated networks, RIP's transmission of the entire routing table every 30 seconds may put a heavy amount of extra traffic in the network.
- RIP sends routing-update messages at regular intervals and when the network topology changes. When a router receives a routing update that includes changes to an entry, it updates its routing table to reflect the new route.
- Each router sends a list of distance-vectors each of its neighbours periodically.
- The metric must be a positive integer. This metric measures the cost to get to the destination. In RIP, this cost describes number of hops.
- Each hop is assigned a hop count value, which is typically 1. The router adds 1 to the metric value when a router receives a routing update and enters the network in the routing table.
- RIP prevents routing loops from continuing indefinitely by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of hops in a path is 15.
- RIP implements the split horizon and holddown mechanisms to prevent incorrect routing information from being propagated.
- RIP uses numerous timers to regulate its performance. These include a routing-update timer, a route-timeout timer, and a route-flush timer.

Limitations of the protocol

- The protocol is limited to networks whose longest path involves 15 hops.
- The protocol depends upon "counting to infinity" to resolve certain unusual situations.
- This protocol uses fixed "metrics" to compare alternative routes.
- It is not appropriate for situations where routes need to be chosen based on real-time parameters such a measured delay, reliability, or load.

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