| Routing Information Protocol is a distance vector protocol that uses hop count as its primary metric. RIP defines how routers should share information when moving traffic among an interconnected group of local area networks (LANs). RIP, which was defined in RFC 1058 in 1988, is known for being easy to configure and easy to use in small networks. In the enterprise, Open Shortest Path First (OSPF) routing has largely replaced RIP as the most widely used Internet Gateway Protocol (IGP). RIP has been supplanted mainly due to its simplicity and its inability to scale to very large and complex networks.
How Routing Information Protocol (RIP) works RIP is a dynamic routing protocol that uses a distance vector algorithm to decide which path to put a packet on to get to its destination. The protocol is limited, however, in that it only allows only 15 hops in a path. If a packet can't reach a destination in 15 hops, the destination is considered unreachable. Each RIP router maintains a routing table, which is a list of all the destinations the router knows how to reach. Each router broadcasts its entire routing table to its closest neighbors every 30 seconds. In this context, neighbors are the other routers to which a router is connected directly -- that is, the other routers on the same network segments this router is on. The neighbors, in turn, pass the information on to their nearest neighbors, and so on, until all RIP hosts within the network have the same knowledge of routing paths. This shared knowledge is known as convergence. If a router receives an update on a route, and the new path is shorter, it will update its table entry with the length and next-hop address of the shorter path. If the new path is longer, it will wait through a "hold-down" period to see if later updates reflect the higher value as well. It will only update the table entry if the new, longer path has been determined to be stable. If a router crashes or a network connection is severed, the network discovers this because that router stops sending updates to its neighbors, or stops sending and receiving updates along the severed connection. If a given route in the routing table isn't updated across six successive update cycles (that is, for 180 seconds), a RIP router will drop that route and let the rest of the network know about the problem through its own periodic updates. | 
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