Routing Information Protocol (RIP)The Routing Information Protocol (RIP) tracks distances or hop counts to nearby routers when establishingnetwork connections and is based on a distance-vector algorithm.RIP protocol standards are listed in the Standards Compliance chapter.Topics:• Protocol Overview• Implementation Information• Configuration InformationProtocol OverviewRIP is the oldest interior gateway protocol.There are two versions of RIP: RIP version 1 (RIPv1) and RIP version 2 (RIPv2). These versions are documentedin RFCs 1058 and 2453.RIPv1RIPv1 learns where nodes in a network are located by automatically constructing a routing data table.The routing table is established after RIP sends out one or more broadcast signals to all adjacent nodes in anetwork. Hop counts of these signals are tracked and entered into the routing table, which defines wherenodes in the network are located.The information that is used to update the routing table is sent as either a request or response message. InRIPv1, automatic updates to the routing table are performed as either one-time requests or periodicresponses (every 30 seconds). RIP transports its responses or requests by means of user datagram protocol(UDP) over port 520.RIP must receive regular routing updates to maintain a correct routing table. Response messages containing arouter’s full routing table are transmitted every 30 seconds. If a router does not send an update within acertain amount of time, the hop count to that route is changed to unreachable (a route hop metric of 16hops). Another timer sets the amount of time before the unreachable routes are removed from the routingtable.This first RIP version does not support variable length subnet mask (VLSM) or classless inter-domain routing(CIDR) and is not widely used.46Routing Information Protocol (RIP) 939
