Routing Information Protocol (RIP)The Routing Information Protocol (RIP) tracks distances or hop counts to nearby routers when establishing network connections and isbased on a distance-vector algorithm.RIP is based on a distance-vector algorithm; it tracks distances or hop counts to nearby routers when establishing network connections.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 documented in 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 a network. Hop counts of thesesignals are tracked and entered into the routing table, which defines where nodes in the network are located.The information that is used to update the routing table is sent as either a request or response message. In RIPv1, automatic updates to therouting table are performed as either one-time requests or periodic responses (every 30 seconds). RIP transports its responses or requestsby means of user datagram protocol (UDP) over port 520.RIP must receive regular routing updates to maintain a correct routing table. Response messages containing a router’s full routing table aretransmitted every 30 seconds. If a router does not send an update within a certain amount of time, the hop count to that route is changedto unreachable (a route hop metric of 16 hops). Another timer sets the amount of time before the unreachable routes are removed from therouting table.This first RIP version does not support variable length subnet mask (VLSM) or classless inter-domain routing (CIDR) and is not widely used.RIPv2RIPv2 adds support for subnet fields in the RIP routing updates, thus qualifying it as a classless routing protocol.The RIPv2 message format includes entries for route tags, subnet masks, and next hop addresses. Another enhancement included in RIPv2is multicasting for route updates on IP multicast address 224.0.0.9.44Routing Information Protocol (RIP) 765
