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Routing Information Protocol (RIP)
The Routing Information Protocol (RIP) tracks distances or hop counts to nearby routers when
establishing network connections and is based on a distance-vector algorithm.
RIP protocol standards are listed in the Standards Compliance chapter.
Protocol Overview
RIP 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.
RIPv1
RIPv1 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 these signals 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 the routing table are performed as either one-time requests or periodic
responses (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 a router’s full routing table are transmitted every 30 seconds. If a router does not send an
update within a certain amount of time, the hop count to that route is changed to unreachable (a route
hop metric of 16 hops). Another timer sets the amount of time before the unreachable routes are
removed from the routing table.
This first RIP version does not support variable length subnet mask (VLSM) or classless inter-domain
routing (CIDR) and is not widely used.
RIPv2
RIPv2 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 RIPv2 is multicasting for route updates on IP multicast address
224.0.0.9.
Routing Information Protocol (RIP)
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