The Routing Information Protocol allows network routers to adapt dynamically to changing network connections by swapping information about which networks each router can reach, and how far away those networks are.
RIP was the most commonly used Interior Gateway Protocol in the Internet. The protocol was first developed in 1969 as part of ARPANET, and used the Bellman-Ford algorithm. RIP is a distance-vector routing protocol which employs hop count as a routing metric. The maximum number of hops allowed with RIP is 15. RIP updates every 30 seconds, generating lots of network traffic in larger networks. It runs above the network layer of the Internet protocol suite, using UDP port 520 to carry its data. Holddowns, split horizon and poison reverse are used to avoid routing loops.
There are two versions of RIP, namely RIPv1 and RIPv2. RIPv1 is only capable of classful routing. The routing updates do not carry subnet information, which means that a network's size is determined solely by the network class of its IP Address, and there is no way to split a network into smaller subnets, each routed along a different path.
Due to the original deficiencies in addressing, RIPv2 was developed in 1994 to use CIDR (Classless interdomain routing). However to maintain backwards compatibility the 15 hop count limit remained. Rudimentary authentication was added to secure routing updates.
In many current networking environments RIP would not be the first choice of routing protocol as its convergence times and scalability are poor compared to OSPF or IS-IS, and the hop limit severely limits the size of network it can be used in. On the other hand, it is easier to configure.