RIP came up at the end of the 80’s. It is a routing protocol that computes the shortest path between networks. It is based on the Bellman-Ford algorithm that distributes the computation of the shortest path among the nodes (routers). The metric of the path is related to the number of hops. Consequently it is one of the most famous distance vector protocol that is used on the IP networks and on the Internet.
The first release RIP v1, that is described by the IETF RFC 1058, was designed for the IPv4 class oriented Internet. RIP v1 uses broadcast UDP on the well-known port 520.
Nowadays, the second release of RIP (RIP v2), which is described by the IETF RFC 2453, fits the IPv4 CIDR that uses VLSMs. RIP v2 uses multicast UDP on the well-known group 18.104.22.168 and port 520. You can use it as in IGP within a small simple network.
The maximum network size that RIP can handle is 16 hops.