The Routing Information Protocol (RIP) is one of the most commonly used Interior Gateway Protocol on internal networks which helps a router dynamically adapt to changes of network connections by communicating information about which networks each router can reach and how far away those networks are.

Although RIP is still actively used, it is generally considered to have been obsolete by Link-state routing protocol such as OSPF.

It is a distance-vector protocol, which employs Hop Count as the metric. In the RIP metric, a router defined to be one hop from directly connected networks, two hops from networks that are reachable from one other router and so on.

Thus, the Hop count along the path refers to the routers the datagram passes though while going from source to destination.

The maximum number of hops allowed with RIP is 15. It runs above Network layer of the Internet protocol suite, using UDP port 520 to carry its data.

RIP uses a distributed version of Bellman-Ford algorithm.

Bellman-Ford algorithm computes single-source shortest paths in a weighted graph. Bellman Ford runs in O(VE) time, where V and E are the number of vertices and edges.

The algorithm is distributed because it involves a number of nodes (routers) within an Autonomous system. It consists of the following steps:

• Each node calculates the distances between itself and all other nodes within the AS and stores this information as a table.
• Each node sends its table to all neighbouring nodes.
• When a node receives distance tables from its neighbours, it calculates the shortest routes to all other nodes and updates its own table to reflect any changes.

RIP partitions participants into active and passive (silent) nodes. Active routers advertise their routes to others; passive node just listen and updates their routes based on the advertisements. Passive nodes do not advertise.

Only routers can run RIP in active mode; other host run RIP in passive mode. A router running in active mode broadcasts a message or advertisement every 30 seconds.

The message contains information taken from the router’s current routing database.

Each message consists of pairs, where each pair contains a IP network address and a integer distance to that network.

All active and passive nodes listen to the advertisements and updates their route tables.

Features of RIP:

1. Updates of the network are exchanged periodically.
2. Updates (routing information) are always broadcast.
3. Full routing tables are sent in updates.
4. Routers always trust on routing information received from neighbour routers. This is also known as Routing on rumor.