Routing Information Protocol (RIP) is one of the oldest and simplest distance-vector routing protocols used in computer networks to help routers determine the best path for forwarding data packets within a local or small-scale network.
RIP uses the distance-vector algorithm (specifically, the Bellman-Ford algorithm) to calculate the best route to each destination. The primary metric it uses is hop count, where each router a packet passes through counts as one hop. RIP supports a maximum of 15 hops. Any destination more than 15 hops away is considered unreachable, making RIP unsuitable for large or complex networks.
Each RIP-enabled router maintains a routing table listing all known destinations and the number of hops to reach them. Routers broadcast their entire routing table to directly connected neighbors every 30 seconds. These neighbors, in turn, update their own tables and propagate the information further, a process known as convergence. When a router receives an update, it adds one to the hop count and updates its table if the new route is shorter. If the new route is longer, it waits to see if the change persists before updating, to avoid instability. If a router does not receive updates from a neighbor for 180 seconds, it marks routes through that neighbor as unreachable (hop count 16), and after 240 seconds, removes those routes from its table.