The Internet is a network of networks. The Internet consists of large number of autonomous systems, each of which further consists of routing domains. Such autonomous systems are usually run by the larger companies or universities. Within the Autonomous system, a router communicates with the other router using the best intra domain routing protocols, which are known as interior gateway protocols. Autonomous system are connected via gateways, these exchange information using inter domain routing protocol, which are also called exterior gateway protocols.
The RIP or (Routing Information Protocol) is the commonest interior gateway protocol and the recent protocol such as open shortest path first (OSPF). The purpose of these protocols is to enable routers to exchange locally so that all the routers in the autonomous system must a have coherent and up to date information.
When a host receives the new routing information, it is likely to update not only to it but also sends this new updated information to all the connected hosts so that they can updated themselves. Hence these changes propagate across the entire network.