Routing protocols are effectively distributed database systems. They propagate information about the topology of the network among the routers within the network. Each router in the network then uses this distributed database to determine the best loop free path through the network to reach any given destination. There are two fundamental ways to distribute the data through a network:
By distributing vectors, each router in the network advertises the destinations it can reach, along with some information which can be used to determine the best path to each reachable destination. A router can determine the best vector (path) by examining the destinations reachable through each adjacent router or neighbor, combined with some additional information, such as the metric, which indicates the desirability of that path. There are two types of vector-based protocols: distance vector and path vector.
By distributing the state of the links attached to the routers; each router floods (or advertises to all other routers in the network, whether directly adjacent or not), the state of each link to which it is attached. This information is used independently by each router within the routing domain to build a tree representing a topology of the network (called a shortest path tree). Routing protocols that distribute the state of attached links are called link state algorithms. Read More....
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