Whenever a change occurs in a network’s topology, all the routers in that network must learn the new topology. This process is both collaborative and independent; the routers share information with each other, but they must calculate the impact of the topology change independently. Because they must mutually develop an independent agreement on the new topology, they are said to converge on this consensus.

Convergence properties include the speed of propagation of routing information and the calculation of optimal paths. The quicker the convergence, the more optimal the routing protocol is said to be.

Convergence time is the time it takes for all routers in a network to agree on the current topology. The size of the network, the routing protocol in use, the network design, and numerous configurable timers can affect convergence time. For example, the use of hierarchical addressing and summarization helps localize topology changes, which speeds convergence.

Network convergence must occur whenever a new routing protocol starts and whenever a change takes place in the network. It occurs in both new networks and those that are already operational. Convergence is also important when changes occur in the network. A network is not completely operable until it has converged. Therefore, short convergence times are required for routing protocols.