Routing convergence

This article is about Routing convergence. For other uses of the term Convergence , please see Convergence (disambiguation).

In routing, the state of routing convergence exists when all routers in a particular address space have a common understanding of reachable destinations. When that address space is an enterprise or other routing domain that is of reasonable size, it is quite reasonable to say that all routers should have an identical list of reachable destinations, although some may not be explicit as long as a default route is present.

When the address space is the global Internet, it is understood that there are too many concurrent changes, too many routers, and too slow a rate of update for routers in the default-free zone to have an identical understanding. In practice, major DFZ routers should be expected to have a very substantial agreement on the set of destinations, with the understanding that complete synchronization is not possible. In fact, complete synchronization is not desirable, as a given number of destinations will be flapping, and trying to keep a large table synchronized would create instability in the routing system as a whole.

Routing convergence may be limited to the control plane alone of router(s), or also the forwarding plane. It is practical and reasonable to speak of convergence between two specific routers:

• Border Gateway Protocol
• Open Shortest Path First

or the routers of an enterprise routing domain,

or sometimes of a single autonomous system.