Editing Routing (section)

===Path-vector protocol===
{{main|Path-vector routing protocol}}
Distance vector and link-state routing are both intra-domain routing protocols. They are used inside an [[Autonomous system (Internet)|autonomous system]], but not between autonomous systems. Both of these routing protocols become intractable in large networks and cannot be used in [[inter-domain]] routing. Distance vector routing is subject to instability if there are more than a few hops in the domain. Link state routing needs significant resources to calculate routing tables. It also creates heavy traffic due to flooding.

Path-vector routing is used for inter-domain routing. It is similar to distance vector routing. Path-vector routing assumes that one node (there can be many) in each autonomous system acts on behalf of the entire autonomous system. This node is called the ''speaker node.'' The speaker node creates a routing table and advertises it to neighboring speaker nodes in neighboring autonomous systems. The idea is the same as distance vector routing except that only speaker nodes in each autonomous system can communicate with each other. The speaker node advertises the path, not the metric, of the nodes in its autonomous system or other autonomous systems.

The path-vector routing algorithm is similar to the distance vector algorithm in the sense that each border router advertises the destinations it can reach to its neighboring router. However, instead of advertising networks in terms of a destination and the distance to that destination, networks are advertised as destination addresses and path descriptions to reach those destinations. The path, expressed in terms of the domains (or confederations) traversed so far, is carried in a special path attribute that records the sequence of routing domains through which the reachability information has passed. A route is defined as a pairing between a destination and the attributes of the path to that destination, thus the name, path-vector routing; The routers receive a vector that contains paths to a set of destinations.<ref>{{IETF RFC|1322}}</ref>