A path-vector routing protocol is a network

routing protocol A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets ...

which maintains the path information that gets updated dynamically. Updates that have looped through the network and returned to the same node are easily detected and discarded. This algorithm is sometimes used in Bellman–Ford routing algorithms to avoid "Count to Infinity" problems. It is different from the distance vector routing and link state routing. Each entry in the routing table contains the destination network, the next router and the path to reach the destination. ''

Border Gateway Protocol Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (AS) on the Internet. BGP is classified as a path-vector routing protocol, and it makes ...

'' (BGP) is an example of a path vector protocol. In BGP, the autonomous system boundary routers (ASBR) send path-vector messages to advertise the reachability of networks. Each router that receives a path vector message must verify the advertised path according to its policy. If the message complies with its policy, the router modifies its routing table and the message before sending the message to the next neighbor. It modifies the routing table to maintain the

autonomous systems An autonomous robot is a robot that acts without recourse to human control. The first autonomous robots environment were known as Elmer and Elsie, which were constructed in the late 1940s by W. Grey Walter. They were the first robots in history t ...

that are traversed in order to reach the destination system. It modifies the message to add its AS number and to replace the next router entry with its identification. ''

Exterior Gateway Protocol An exterior gateway protocol is an IP routing protocol used to exchange routing information between autonomous systems. This exchange is crucial for communications across the Internet. Notable exterior gateway protocols include Exterior Gateway ...

'' (EGP) does not use path vectors. It has three phases: # Initiation # Sharing # Updating Of note, BGP is commonly referred to as an External Gateway Protocol (EGP) given its role in connecting Autonomous Systems (AS). Communication protocols within AS are therefore referred to as Internal Gateway Protocols (IGP) which contain OSPF and IS-IS among others. This being said, BGP can be used within an AS, which typically occurs within very large organizations such as Facebook or Microsoft.

See also