Path vector protocol

A path vector protocol is a routing protocol for computer networks, each of which carries the vector for the individual elements (paths), the Element has taken through the network in the spread. By the vector, a path can be easily recognized as a loop if the receiving system is already part of the vector. This infinity problems are avoided.

Basic principle

In order to find the best route to a specific destination in a network, the router must have a list of possible paths and the associated vectors, so ways have. In the various techniques of routing protocols, the path vector protocols are among the most distance vector protocols. A router sends the paths which are accessible through it to all neighboring routers. Here, the path vector with the identification of the initiating ( starting ) is initialized at the beginning of the router. Each router that receives this path, examines the vector of its own identifier. This is not, the path with the associated vector is added to the local database. This has every router in its database the paths of the network and each of the associated vectors.

Operation

Each router must store for each path element can also be the associated vector. For the example model

Then sees the database in the router 7 as a section like this:

The entire table contains 42 entries. This presents a spanning tree dar. In this unfiltered form the dataset would be very very large very quickly. Therefore, only the path with the shortest vector is, for example, in BGP, a path vector protocol, passed. This reduces the table to the variants, the best vectors represent the goal.

This optimized table only contains 15 entries.

Application

The routing of the Internet is based on BGP, which is a path vector protocol from the group of distance vector protocols. As an element of identification, the IP prefix, that is the network address and the network mask is taken.

Each router is one of an autonomous system (AS ), and this SID is written as an identifier, respectively in the path vector. In addition, policies are installed on each router that will affect when a route to adjacent routers to be forwarded.

Path vector routing protocols to exchange the data not only for changes in the topology, but also in certain cycles, in order to ensure consistency. In contrast to link state protocols, they generally have higher convergence times.