Distance-Vector Routing

Ideas for Fixing the Algorithm

Path Vector:

The reason that propagates a distance of infinity is that when updates its path to , it doesn't "know" that the path from to developed in the preceding stage goes through .

The path-vector idea for fixing this problem is to add information to the distance vector to eliminate the problem just described. One way to do this is to supply each entry in the distance vector with a specific path which takes into account the current estimate of the distance.

Warning: This approach may significantly increase the size of the tables containing the distance vectors.

Split Horizon:

In the split horizon approach, a router remembers not the whole path to the destinations, but just the first nodes of those paths. If a neighbor of a router is the first node on such a path, the router does not submit this information to the neighbor.

Warning: This approach eliminates the problem of counting to infinity if the problem is caused by two adjacent routers. In more complicated networks, the problem will persist.

Source Tracing:

The idea of source tracing is to augment the distance vectors with the name of the router which immediately precedes the destination on the path from the router to the destination. If a router changes its notion of the next hop for a destination , then it uses the same neighbor for all destinations for which lies along the shortest path.