# What is the "count to infinity" problem in distance vector routing?

by (user.guest)

“Count to infinity” problem in distance-vector routing:

Count to infinity problem is due to the routing loops like A, B routes through C, and C routes through B. The routing loops occur when the network links break between the devices. The routing loops make the data bounce back and forth between the devices.

• For example, consider the graph X-> Y-> Z-> W

• The packets transfer through this link between the nodes X, Y, Z, and W.

• If the link between the nodes X and Y is damaged, then the node Y updates its routing table.

• The nodes exchange their routing tables and Y receives Z's routing table.

• Here Z doesn't know that the link between X and Y is damaged and it informs that it has a link to X with the link cost of 2.

• The node Y receives the table from the node Z and thinks there is a separate link between the nodes Z and X, it updates its routing table and changes infinity to 3.

• Again, the nodes exchange their routing tables. When Z receives Y's routing table, it identifies that Y has changed the weight of its link to X from 1 to 3, then the node Z updates its table and changes the link cost to the node X to 4.

• This process continues until all nodes find out that the link cost of node X is infinity. This results in the increase in the link cost between the nodes.

Hence, Count to infinity problem means infinity loop of calculation of the shortest path.

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