“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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