Defining a maximum count

Defining a maximum count 

7.1.3
This page will teach students how to define a maximum count to prevent routing loops.
The invalid updates of Network 1 will continue to loop until some other process stops the looping. This condition, which is called count to infinity, loops packets around the network in spite of the fact that the destination network, which is Network 1, is down. While the routers count to infinity, the invalid information allows a routing loop to exist.
Without countermeasures to stop the count to infinity process, the distance vector metric of hop count increases each time the packet passes through another router. These packets loop through the network because of incorrect information in the routing tables.
Distance vector routing algorithms are self-correcting, but a routing loop problem can require a count to infinity. To avoid this prolonged problem, distance vector protocols define infinity as a specific maximum number. This number refers to a routing metric, which may simply be the hop count.
With this approach, the routing protocol permits the routing loop to continue until the metric exceeds its maximum allowed value. The graphic shows the metric value as 16 hops. This exceeds the distance vector default maximum of 15 hops so the packet is discarded by the router. When the metric value exceeds the maximum value, Network 1 is considered unreachable.
The next page will discuss another solution for routing loops