Metric

The RIP metric is based on hop count and can be between 1 and 15. The metric 16 is used for infinity, which means that if the route is unreachable, a metric of 16 is displayed. The question is, why was the metric chosen as 16? Why not 17 or 18? The metric filed in RIP-1 packet format clearly shows that it is 32 bits long. This means that, theoretically, RIP can support 2 ³² hops. Although this is a large number, the metric of 15 was chosen to avoid a count to infinity problem. (This is also referred to as a routing loop. ) In a large network with a few hundred routers, a routing loop results in a long time for convergence if the metric for infinity has a large value. The number 16 was chosen to get a shorter convergence time.

The 15-hop limit was chosen also because RIP was intentionally designed for small networks. It was not intended for the large networks that potentially can have more than 15 hops.