Stability of a class of dynamic routing protocols (IGRP)

An exact analysis of the dynamic behavior of IGRP, an adaptive shortest-path routing algorithm, is performed. The distance metric is a weighted sum of traffic-sensitive and traffic-insensitive delay components. The optimality and stability of the protocol is related to the ratio of the weights. In particular, it is shown that if the traffic-sensitive component is not given enough weight, then starting from any initial routing, the subsequent routings after finitely many update periods will oscillate between two worst cases. Otherwise, the successive routings will converge to the unique equilibrium routing. It is also shown that load sharing among routes whose distances are within a threshold of the minimum distance helps stabilize the dynamic behavior.