Analyzing the Hold Time Schemes to Limit the Routing Table Calculations in OSPF Protocol

OSPF is a popular interior gateway routing protocol. Commercial OSPF routers limit their processing load by using a hold time between successive routing table calculations as new link state advertisements (LSAs) arrive following a topology change. A large hold time value limits the frequency of routing table calculations but also causes large delays in convergence to the topology change. Hence, commercial routers now use an exponential back off scheme, where the hold time is initially set to a small value that is expected to rapidly increase, and hence limit the frequency of routing table calculations, in face of continuous LSA arrivals. In this paper, we analyze the ability of different hold time schemes to limit the frequency of routing table calculations under continuous LSA arrivals starting with a small value for the hold time. This analysis is performed using Markov regenerative process based stochastic models as well as simulations using an extensively modified OSPFD simulator.