Effects of OSPF Timers Configurations on Network Convergence in New Generation Routers

Abstract

QoS provided by a routing protocol is determined by several factors, one of which is network convergence time. It is the time taken by network to recover from a link failure. Hello protocol is used by Open Shortest Path First routing algorithm to detect such a failure. With default settings of the OSPF parameters, the network takes a long time in recovery process. The primary reason of this is the time required in failure detection using Hello protocol. Detection time can be reduced by reducing the value of HelloInterval. However, a small value of HelloInterval increases the network congestion causing loss of some consecutive Hellos, thus leading to false failure detection. Traditional routers could not afford such strict configurations of OSPF parameters.  In this paper, we investigate the effects of such configurations of parameters in new generation routers which provide higher bandwidth and higher tolerance for congestion. We conducted experiments with Cisco ASA and Cisco IOS devices and this paper presents the results with different configurations and their effects on fast failure detection, false alarm, network congestion and failure recovery.

Keywords: OSPF, Hello protocol, Fast Hello, Network Convergence, Fast Failure Detection, Computer Networks