A method of determining the state of network links based on differences in corresponding distance-vectors in a sequence routing table updates, and a network management system performing the method. The network management system comprises least one monitoring apparatus adapted to determine the state of network links. The monitoring apparatus may be a router in the network adapted to determine link status, or a personal computer or server peered with a router and configured to determine the state of network links based on differences in corresponding distance-vectors in a sequence of routing table updates.