In operational networks, nodes are connected via multiple links for load
sharing and redundancy. This is done to make sure that a failure of a link does
not disconnect or isolate some parts of the network. However, link failures
have an effect on routing, as the routers find alternate paths for the traffic
originally flowing through the link which has failed. This effect is severe in
case of failure of a critical link in the network, such as backbone links or
the links carrying higher traffic loads.