1. For use by a router in a survivable portion of a network, a computer-implemented method comprising: a) receiving a packet addressed to a destination node within the survivable portion of the network, wherein the packet includes an information indicating that the packet has encountered a failure; and b) selecting one of (A) a primary port, (B) a primary backup port and (C) a secondary backup port on which to forward the received packet, such that, in the event of a double link failure, a backup path with no dead loops is defined.