Patent ID: 8717935

Claim:
A method in a network element for open shortest path first (OSPF) non-stop routing with reliable flooding, the method comprising the steps of: responsive to a first OSPF instance of the network element that is currently acting as an active OSPF instance determining to flood a link-state advertisement (LSA), performing the following steps: synchronizing the LSA with a second OSPF instance of the network element currently acting as a backup OSPF instance, wherein the step of synchronizing includes storing by the second OSPF instance the LSA with a status that indicates that flooding is pending; attempting to reliably flood by the first OSPF instance the LSA to a set of one or more adjacent network elements of a flooding scope of the LSA, the step of attempting includes: transmitting the LSA to each of the set of adjacent network elements in the flooding scope of the LSA with an exception of one adjacent network element if the LSA was received from that adjacent network element, including the LSA on a plurality of retransmission lists for the plurality of adjacent network elements that the LSA was transmitted to, and maintaining the plurality of retransmission lists on the first OSPF instance, wherein the plurality of retransmission lists are not synchronized with the second OSPF instance, wherein the step of maintaining includes removing the LSA from a retransmission list for a network element responsive to receiving an acknowledgement of receipt of that LSA from that network element, if flooding of the LSA is complete, then the first OSPF instance causing the second OSPF instance to alter the status of the LSA to indicate that flooding is complete, wherein the flooding of the LSA is complete when the LSA is not indicated on any of the plurality of retransmission lists; and if the second OSPF instance has become the currently active OSPF instance prior to the flooding of the LSA completing, then the second OSPF instance attempting to reliably flood the LSA to all of the set of adjacent network elements of the flooding scope of the LSA.