Open shortest path first (OSPF) nonstop routing (NSR) with link derivation

A method of operation of a network element for open shortest path first (OSPF) non-stop routing, wherein the network element comprises a first OSPF instance currently acting as an active OSPF instance and a second OSPF instance currently acting as a standby OSPF instance, the method comprising:

• attempting to create a FULL adjacency with a neighbor network element using a neighbor state machine of the active OSPF instance, the step of attempting comprising:
• maintaining a neighbor data structure for the neighbor network element prior to the neighbor state machine transitioning to or from a full state;
• installing link state advertisements (LSAs) received from the neighbor network element in both a link state database (LSDB) of the active OSPF instance and the standby OSPF instance;
• synchronizing the neighbor data structure of the first OSPF instance to the second OSPF instance only when the neighbor network element is a non-virtual neighbor;
• and
• if and when the neighbor state machine of the active OSPF instance transitions to the full state and if a switch causes the second OSPF instance to act as the active OSPF instance, retrieving neighbor information from the LSAs of the second OSPF instance and deriving a link between the network element and the neighbor network element based on the retrieved neighbor information in order to create the FULL adjacency with the neighbor network element.

A network element for open shortest path first (OSPF) non-stop routing, comprising:

• a first OSPF instance currently acting as an active OSPF instance and a second OSPF instance currently acting as a standby OSPF, wherein each of the first and second OSPF instances comprise a link state database (LSDB) configured to store link state advertisements (LSAs) and a neighbor data structure comprising a neighbor state machine configured to maintain a neighbor data structure for a neighbor network element;
• and
• at least one processor configured to:
• attempt to create a FULL adjacency with a neighbor network element using a neighbor state machine of the active OSPF instance by:
• maintaining a neighbor data structure for the neighbor network element prior to the neighbor state machine transitioning to or from a full state;
• installing link state advertisements (LSAs) received from the neighbor network element in both a link state database (LSDB) of the active OSPF instance and the standby OSPF instance;
• and
• if and when the neighbor state machine of the active OSPF instance transitions to the full state and if a switch causes the second OSPF instance to act as the active OSPF instance, retrieve virtual neighbor information from the Router-LSAs of the second OSPF instance and derive a virtual link between the network element and the neighbor network element based on the retrieved virtual neighbor information in order to create the FULL adjacency with the neighbor network element, and wherein the virtual link between the network element and the neighbor network element is derived without synchronizing the virtual neighbor information between the first OSPF instance and the second OSPF instance.

A network element for open shortest path first (OSPF) non-stop routing, comprising:

• a first OSPF instance currently acting as an active OSPF instance and a second OSPF instance currently acting as a standby OSPF, wherein each of the first and second OSPF instances comprise a link state database (LSDB) configured to store link state advertisements (LSAs) and a neighbor data structure comprising a neighbor state machine configured to maintain a neighbor data structure for a neighbor network element;
• and
• at least one processor configured to:
• attempt to create a FULL adjacency with a neighbor network element using a neighbor state machine of the active OSPF instance by:
• maintaining a neighbor data structure for the neighbor network element prior to the neighbor state machine transitioning to or from a full state:
• installing link state advertisements (LSAs) received from the neighbor network element in both a link state database (LSDB) of the active OSPF instance and the standby OSPF instance;
• synchronize the neighbor data structure of the first OSPF instance to the second OSPF instance only when the neighbor network element is a non-virtual neighbor;
• and,
• if and when the neighbor state machine of the active OSPF instance transitions to the full state and if a switch causes the second OSPF instance to act as the active OSPF instance, retrieve neighbor information from the Router-LSAs of the second OSPF instance and derive a link between the network element and the neighbor network element based on the retrieved neighbor information in order to create the FULL adjacency with a neighbor network element.