Patent ID: 7269133

Claim:
A method of highly-available Intermediate System to Intermediate System (HA IS-IS) routing in a network, comprising the steps of: creating a backup IS-IS instance running on a Master Control Processor (MCP) platform; creating local link state PDU (LSP) initially synchronizing the state of said backup IS-IS instance with the state of an active IS-IS instance running separately on said Master Control Processor (MCP) platform and linked with said backup IS-IS instance; dynamically synchronizing the ongoing state of said backup IS-IS instance with said active IS-IS instance using a combination of explicit message updates from said active IS-IS instance to said backup IS-IS instance together with a message flow-through mechanism; and in the event of protected fail-over of said active IS-IS instance, then seamlessly recovering from said fail-over without reconfiguring or interrupting traffic among peer routers in said network, by functionally substituting and recovery synchronizing said backup IS-IS instance for said protected active IS-IS instance, such that said recovery synchronized backup IS-IS instance establishes itself as the new active IS-IS instance, changing the role of said backup IS-IS instance to active, downloading “Hello” packets to an operating system kernel, retransmitting local LSPs to peer IS-IS routers when the respective LSP refresh interval expires, examining an SRM and SSN flag on each LSP, and adding configured summary address to proper non-pseudonode LSPs; and building LSP and PSNP transmit queues.