IS-IS high availability design
View Patent ↗The HA IS-IS system provides a redundant backup IS-IS protocol instance that can seamlessly assume the function of the active IS-IS instance in the event of active MCP failure. Once the backup is online, the active synchronizes its global, interface, adjacency, neighbor, and LSP system state information. In the ongoing synchronization phase, the active and the backup maintain synchronization using a combination of explicit message updates from active to backup together with message flow-through. In the recovery phase, the operating system detects the failure of the active and notifies the backup, which assumes the active function as a standalone system without reconfiguring or interrupting traffic among peer network routers, and starts computing forwarding tables and updating routing tables.
1. 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.
2. The method of claim 1 wherein said step of recovery synchronizing further comprises conducting a designated router election.
3. The method of claim 2 wherein said step of recovery synchronizing further comprises building pseudonode and non-pseudonode LSPs.
4. The method of claim 3 wherein said step of recovery synchronizing further comprises starting a Shortest Path First (SPF) algorithm.
5. The method of claim 4 wherein said step of recovery synchronizing further comprises maintaining two LSP databases, a local LSP database being generated by the currently active MCP and a previous LSP database being from the previous active MCP.
6. The method of claim 5 wherein said step of recovery synchronizing further comprises: if content is changed, setting sequence number of local generated LSP to previous LSP sequence number plus one; inserting said local generated LSP into LSP database; removing previous LSP; and purging unused LSP.
7. A system for highly-available Intermediate System to Intermediate System (HA IS-IS) routing in a network, comprising
a local IS-IS router and peer IS-IS routers, said local IS-IS router including:
a Master Control Processor (MCP) platform containing an active IS-IS instance running on an active MCP and
a backup IS-IS instance running on a separate backup MCP, said backup IS-IS instance connected with said active IS-IS instance through HA nodes linked together through a MCP network (MNET);
a plurality of line cards interconnected with said MCP platform through a routing network (RNET), said line cards operable to use routing tables to distribute protocol and transit traffic data packets among said peer IS-IS routers;
and a message flow-through architecture, such that if said active MCP is operated as a standalone system, then all incoming protocol control traffic is configured to flow directly between said line cards and said active MCP; whereas if said active MCP is protected by said backup MCP, then all incoming protocol control traffic from said peer network routers through said line cards is configured to flow first through said backup MCP before flowing to said active MCP, and all protocol control traffic originating at said active MCP is configured to flow first through said backup MCP before being distributed through said line cards among said peer network routers.
8. The system of claim 7 wherein said MNET comprises a GbE Ethernet connection.
9. The system of claim 7 further comprising a RS232 serial link interconnecting said active MCP and said backup MCP.