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Configuring a Dynamic LSP Metric

If no specific metric is configured, an LSP attempts to track the IGP metric toward the same destination (the to address of the LSP). IGP includes Open Shortest Path First (OSPF), IS-IS, Routing Information Protocol (RIP), and static routes. BGP and other RSVP/LDP routes are excluded.

For example, if the OSPF metric toward a router is 20, all LSPs toward that router automatically inherit metric 20. If the OSPF toward a router later changes to a different value, all LSP metrics change accordingly. If there are no IGP routes toward the router, the LSP raises its metric to 65,535.

Note that in this case, the LSP metric is completely determined by IGP; it bears no relationship to the actual path the LSP is currently traversing. If LSP reroutes (such as through reoptimization), its metric does not change, and thus it remains transparent to users. Dynamic metric is the default behavior; no configuration is required.

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