Explains minimum LSP lifetime thresholds in IS-IS, including their role in preventing premature purging, configuring maximum lifetimes, handling Zero Age Lifetime behavior, and identifying corrupted lifetime events.
A minimum LSP lifetime threshold is an IS-IS protocol safeguard that
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prevents premature purging and unnecessary flooding of Link State Protocol Data Units (LSPs)
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ensures accurate handling of potentially corrupted Remaining Lifetime fields during LSP flooding events, and
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allows IS-IS to reset the Remaining Lifetime value of received LSPs to the maximum LSP lifetime for reliable network operation.
Maximum LSP lifetime configuration
By default, the maximum LSP lifetime is set to 1200 seconds. You can configure a different value using the max-lsp-lifetime seconds command. This rule ensures that, regardless of the Remaining Lifetime received, only the LSP originator can purge an LSP from the database before the maximum LSP lifetime elapses.
Zero Age Lifetime behavior
If the remaining lifetime for an LSP reaches 0, the LSP remains in the link state database for an additional 60 seconds, known as the Zero Age Lifetime. If the originating router does not refresh the LSP within this timeframe, the LSP is deleted from the database.
If the received LSP lifetime value is less than the Zero Age Lifetime (60 seconds), IS-IS generates an error indicating a corrupted lifetime event. For example:
Dec 14 15:36:45.663 : isis[1011]: RECV L2 LSP 1111.1111.1112.03-00 from 1111.1111.1112.03:
possible corrupted lifetime 59 secs for L2 lsp 1111.1111.1112.03-00 from SNPA 02e9.4522.5326 detected.IS-IS saves the received remaining lifetime value in the LSP database. The value appears in the show isis database command output under the Rcvd field.
Further reference
For more information about the show isis database command, refer to the IS-IS Commands chapter in the Routing Command Reference for Cisco NCS 5500 Series Routers.