ISIS Timers
Load isis.inter.area.cfg
Set R1 and XR2 to use the following ISIS timers:
Local LSPs should have a max lifetime of 600 seconds. These LSPs should be refreshed every 300 seconds.
Locally-generated LSPs should be throttled 500 msec after a change, 750 msec if occuring after an LSP was just generated previously, and a max backoff of 3 seconds.
SPF calculation should be throttled 250 msec after receiving an update, 500 msec if an SPF run has just occured, and a max wait time of 3 seconds.
Partial route calculation should use the same timers as SPF calculation.
During flooding, interfaces should pace LSPs at 20 msec intervals
During flooding, the router should allow for up to 3 seconds before retransmitting the same LSP. If LSPs do need to be retransmitted, these should be paced at 40 msec intervals.
Answer
Explanation
The lsp-max-lifetime command sets the lifetime on locally generated LSPs. By default this appears to be 1200 seconds. This defines how long an LSP is valid in the LSDB. A longer interval allows for less frequent refreshes, which saves some bandwidth in a large network.
The lsp-refresh-interval controls how frequently locally-generated LSPs are refreshed. This timer cannot be larger than the lsp-max-lifetime timer.
When an IGP topology change is detected, either via a local change or a received LSP, SPF should be delayed incase subsequent changes occur. The more you delay this, the more you can “batch” multiple topology changes together, but the less quickly the IGP will converge. The first parameter is the maxmium wait time. The second parameter is the initial wait time. The last parameter is the wait time between the first and second SPF run. Subsequent SPF runs will continue to backoff until reaching the max wait time.
Partial route calculation is any change that does not affect the topology. For example, if a prefix is removed/added from a node, the IGP topology has not changed, so an SPF run is not needed. Instead, a partial rotue calculation is used to more quickly update the RIB. The timers for PRC is configured in a similar manner to the SPF timers. This does not appear to be configurable for IOS-XR.
The interface-level command isis lsp-interval controls pacing during LSP flooding. During LSP flooding, you may want the router to send the LSPs at a slower pace to give the remote router a better chance of processing the LSPs. This command sets the delay between subsequent LSP transmissions on the interface.
During flooding, it’s possible that some LSPs are lost and need to be retransmitted. The amount of time to wait for an ACK to an LSP is controlled with the isis retransmit-interval interface command.
If many LSPs need to be retransmitted, these can be paced using a separate retransmit-throttle-interval setting. It may be the case that the router was pacing these LSPs too quickly at first, so retransmited LSPs can be paced at a slower timer.
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