Setting the SPF Calculation Interval

To improve the fault location efficiency on an IS-IS network and prevent SPT calculation from consuming excessive system resources, set the SPF calculation interval to a proper value.

Context

A network change can trigger IS-IS to perform SPT calculation. Frequent SPT calculation will consume excessive CPU resources, affecting services.

To solve this problem, configure an intelligent timer to control the SPT calculation interval. For example, to speed up IS-IS route convergence, set the interval for SPT calculation to a small value, and set the interval to a large value after the IS-IS network becomes stable.

Procedure

Run system-view
The system view is displayed.
Run isis [ process-id ]
The IS-IS view is displayed.
Run timer spf max-interval [ init-interval [ incr-interval ] ]
The SPT intelligent timer is configured.
The delay for SPF calculation is described as follows:
- The delay for the first SPF calculation is init-interval; the delay for the second SPF calculation is incr-interval. From the third time on, the delay for SPF calculation doubles each time until the delay reaches max-interval.If network flapping persists within the max-interval period, max-interval is used as the delay for SPF calculation. If network flapping does not occur within the max-interval period or if the IS-IS process is restarted, init-interval is used as the delay for SPF calculation.
- If incr-interval is not specified, the delay for SPF calculation for the first time is init-interval. From the second time on, the delay is max-interval. If the local routing information keeps being updated within the max-interval period, the delay remains at max-interval until the time the local routing information is not updated within the max-interval period or the IS-IS process is restarted. Then the delay decreases to init-interval.
- When only max-interval is specified, the intelligent timer functions as an ordinary one-time triggering timer.
Run suppress-flapping route-calculate timer delay-interval [ threshold threshold-value ]
Run timer purge-zero-lsp route-calculate-delay delay-interval
Run commit
The configuration is committed.