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Configuring SPF Options for IS-IS

You can configure the following shortest-path-first (SPF) options:

The delay in the time between the detection of a topology change and when the SPF algorithm actually runs.
The maximum number of times that the SPF algorithm can run in succession before the hold-down timer begins.
The time to hold down, or wait, before running another SPF calculation after the SPF algorithm has run in succession the configured maximum number of times.

To configure SPF options, include the spf-options statement:




spf-options {
delay milliseconds;
holddown milliseconds;
rapid-runs number;
}

To configure the SPF delay, include the delay statement when specifying the spf-options statement:



delay milliseconds;

By default, the SPF algorithm runs 200 milliseconds after the detection of a topology change. The range that you can configure is from 50 through 1000 milliseconds.

To configure the maximum number of times that the SPF algorithm can run in succession, include the rapid-runs statement when specifying the spf-options statement:



rapid-runs number;

The default number of SPF calculations that can occur in succession is 3. The range that you can configure is from 1 through 5. Each SPF algorithm is run after the configured SPF delay. When the maximum number of SPF calculations occurs, the hold-down timer begins. Any subsequent SPF calculation is not run until the hold-down timer expires.

To configure the SPF hold-down timer, include the holddown statement when specifying the spf-options statement:



holddown milliseconds;

The default is 5000 milliseconds, and the range that you can configure is from 2000 through 10,000 milliseconds. Use the hold-down timer to hold down, or wait, before running any subsequent SPF calculations after the SPF algorithm runs for the configured maximum number of times. If the network stabilizes during the hold-down period and the SPF algorithm does not need to run again, the system reverts to the configured values for the delay and rapid-runs statements.

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