Tuning the SPF calculation timer
The SPF calculation timer sets the delay between consecutive SPF calculations. You can decrease the timer for ISIS-SPB to react quickly to topology changes, and decrease the timer to protect the CPU from frequent SPF calculations.
The SPF timer is an exponential generation timer. With this timer, ISIS-SPB quickly responds to the first events that trigger SPF calculation, and then slows down to protect the CPU from frequent SPF calculations.
The SPF calculation timer value is derived from three parameters: minimum wait time (minimum-interval), base number for incremental wait time (incremental-interval), and maximum wait time (maximum-interval).
When the network is stable, the SPF calculation timer is set to the minimum wait time for each SPF computation. When the network is unstable, the SPF calculation timer increments by incremental-interval×2n-2 (n is the number of calculations) for each SPF calculation until the maximum wait time is reached. If an event triggers SPF calculation after the maximum wait time is reached, the SPF calculation timer re-initiates with the minimum wait time.
![[NOTE: ]](images/note.png) | NOTE: The network is considered unstable if the interval between consecutive SPF calculations is smaller than two times the maximum wait time. | |
To tune the SPF calculation timer:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter SPBM view. | spbm | N/A |
3. Set the SPF calculation exponential backoff timers. | timer spf maximum-interval [ minimum-interval [ incremental-interval ] ] | Default values for the SPF calculation timer parameters:
The minimum interval and the incremental interval must be shorter than the maximum interval. |