For IS-IS , when the LSDB is changed, SPF calculation is required. However, if the SPF calculation is performed too frequently, the system efficiency will be lowered and a great number of resources on the system will be occupied. To delay SPF calculation can improve route calculation efficiency to some degree. On the other hand, if the delay time for route calculation is too long, the route convergence becomes slow.
To accelerate the route convergence speed and not to affect the efficiency of routers, the intelligent timer is used during the SPF calculation. The intelligent timer can adjust the delay time according to the change frequency of the LSDB.


The initial delay time for SPF calculation is init-interval. The delay time for the SPF calculation the second time is incr-interval. When the routes change each time, the delay time for SPF calculation is twice as the previous value until the delay time reaches max-interval. After the delay reaches max-interval for three times or the IS-IS process is reset, the delay time is reduced to init-interval.
When incr-interval is not used and the SPF calculation is performed for the first time, init-interval is used as the initial delay time for SPF calculation. Then, the delay time for SPF calculation is max-interval. After the delay reaches max-interval for three times or the IS-IS process is reset, the delay time is reduced to init-interval.


When only max-interval is used, the intelligent timer becomes an one-short triggered timer.


Example:

Set the SPF calculation delay to 5s

[SAVAR_NE40E] isis 

[SAVAR_NE40E-isis-1] timer spf 5

Set the maximum SPF calculation delay to 15s, the initial delay to 10 ms and the ascending delay to 5000 ms.

[SAVAR_NE40E] isis 

[SAVAR_NE40E-isis-1] timer spf 15 10 5000

good post

useful document, thanks