OSPF SPF Scheduling and throttling timers
The OSPF SPF scheduling and throttling feature is used to keep an OSPF topology stable in the event that there is a continuous inflow of LSAs, causing continuous recalculation of the SPF algorithm. This feature uses the following timers and parameters:
spf-startvalue is the the initial time interval to wait before running the SPF algorithm upon recipt of the first updated LSA.
spf-holdvalue is the initial amount of time to wait between one SPF calculation and the next. Every time a new LSA is received before
sfp-holdhas elapsed, this value doubles, so it waits longer before running the SPF calculation again. You can see this clearly in the diagrams in the lesson.
- Now imagine that you keep getting LSAs all the time. This
spf-holdvalue will continue to double. It could potentially continue to double forever, reaching values of several minutes or hours!! This doubling must have a limit, and that's where the
spf-max-waitvalue comes in. The
spf-holdvalue, as it doubles, will hit a maximum of
spf-max-wait, and will not double further, but will remain at that maximum. The original
spf-holdvalue is reset only if
spf-max-waithas elapsed without any new incoming LSAs.