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:
- The
spf-start
value is the the initial time interval to wait before running the SPF algorithm upon recipt of the first updated LSA. - The
spf-hold
value is the initial amount of time to wait between one SPF calculation and the next. Every time a new LSA is received beforesfp-hold
has 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-hold
value 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 thespf-max-wait
value comes in. Thespf-hold
value, as it doubles, will hit a maximum ofspf-max-wait
, and will not double further, but will remain at that maximum. The originalspf-hold
value is reset only ifspf-max-wait
has elapsed without any new incoming LSAs.
In addition to throttling, it is also possible to configure OSPF update pacing timers.
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