Friday, November 30, 2012

OSPF Fast Convergence Tools - Event Propagation

In continuation to my previous post about OSPF Fast Convergence – Event Detection, I will share my ideas about OSPF Event Propagation tool. Event propagation mainly covers LSA generation process. Once the event has been detected, LSA is generated to reflect the change. LSA is not generated immediately; OSPF waits 5000 msec until generating new LSA. This is only used for Router and Network LSA.

To get OSPF faster convergence(Read More About OSPF High Availability), LSA’s can be rate limited. This will increase OSPF convergence time.

Below is the command line to configure LSA throttling
router ospf 10
timers throttle lsa all (start) (hold) (max)
timers lsa arrival

start:[default = 0 ms] Default is to generate LSA immediately after receiving first trigger.
Recommended = 10 ms

hold : [default = 5000 ms] Small increments of 20ms should be considered if multiple link failures may occur on same router. This ensures if all failures have not been advertised by first regenerated LSA, following one will be promptly triggered.
Recommended = 100 ms

max : [default = 5000 ms] Default value may be kept unchanged. Prior to introduction of LSA throttle timer, bevahior was to wait MinLSInterval between distinct originations of any particular LSA with default MinLSInterval = 5s. Default value provides response equivalent to pre LSA-throttle.
Recommended = 5000ms

timer: [default 1000 ms] This controls minimum interval for accepting the same LSA. “Same LSA" is defined as an LSA instance containing same LSA ID, LSA type, and advertising router ID. If an instance of same LSA arrives sooner than interval that is set, LSA is dropped.
Recommended = 80 ms

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