[Xorp-users] Xorp delayed actions

[Hasso Tepper]

Atanu Ghosh wrote:
> As a general principle in our routing protocol implementations we have
> tried to react immediately to a protocol packet (or other event)
> signalling a topology change. The one exception at the moment is OSPF,
> which, when it notices a topology change schedules a full routing
> computation to take place in 5 seconds (perhaps 1 second would be
> better choice).

Sure, and subsecond would be even better. Actually adaptive timers should 
be really used in modern link state protocol implementation. IOS and 
Junos took different approaches with SPF timers.

IOS uses exponential algorithm described in 
http://www.cisco.com/en/US/products/sw/iosswrel/ps1838/products_feature_guide09186a0080134ad8.html

Junos has taken much simpler approach. Only initial SPF interval is 
configurable - 50..1000 milliseconds (200ms by default). If there have 
been three sequential SPF runs with minimal delay (=> topology is 
unstable), Junos switches to 5 seconds spf delay (not configurable). If 
there have been no SPF run during 20 seconds (=> topology is stable 
again), Junos switches back to fast spf delay. 

I hope this helps.


-- 
Hasso Tepper