BGP route dampening

[ziutek]

I have a quesiton regarding route dampening. I understand how the process works, and after a certain penalty threshold is reached, the route is suppressed, and after a certain amount of time the penalty is cut in half, and then un-suppressed if that value is less than the threshold.

Now what I don't understand is does the half-time time start after no route flap has been detected? Or when the route becomes suppressed? If the route is suppressed, and the route continues to flap, does the penalty continue to increase?

Thank you in advance for clarification.

[Harold Ritter]

The half-time takes affect as soon as a penalty has been assigned.

The penalty continues to increase even if the route is suppressed.

Hope this helps,

[ziutek]

So every time there is a flap the half-time timer restarts?

[ruwhite]

Yes, each time a new flap occurs, the timer is reset. It's really a bit more complex than that--the current penalty applied is first decayed, then the new penalty is applies, and then the timer is reset.

:-)

Russ.W

[Harold Ritter]

The IOS decays the penalty every 5 seconds.

So for the first penalty (1000), the following calculation is made to find out how much we should decay on a 5 seconds basis:

(penalty/2)/half-time/12. the half-time value being 15min and the initial penalty being 1000, you endup with the following result:

~2.78 per 5 seconds

If you have another flap another 1000 is added to the remaining penalty and the same calculation has to be reran:

(penalty/2)/half-time/12

Hope this helps,

[Harold Ritter]

Sorry, the decay is actually exponential. Same concept though.