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Community Member

## BGP route dampening

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.

5 REPLIES
Cisco Employee

## Re: BGP route dampening

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,

Harold Ritter
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
México
Community Member

## Re: BGP route dampening

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

Gold

## Re: BGP route dampening

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

Cisco Employee

## Re: BGP route dampening

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
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
México
Cisco Employee

## Re: BGP route dampening

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

Harold Ritter
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez