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BGP Route Dampening ?

Hi,

Under default conditions, if a route flaps twice incurring a penalty of 2000 will the router wait 30 minutes before it advertises the route again ?

I am thinking it will, since after 15 mins (half-life) the route penalty will be reduced to 1000 which is above the reuse limit of 750, and so another half-life (15 mins) will need to elapse before the penalty is reduced to 500 which is below the reuse limit.

Just need confirmation that my thinking is correct.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: BGP Route Dampening ?

Hi, not quite.

The point is: while the path is removed and then announced (1st flap) and then removed and announced again (2nd flap) the penalty will already be decreasing with half time. so two flaps in a real environment will give you less than 2000 accumulated penalty after 2nd flap. Only the third flap takes you out of business.

By the way RIPE discurrages route flap dampening now, which means ISPs should turn it off (RIPE-338).

Hope this helps! Please rate all posts.

Regards, Martin

1 REPLY

Re: BGP Route Dampening ?

Hi, not quite.

The point is: while the path is removed and then announced (1st flap) and then removed and announced again (2nd flap) the penalty will already be decreasing with half time. so two flaps in a real environment will give you less than 2000 accumulated penalty after 2nd flap. Only the third flap takes you out of business.

By the way RIPE discurrages route flap dampening now, which means ISPs should turn it off (RIPE-338).

Hope this helps! Please rate all posts.

Regards, Martin

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