Dampening is done on the eBGP router where the route enters the AS, and, unless I'm mistaken, per route/path and not per prefix. So the flapping that ISP A sees from ISP B is a completely seperate thing from the flapping that ISP A sees from its customer's customer as far as the dampening algorithm is concerned.
Nope. It's per-prefix. Have a look at the pointer Randy provided. I think one of the section of RFC 2439 alludes to this as well. -danny
On Wed, 12 Mar 2003, Danny McPherson wrote:
Dampening is done on the eBGP router where the route enters the AS, and, unless I'm mistaken, per route/path and not per prefix. So the flapping that ISP A sees from ISP B is a completely seperate thing from the flapping that ISP A sees from its customer's customer as far as the dampening algorithm is concerned.
Nope. It's per-prefix.
If that is the case then dampening is severely broken, because then a router that receives a prefix over two paths will lose *both* if _one_ flaps. In any case, it is done on the eBGP router receiving the prefix/route, so unless the two ISPs in question peer using the same router as they use to connect to Jack's AS, there still shouldn't be any flapping multiplication. (Hm, unless that happened inside Jack's network...?) Iljitsch
From: "Iljitsch van Beijnum"
Nope. It's per-prefix.
If that is the case then dampening is severely broken, because then a router that receives a prefix over two paths will lose *both* if _one_ flaps.
Which makes me wonder what happens when one of my BGP peers is flapping and the other is holding stable with an AS prepend on it.
In any case, it is done on the eBGP router receiving the prefix/route, so unless the two ISPs in question peer using the same router as they use to connect to Jack's AS, there still shouldn't be any flapping multiplication. (Hm, unless that happened inside Jack's network...?)
My network is too simplistic to have flapping multiplication. The only difference between the customers routes and my own are that I do an AS prepend on all my networks going out to one of my peers so that the peer only sends customer traffic to me and serves as a last resort, while my customers routes out all peers without modification. -Jack
participants (3)
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Danny McPherson -
Iljitsch van Beijnum -
Jack Bates