[76587] in North American Network Operators' Group
Re: Dampening considered harmful? (Was: Re: verizon.net and other email grief)
daemon@ATHENA.MIT.EDU (Iljitsch van Beijnum)
Thu Dec 16 18:43:09 2004
In-Reply-To: <a06200709bde7c21b287a@[65.199.121.152]>
Cc: nanog@merit.edu
From: Iljitsch van Beijnum <iljitsch@muada.com>
Date: Fri, 17 Dec 2004 00:42:21 +0100
To: Jerry Pasker <info@n-connect.net>
Errors-To: owner-nanog-outgoing@merit.edu
On 17-dec-04, at 0:21, Jerry Pasker wrote:
>> ie: does dampening cause more problems than it tries to solve/avoid
>> these days.
> I don't know what takes more router resources; dampening enabled
> doing the dampening calculations, or no dampening and constantly
> churning the BGP table. I would assume dampening generally saves
> router resources, or operators wouldn't chose to enable it.
I generally don't use dampening in most setups, and continuous churning
is rare these days, as far as I can tell. I seem to remember that it
was mostly caused by bad implementations in the days that it was a big
issue.
The trouble with dampening is that it only works on stuff that happens
beyond the routers your AS talks to. When your neighbors or your own
stuff flap you don't get to dampen that. So I guess it's still useful
for large networks that have a significant number of views on the same
stuff, but it's not really worth the trouble for smaller networks.
One reason to be careful with dampening is that flaps can be
multiplied. (Connect to routeviews and see the different flap counts
under different peers for the same flap at your end to observe this.)
