Dampening considered harmful? (Was: Re: verizon.net and other email grief)

Thu Dec 16 23:42:21 UTC 2004

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.)