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

Tue Dec 21 08:16:21 UTC 2004

>Well, a particular router doesn't get to set its dampening according 
>to its 'view' today, and that view is going to vary depending on 
>prefix.
>
>I would like to argue that how we define flapping today is simply a 
>broken concept.  We count up/down/path change transitions, but such 
>transitions can exist due to connectivity or implementation 
>differences and may have nothing to do with not complying with 
>ettiquette.

If people were damped for a single up/down, then yes, that's a 
problem.  Dampening someone because they have a single path change is 
not the idea.  That would sort of nullify the spirit of being 
multihomed with BGP, or even using BGP in any production or transit 
network for that matter.

IF there's a connection problem, or implementation difference that 
makes a lot of up/down, then dampening could occur close to the 
"problem" but it will be contained close, and won't spread to the 
rest of the internet.

>I submit that a better way of measuring flap is to look at the 
>period over which a particular prefix is flapping.  Anti-social 
>behavior is many changes occurring over long periods of time. 
>However, many changes over a short period may well not be a problem.
>
>Regards,
>Tony
>

So configure your route dampening that way.  No one's twisting your 
arm to use the defaults. Want many flaps in the short term to not be 
damped?  Simply increase your suppress limit.  Way way up.   Increase 
or decrease your half-life as you see fit.  Just don't expect the 
rest of the world to do the same.  But do expect to see others damp 
the flapping that you leak to their network.

<gut feeling> If no one on the net ran dampening, routers wouldn't 
get anything done except processing constant churn. </gut feeling> 
I'm grateful that routers out there in the world are doing route-damp 
so my router's CPU doesn't have to deal with needless route-churn, 
even if it does impact my connectivity (to poorly connected) end 
sites somewhat.  The stability is worth it.

Another item to consider, is this is a sentence from RFC2439 " By 
damping their own routing information, providers can reduce their
    own need to make requests of other providers to clear damping state
    after correcting a problem."

Using that logic,  I'm also grateful for my transit providers 
dampening the advertisements to their peers, of my flapping transit 
links to them.  That way, when they flap, (hey, it happens to 
everyone eventually) it doesn't get me damped by the rest of the 
internet, and my connections to different transit providers can do 
their job of carrying the traffic.

Dampening, in it's current state, really is a good idea.

-Jerry