North American Network Operators Group
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Re: RIPE "Golden Networks" Document ID - 229/210/178

  • From: Deepak Jain
  • Date: Thu Sep 02 15:21:14 2004 


        Is bgp dampening really necessary anymore?  Obviously we should
dampen people that flap a high number of times in an hour, but the vast
majority of the internet operates in a state where dampening  causes more
pain than benifit, imho.


I agree with your line of reasoning. However, if you follow the RIPE document's guidelines [ included below for reference ]...

I don't fundamentally have a problem with any of it. 4 flaps before you start dampening in a time window is a lot of flapping. Which means you are flapping that prefix throughout your internal network views as well * the number of distributed forwarding line cards you have, etc, etc. Its not necessarily a good thing to leave unmanaged, no matter how slightly.

I don't know if everything needs to be stable for an hour when it takes 4 flaps to bring the wrath of dampening on it in the first place though.

Maybe 15-20 minutes of stability on the high end (/24 and longer prefixes). If someone flapped every 30 minutes or so, while not ideal, its certainly not causing wide-spread network failures and its keeping you from blackholing a good chunk of their traffic.

I think the idea harkens to a day when coming up with 100% of your sessions & recalcs could bring your router down as traffic started to flow. So dampening helped you and everyone else stabilize before significant amounts of traffic started flowing through the 2500, 3600, AGS or whathaveyou. Clearly this isn't really the case anymore. If your router needs to protect itself from the big-bad-bgp sessions of its more powerful upstream routers, it can dampening more aggressively.

Just my opinion,

Deepak Jain
AiNET

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2.2 Description of recommended damping parameters

Basically the recommended values do the following with harsher treatment
for /24 and longer prefixes:

* don't start damping until the 4th flap
* /24 and longer prefixes: max=min outage 60 minutes
* /22 and /23 prefixes: max outage 45 minutes; min outage of 30 minutes
* all other prefix lengths: max outage 30 minutes; min outage 10 minutes

If a specific damping implementation does not allow configuration of
prefix-dependent parameters the least aggressive set should be used:

    * don't start damping before the 4th flap in a row
    * max outage 30 minutes; min outage 10 minutes

Sample configurations for different vendors are referenced in Appendix A.2.
These samples can be used as a basis for a configuration on other router
platforms not listed there.