The Big Squeeze

> When dampening was first being rolled out I remember one of the early
> networks that got hit was PSI's net 38/8. Treating flapping prefixes
> differently based on length has more to do with how many people scream
> when prefixes covering a large amount of address space get dampened
> than the impact of the route flap of an individual prefix on the router.

Also, it is thought that longer prefixes tend to flap more than shorter.


Sean has a good point here. A flap of a /8 is the same as a flap of a /24
from a computational point of view. There is clearly some social engineering
going on here. If you want your long prefix to be golbally visable and you
allow it to flap, then you will be subject to dampening. On the other hand
if you renumber into a larger aggregate, then you are protected from dampening
(to a greater degree). Kind of a 'carrot and stick' approch. :slight_smile:


Computational power required for a route flap is not the issue here.

Many people have stated that, statistically longer prefixes flap
more. Unfortunately, they have then said that because of this shorter
prefixes should have looser dampening parameters put on them, when
what they really meant was that the longer prefixes should have more
strict dampening parameters put on them. Yes it is exactly the same
thing, but it is an important semantic distinction. If a group of
prefixes categorized by a its length tends to flap more than the
average, then said group should have more strict dampening parameters
placed on it.