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Re: The Big Squeeze

  • From: Sean Donelan
  • Date: Tue Mar 04 11:42:45 1997

>To back Paul up here..
>Tests we have run would indicate that this is not _generally_ the case.
>I guess it depends on your point of viewing but we certainly see an
>inordinate amount of oscillation in the longer prefix ranges.
>(It also depends on the parameters you associate with certain prefixes of 
>course ;-)
>(Sorry - no facts and figures to back that up)

It also depends on how you mentally group things.  I agree, there are a
few prefixes that have an inordinate amount of oscillation.   But what
group membership would I assign them?  I've noticed more recently assigned
network numbers seem to flap more than older network numbers.  Perhaps
more importantly, networks in more recently assigned AS numbers seem to
flap more.  Again, this is just raw observations, no real numbers to back
up my feelings.  Don't let the way "show ip bgp flap" happens to group
networks by prefix control your mental schema.

I would much rather see the decision based on how any individual route
behaves rather than the 'neighborhood' the network happens to be located
in.  We might be willing to give a network that has been stable for a
long time a few extra flaps.  While brand new networks that flap would be
better off being 'covered' by a shorter, more stable prefix.

Is the goal to encourage stable routes? or encourage short prefixes?

>For instance, take this snapshot and note the /24 from within the 153.96 
>network.  The flap column is the interesting one compared with other class Bs.
>This is not representative but gives a flavour of what we have been seeing.
>
>They are all from the same originator and it would not take a great amount 
>of effort to apply a null0 tie down !

Or even aggregate them.  But you bring up an important point.  Often all
the routes from the same originator flap together, irregardless of their
prefix length.
-- 
Sean Donelan, Data Research Associates, Inc, St. Louis, MO
  Affiliation given for identification not representation
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