North American Network Operators Group

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Re: /24's run amuck?

  • From: Valdis.Kletnieks
  • Date: Wed Feb 07 00:07:26 2001

On Tue, 06 Feb 2001 15:07:10 MST, Danny McPherson <danny@ambernetworks.com>  said:
> > Umm... because if you filter the /24s you will remove 58K of 95K,
> > or some 61%.  I'm *sure* that having a routing table 40% of the original
> > size will help the next time you have a BGP flap.
> 
> Of course, some attentive customers MAY notice reachability issues 
> with those 58K prefixes, but no big deal, at least the routing table 
> is smaller.  Heck, might as well go ahead and filter /23 and longer, 
> that'll loss another ~10K, or better yet... :-)

Hey, I *said* your milage may vary. ;)

And now for the *tough* question - of those 58K /24's, how
many could be eliminated by more careful aggregation and filtering?
I'm willing to bet that at least 25% are sites that have
two connections to their provider, and are therefore advertised
within the provider's net, and are simply escaping due to 
misconfiguration at the border.

So - who wants to crunch the numbers and figure out how many
of those 58K are useless punchouts ("Route all of 128.257.x.x
to me, except for 128.257.219.x, which also goes to me")....

Bonus points for identifying the AS that covers the greatest
percentage of its address space with aggregable punchouts
(although I'm willing to bet that there's some offenders out
there with greater than 100% ;)

				Valdis Kletnieks
				Operating Systems Analyst
				Virginia Tech