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Re: /24's run amuck?

  • From: James Aldridge
  • Date: Wed Feb 07 10:59:53 2001

Valdis.Kletnieks@vt.edu wrote:
> 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% ;)

You might want to take a look at the aggregation possibilities I've been
finding at http://www.mcvax.org/~jhma/routing/ (everything there is updated on
a daily basis).  Based purely on origin AS, for any AS where any form of
aggregation could occur, it lists which new aggregates should be announced (in
place of individual specific routes), and which should be withdrawn (your
"useless punchout" case above) or advertised with a different origin (because
all the address space covered is being announced with longer prefixes from
another AS).

Since today, there are also some pretty(?) pictures showing prefix length
distribution from my view of the BGP table.

Regards,
James





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