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Re: The Cidr Report

  • From: Tony Li
  • Date: Mon Aug 17 23:47:12 1998

> > | AS762        118       81       37   31.4%   WELLFLEET-AS
> 
> Oddly enough, they are announcing the aggregate *and* the specifics:
> 
> 
> brd1>sho ip bgp reg _762_
> *> 192.32.0.0/16    207.106.96.5                         0 4969 6461 1673
> *> 192.32.2.0       207.106.96.5                         0 4969 6461 1673
> *> 192.32.3.0       207.106.96.5                         0 4969 6461 1673
> *> 192.32.4.0       207.106.96.5                         0 4969 6461 1673
> *> 192.32.6.0       207.106.96.5                         0 4969 6461 1673


If one were paranoid, one might imagine that they are doing so
intentionally to see how many Cisco routers they can tank through prefix
overload.  The problem with this is that a) they aren't also announcing the
/17's, /18's, ... /25's and b) overloading a Cisco seems to mean that
someone buys a bigger Cisco, thereby enhancing Cisco's revenue stream.

One is then left with the theory that they are advertising more specifics
for optimality, but haven't discovered communities yet.

Exercise for the reader: If prefixes of length F and longer are filtered,
and a domain has a prefix of length N, how many prefixes can they propagate
into the backbone?  How many before people start proxy aggregating them?

Tony





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