[99912] in North American Network Operators' Group
Re: Upstreams blocking /24s? (was Re: How Not to Multihome)
daemon@ATHENA.MIT.EDU (Justin M. Streiner)
Mon Oct 8 20:59:53 2007
Date: Mon, 8 Oct 2007 20:55:19 -0400 (EDT)
From: "Justin M. Streiner" <streiner@cluebyfour.org>
To: nanog@merit.edu
In-Reply-To: <FB24A26E-C81B-4743-BDB9-4937C9D82A83@virtualized.org>
Errors-To: owner-nanog@merit.edu
On Mon, 8 Oct 2007, David Conrad wrote:
> Others have indicated that such filters (assuming they exist) will not last
> in the face of paying customers presenting longer than /24 prefixes for
> routing. Specifically, that ISPs will relax their filters (allowing longer
> than /24) in order to get their peers to accept their long prefixes. Anybody
> have an opinion on the likelihood of this?
The only exceptions I've seen to the /24 policy are when the customer in
question multihomes to the same upstream - sometimes done with a specific
AS designated for that purpose, i.e. what UUNET does with AS7046. Those
routes are then aggregated that provider's parent block(s).
As far as allowing prefixes longer than a /24, that decision was made when
the Internet was considerably smaller than it is now, and many networks
adopted /24 as the cutoff point. If you make the cutoff point smaller,
what is the new point... /26? /32? Many networks see customers
multi-homing as pretty easy justification to provide them with a /24 of PA
space, even if they're small enough that justifying a /24 while
single-homed wouldn't work.
jms
