[99913] in North American Network Operators' Group
Re: Upstreams blocking /24s? (was Re: How Not to Multihome)
daemon@ATHENA.MIT.EDU (Jon Lewis)
Mon Oct 8 21:24:45 2007
Date: Mon, 8 Oct 2007 21:19:22 -0400 (EDT)
From: Jon Lewis <jlewis@lewis.org>
To: nanog@merit.edu
In-Reply-To: <Pine.LNX.4.64.0710082048420.29005@whammy.cluebyfour.org>
Errors-To: owner-nanog@merit.edu
On Mon, 8 Oct 2007, Justin M. Streiner wrote:
> 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?
Anything longer than /24 is unlikely to propogate far on the internet.
You can all check your filters to see. I just checked mine, and neither
Level3 nor Time Warner has tried to send me anything longer than /24 in
recent history. If they did, it'd show up as hits on a distribute-list
deny rule.
Rather than ISPs relaxing filters, you're likely to see them get more
strict, filtering shorter prefixes, when routers start falling over in the
next few months.
> 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.
This is actually in the ARIN "rules". Multihoming is justification
(regardless of utilization) for one of the multihomed network's providers
to assign them a /24.
----------------------------------------------------------------------
Jon Lewis | I route
Senior Network Engineer | therefore you are
Atlantic Net |
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