[30133] in North American Network Operators' Group
Re: RFC 1918
daemon@ATHENA.MIT.EDU (Bennett Todd)
Sun Jul 16 12:33:12 2000
Date: Sun, 16 Jul 2000 12:29:39 -0400
From: Bennett Todd <bet@rahul.net>
To: North America Network Operators Group Mailing List <nanog@merit.edu>
Message-ID: <20000716122939.C578@oven.com>
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In-Reply-To: <20000714200630.A29379@eiv.com>; from smcmahon@eiv.com on Fri, Jul 14, 2000 at 08:06:30PM -0400
Errors-To: owner-nanog-outgoing@merit.edu
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2000-07-14-20:06:30 Shawn McMahon:
> On Fri, Jul 14, 2000 at 07:42:08PM -0400, Greg A. Woods wrote:
> > Unfortunately an increasing number of Internet users, with servers I
> > might add, are now behind DSL lines that have <1500-byte MTUs.....
> [...]
> So what are we going to do, folks; are we going to react to people
> who are in this situation by saying "oh, well; guess I'm walled
> off from you, too bad, so sad, dump that $50 connection and get a
> T1 or get off my Internet", or are we going to adapt?
What kind of adaptation is necessary?
Traditionally that sort of thing hasn't been a problem; that's what
fragmentation is for.
If Path MTU Discovery is working it's even less of a problem: if
there's a link MTU in the middle of a path that's smaller than the
MTUs of the final links at each end, then Path MTU Discovery will
find out and adjust the session MTU to fit.
The only place where this is a problem is where people are trying to
run Path MTU Discovery, and so have servers that are initiating
sessions with packets with the Don't Frag bit set, and then have
firewalls or load balancers or something blocking the ICMP Must Frag
error returns.
And to haul this back to the original thread, I've still heard no
claim made that there's an operational problem introduced by using
RFC 1918 addrs for endpoints of router-router links where neither
router routes traffic over interfaces with different MTUs.
If people don't want whiners niggling them about the RFC 1918 addrs
showing up in traceroutes, they should just put RFC 1918 filters on
their borders, so that the whiners simply won't get returns to their
traceroutes.
-Bennett
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