[75824] in North American Network Operators' Group
MTU (was Re: ULA and RIR cost-recovery)
daemon@ATHENA.MIT.EDU (Alex Bligh)
Thu Nov 25 09:06:00 2004
Date: Thu, 25 Nov 2004 14:05:25 +0000
From: Alex Bligh <alex@alex.org.uk>
Reply-To: Alex Bligh <alex@alex.org.uk>
To: Michael.Dillon@radianz.com, NANOG@merit.edu
Cc: Alex Bligh <alex@alex.org.uk>
In-Reply-To: <OFB63B354D.95E7BB1E-ON80256F57.00486F41-80256F57.0048F126@radianz.com>
Errors-To: owner-nanog-outgoing@merit.edu
--On 25 November 2004 13:16 +0000 Michael.Dillon@radianz.com wrote:
> In today's network, is there anyone left who uses 1500 byte
> MTUs in their core?
I expect there are quite a few networks who will give you workable
end-to-end MTU's >1500 bytes, either because of the above or because of
peering links.
Given how pMTUd works, this speculation should be relatively easy to test
(take end point on >1500 byte MTU, run traceroute with appropriate MTU to
various points and see where fragmentation required comes back). Of course
I'd have tried this myself before posting, except, urm, I can't find a
single machine I have root on that I can get more than a hop or two from
without running into 1500 byte (or less) MTU.
I am guessing also that a recent netflow sample from a commercial core (not
Internet2), even with jumbo frames enabled, will show <0.01% of packets
will not fit in 1500 byte MTU. Anyone have data?
Alex
