[95983] in North American Network Operators' Group
Re: Thoughts on increasing MTUs on the internet
daemon@ATHENA.MIT.EDU (Randy Bush)
Thu Apr 12 15:34:00 2007
From: Randy Bush <randy@psg.com>
Date: Thu, 12 Apr 2007 09:28:09 -1000
To: NANOG list <nanog@merit.edu>
Errors-To: owner-nanog@merit.edu
mark does not have posting privs and has asked me to post the
following for him:
---
To: Gian Constantine <constantinegi@corp.earthlink.net>
From: Mark Allman <mallman@icir.org>
cc: NANOG list <nanog@merit.edu>
Subject: Re: Thoughts on increasing MTUs on the internet
Date: Thu, 12 Apr 2007 11:47:35 -0400
Folks-
> I agree. The throughput gains are small. You're talking about a
> difference between a 4% header overhead versus a 1% header overhead
> (for TCP).
This does not begin to reflect the gain. Check out the model of TCP
performance given in:
M. Mathis, J. Semke, J. Mahdavi, T. Ott, "The Macroscopic Behavior of
the TCP Congestion Avoidance Algorithm", Computer Communication Review,
volume 27, number3, July 1997.
(number 35 at http://www.psc.edu/~mathis/papers/index.html)
The key point is that performance is directly proportional to packet
size. So, an increase in the packet size is much more than a simple
lowering of the overhead.
In addition, the newly published RFC 4821 offers a different way to do
PMTUD without relying on ICMP feedback (essentially by trying different
packet sizes and trying to infer things from whether they get dropped).
A good general reference to the subject of bigger MTUs is Matt Mathis'
page on the subject:
http://www.psc.edu/~mathis/MTU/
allman
--
Mark Allman -- ICIR/ICSI -- http://www.icir.org/mallman/
