[40827] in North American Network Operators' Group
Re: Ethernet NAPs (was Re: Miami ...)
daemon@ATHENA.MIT.EDU (RJ Atkinson)
Thu Aug 23 10:35:07 2001
Message-Id: <5.1.0.14.2.20010823102412.01d94dd0@10.30.15.2>
Date: Thu, 23 Aug 2001 10:28:10 -0400
To: jtk@aharp.is-net.depaul.edu
From: RJ Atkinson <rja@inet.org>
Cc: Nanog <nanog@merit.edu>
In-Reply-To: <3B8510A1.B596C9B5@depaul.edu>
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At 10:18 23/08/01, John Kristoff wrote:
>Certainly. In a nutshell, it might be best to take steps to avoid
>fragmentation elsewhere in the network. Perhaps a rule of thumb that
>should be stressed is to use jumbo frames if you know for sure the other
>end system(s) support it, otherwise default to 1500.
Or just use Path MTU Discovery.
For IP traffic that is traversing more than one layer-2 network,
the variety in network technologies (e.g. ATM, SMDS, POS, Radio,
Satellite, other) means that even ~1500 byte IP frames might not
always work end-to-end. For example, I know of several commercial
IP/SATCOM systems that have an MTU of 576 bytes.
Many ISPs, not all, seem to try to engineer an end-to-end MTU
of 4470 (that number chosen for historical reasons relating to FDDI).
Some ISPs use a smaller MTU number and some use a higher MTU number.
Ran
rja@inet.org
