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Date:      Wed, 5 Jul 2000 09:20:53 -0400 (EDT)
From:      David Gilbert <dgilbert@velocet.ca>
To:        tim@iafrica.com.na
Cc:        David Gilbert <dgilbert@velocet.ca>, Kevin Oberman <oberman@es.net>, "Louis A. Mamakos" <louie@TransSys.COM>, Joerg Micheel <joerg@cs.waikato.ac.nz>, freebsd-stable@FreeBSD.ORG
Subject:   Re: Ethernet MTUs > 1500?
Message-ID:  <14691.13877.728401.523160@trooper.velocet.net>
In-Reply-To: <39632E3D.1E1258A@polytechnic.edu.na>
References:  <200007040508.BAA59763@whizzo.transsys.com> <200007042325.e64NPCn20451@ptavv.es.net> <14690.37799.546582.824877@trooper.velocet.net> <39632E3D.1E1258A@polytechnic.edu.na>

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>>>>> "Tim" == Tim Priebe <tim@polytechnic.edu.na> writes:

Tim> David Gilbert wrote:
>>  >>>>> "Kevin" == Kevin Oberman <oberman@es.net> writes:
>> 
Kevin> Louis has it exactly right. 802.3 was modified a couple of
Kevin> years ago to allow for a maximum frame size of 1522 octets, up
Kevin> from the original 1518. This was to allow the VLAN information
Kevin> to fit in the frame.

Tim> Exactly, my point also we must update our code to conform to the
Tim> new standard.

This is all I'm looking for, really.  When you configure vlan support
in FreeBSD, all the interfaces come up with 1496 byte MTUs.  I suppose 
I don't really care what the IP MTU of the ethernet port is --- I just 
want a 1500 byte MTU on the vlan.  I'm even willing to buy new
ethernet ports (although the Intel 21143-based 4 port cards have
worked well in the past for me).

The problem is that chaging the MTU on windoze based boxes (my
customers) is problematic.  Even changing the MTU on some BSD network
interfaces is not easy.  I suppose this means that my MRU is low,
too...

But the problem here is also that path MTU discovery is somewhat
broken on the internet and this low-MTU service is a pain for
customers.

Dave.

-- 
============================================================================
|David Gilbert, Velocet Communications.       | Two things can only be     |
|Mail:       dgilbert@velocet.net             |  equal if and only if they |
|http://www.velocet.net/~dgilbert             |   are precisely opposite.  |
=========================================================GLO================


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