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Date:      Tue, 4 Jul 2000 00:37:44 -0400 (EDT)
From:      David Gilbert <dgilbert@velocet.ca>
To:        "Louis A. Mamakos" <louie@TransSys.COM>
Cc:        David Gilbert <dgilbert@velocet.ca>, Joerg Micheel <joerg@cs.waikato.ac.nz>, freebsd-stable@FreeBSD.ORG
Subject:   Re: Ethernet MTUs > 1500? 
Message-ID:  <14689.27160.907313.347624@trooper.velocet.net>
In-Reply-To: <200007040353.XAA03131@whizzo.transsys.com>
References:  <14689.22689.894466.908666@trooper.velocet.net> <20000704153914.C60136@cs.waikato.ac.nz> <14689.23903.87264.511506@trooper.velocet.net> <200007040353.XAA03131@whizzo.transsys.com>

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>>>>> "Louis" == Louis A Mamakos <louie@TransSys.COM> writes:

Louis> There's some confusion here, because the MTU is typically
Louis> associated with a protocol stack like IP and refers to the
Louis> largest sized (IP in this case) packet that can be sent on the
Louis> network interface.  In the case of Ethernet interfaces that
Louis> support and use VLAN tags, the MTU is still 1500 bytes,
Louis> regardless of the fact that the frame size is a few bytes
Louis> longer to accomodate the VLAN tag information.

Louis> So, this has no effect on the Ethernet type field (or 802.3
Louis> length fields) since the higher level protocol packet size is
Louis> unchanged.

Why, then, are the vlan MTUs hardwired at 1496?

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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