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From: David Gilbert <dgilbert@velocet.ca>
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Date: Thu, 17 Apr 2003 21:10:31 -0400
To: Brooks Davis <brooks@one-eyed-alien.net>
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Subject: Re: vlan0 on em0 has mtu 1496
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>>>>> "Brooks" == Brooks Davis <brooks@one-eyed-alien.net> writes:

Brooks> On Thu, Apr 17, 2003 at 08:13:55PM -0400, David Gilbert wrote:
>> Why does a vlan created against em0 have a mtu of 1496.

Brooks> Because the vlan header takes up 4 bytes.  With em(4) devices
Brooks> it looks like fixing that should be a simple matter of raising
Brooks> the real interface's MTU to 1504.

On many cards, like the fxp, the ability to send 1526 byte packets
(which include vlan) is encoded in the header size abilities of the
card, not the mtu.  It would seem that em is missing this.

Dave.

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