Subject: Re: 802.1Q & ETHER_MAX_LEN
To: Manuel Bouyer <firstname.lastname@example.org>
From: Jasper Wallace <email@example.com>
Date: 10/02/2000 13:18:56
On Sun, 1 Oct 2000, Manuel Bouyer wrote:
> I tested our 802.1Q support with a cisco switch today, and ran into the
> problem mentionned in kern/11109 (I expected to run into this anyway :),
> which is that on a cisco trunk port we can expect to see packets of
> 1522 bytes instead of 1518 (the 4 extra bytes being the 802.1Q tag).
> If we want to be able to talk with others 802.1Q devices we need to solve
> There are several issue here:
> - hardware: does the ethernet adapter supports frames of 1522 bytes ?
> I looked quickly at the tulip and smc83c170 sources and found no way to
> change this, it looks like the 1518 bytes values is hardcoded in hardware.
> Does anyone know if there are (10/100) ethernet chips that can send/receive
> frames bigger than the standart len ?
fxp's can, the older ones can be told to ignore large frames, and newer ones
can fo hardware vlan tagging/detagging.
It's the same for recent 3com cards.
Patches for both (for freebsd) are here:
http://pointless.net/ : Another Great waste of bandwidth!
http://advogato.com/ : nothing to do with me, but worth a look.
http://www.ivision.co.uk/ : I pretend to work for these people.
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