Subject: Re: 802.1Q & ETHER_MAX_LEN
To: Jason R Thorpe <firstname.lastname@example.org>
From: Manuel Bouyer <email@example.com>
Date: 10/03/2000 17:29:34
On Tue, Oct 03, 2000 at 07:17:33AM -0700, Jason R Thorpe wrote:
> On Tue, Oct 03, 2000 at 03:12:10PM +0200, Manuel Bouyer wrote:
> > Is there other case where we need something like this (different MTU at
> > the hardware level depending on the frame type) ? If not maybe we could just
> > hack something simpler: change ifnet (or maybe, really if_data) to include
> > the max frame length the HW can do; which may be bigger than
> > if_mtu + if_hdrlen. Then extra encap layers such as 802.1Q can use it to
> > recompute a MTU. Anyway we won't be able to have a completely clean separation
> > between 802.1Q and ethernet.
> How is this problem really any different than e.g. FDDI using a different
> MTU for IP than it does for anything else?
How is this handled ?
The difference I can see if that, with fddi, we know the max len; for IP and
for anything else. In our case, the driver needs to inform if_vlan whenever
it can do 1522 or only 1518. Not all ethernet boards can do 1522.
Manuel Bouyer, LIP6, Universite Paris VI. Manuel.Bouyer@lip6.fr