Date: Thu, 3 Feb 2000 15:04:29 -0500 (EST) From: "Matthew N. Dodd" <winter@jurai.net> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: "Pedro J. Lobo" <pjlobo@euitt.upm.es>, freebsd-net@FreeBSD.ORG Subject: Re: 802.1Q VLANs Message-ID: <Pine.BSF.4.21.0002031454550.479-100000@sasami.jurai.net> In-Reply-To: <200002031847.NAA62013@khavrinen.lcs.mit.edu>
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On Thu, 3 Feb 2000, Garrett Wollman wrote:
> No, you've got it the wrong way 'round.
>
> If the interface driver is written to be able to accept 1500-byte
> frames with an 18-byte header (as opposed to the ``normal'' 14-byte
> header), it needs to inform the upper layers of this by setting its
> advertised header length (ifi_hdrlen) to 18 rather than 14. The
> driver should always do this, if the hardware is capable, so that
> those frames will be made available to bpf.
Humm... Isn't this going to confuse BPF when its receiving normal
ethernet headers?
Regardless, any further effort on my part for the VLAN driver is going to
be restricted to vlan_output(); someone else can wrangle with the MTU
issues since they're outside of the scope of things I'm willing to
fix. (I'd like to see 802.1Q work with FDDI and Token Ring, but thats
another issue; we'd probably need to move the encapsulation/decapsulation
code into sys/net/if_{ether,fddi,iso88025}subr.c.)
My questions about large packets and MTU assumed that we would rather that
network drivers only receive large frames when we tell them to (setting
the MTU) or when we attach a VLAN device to a physical network
interface. I'm not sure we want to have the drivers always accept large
packets, just because we've compiled a kernel with VLAN devices in it.
--
| Matthew N. Dodd | '78 Datsun 280Z | '75 Volvo 164E | FreeBSD/NetBSD |
| winter@jurai.net | 2 x '84 Volvo 245DL | ix86,sparc,pmax |
| http://www.jurai.net/~winter | This Space For Rent | ISO8802.5 4ever |
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