From owner-freebsd-net Thu Feb 3 12:40:52 2000 Delivered-To: freebsd-net@freebsd.org Received: from sasami.jurai.net (sasami.jurai.net [63.67.141.99]) by builder.freebsd.org (Postfix) with ESMTP id 2C1BC400D for ; Thu, 3 Feb 2000 12:40:48 -0800 (PST) Received: from localhost (winter@localhost) by sasami.jurai.net (8.9.3/8.8.7) with ESMTP id PAA54042; Thu, 3 Feb 2000 15:04:29 -0500 (EST) Date: Thu, 3 Feb 2000 15:04:29 -0500 (EST) From: "Matthew N. Dodd" To: Garrett Wollman Cc: "Pedro J. Lobo" , freebsd-net@FreeBSD.ORG Subject: Re: 802.1Q VLANs In-Reply-To: <200002031847.NAA62013@khavrinen.lcs.mit.edu> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org 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 | To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message