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Date: Tue, 24 Jan 2006 22:24:43 +0300
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: Gregory Nou <gregorynou@altern.org>
Message-ID: <20060124192443.GR83922@FreeBSD.org>
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	Gregory Nou <gregorynou@altern.org>, freebsd-net@freebsd.org
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Cc: freebsd-net@FreeBSD.org
Subject: Re: Question on VLAN
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On Mon, Jan 23, 2006 at 11:24:48PM +0100, Gregory Nou wrote:
G> What is the difference between
G> if (m->m_flags & M_VLANTAG)
G> and
G> if (ether_type == ETHERTYPE_VLAN) ?
G> 
G> I suppose that m->m_flags are set using ether_type at one point. Still, 
G> I was not able to find a location in the source where it would happen.
G> 
G> The fact is, I do not understand the difference between these two 
G> things, nor do I understand why we need the code in if_ethersubr.c[691-717]

Some drivers are capable to recognise VLAN frames. In this case
mbuf has M_VLANTAG set on it, vlan tag is stored in mbuf tag, and mbuf
contains untagged frame. For those drivers that aren't capable to
handle VLAN frames, we need to look into frame and see the tag.

-- 
Totus tuus, Glebius.
GLEBIUS-RIPN GLEB-RIPE