netdev - Re: [PATCH 2/2] [e1000 VLAN] Disable vlan hw accel when promiscuous mode

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Date:	Tue, 13 Nov 2007 10:21:41 +0900
From:	"Joonwoo Park" <joonwpark81@...il.com>
To:	"Willy Tarreau" <w@....eu>
Cc:	"David Miller" <davem@...emloft.net>, cfriesen@...tel.com,
	kaber@...sh.net, auke-jan.h.kok@...el.com, netdev@...r.kernel.org,
	djohnson+linux-kernel@...starentnetworks.com,
	linux-kernel@...r.kernel.org, e1000-devel@...ts.sourceforge.net
Subject: Re: [PATCH 2/2] [e1000 VLAN] Disable vlan hw accel when promiscuous mode

2007/11/13, Willy Tarreau <w@....eu>:
> On Mon, Nov 12, 2007 at 02:57:16PM -0800, David Miller wrote:
> > From: "Chris Friesen" <cfriesen@...tel.com>
> > Date: Mon, 12 Nov 2007 16:43:24 -0600
> >
> > > David Miller wrote:
> > >
> > > > When you select VLAN, you by definition are asking for non-VLAN
> > > > traffic to be elided.  It is like plugging the ethernet cable
> > > > into one switch or another.
> > >
> > > For max functionality it seems like the raw eth device should show
> > > everything on the wire in promiscuous mode.
> > >
> > > If we want to sniff only the traffic for a specific vlan, we can sniff
> > > the vlan device.
> >
> > VLAN settings are a filter of sorts, much like plugging into
> > one switch or another filters traffic physically.
> >
> > If you don't want that filter, turn the VLAN settings off.
>
> I don't really agree with that view. Having spent a lot of time with
> tcpdump on production systems, I can say that sometimes you'd like to
> be aware that one of your VLANs is wrong and you'd simply like to
> sniff the wire to guess the correct tag. And on production, you simply
> cannot remove other VLANs, otherwise you disrupt the service.
>

I agree.
If I had a mis-plugged cable, I can guess it with tcpdump.
Because I cannot see the packets. It means no such packets on the wire 100%.
But if I had a incorrect vlan configuration, it's hard to sure.
In a case both of mis-plugged and mis-configured situation, I cannot
see anything.
Moreover, if I am configuring a machine via vlan interface which is
mis-configured partially, I cannot disable vlan hw acceleration
feature.

Thanks.
Joonwoo
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