2007/11/13, Willy Tarreau <w@1wt.eu>:
quoted text
> On Mon, Nov 12, 2007 at 02:57:16PM -0800, David Miller wrote:
> > From: "Chris Friesen" <cfriesen@nortel.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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