netdev - Re: e100 + VLANs?

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Date:	Mon, 10 Oct 2011 17:28:45 +0200
From:	David Lamparter <equinox@...c24.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Lamparter <equinox@...c24.net>,
	Michael Tokarev <mjt@....msk.ru>, jeffrey.t.kirsher@...el.com,
	netdev <netdev@...r.kernel.org>
Subject: Re: e100 + VLANs?

On Mon, Oct 10, 2011 at 05:23:55PM +0200, Eric Dumazet wrote:
> Le lundi 10 octobre 2011 à 17:13 +0200, David Lamparter a écrit :
> > On Mon, Oct 10, 2011 at 05:05:52PM +0200, Eric Dumazet wrote:
> > > > When pinging this NIC from another machine over VLAN5, I see
> > > > ARP packets coming to it, gets recognized and replies going
> > > > back, all on vlan 5.  But on the other side, replies comes
> > > > WITHOUT a VLAN tag!
> > > > 
> > > > From this NIC's point of view, capturing on whole ethX:
> > > > 
> > > > 00:1f:c6:ef:e5:1b > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 60: vlan 5, p 0, ethertype ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 10.48.11.2 tell 10.48.11.1, length 42
> > > > 00:90:27:30:6d:1c > 00:1f:c6:ef:e5:1b, ethertype 802.1Q (0x8100), length 46: vlan 5, p 0, ethertype ARP, Ethernet (len 6), IPv4 (len 4), Reply 10.48.11.2 is-at 00:90:27:30:6d:1c, length 28
> > > > 
> > > > From the partner point of view, also on whole ethX:
> > > > 
> > > > 00:1f:c6:ef:e5:1b > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 46: vlan 5, p 0, ethertype ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 10.48.11.2 tell 10.48.11.1, length 28
> > > > 00:90:27:30:6d:1c > 00:1f:c6:ef:e5:1b, ethertype ARP (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply 10.48.11.2 is-at 00:90:27:30:6d:1c, length 46
> > > > 
> > > > So, the tag gets eaten somewhere along the way... ;)
> > 
> > Hmm. Looks like broken VLAN TX offload, but the driver doesn't even
> > implement VLAN offload. Maybe it's broken in its non-implementation...
> > 
> > Your "partner" is a known-good setup and can be assumed to be working
> > correctly? This is over a crossover cable, no evil switches involved?
> > 
> > > > And I can't really recreate the situation which I had - I know
> > > > some packets were flowing, so at least ARP worked.  Now it
> > > > does not work anymore.
> > > 
> > > What the 'partner' setup looks like ?
> > > 
> > > ip link
> > > ip addr
> > > ip ro
> > 
> > 'local' setup too please :)
> 
> But here, the remote cleary sends an answer without VLAN tag ;)

Huh? The remote sends the ARP request to ff:f..f:ff, which has a VLAN
tag in both dumps - but the packet sent from the e100 only has a tag in
its own tcpdump... so it might pretty much wind up on the wire without a
tag due to some TX bug...

-David

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