[Bridge] 802.1q tagging broken when used with bridging in 2.6.38

[Andy Gospodarek]

On Tue, Mar 29, 2011 at 2:36 PM, Jiri Pirko <jpirko at redhat.com> wrote:
> Tue, Mar 29, 2011 at 06:54:58PM CEST, andy at greyhouse.net wrote:
>>On Mon, Mar 28, 2011 at 1:54 PM, igor serebryany <igor47 at moomers.org> wrote:
>>> it appears that 802.1q tagging is broken in 2.6.38 when combined with bridging.
>>> here is how to reproduce the problem:
>>>
>>> i set up an interface for the machine running 2.6.38 on my cisco router, and
>>> assign a subnet to that interface. i am using ping from the router to do the
>>> testing. i am getting all the data here with 'tcpdump -e -n' from the machine.
>>>
>>> i ping the machine from the router, and i see properly-tagged ARP requests
>>> coming in on eth0:
>>>
>>> 12:12:05.052465 00:11:20:dd:81:00 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q
>>> (0x8100), length 64: vlan 234, p 0, ethertype ARP, Request who-has 10.0.0.206
>>> tell 10.0.0.205, length 46
>>>
>>> i then create a vlan interface on the machine:
>>>
>>> vconfig add eth0 234
>>> ifconfig eth0.234 up
>>>
>>> i tcpdump the newly-created interface, and i see the arp packets appearing on
>>> it, now properly untagged
>>>
>>> 12:14:33.549939 00:11:20:dd:81:00 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
>>> length 60: Request who-has 10.0.0.206 tell 10.0.0.205, length 46
>>>
>>> if i assign an ip to this interface, i can see pings being exchanged on eth0.234
>>>
>>> 12:17:12.681079 00:11:20:dd:81:00 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
>>> length 60: Request who-has 10.0.0.206 tell 10.0.0.205, length 46
>>> 12:17:12.681090 00:30:48:fd:98:d8 > 00:11:20:dd:81:00, ethertype ARP (0x0806),
>>> length 42: Reply 10.0.0.206 is-at 00:30:48:fd:98:d8, length 28
>>> 12:17:14.682076 00:11:20:dd:81:00 > 00:30:48:fd:98:d8, ethertype IPv4 (0x0800),
>>> length 114: 10.0.0.205 > 10.0.0.206: ICMP echo request, id 24, seq 1, length 80
>>> 12:17:14.682088 00:30:48:fd:98:d8 > 00:11:20:dd:81:00, ethertype IPv4 (0x0800),
>>> length 114: 10.0.0.206 > 10.0.0.205: ICMP echo reply, id 24, seq 1, length 80
>>>
>>> now, i want to assign eth0 to a bridge
>>>
>>> brctl addbr xenbr0
>>> ifconfig xenbr0 up
>>> brctl addif xenbr0 eth0
>>>
>>> i now attempt to ping the machine again. watching tcpdump on eth0.234, i don't
>>> see any of my packets anymore!
>>>
>>> instead, if i watch xenbr0 with tcpdump, i can see the tagged packets being
>>> dumped straight into xenbr0, without the vlan tags stripped out!
>
> Yep, that seems expected. rx_handler for bridge is earlier in rx path
> than vlan processing. This is was not changed in 2.6.38. This is with us
> for a long time. I plan to refuse this topo in future (not sure yet
> thought)
>

I have no idea what version Igor was using before.  Even if Igor's
upgrade as not from 2.6.37, this sounds like a regression.