Re: 802.1q tagging broken when used with bridging in 2.6.38

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On Mon, Mar 28, 2011 at 1:54 PM, igor serebryany <igor47@xxxxxxxxxxx> 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!
>
> 12:20:53.041487 00:11:20:dd:81:00 > 00:30:48:fd:98:d8, ethertype 802.1Q
> (0x8100), length 118: vlan 234, p 0, ethertype IPv4, 10.0.0.205 > 10.0.0.206:
> ICMP echo request, id 26, seq 2, length 80
>
> obviously there are no icmp replies because there is no listening interface on
> xenbr0.
>
> i tried doing something really silly:
>
> vconfig add xenbr0 234
> ifconfig xenbr0.234 10.0.0.206 netmask 255.255.255.252
>
> when watching this unusual interface with tcpdump, i would see properly-untagged
> packets making their way there. but arp requests couldn't make their way back
> out again:
>
> 12:44:29.952443 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 30, seq 4, length 80
> 12:44:29.954549 00:30:48:fd:98:d8 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806),
> length 42: Request who-has 10.0.0.205 tell 184.154.127.206, length 28
>
> so, that doesn't work...
>
> this is a pretty severe bug for me. my virtual machine setup depends on being
> able to assign VMs to vlans and forward packets to them, and this totally breaks
> my networking model, taking some of my vms offline. of course, any vm using the
> native vlan on the port is unaffected.
>

This is probably something Jiri (cc'd) should know about as it sounds
like it might be related to some of the VLAN changes he has made in
the receive path.
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