Re: Linux 802.1ad VLAN unexpected beaviour

[Daniel Borkmann <dborkman@redhat.com>]

On 05/26/2014 09:39 PM, Gioacchino Mazzurco wrote:
> Hi All!
>
> As part of my GSoC project I am implementing 802.1ad support for netifd, while
> testing this new code I encountered a very strange behavior on linux kernel,
> the netifd tests just made me notice the unexpected behavior, but are not
> involved in the problem and doesn't are needed to reproduce it.
>
> Interfaces created as 802.1ad VLAN appear to the system as 802.1ad but seems
> they are injecting on the cable 802.1q frames instead of 802.1ad ones.
>
> I have tested various version of linux kernel from 3.10 (the one in wich this
> feature was introtuced) to 3.12.13 and everyone were affected, so it doesn't
> seems to me a regression or something fixed in newer release.
>
> Following how to reproduce the unexpected behavior and some output from my
> commandline.
>
> My setup have two linux host connected by ethernet cable.
>
> #### On host A
>
> # first configure the vlan interface
>
> ip link add link eth0 test1 type vlan proto 802.1ad id 1000
> ip link set up dev test1
>
> # then send some traffic on that new device with
> ping6 ff02::3%test1
>
> # on another window on the same device sniff what seems is going out from eth0
>
> tcpdump -n -e -vv -ttt -i eth0 not tcp port 23 and not arp

I think, as we already had a similar discussion on this topic on netdev, it's
a libpcap problem, not a kernel one. See also the thread:

   http://lists.openwall.net/netdev/2014/04/14/19

Perhaps the given patch there works for you.

> # the output will be something like that:
> OUTPUT<<
>
> tcpdump: WARNING: eth0: no IPv4 address assigned
> tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535
> bytes
> 00:00:00.000000 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q-QinQ
> (0x88a8), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 1
> 00:00:01.005251 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q-QinQ
> (0x88a8), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 2
> 00:00:00.999914 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q-QinQ
> (0x88a8), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 3
>
> OUTPUT
>
> # as you can see the ethertype is the expected one 802.1Q-QinQ (0x88a8) ==
> 802.1ad
>
>
> # on host B
>
> # at the same time run tcpdump on host B with similar parameters
>
> tcpdump -n -e -vv -ttt -i ethernet0 not tcp port 23 and not arp
>
> # you will see something like that:
>
> OUTPUT<<
>
> tcpdump: listening on ethernet0, link-type EN10MB (Ethernet), capture size
> 65535 bytes
> 00:00:00.000000 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q
> (0x8100), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 1
> 00:00:01.005301 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q
> (0x8100), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 2
> 00:00:01.000044 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q
> (0x8100), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 3
> 00:00:01.000014 00:15:6d:9f:48:72 > 33:33:00:00:00:03, ethertype 802.1Q
> (0x8100), length 122: vlan 1000, p 0, ethertype IPv6, (hlim 1, next-header
> ICMPv6 (58) payload length: 64) fe80::215:6dff:fe9f:4872 > ff02::3: [icmp6 sum
> ok] ICMP6, echo request, seq 4
>
> OUTPUT
>
> # as you can see the ethertype is not the expected one 802.1Q (0x8100) !=
> 802.1ad
>
> # Inverting Host A and B give same behavior
>
> Thanks for help and attention :)
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