Duplicates on multi-hop mesh paths when using bridges

[Javier Cardona]

Hi Thomas,

Thanks a lot for the detailed report.  What you have encountered is
clearly a bug:  there should be no duplicate traffic in that
particular configuration.  I recall seeing this problem on a similar
deployment where each mesh node was configured as a portal.  In that
particular instance the duplicate packets appeared sporadically and at
times there were no duplicates at all.  Is this something that you've
seen?

I'd be happy to help resolve this issue.  If you can provide sniffer
captures I can take a look.

Cheers,

Javier

PS.  I'm copying Yanbo, the author of the mesh portal code.  Maybe he
can offer some advice.

On Wed, Mar 31, 2010 at 5:54 AM,  <Thomas.Peter2 at swisscom.com> wrote:
> Hi again!
>
> As I have already mentioned I'm running a little project at my company to
> evaluate the current performance of open80211s. I have run into a problem
> with duplicates appearing on multi-hop connections when using portals
> (wlan-ethernet linux bridges). Maybe this is a bug or I'm doing something
> wrong.
>
> Let me explain my setup:
>
> I have three alix boards serving as mesh nodes
> (http://www.pcengines.ch/alix.htm, basically an embedded x86 computer with
> an AMD Geode LX CPU). I'm running the linville wireless-testing Linux kernel
> (commit ffe12e4fd3989b24295ed14424ff482f4809b532 Feb 9 15:36:32 2010) on
> these boards, the kernel image was created using buildroot. All three boards
> have an ath9k abgn Mini-PCI WLAN card and all three boards have a laptop
> (running Ubuntu) connected via Ethernet. On each board I create and
> configure a mesh interface and assign the same mesh id, as described on
> open80211s.org/trac/wiki/HOWTO. Afterwards each mesh node (each alix board)
> can ping the other mesh nodes on their mesh interface. Then I bridge each
> mesh interface with the eth0 interface on each mesh node exactly as
> described in the HOWTO (after bridging the mesh interfaces don't have an IP
> address any more). Each bridge interface and each laptop have an IP address
> in the same subnet (as stated in the HOWTO in the note about portals, the
> laptops cannot ping any mesh nodes, but each laptop can ping the other
> laptops).
>
> Without tinkering with the mesh paths everything works fine. Because of the
> proximity of the mesh nodes no multi-hop mesh paths are established
> automatically.
>
> Now, let's name the three mesh nodes n1, n2 and n3 and the laptops l1, l2
> and l3 (l1 being connected to n1 via Ethernet, etc.). If I manually
> introduce a multi-hop mesh path from n1 through n2 to n3 using the 'iw dev
> mesh0 mpath del/new/next_hop' commands (I also do that in the other
> direction and make sure that n2 has single-hop mesh paths to n1 and n3) and
> then ping l3 from l1 'ping' (running on l1) reports duplicates.
>
> I have also confirmed this problem with iperf. There, when I send UDP
> traffic with data rate x Mbps from l1 to l3 (on a two-hop mesh path), l3
> receives UDP traffic with a data rate of 2x Mbps (lol :-).
>
> I'm positive that I have not assigned any IP address twice. In fact, I have
> tried not assigning any IP addresses to the mesh nodes at all (starting from
> a clean boot). The laptops still have connectivity (of course), but the
> duplicates remain. I have also tried turning on STP on the bridges.
>
> Can anybody tell me what might be going on?
>
> Greetings and Happy Easter!
>
> Thomas
>
> PS: I realize that I can just run iperf on the mesh nodes, which works fine.
> But that's not the answer to my question.
>
>
> Thomas Peter
> thomas.peter2 at swisscom.com
> ___________________________________________________________________________
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>



-- 
Javier Cardona
cozybit Inc.
http://www.cozybit.com