Re: [B.A.T.M.A.N.] Looping unicast packets when using BLA

[Simon Wunderlich <sw@simonwunderlich.de>]

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Hi Andreas,

On Monday 08 February 2016 12:35:35 Andreas Pape wrote:
> Hello
> 
> I have a problem in my mesh setup which is quite similiar to Bug#216 of
> the bug tracker.
> I'm using batman-adv 2014.4.0 in a BLA setup consisting of 3 Mesh Nodes
> (A, B, C) connected to the same backone network via a common switch and a
> mesh node D connected to an end device E. I ping that single mesh node D
> and the connected end device E from a PC which is connected to the same
> switch as the three Nodes A to C. BLA is compiled and enabled.

First of all, did you test v2016.0? v2014.4.0 is pretty old, the bug was 
created and closed in 2015 after all ...

> 
> From time to time I see looping unicast packets in my backbone network.
> This unicast looping starts directly after one of the nodes A to C claimed
> the mac address of my PC. The looping telegram is then the ping request
> sent by the PC. I have a wireshark recording made in my backbone via port
> mirroring of one of the switch ports where a mesh node is connected to
> which shows this behaviour.

Is it really the ping packet looping? If yes, which nodes are part of the 
loop? Normally we only see broadcast packets looping. In #216 it was also 
broadcast packets where we have seen duplicates, and this was more a locking 
problem leading to creation of the same packets again and again.

> 
> I am not sure if I understood bla correctly but isn't it nonsense that a
> bla backbone gateway claims MAC addresses from its own backbone (i.e. the
> one it is directly connected to via its ethernet port)?

Yes, that appears to be nonsense indeed. Do you happen to have DAT enabled? 
There were also some problems with that which are fixed by now.

> 
> A simple change in batadv_bla_rx seems to solve this problem: add an
> additional check before claiming a new mac address: if this address is
> already known from the tt local table (via command batadv_is_my_client)
> don't claim it.
> 
> This seems to solve my problem as far as I have tested so far. Any
> thoughts about that?

This will prevent roaming from on of your nodes connected to the backbone (A-
C) to the mesh-only node D.

I would like to suggest to upgrade and test again, and try disabling DAT if 
the problem is still present (you should still report it if DAT makes a 
difference in that case). If you still see a problem then, we probably have 
something unsolved, and then I'd like to understand which nodes are part of 
the loop.

Thank you!
     Simon

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