Re: Multiple ARP replies for same address on openwrt module 6.6.69.2024.3-r3

[Sven Eckelmann <sven@narfation.org>]

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On Thursday, 9 January 2025 11:31:06 CET Matteo Fortini wrote:
> I am noticing random unreachability of hosts in my network, in 
> particular if I just nmap -sP the whole range.
> 
> I traced it down to ARP poisoning, and the source seems to be two hosts 
> running batman-adv which are claiming the same address.
[...]
> 
> issue is, 02:00:06:bb:00:07 is not the right node and the host is 
> unreachable. The other MAC is the right one.
> 
> If I clear the ARP cache in my source host, then the remote host is 
> reachable again as it gets the right answer.

Might be DAT related. But I am not sure of it. Can you please add the output 
of

$ batctl mj

to see the (batadv interface specific) configuration.

This might be helpful for Antonio/Linus. If it is enabled, you could also try 
to disable it on all involved hosts via:

$ batctl dat disable

Just to see if it has any influence on the behavior (to see if there is any 
ARP poisoning in the long run - not to solve the intermediate problem).


> The problem started after updating to the 24.10RC series of openwrt.

When you used 23.05.x before, then this would suggest that it was introduced 
somewhere between 2023.1 and 2024.3 (or OpenWrt) somehow.

I didn't test it but a quick check in the sources suggest that the 23.05 
batman-adv sources (from the routing feed) should also work with 24.10 - so 
you could actually git-bisect openwrt routing from 
6afc0452c2534ed0bc65b59b1fb6fd74439ddf27 to 
eaa4aba30b017de66bece8ef9d3dde5299fc787d

Kind regards,
	Sven

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