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I enabled blaII on one node, and after that all nodes connected to the vpn went unreachable. Most of them use 2011.0.0, some others 2011.4.0, running an ad-hoc iface as bat-adv-iface and bat0, tap0 and ath0(master, for clients) as a bridge. Do the blaII-packets "kill" all the other nodes? I thought the blaII-packets would have no effect on the other nodes because of the compat- layer.
You should use the same version everywhere. The compat layer is only to get a version running on an older kernel... not for incompatibilities between the different features/versions of batman-adv.
Marek already suggested that the packet format version should be increased to clearly state that these versions are not compatible. But it could also be that you triggered a bug in the new bla implementation... still I don't understand why you are doing this. Which node should detect the ARP packets? Maybe you can explain it again to better understand your network architecture.
Thanks, Sven