Re: [PATCH maint v5 2/3] batman-adv: mcast: fix duplicate mcast packets in BLA backbone from mesh

[Simon Wunderlich <sw@simonwunderlich.de>]

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On Monday, September 14, 2020 9:53:46 PM CEST Linus Lüssing wrote:
> Scenario:
> * Multicast frame send from mesh to a BLA backbone (multiple nodes
>   with their bat0 bridged together, with BLA enabled)
> 
> Issue:
> * BLA backbone nodes receive the frame multiple times on bat0,
>   once from mesh->bat0 and once from each backbone_gw from LAN
> 
> For unicast, a node will send only to the best backbone gateway
> according to the TQ. However for multicast we currently cannot determine
> if multiple destination nodes share the same backbone if they don't share
> the same backbone with us. So we need to keep sending the unicasts to
> all backbone gateways and let the backbone gateways decide which one
> will forward the frame. We can use the CLAIM mechanism to make this
> decision.
> 
> One catch: The batman-adv gateway feature for DHCP packets potentially
> sends multicast packets in the same batman-adv unicast header as the
> multicast optimizations code. And we are not allowed to drop those even
> if we did not claim the source address of the sender, as for such
> packets there is only this one multicast-in-unicast packet.
> 
> How can we distinguish the two cases?
> 
> The gateway feature uses a batman-adv unicast 4 address header. While
> the multicast-to-unicasts feature uses a simple, 3 address batman-adv
> unicast header. So let's use this to distinguish.
> 
> Fixes: e32470167379 ("batman-adv: check incoming packet type for bla")
> Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>

Acked-by: Simon Wunderlich <sw@simonwunderlich.de>

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