On Monday, September 14, 2020 9:53:45 PM CEST Linus Lüssing wrote:
> Scenario:
> * Multicast frame send from a BLA backbone (multiple nodes with
> their bat0 bridged together, with BLA enabled)
>
> Issue:
> * BLA backbone nodes receive the frame multiple times on bat0
>
> For multicast frames received via batman-adv broadcast packets the
> originator of the broadcast packet is checked before decapsulating and
> forwarding the frame to bat0 (batadv_bla_is_backbone_gw()->
> batadv_recv_bcast_packet()). If it came from a node which shares the
> same BLA backbone with us then it is not forwarded to bat0 to avoid a
> loop.
>
> When sending a multicast frame in a non-4-address batman-adv unicast
> packet we are currently missing this check - and cannot do so because
> the batman-adv unicast packet has no originator address field.
>
> However, we can simply fix this on the sender side by only sending the
> multicast frame via unicasts to interested nodes which do not share the
> same BLA backbone with us. This also nicely avoids some unnecessary
> transmissions on mesh side.
>
> Note that no infinite loop was observed, probably because of dropping
> via batadv_interface_tx()->batadv_bla_tx(). However the duplicates still
> utterly confuse switches/bridges, ICMPv6 duplicate address detection and
> neighbor discovery and therefore leads to long delays before being able
> to establish TCP connections, for instance. And it also leads to the Linux
> bridge printing messages like:
> "br-lan: received packet on eth1 with own address as source address ..."
>
> Fixes: 405cc1e5a81e ("batman-adv: Modified forwarding behaviour for
> multicast packets") Signed-off-by: Linus Lüssing <linus.luess...@c0d3.blue>
> ---Acked-by: Simon Wunderlich <s...@simonwunderlich.de>
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