netdev - Re: What is the correct way to install an L2 multicast route into a bridge?

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Message-ID: <6e654725-ec5e-8f6d-b8ae-3cf8b898c62e@cumulusnetworks.com>
Date:   Wed, 8 Jul 2020 12:16:27 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Vladimir Oltean <olteanv@...il.com>, roopa@...ulusnetworks.com,
        netdev@...r.kernel.org
Subject: Re: What is the correct way to install an L2 multicast route into a
 bridge?

On 08/07/2020 12:04, Vladimir Oltean wrote:
> Hi,
> 
> I am confused after reading man/man8/bridge.8. I have a bridge br0 with
> 4 interfaces (eth0 -> eth3), and I would like to install a rule such
> that the non-IP multicast address of 09:00:70:00:00:00 is only forwarded
> towards 3 of those ports, instead of being flooded.
> The manual says that 'bridge mdb' is only for IP multicast, and implies
> that 'bridge fdb append' (NLM_F_APPEND) is only used by vxlan. So, what
> is the correct user interface for what I am trying to do?
> 
> Thank you,
> -Vladimir
> 

Hi Vladimir,
The bridge currently doesn't support L2 multicast routes. The MDB interface needs to be extended
for such support. Soon I'll post patches that move it to a new, entirely netlink attribute-
based, structure so it can be extended easily for that, too. My change is motivated mainly by SSM
but it will help with implementing this feature as well.
In case you need it sooner, patches are always welcome! :)

Current MDB fixed-size structure can also be used for implementing L2 mcast routes, but it would
require some workarounds. 

Cheers,
 Nik