netdev - Re: [PATCH net-next] bridge: multicast to unicast

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Date:   Mon, 9 Jan 2017 22:23:45 +0100
From:   Linus Lüssing <linus.luessing@...3.blue>
To:     "M. Braun" <michael-dev@...i-braun.de>
Cc:     Johannes Berg <johannes@...solutions.net>,
        Felix Fietkau <nbd@....name>, netdev@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        bridge@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-wireless@...r.kernel.org
Subject: Re: [PATCH net-next] bridge: multicast to unicast

On Mon, Jan 09, 2017 at 12:44:19PM +0100, M. Braun wrote:
> Am 09.01.2017 um 09:08 schrieb Johannes Berg:
> > Does it make sense to implement the two in separate layers though?
> > 
> > Clearly, this part needs to be implemented in the bridge layer due to
> > the snooping knowledge, but the code is very similar to what mac80211
> > has now.
> 
> Does the bridge always know about all stations connected?

The bridge does not always know about all stations, especially the
silent ones like in your DVB-T example.

However, concerning IP multicast, there is IGMP/MLD. So the bridge
does know about all stations which are interested in a specific IP
multicast stream.

(As long as there is a querier on the link, which periodically
queriers for IGMP/MLD reports from any listener. If there is no
querier then the bridge multicast snooping, including the bridge
multicast-to-unicast will fall back to flooding)

So if your television example uses IP multicast properly, it is
completely doable with the bridge multicast-to-unicast, thanks to
IGMP/MLD.