Date: Mon, 9 Jan 2017 22:23:45 +0100
From: Linus =?utf-8?Q?L=C3=BCssing?= <linus.luessing@c0d3.blue>
To: "M. Braun" <michael-dev@fami-braun.de>
Cc: Johannes Berg <johannes@sipsolutions.net>,
        Felix Fietkau <nbd@nbd.name>, netdev@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>,
        Stephen Hemminger <stephen@networkplumber.org>,
        bridge@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH net-next] bridge: multicast to unicast
Message-ID: <20170109212345.GA5513@otheros> (sfid-20170109_222414_863109_E4B7C50B)
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 <22fad045-57c6-7789-d19f-f47bd0faf441@fami-braun.de>
 <20170107145516.GE3134@otheros>
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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.