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

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Date:   Mon, 9 Jan 2017 13:30:32 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Linus Lüssing <linus.luessing@...3.blue>
Cc:     "M. Braun" <michael-dev@...i-braun.de>,
        Johannes Berg <johannes@...solutions.net>,
        Felix Fietkau <nbd@....name>, netdev@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        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, 9 Jan 2017 22:23:45 +0100
Linus Lüssing <linus.luessing@...3.blue> wrote:

> 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.

I wonder if MAC80211 should be doing IGMP snooping and not bridge
in this environment.