Linux Ethernet Bridging - Jan 2017 - [Bridge] [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.

On Mon, 9 Jan 2017 22:23:45 +0100
Linus L?ssing <linus.luessing at c0d3.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.