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

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Date:   Mon, 09 Jan 2017 13:15:59 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     "M. Braun" <michael-dev@...i-braun.de>,
        Linus Lüssing <linus.luessing@...3.blue>
Cc:     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, 2017-01-09 at 12:44 +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?
> 
> That is bridge fdb entries (need to) expire so the bridge might
> "forget" a still-connected station not sending but only consuming
> broadcast traffic.
> 
> E.g. there is a television broadcast station here that receives a
> video stream (via wifi, udp packets) and then airs it (dvb-t) but (on
> its own) would not send any data packet on wifi (static ip, etc.).

Ok, that I don't know. Somehow if you address a unicast packet there
the bridge has to make a decision - so it really should know? Would it
query the port somehow to see if the device is behind it, if getting a
packet for a station it forgot about?

> An other reason to implement this in mac80211 initially was that
> mac80211 could encapsulate broacast/multicast ethernet packtes in
> unicast A-MSDU packets in a way, so that the receiver would still see
> process ethernet packets (after conversion) but have unicast wifi
> frames. This cannot be done in bridge easily but one might want to
> add this later to mac80211.

Yes, DMG would have to be done in mac80211, but that's a lot clearer
case too since it requires negotiation functionality etc.

johannes