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

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Date:   Wed, 11 Jan 2017 10:17:58 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Linus Lüssing <linus.luessing@...3.blue>
Cc:     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, Felix Fietkau <nbd@....name>,
        Michael Braun <michael-dev@...i-braun.de>
Subject: Re: [PATCH net-next] bridge: multicast to unicast


> > Exactly. My point is that this is breaking the expectation that
> > hosts are actually able to drop such packets.
> 
> [readding CCs I removed earlier]
> 
> Ah! Thanks. I was worried about creating packetloss :D.

Ah, well, no - at least not in this case.

> Hm, for this other other way round, I think it does not apply for
> the bridge multicast-to-unicast patch if I'm not misreading the
> bridge code:
> 
> For a packet with a link-layer multicast address but a unicast IP
> destination, the bridge MDB lookup will fail.
> (http://lxr.free-electrons.com/source/net/bridge/br_multicast.c?v=4.8
> #L178
>  returns NULL)
> 
> Case A): No multicast router on port:
> -> bridge, br_multicast_flood(), will drop the packet already
>    (no matter if multicast-to-unicast is enabled or not)
> 
> Case B): Multicast router present on port:
> -> The new patch does not apply multicast-to-unicast but just floods
>    packet unaltered
>    ("else { port = rport; addr = NULL; }" branch)

Ah, interesting. This is different then - the mac80211 code is not L3
aware at all.

johannes