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

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Message-ID: <20170107151530.GG3134@otheros>
Date:   Sat, 7 Jan 2017 16:15:30 +0100
From:   Linus Lüssing <linus.luessing@...3.blue>
To:     Johannes Berg <johannes@...solutions.net>
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

On Fri, Jan 06, 2017 at 01:47:52PM +0100, Johannes Berg wrote:
> How does this compare and/or relate to the multicast-to-unicast feature
> we were going to add to the wifi stack, particularly mac80211? Do we
> perhaps not need that feature at all, if bridging will have it?
> 
> I suppose that the feature there could apply also to locally generated
> traffic when the AP interface isn't in a bridge, but I think I could
> live with requiring the AP to be put into a bridge to achieve a similar
> configuration?
> 
> Additionally, on an unrelated note, this seems to apply generically to
> all kinds of frames, losing information by replacing the address.
> Shouldn't it have similar limitations as the wifi stack feature has
> then, like only applying to ARP, IPv4, IPv6 and not general protocols?

(should all three be answered with Michael's and my reply to
Michael's mail, I think)

> 
> Also, it should probably come with the same caveat as we documented for
> the wifi feature:
> 
>     Note that this may break certain expectations of the receiver,
>     such as the ability to drop unicast IP packets received within
>     multicast L2 frames, or the ability to not send ICMP destination
>     unreachable messages for packets received in L2 multicast (which
>     is required, but the receiver can't tell the difference if this
>     new option is enabled.)

Actually, I do not quite understand that remark in the mac80211
multicast-to-unicast patch. IP should not care about the ethernet
header?