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

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Message-ID: <8d3f0bd9-8b66-ce49-ab1d-56e8c73764fc@nbd.name>
Date:   Wed, 11 Jan 2017 13:21:34 +0100
From:   Felix Fietkau <nbd@....name>
To:     IgorMitsyanko <igor.mitsyanko.os@...ntenna.com>,
        Johannes Berg <johannes@...solutions.net>,
        Linus Lüssing <linus.luessing@...3.blue>,
        Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        "M. Braun" <michael-dev@...i-braun.de>
Subject: Re: [PATCH net-next] bridge: multicast to unicast

On 2017-01-11 13:15, IgorMitsyanko wrote:
> On 01/11/2017 02:30 PM, Felix Fietkau wrote:
>> On 2017-01-11 12:26, IgorMitsyanko wrote:
>>> On 01/11/2017 12:27 AM, Felix Fietkau wrote:
>>>> On 2017-01-10 11:56, Johannes Berg wrote:
>>>>> On Tue, 2017-01-10 at 05:18 +0100, Linus Lüssing wrote:
>>>>>> On Mon, Jan 09, 2017 at 01:30:32PM -0800, Stephen Hemminger wrote:
>>>>>>> I wonder if MAC80211 should be doing IGMP snooping and not bridge
>>>>>>> in this environment.
>>>>>> In the long term, yes. For now, not quite sure.
>>>>> There's no "for now" in the kernel. Code added now will have to be
>>>>> maintained essentially forever.
>>>> I'm not sure that putting the IGMP snooping code in mac80211 is a good
>>>> idea, that would be quite a bit of code duplication.
>>>> This implementation works, it's very simple, and it's quite flexible for
>>>> a number of use cases.
>>>>
>>>> Is there any remaining objection to merging this in principle (aside
>>>> from potential issues with the code)?
>>>>
>>>> - Felix
>>>>
>>>
>>> Hi Felix, can we consider two examples configurations with multicast
>>> traffic:
>>>
>>> 1. AP is a source of multicast traffic itself, no bridge on AP. For
>>> example, wireless video server streaming to several clients.
>>> In this situation, we can not make use of possible advantages given by
>>> mc-to-uc conversion?
>> You could simply put the AP interface in a bridge, no need to have any
>> other bridge members present.
>>
>>> 2. A configuration with AP + STA + 3 client devices behind STA.
>>>                               ----|client 1|
>>>                              |
>>> |  mc  |----|AP|----|STA|---|---|client 2|
>>> |server|                    |
>>>                               ----|client 3|
>>>
>>> Multicast server behind AP streams MC video traffic. All 3 clients
>>> behind the STA have joined the multicast group.
>>> I'm not sure if this case will be handled correctly with mc-to-uc
>>> conversion in bridge on AP?
>> What do you mean by "3 client devices behind STA"? Are you using a
>> 4-addr STA, multicast routing, or some kind of vendor specific "client
>> bridge" hackery?
> 
> 3 client devices connected by backbone Ethernet network. Generic
> case is probably STA/AP operating in 4-addr mode (more or less standard
> solution as far as I know).
If the AP is running in 4-addr mode, it will need to have a bridge
interface anyway, because the link to the STA will be split out into a
separate virtual interface (AP_VLAN iftype).

In this case you don't actually need any multicast-to-unicast
conversion, because the multicast traffic will be unicast on 802.11
already (due to use of 4-addr mode).

- Felix