netdev - Re: cpsw_switch: unable to selectively forward multicast

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Message-ID: <YpBzDaZOzUYG0U/9@e495>
Date:   Fri, 27 May 2022 08:43:25 +0200
From:   Markus Klotzbuecher <mk@...o.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org
Subject: Re: cpsw_switch: unable to selectively forward multicast

Hi Andrew,

thank you for your feedback.

On Wed, May 25, 2022 at 11:05:14PM +0200, Andrew Lunn wrote:
>On Wed, May 25, 2022 at 11:30:40AM +0200, Markus Klotzbuecher wrote:
>> Hi All,
>> 
>> I'm using multiple am335x based devices connected in a daisy chain
>> using cpsw_new in switch mode:
>> 
>>              /-br0-\          /-br0-\         /-br0-\
>>             |       |        |       |       |       |
>>         ---swp0    swp1-----swp0    swp1----swp0    swp1
>>             |       |        |       |       |       |
>>              \-----/          \-----/         \-----/
>>                #1               #2              #3
>> 
>> The bridge is configured as described in cpsw_switchdev.rst
>> [1]. Regular unicast traffic works fine, however I am unable to get
>> traffic to multicast groups to be forwarded in both directions via the
>> switches.
>
>Do you have listens reporting they are interested in the traffic via
>IGMP? Do you have an IGMP quirer in your network? Without these, IGMP
>snooping will not work.

The userspace application running on each device in the chain calls
setsockopt + IP_ADD_MEMBERSHIP and peer devices receive IGMP packets
such as

 7 10.399981403 192.168.178.51 ? 224.0.0.22   IGMPv3 62 Membership Report / Join group 239.253.253.239 for any sources
 8 10.399981403 192.168.178.51 ? 224.0.0.22   IGMPv3 56 Membership Report / Join group 239.253.253.239 for any sources

and corresponding bridge mdb records appear for swpX and br0
subsequently. Shouldn't this suffice for multicast to work or do I
really need an additional IGMP querier? I realize that these mdb
entries will expire, however multicast traffic isn't forwarded even
temporarily and manually adding the same entries as 'permanent' didn't
help either.

Thanks,

Markus