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Date:      Tue, 7 Jul 2020 12:01:05 +0200
From:      Fabrice Colliot <f.colliot@gmail.com>
To:        freebsd-net@freebsd.org
Subject:   Multicast: membership to (*, G) group after leaving a (S, G) group
Message-ID:  <CAC-yrDdYJbfcr=EqJ%2BQOZZCPVt6S7o=cQWNqfM6LQz=ffZi1-A@mail.gmail.com>
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Hi,

I'm using smcroute to join and leave multicast groups and I don't
understand the behavior of FreeBSD when the group is left.

Here is what I do:

smcroute join em1 10.3.4.5 224.0.55.55
ifmcstat -i em1
em1:
        inet 10.10.0.1
        igmpv3 rv 2 qi 125 qri 10 uri 3
                group 224.0.55.55 mode include
                        mcast-macaddr 01:00:5e:00:37:37
                group 224.0.0.1 mode exclude
                        mcast-macaddr 01:00:5e:00:00:01

smcroute leave em1 10.3.4.5 224.0.55.55
ifmcstat -i em1
em1:
        inet 10.10.0.1
        igmpv3 rv 2 qi 125 qri 10 uri 3
                group 224.0.55.55 mode undefined
                        mcast-macaddr 01:00:5e:00:37:37
                group 224.0.0.1 mode exclude
                        mcast-macaddr 01:00:5e:00:00:01

At this point, I expected to have no membership left on em1 for 224.0.55.55
but ifmcstat shows that the interface is still a member of the group but in
undefined mode.

I was wondering if anybody could tell me why the group membership seems to
be transitioned to a (*, G) membership when all the (S, G) memberships are
removed.

Thanks!
Fabrice

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