What happens when the client wants to leave an ASM group?
We might be expecting to see a done message,
but again, similar to IGMPv3, we see a new report.
Like all reports, the source is the Globomantics client link local address,
and the destination is the MLDv2 specific link local multicast address.
The packet is still an MLDv2 listener report with code 0,
making use of the existing format.
The packet contains a single multicast record for FF08::1,
the group that the client wishes to leave.
The type is changed to include, implying that the old type was exclude.
By changing to an include record and not specifying any sources,
the client is saying I want to receive multicast for FF08::1 from no one.
This is a clever way of leaving a group without
requiring a custom leave or done message.
Having seen this exchange many times before,
we already know that the multicast router needs to check to see if anyone
else on the LAN segment still wants multicast for FF08::1.
It accomplishes this with a group-specific query destined to that specific
group address so as not to disturb disinterested listeners.
The MLDv2 group-specific query is very similar to the
MLDv2 general query we saw previously.
The max response time is now 1000 ms, or 1 s,
which requires clients to reply rapidly if they want to keep
receiving multicast traffic on this group.
The most significant difference is the addition of the specific multicast
group of FF08::1 to identify the group in question. All minor options hereafter are exactly the same.