376
2.
After receiving the MLD done message, the querier sends a configurable number of
multicast-address-specific queries to the group that the host is leaving. The destination address
field and group address field of the message are both filled with the address of the IPv6
multicast group that is being queried.
3.
One of the remaining members (if any on the subnet) of the group being queried should send a
report within the time of the maximum response delay set in the query messages.
4.
If the querier receives a report for the group within the maximum response delay time, it will
maintain the memberships of the IPv6 multicast group. Otherwise, the querier will assume that
no hosts on the subnet are still interested in IPv6 multicast traffic addressed to that group and
will stop maintaining the memberships of the group.
How MLDv2 operates
Compared with MLDv1, MLDv2 provides the following new features:
IPv6 multicast group filtering
MLDv2 has introduced IPv6 multicast source filtering modes (Include and Exclude), so that a host
not only can join a designated IPv6 multicast group, but also can specify to receive or reject multicast
data from designated IPv6 multicast sources. When a host joins an IPv6 multicast group, one of the
following situation occurs:
•
If it expects IPv6 multicast data from specific IPv6 multicast sources like S1, S2, …, it sends a
report with Filter-Mode denoted as "Include Sources (S1, S2, …)."
•
If it does not expect IPv6 multicast data from specific IPv6 multicast sources like S1, S2, …, it
sends a report with Filter-Mode denoted as "Exclude Sources (S1, S2, …)."
As shown in
, the network has two IPv6 multicast sources, Source 1 (S1) and Source 2
(S2). Both of the sources can send IPv6 multicast data to IPv6 multicast group G. Host B is
interested only in the IPv6 multicast data that Source 1 sends to G but not in the data from Source 2.
Figure 108 Flow paths of multicast-address-and-source-specific multicast traffic
In MLDv1, Host B cannot select IPv6 multicast sources when it joins IPv6 multicast group G. The
IPv6 multicast streams from both Source 1 and Source 2 flow to Host B whether it needs them or not.
When MLDv2 is running on the hosts and routers, Host B can explicitly express its interest in the
IPv6 multicast data that Source 1 sends to G—denoted as (S1, G). It can also explicitly express that
it does not want to receive the IPv6 multicast data that Source 2 sends to G—denoted as (S2, G).
Thus, only IPv6 multicast data from Source 1 will be delivered to Host B.
