H3C Technologies H3C S7500E Series Switches - Manual (Page 325)

12-5
In the case of MLDv1, Host B cannot select IPv6 multicast sources when it joins IPv6 multicast group
G. Therefore, IPv6 multicast streams from both Source 1 and Source 2 will 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 Source 1 sends to G (denoted as (S1, G)), rather than the IPv6 multicast data Source 2
sends to G (denoted as (S2, G)). Thus, only IPv6 multicast data from Source 1 will be delivered to
Host B.
MLD state
A multicast router running MLDv2 maintains the multicast address state per multicast address per
attached subnet. The multicast address state consists of the following:
z Filter mode: The router keeps tracing the Include or Exclude state.
z List of sources: The router keeps tracing the newly added or deleted IPv6 multicast source.
z Timers: Filter timer (the time the router waits before switching to the Include mode after an IPv6
multicast address times out), source timer (for source recording), and so on.
Receiver host state listening
By listening to the state of receiver hosts, a multicast router running MLDv2 records and maintains
information of hosts joining the source group on the attached subnet.
MLD Message Types
The following descriptions are based on MLDv2 messages.
MLD query message
An MLD querier learns the multicast listening state of neighbor interfaces by sending MLD query
messages. Figure 12-3 shows the format of an MLD query message. The dark blue area in the figure
shows the format of an MLDv1 message.