HP FlexNetwork 7500 Series Configuration Manual page 295

Joining an IPv6 multicast group
Figure 88 MLD queries and reports
As shown in
multicast group G1. Host A wants to receive the IPv6 multicast data addressed to G2. The following
process describes how the hosts join the IPv6 multicast groups and how the MLD querier (Router B
in Figure 88) maintains the IPv6 multicast group memberships:
The hosts send unsolicited MLD reports to the IPv6 multicast groups they want to join without
1.
having to wait for the MLD queries from the MLD querier.
The MLD querier periodically multicasts MLD queries (with the destination address FF02::1) to
2.
all hosts and routers on the local subnet.
After receiving a query, the host whose report delay timer expires first sends an MLD report to
3.
the IPv6 multicast group G1 to announce its membership for G1. In this example, Host B sends
the report. Host C, which is on the same subnet as Host B, suppresses its own report for G1
after hearing the report from Host B.
Because the MLD routers already know that G1 has at least one member, other members do
not need to report their memberships. This host MLD report suppression mechanism helps
reduce traffic on the local subnet.
At the same time, because Host A is interested in G2, it sends a report to the IPv6 multicast
4.
group G2.
Through the query/report process, the MLD routers determine that G1 and G2 have members
5.
on the local subnet. The IPv6 multicast routing protocol (for example, IPv6 PIM) that is running
on the routers generates (*, G1) and (*, G2) multicast forwarding entries. These entries are the
basis for subsequent IPv6 multicast forwarding. The asterisk (*) represents any IPv6 multicast
source.
When the IPv6 multicast data addressed to G1 or G2 reaches an MLD router, the router looks
6.
up the IPv6 multicast forwarding table. Based on the (*, G1) and (*, G2) entries, the router
forwards the IPv6 multicast data to the local subnet. Then, the receivers on the subnet receive
the data.
Leaving an IPv6 multicast group
When a host is leaving a multicast group, the following process occurs:
The host sends an MLD done message to all IPv6 multicast routers on the local subnet. The
1.
destination address of done messages is FF02::2.
Figure 88, Host B and Host C want to receive the IPv6 multicast data addressed to IPv6
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