R21xx-HP FlexFabric 11900 IP Multicast Configuration Guide

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Joining an IPv6 multicast group
Figure 42 MLD queries and reports
Assume that Host B and Host C want to receive the IPv6 multicast data addressed to IPv6 multicast group
G1, and Host A wants to receive the IPv6 multicast data addressed to G2, as shown in Figure 42. T
he
following process describes how the hosts join the IPv6 multicast groups and how the MLD querier (Router
B in Figure 42) main
tains the IPv6 multicast group memberships:
1. The hosts send unsolicited MLD reports to the IPv6 multicast groups they want to join without having
to wait for the MLD queries from the MLD querier.
2. The MLD querier periodically multicasts MLD queries (with the destination address FF02::1) to all
hosts and routers on the local subnet.
3. After receiving a query, Host B or Host C (the delay timer of whichever expires first) sends an MLD
report to the IPv6 multicast group G1 to announce its membership for G1. Assume that Host B
sends the report. After hearing the report from Host B, Host C, which is on the same subnet as Host
B, suppresses its own report for G1 because the MLD routers (Router A and Router B) already know
that at least one host on the local subnet is interested in G1. This mechanism, known as the "MLD
report suppression," helps reduce traffic on the local subnet.
4. At the same time, because Host A is interested in G2, it sends a report to the IPv6 multicast group
G2.
5. Through the query/report process, the MLD routers learn that G1 and G2 have members on the
local subnet, and 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.
Query
Report
Querier
Host A
(G2)
Host B
(G1)
Host C
(G1)
Ethernet
Router A Router B
IPv6 network