3Com MSR 50 Series Configuration Manual page 1218

1218 C 73: MLD C
HAPTER ONFIGURATION
MLD querier election
Of multiple IPv6 multicast routers on the same subnet, all the routers can hear
MLD listener report messages (often referred to as reports) from hosts, but only
one router is needed for sending MLD query messages (often referred to as
queries). So, a querier election mechanism is required to determine which router
will act as the MLD querier on the subnet.
1 Initially, every MLD router assumes itself as the querier and sends MLD general
query messages (often referred to as general queries) to all hosts and routers on
the local subnet (the destination address is FF02::1).
2 Upon hearing a general query, every MLD router compares the source IPv6 address
of the query message with its own interface address. After comparison, the router
with the lowest IPv6 address wins the querier election and all other routers
become non-queriers.
3 All the non-queriers start a timer, known as "other querier present timer". If a
router receives an MLD query from the querier before the timer expires, it resets
this timer; otherwise, it assumes the querier to have timed out and initiates a new
querier election process.
Joining an IPv6 multicast group
Figure 353 Joining IPv6 multicast groups
Router A
Ethernet
Host A
(G2)
Query
Report
Assume that Host B and Host C are expected to receive IPv6 multicast data
addressed to IPv6 multicast group G1, while Host A is expected to receive IPv6
multicast data addressed to G2, as shown in
hosts join the IPv6 multicast groups is as follows:
1 The MLD querier (Router B in the figure) periodically multicasts MLD queries (with
the destination address of FF02::1) to all hosts and routers on the local subnet.
2 Upon receiving a query message, Host B or Host C (the delay timer of whichever
expires first) sends an MLD report to the IPv6 multicast group address of G1, to
announce its interest in G1. Assume it is Host B that sends the report message.
Querier
Router B
Host B Host C
(G1)
Figure
(G1)
353. The basic process that the