How Mldv1 Works - HP 4800G Series Configuration Manual

For more information about the ASM and SSM models, see Multicast Overview in the IP Multicast
Volume.

How MLDv1 Works

MLDv1 implements IPv6 multicast listener management based on the query/response mechanism.
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 1-1 MLD queries and reports
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
IPv6 network
Querier
Router B
Host B
(G1)
Host C
(G1)
1-2