H3C Technologies H3C S7500E Series Switches - Manual (Page 322)

12-2
All MLD versions support the Any-Source Multicast (ASM) model. In addition, MLDv2 can be directly
deployed to implement the Source-Specific Multicast (SSM) model, while MLDv1 needs to work with
the MLD SSM mapping function to implement SSM service.
For more information about the ASM and SSM models, see Multicast Overview in the IP Multicast
Configuration Guide.
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
that the querier has timed out and initiates a new querier election process.