H3C Technologies H3C S12500-X Series Switches - Manual (Page 144)

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Configuring MLD
Overview
Multicast Listener Discovery (MLD) establishes and maintains IPv6 multicast group memberships between
a Layer 3 multicast device and its directly connected hosts.
MLD has two versions:
• MLDv1 (defined by RFC 2710), which is derived from IGMPv2.
• MLDv2 (defined by RFC 3810), which is derived from IGMPv3.
The two MLD versions support the ASM model. In addition, MLDv2 can directly implement the SSM
model, but MLDv1 must work with the MLD SSM mapping function to implement the SSM model. For
more information about the ASM and SSM models, see " Multicast overview ."
The term "interface" in this chapter collectively refers to VLAN interfaces and Layer 3 Ethernet interfaces.
You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see
Layer 2—LAN Switching Configuration Guide).
How MLDv1 works
MLDv1 implements IPv6 multicast listener management based on the query and response mechanism.
Electing the MLD querier
All IPv6 multicast routers that run MLD on the same subnet can monitor MLD listener report messages
(often called "reports") from hosts, but the subnet needs only one router to act as the MLD querier to send
MLD query messages (often called "queries"). A querier election mechanism determines which router
acts as the MLD querier on the subnet.
1. Initially, every MLD router assumes itself as the querier and sends MLD general query messages
(often called "general queries") to all hosts and routers on the local subnet. The destination address
of the messages is FF02::1.
2. After receiving a general query, every MLD router compares the source IPv6 address of the query
with its own link-local interface address. After comparison, the router with the lowest IPv6 address
becomes the querier and all other routers become non-queriers.
3. All the non-queriers start a timer called the "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 has timed out and initiates a new querier election process.