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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 the hosts on the directly connected subnet.
MLD has the following versions:
MLDv1 (defined by RFC 2710), which is derived from IGMPv2.
MLDv2 (defined by RFC 3810), which is derived from IGMPv3.
MLDv1 and MLDv2 support the ASM model. MLDv2 can directly implement the SSM model, but
MLDv1 must work with the MLD SSM mapping feature to implement the SSM model. For more
information about the ASM and SSM models, see "Multicast overview."
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. However, only one router can 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. Each router sends MLD general query
messages (often called general queries) to all hosts and routers on the local subnet. The
destination address of the general queries 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. The router with the lowest IPv6 address wins the
querier election and becomes the querier. All the 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 considers
that the querier has timed out. In this case, the router initiates a new querier election process.
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