Cisco Nexus 7000 Series Configuration Manual page 53

Configuring MLD
Note MLDv1 membership report suppression occurs only on hosts that are connected to the same port.
In this figure, router A sends the MLDv2 group-and-source-specific query to the LAN. Hosts 2 and 3 respond
to the query with listener reports that indicate that they want to receive data from the advertised group and
source. This MLDv2 feature supports SSM.
Note In MLDv2, all hosts respond to queries.
Figure 13: MLDv2 Group-and-Source-Specific Query
The software elects a router as the MLD querier on a subnet if it has the lowest IP address. As long as a router
continues to receive query messages from a router with a lower IP address, it remains a nonquerier and resets
a timer that is based on its querier timeout value. If the querier timer of a router expires, it becomes the
designated querier. If that router later receives a host query message from a router with a lower IP address, it
drops its role as the designated querier and sets its querier timer again.
Messages sent by the designated querier have a time-to-live (TTL) value of 1, which means that the messages
are not forwarded by the directly connected routers on the subnet, and you can configure the frequency and
number of query messages sent specifically for MLD startup. You can configure a short query interval at
startup so that the group state is established as quickly as possible. Although usually unnecessary, you can
tune the query interval used after startup to a value that balances responsiveness to host group membership
and the traffic created on the network.
Caution
If you change the query interval, you can severely impact multicast forwarding in your network.
When a multicast host leaves a group, it should send a done message for MLDv1, or a listener report that
excludes the group to the link-scope all-routers multicast address FF02::2. To check if this host is the last host
to leave the group, the software sends an MLD query message and starts a timer that you can configure called
the last member query response interval. If no reports are received before the timer expires, the software
removes the group state. The router continues to send multicast traffic for a group until its state is removed.
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
MLD Basics
39