Mld Basics - Cisco Nexus 7000 Series Configuration Manual

MLD Basics

By default, the software enables MLDv2 when it starts the MLD process. You can enable MLDv1 on interfaces
where you want only its capabilities.
MLDv2 includes the following key changes from MLDv1:
• Support for Source-Specific Multicast (SSM), which builds shortest path trees from each receiver to the
• Hosts no longer perform report suppression, which means that hosts always send MLD listener reports
For detailed information about MLDv1, see RFC 2710.For detailed information about MLDv2, see RFC 3810.
MLD Basics
The basic MLD process of a router that discovers multicast hosts is shown in the figure below. Hosts 1, 2,
and 3 send unsolicited MLD listener report messages to initiate receiving multicast data for a group or channel.
Figure 12: MLD Query-Response Process
In this figure, router A, which is the MLD designated querier on the subnet, sends a general query message
to the link-scope all-nodes multicast address FF02::1 periodically to discover what multicast groups hosts
want to receive. The group-specific query is used to discover whether a specific group is requested by any
hosts. You can configure the group membership timeout value that the router uses to determine that no members
of a group or source exist on the subnet.
In this figure, host 1's listener report is suppressed, and host 2 sends its listener report for group
FFFE:FFFF:90::1 first. Host 1 receives the report from host 2. Because only one listener report per group
needs to be sent to the router, other hosts suppress their reports to reduce network traffic. Each host waits for
a random time interval to avoid sending reports at the same time. You can configure the query maximum
response time parameter to control the interval in which hosts randomize their responses.
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
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source, through the following features:
• Host messages that can specify both the group and the source.
• The multicast state that is maintained for groups and sources, not just for groups as in MLDv1.
when an MLD query message is received.
Configuring MLD