4-1
4 MLD Snooping Configuration
When configuring MLD Snooping, go to these sections for information you are interested in:
z MLD Snooping Overview
z MLD Snooping Configuration Task List
z Displaying and Maintaining MLD Snooping
z MLD Snooping Configuration Examples
z Troubleshooting MLD Snooping
MLD Snooping Overview
Multicast Listener Discovery Snooping (MLD Snooping) is an IPv6 multicast constraining mechanism
that runs on Layer 2 devices to manage and control IPv6 multicast groups.
Introduction to MLD Snooping
By analyzing received MLD messages, a Layer 2 device running MLD Snooping establishes mappings
between ports and multicast MAC addresses and forwards IPv6 multicast data based on these
mappings.
As shown in
Figure 4-1, when MLD Snooping is not running, IPv6 multicast packets are broadcast to
all devices at Layer 2. When MLD Snooping runs, multicast packets for known IPv6 multicast groups
are multicast to the receivers at Layer 2.
Figure 4-1 Before and after MLD Snooping is enabled on the Layer 2 device
IPv6 multicast packet transmission
without MLD Snooping
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
IPv6 multicast packets
Layer 2 switch
IPv6 multicast packet transmission
when MLD Snooping runs
Source
Multicast router
Host A
Receiver
Host B
Host C
Receiver
Layer 2 switch
MLD Snooping forwards multicast data to only the receivers requiring it at Layer 2. It brings the
following advantages:
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