H3C Technologies H3C S10500 Series Switches - Manual (Page 271)

256
MLD snooping configuration
MLD snooping overview
Multicast Listener Discovery (MLD) snooping is an IPv6 multicast constraining mechanism that runs on
Layer 2 devices to manage and control IPv6 multicast groups.
By analyzing received MLD messages, a Layer 2 device that runns MLD snooping establishes mappings
between ports and multicast MAC addresses and forwards IPv6 multicast data based on these
mappings.
As shown in
Figure 67 , 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 67 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 has the following
advantages:
• Reducing Layer 2 broadcast packets, thus saving network bandwidth
• Enhancing the security of multicast traffic
• Facilitating the implementation of per-host accounting
Basic concepts in MLD snooping
MLD snooping related ports
As shown in Figure 68 , Router A connects to the multicast source, MLD snooping runs on Switch A and
Switch B, and Host A and Host C are receiver hosts (namely, IPv6 multicast group members).