HP IPv6 5400zl, IPv6 6200yl, IPv6 2900 manual Without MLD, multicast traffic is flooded to all ports

Multicast Listener Discovery (MLD) Snooping

Introduction to MLD Snooping

General operation. Multicast communication can take place without MLD, and by default MLD is disabled. In that case, if a switch receives a packet with a multicast destination address, it floods the packet to all ports in the same VLAN (except the port that it came in on). Any network nodes that are listening to that muticast address will see the packet; all other hosts ignore the packet.

MLD disabled

Listener

Switch

Source

Listener

Figure 7-1. Without MLD, multicast traffic is flooded to all ports.

When MLD snooping is enabled on a VLAN, the switch acts to minimize unnecessary multicast traffic. If the switch receives multicast traffic destined for a given multicast address, it forwards that traffic only to ports on the VLAN that have MLD hosts for that address. It drops that traffic for ports on the VLAN that have no MLD hosts (except for a few special cases explained below).

MLD snooping enabled

Listener

(MLD host)

Switch

Source

Listener

(MLD host)

Figure 7-2. With MLD snooping, traffic is sent to MLD hosts.

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