D-Link xStack DGS-3426P User Manual - Mld Snooping

xStack DGS-3400 Series Layer 2 Gigabit Ethernet Managed Switch 

MLD Snooping 

Multicast Listener Discovery (MLD) Snooping is an IPv6 function used similarly to IGMP snooping in IPv4. It is used to discover 

ports on a VLAN that are requesting multicast data. Instead of flooding all ports on a selected VLAN with multicast traffic, MLD 

snooping will only forward multicast data to ports that wish to receive this data through the use of queries and reports produced by 

the requesting ports and the source of the multicast traffic.  

MLD snooping is accomplished through the examination of the layer 3 part of an MLD control packet transferred between end 

nodes and a MLD router. When the Switch discovers that this route is requesting multicast traffic, it adds the port directly attached 

to it into the correct IPv6 multicast table, and begins the process of forwarding multicast traffic to that port. This entry in the 

multicast routing table records the port, the VLAN ID and the associated multicast IPv6 multicast group address and then 

considers this port to be a active listening port. The active listening ports are the only ones to receive multicast group data. 

MLD Control Messages 

Three types of messages are transferred between devices using MLD snooping. These three messages are all defined by three 

ICMPv6 packet headers, labeled 130, 131 and 132. 

1.

Multicast Listener Query

 – Similar to the IGMPv2 Host Membership Query for IPv4, and labeled as 130 in the 

ICMPv6 packet header, this message is sent by the router to ask if any link is requesting multicast data. There are two 

types of MLD query messages emitted by the router. The General Query is used to advertise all multicast addresses that 

are ready to send multicast data to all listening ports, and the Multicast Specific query, which advertises a specific 

multicast address that is also ready. These two types of messages are distinguished by a multicast destination address 

located in the IPv6 header and a multicast address in the Multicast Listener Query Message.  

2.

Multicast Listener Report 

– Comparable to the Host Membership Report in IGMPv2, and labeled as 131 in the ICMP 

packet header, this message is sent by the listening port to the Switch stating that it is interested in receiving multicast 

data from a multicast address in response to the Multicast Listener Query message. 

3.

Multicast Listener Done

 – Akin to the Leave Group Message in IGMPv2, and labeled as 132 in the ICMPv6 packet 

header, this message is sent by the multicast listening port stating that it is no longer interested in receiving multicast data 

from a specific multicast group address, therefore stating that it is “done” with the multicast data from this address. Once 

this message is received by the Switch, it will no longer forward multicast traffic from a specific multicast group address 

to this listening port.  

MLD Snooping Settings 

To configure the settings for MLD snooping, click 

L2 Features > MLD Snooping > MLD Snooping Settings

, which will open 

the following window. 

Figure 7- 31. MLD Snooping Settings window 

This window displays the current MLD Snooping settings set on the Switch, defined by VLAN. To configure a specific VLAN for 

MLD snooping, click the VLAN’s corresponding 

 button, which will display the following window for the user to configure. 

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