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DES-3810 Series Layer 3 Managed Ethernet Switch Web UI Reference Guide
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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 an 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 four ICMPv6 packet headers, labeled 130, 131, 132, and 143.
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, Version 1
– 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.
4.
Multicast Listener Report, Version 2
- Comparable to the Host Membership Report in IGMPv3, and
labeled as 143 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.
Data Driven Learning
The Switch allows you to implement data driven learning for MLD snooping groups. If data-driven learning, also known
as dynamic IP multicast learning, is enabled for a VLAN, when the Switch receives IP multicast traffic on the VLAN, an
MLD snooping group is created. Learning of an entry is not activated by MLD membership registration, but activated
by the traffic. For an ordinary MLD snooping entry, the MLD protocol will take care of the aging out of the entry. For a
data-driven entry, the entry can be specified not to age out or to age out by a timer.
When the data driven learning State is enabled, the multicast filtering mode for all ports is ignored. This means
multicast packets will be flooded as a forwarding table.
NOTE:
If a data-driven group is created and MLD member ports are learned later, the entry will become an
ordinary MLD snooping entry. In other words, the aging out mechanism will follow the conditions of an
ordinary MLD snooping entry.
Data driven learning is useful on a network which has video cameras connected to a Layer 2 switch that is recording
and sending IP multicast data. The switch needs to forward IP data to a data centre without dropping or flooding any
packets. Since video cameras do not have the capability to run MLD protocols, the IP multicast data will be dropped
with the original MLD snooping function.
MLD Snooping Settings
Users can configure the settings for MLD snooping.
To view the following window, click
L2 Features > L2 Multicast Control > MLD Snooping > MLD Snooping
Settings
, as shown below:
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