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Chapter 44 Multicast
XS3800-28 User’s Guide
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MLD Messages
A multicast router or switch periodically sends general queries to MLD hosts to update the multicast
forwarding table. When an MLD host wants to join a multicast group, it sends an MLD Report message
for that address.
An MLD Done message is similar to an IGMP Leave message. When an MLD host wants to leave a
multicast group, it can send a Done message to the router or switch. If the leave mode is not set to
Immediate , the router or switch sends a group-specific query to the port on which the Done message is
received to determine if other devices connected to this port should remain in the group.
MVR Overview
Multicast VLAN Registration (MVR) is designed for applications (such as Media-on-Demand (MoD)) that
use multicast traffic across an Ethernet ring-based service provider network.
MVR allows one single multicast VLAN to be shared among different subscriber VLANs on the network.
While isolated in different subscriber VLANs, connected devices can subscribe to and unsubscribe from
the multicast stream in the multicast VLAN. This improves bandwidth utilization with reduced multicast
traffic in the subscriber VLANs and simplifies multicast group management.
MVR only responds to IGMP join and leave control messages from multicast groups that are configured
under MVR. Join and leave reports from other multicast groups are managed by IGMP snooping.
The following figure shows a network example. The subscriber VLAN ( 1 , 2 and 3 ) information is hidden
from the streaming media server, S . In addition, the multicast VLAN information is only visible to the
Switch and S .
Figure 219 MVR Network Example
Types of MVR Ports
In MVR, a source port is a port on the Switch that can send and receive multicast traffic in a multicast
VLAN while a receiver port can only receive multicast traffic. Once configured, the Switch maintains a
forwarding table that matches the multicast stream to the associated multicast group.
MVR Modes
You can set your Switch to operate in either dynamic or compatible mode.
In dynamic mode, the Switch sends IGMP leave and join reports to the other multicast devices (such as
multicast routers or servers) in the multicast VLAN. This allows the multicast devices to update the
multicast forwarding table to forward or not forward multicast traffic to the receiver ports.