Chapter 24 Multicast
GS2220 Series User’s Guide
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MLD Me ssa g e s
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
Imme dia te , 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 O ve rvie w
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.
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