Understanding Multicast Vlan Registration; Using Mvr In A Multicast Television Application - Cisco WS-C3750-48PS-S Software Configuration Manual

Chapter 23 Configuring IGMP Snooping and MVR

Understanding Multicast VLAN Registration

Multicast VLAN Registration (MVR) is designed for applications using wide-scale deployment of
multicast traffic across an Ethernet ring-based service provider network (for example, the broadcast of
multiple television channels over a service-provider network). MVR allows a subscriber on a port to
subscribe and unsubscribe to a multicast stream on the network-wide multicast VLAN. It allows the
single multicast VLAN to be shared in the network while subscribers remain in separate VLANs. MVR
provides the ability to continuously send multicast streams in the multicast VLAN, but to isolate the
streams from the subscriber VLANs for bandwidth and security reasons.
MVR assumes that subscriber ports subscribe and unsubscribe (join and leave) these multicast streams
by sending out IGMP join and leave messages. These messages can originate from an IGMP
Version-2-compatible host with an Ethernet connection. Although MVR operates on the underlying
mechanism of IGMP snooping, the two features operate independently of each other. One can be enabled
or disabled without affecting the behavior of the other feature. However, if IGMP snooping and MVR
are both enabled, MVR reacts only to join and leave messages from multicast groups configured under
MVR. Join and leave messages from all other multicast groups are managed by IGMP snooping.
The switch CPU identifies the MVR IP multicast streams and their associated IP multicast group in the
switch forwarding table, intercepts the IGMP messages, and modifies the forwarding table to include or
remove the subscriber as a receiver of the multicast stream, even though the receivers might be in a
different VLAN from the source. This forwarding behavior selectively allows traffic to cross between
different VLANs.
You can set the switch for compatible or dynamic mode of MVR operation.
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Only Layer 2 ports take part in MVR. You must configure ports as MVR receiver ports. Only one MVR
multicast VLAN per switch stack is supported.
Receiver ports and source ports can be on different switches in a switch stack. Multicast data sent on the
multicast VLAN is forwarded to all MVR receiver ports across the stack. When a new switch is added
to a stack, by default it has no receiver ports.
If a switch fails or is removed from the stack, only those receiver ports belonging to that switch will not
receive the multicast data. All other receiver ports on other switches continue to receive the multicast
data.

Using MVR in a Multicast Television Application

In a multicast television application, a PC or a television with a set-top box can receive the multicast
stream. Multiple set-top boxes or PCs can be connected to one subscriber port, which is a switch port
configured as an MVR receiver port.
address to the set-top box or the PC. When a subscriber selects a channel, the set-top box or PC sends
an IGMP report to Switch A to join the appropriate multicast. If the IGMP report matches one of the
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In compatible mode, multicast data received by MVR hosts is forwarded to all MVR data ports,
regardless of MVR host membership on those ports. The multicast data is forwarded only to those
receiver ports which MVR hosts have explicitly joined, either by IGMP reports or by MVR static
configuration. Also, IGMP reports received from MVR hosts are never forwarded out of MVR data
ports that were configured in the switch.
In dynamic mode, multicast data received by MVR hosts on the switch is forwarded from only those
MVR data and client ports that the MVR hosts have explicitly joined, either by IGMP reports or by
MVR static configuration. Any IGMP reports received from MVR hosts are also forwarded from all
the MVR data ports in the switch. This eliminates using unnecessary bandwidth on MVR data port
links, which occurs when the switch runs in compatible mode.
Figure 23-3 is an example configuration. DHCP assigns an IP
Catalyst 3750 Switch Software Configuration Guide
Understanding Multicast VLAN Registration
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