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Chapter 23 Configuring IGMP Snooping and MVR
Understanding Multicast VLAN Registration
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 blade server 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:
•
In compatible mode, multicast data received by MVR blade servers is forwarded to all MVR data
ports, regardless of MVR blade server membership on those ports. The multicast data is forwarded
only to those receiver ports that MVR blade servers have joined, either by IGMP reports or by MVR
static configuration. IGMP reports received from MVR blade servers are never forwarded from
MVR data ports that were configured in the blade server.
•
In dynamic mode, multicast data received by MVR blade servers on the switch is forwarded from
only those MVR data and client ports that the MVR blade servers have joined, either by IGMP
reports or by MVR static configuration. Any IGMP reports received from MVR blade servers are
also forwarded from all the MVR data ports in the blade server. This eliminates using unnecessary
bandwidth on MVR data port links, which occurs when the blade server runs in compatible mode.
Only Layer 2 ports take part in MVR. You must configure ports as MVR receiver ports. Only one MVR
multicast VLAN per switch or 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.
