Netis ST3326(ST-3302) [96/118] Igmp snooping

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 MAC addresses 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.

10.1 IGMP Snooping