Install guide

IP Multicasting 29
Multicast Switching
IP multicast switching (in hardware) between VLANs is automatically enabled
when both of the following are true:
■ a multicast routing protocol (PIM-SM or PIM-DM) is enabled
■ an interface is configured for that multicast routing protocol.
VLAN tagging is fully supported, and the Time To Live (TTL) value in the IP
header is decremented. Multicast switching cannot be disabled.
Multicast VLAN Registration (MVR)
Multicast VLAN Registration (MVR) is used by applications receiving
multicast traffic across an Ethernet ring-based service provider network (for
example, broadcasting several television channels).
MVR operates on the underlying mechanism of the Internet Group
Management Protocol (IGMP) function (see “Internet Group Management
Protocol (IGMP)” on page 17), and requires that IGMP be enabled. Receiver
ports join and leave multicast streams by sending IGMP messages. With IGMP
and MVR both enabled, MVR reacts to join and leave messages from the
multicast group configured under MVR. IGMP reacts to all messages.
Once MVR is configured, the CPU sets up a forwarding table in which each
entry matches the multicast stream to an associated MAC address. The CPU
then intercepts the IGMP messages and modifies the forwarding table to
include or remove the receiver port as a receiver of the multicast stream. This
selectively allows traffic to cross between different VLANs.
Up to five multicast VLANs can be set up on a switch, and a total of 256 group
IP addresses can be added to the switch, divided up to belong to different
multicast VLANs.
Whenever MVR is enabled on the switch, multicast routing must be disabled.
Dynamic MVR
In dynamic mode, after the switch receives IGMP information packets, it
processes the data message, and resends those messages to a multicast router
through its source ports. The switch knows which multicast groups exist on
which interface when it receives a join message from the interface for the
group. It forwards the multicast stream to that interface.
Compatible MVR
In compatible mode, IGMP report messages are not sent through source ports.
The multicast router must be statically configured so it can forward multicast
streams to particular interfaces.