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Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
OL-12247-01
Chapter 23 Configuring IGMP Snooping and MVR
Understanding Multicast VLAN Registration
Using MVR in a Multicast Television Application
Figure 23-3
Multicast VLAN Registration Example
When the subscriber changes channels or stops the multicast stream, the server sends an IGMP leave
message for the multicast stream. The switch CPU sends a MAC-based general query through the
receiver port VLAN. If there is another device in the VLAN still subscribing to this group, that device
must respond within the maximum response time specified in the query. If the CPU does not receive a
response, it eliminates the receiver ports as a forwarding destination for this group.
Without Immediate Leave, when the switch receives an IGMP leave message from a subscriber on a
receiver port, it sends out an IGMP query on that port and waits for IGMP group membership reports. If
no reports are received in a configured time period, the receiver port is removed from multicast group
membership. With Immediate Leave, an IGMP query is not sent from the receiver port on which the
IGMP leave was received. As soon as the leave message is received, the receiver port is removed from
multicast group membership, which speeds up leave latency. Enable the Immediate-Leave feature only
on receiver ports to which a single receiver device is connected.
MVR eliminates the need to duplicate multicast traffic for subscribers in each VLAN. Multicast traffic
for all channels is only sent around the VLAN trunk once—only on the multicast VLAN. The IGMP
leave and join messages are in the VLAN to which the subscriber port is assigned. These messages
dynamically register for streams of multicast traffic in the multicast VLAN on the Layer 3 device. The
access layer blade switch modifies the forwarding behavior to allow the traffic to be forwarded from the
multicast VLAN to the subscriber port in a different VLAN, selectively allowing traffic to cross between
two VLANs.
Multicast VLAN
SP
SP
SP
SP
RP1
RP2
RP3
RP4
RP5
RP = Receiver Port
SP = Source Port
Note: All source ports belong to
the
multicast
VLAN.
SP
Cisco router
Multicast
server
Server
Switch
Blade Switch
Switch
Switch
201915
Server
Server
Server
Server