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Catalyst 3750 Switch Software Configuration Guide
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Chapter 23 Configuring IGMP Snooping and MVR
Understanding Multicast VLAN Registration
configured IP multicast group addresses, the switch CPU modifies the hardware address table to include
this receiver port and VLAN as a forwarding destination of the specified multicast stream when it is
received from the multicast VLAN. Uplink ports that send and receive multicast data to and from the
multicast VLAN are called MVR source ports.
Figure 23-3 Multicast VLAN Registration Example
When a subscriber changes channels or turns off the television, the set-top box 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 set-top box in the VLAN still subscribing to this group, that
set-top box must respond within the maximum response time specified in the query. If the CPU does not
receive a response, it eliminates the receiver port as a forwarding destination for this group.
If the Immediate-Leave feature is enabled on a receiver port, the port leaves a multicast group more
quickly. 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
SP1
Multicast
data
Multicast
data
Customer
premises
Multicast VLAN
SP
SP
RP = Receiver Port
SP = Source Port
Note: All source ports belong to
the multicast VLAN.
Hub
TV
data
Set-top boxSet-top box
TV TV
PC
SP
SP
SP
SP
IGMP join
Cisco router
Multicast
server
Switch B
SP2
RP1 RP2 RP3 RP4 RP5 RP6 RP7
101364
Switch A
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