Cisco Catalyst 2975 Software Configuration Manual page 570

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 22-3
Multicast VLAN
SP
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.
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
Catalyst 2975 Switch Software Configuration Guide
22-18
Multicast VLAN Registration Example
Switch B
SP
SP
SP1
Multicast
data
RP1 RP2 RP3 RP4 RP5 RP6 RP7
Customer
premises
IGMP join
Set-top box
TV
data
TV
RP = Receiver Port
SP = Source Port
Chapter 22
Cisco router
Multicast
server
SP
SP
SP2
Switch A
Hub
Set-top box
PC
TV
Note: All source ports belong to
the multicast VLAN.
Configuring IGMP Snooping and MVR
SP
Multicast
data
OL-19720-02