Cisco Catalyst 2950 Software Manual page 275

Chapter 11 Configuring IGMP Snooping and MVR
Figure 11-3 Multicast VLAN Registration Example
Catalyst
2950 switch
SP
MVR eliminates the need to duplicate television-channel multicast traffic for subscribers in each VLAN.
Multicast traffic for all channels is sent only once around the VLAN trunk—only on the multicast
VLAN. Although the IGMP leave and join messages originate with a subscriber, they appear to be
initiated by a port in the multicast VLAN rather than 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 switch (S1 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.
IGMP reports are sent to the same MAC addresses as the multicast data. The S1 CPU must capture all
IGMP join and leave messages from receiver ports and forward them to the multicast VLAN of the
source (uplink) port.
78-11380-03
Catalyst
2950 switch
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
Cisco router
Multicast
server
SP
SP
Catalyst
2950 switch
SP2
S1
Hub
Set-top box
PC
TV
Note: All source ports belong to
the multicast VLAN.
Catalyst 2950 Desktop Switch Software Configuration Guide
Understanding Multicast VLAN Registration
Catalyst
2950 switch
SP
Multicast
data
11-9