Joining A Multicast Group - Cisco 3020 - Catalyst Blade Switch Configuration Manual

Chapter 18 Configuring IGMP Snooping and MVR
IGMPv3 join and leave messages are not supported on switches running IGMP filtering or MVR.
Note
An IGMPv3 switch can receive messages from and forward messages to a device running the Source
Specific Multicast (SSM) feature. For more information about source-specific multicast with IGMPv3
and IGMP, see the following URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121t/121t5/dtssm5t.htm

Joining a Multicast Group

When a blade server connected to the switch wants to join an IP multicast group and it is an IGMP
Version 2 client, it sends an unsolicited IGMP join message, specifying the IP multicast group to join.
Alternatively, when the switch receives a general query from the router, it forwards the query to all ports
in the VLAN. IGMP Version 1 or Version 2 blade servers wanting to join the multicast group respond
by sending a join message to the switch. The switch CPU creates a multicast forwarding-table entry for
the group if it is not already present. The CPU also adds the interface where the join message was
received to the forwarding-table entry. The blade server associated with that interface receives multicast
traffic for that multicast group. See
Figure 18-1
Forwarding
OL-8915-01
Initial IGMP Join Message
Switching engine
CPU
0
table
1 3
Blade Blade
Server 1 Server 2
Figure 18-1.
Router A
19
IGMP report 224.1.2.3
VLAN
5 7
Blade Blade
Server 3 Server 4
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
Understanding IGMP Snooping
18-3