Cisco Catalyst 3120 User Manual

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Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
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Chapter 23 Configuring IGMP Snooping and MVR
Understanding IGMP Snooping
Figure 23-1 Initial IGMP Join Message
Router A sends a general query to the switch, which forwards the query to ports 2 through 5, which are
all members of the same VLAN. Blade Server 1 wants to join multicast group 224.1.2.3 and multicasts
an IGMP membership report (IGMP join message) to the group. The switch CPU uses the information
in the IGMP report to set up a forwarding-table entry, as shown in Table 23-1, that includes the port
numbers of Blade Server 1 and the router.
The switch hardware can distinguish IGMP information packets from other packets for the multicast
group. The information in the table tells the switching engine to send frames addressed to the 224.1.2.3
multicast IP address that are not IGMP packets to the router and to the host that has joined the group.
Forwarding
table
CPU
Router A
IGMP report 224.1.2
.3
VLAN
Switching engine
19
0
135 7
201772
Blade
Server 1
Blade
Server 2
Blade
Server 3
Blade
Server 4
Table 23-1 IGMP Snooping Forwarding Table
Destination Address Type of Packet Ports
224.1.2.3 IGMP 1, 2

Cisco Catalyst 3120 Specifications

General

Brand	Cisco
Model	Catalyst 3120
Category	Switch
Language	English