Cisco 3750G - Catalyst Integrated Wireless LAN Controller Configuration Manual page 548

Understanding IGMP Snooping
Figure 24-1
Forwarding
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. Host 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
connected to Host 1 and the router.
Table 24-1
Destination Address
224.1.2.3
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.
Catalyst 3750 Switch Software Configuration Guide
24-4
Initial IGMP Join Message
PFC
CPU
0
table
2 3
Host 1 Host 2
IGMP Snooping Forwarding Table
Type of Packet
IGMP
Router A
1
IGMP report 224.1.2.3
VLAN
4 5
Host 3 Host 4
Table 24-1, that includes the port numbers
Ports
1, 2
Chapter 24 Configuring IGMP Snooping and MVR
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