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Catalyst 3750 Switch Software Configuration Guide
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Chapter 23 Configuring IGMP Snooping and MVR
Configuring IGMP Snooping
IGMP Snooping and Switch Stacks
IGMP snooping functions across the switch stack; that is, IGMP control information obtained from one
switch is distributed to all switches in the stack. (See Chapter 5, “Managing Switch Stacks,” for more
information about switch stacks.) Regardless of the stack member through which IGMP multicast data
enters the stack, the data reaches the hosts that have registered for that group.
If a switch in the stack fails or is removed from the stack, only the members of the multicast group that
are on that switch will not receive the multicast data. All other members of a multicast group on other
switches in the stack continue to receive multicast data streams. However, multicast groups that are
common for both Layer 2 and Layer 3 (IP multicast routing) might take longer to converge if the stack
master is removed.
Configuring IGMP Snooping
IGMP snooping allows switches to examine IGMP packets and make forwarding decisions based on their
content.
These sections describe how to configure IGMP snooping:
• Default IGMP Snooping Configuration, page 23-6
• Enabling or Disabling IGMP Snooping, page 23-7
• Setting the Snooping Method, page 23-7
• Configuring a Multicast Router Port, page 23-9
• Configuring a Host Statically to Join a Group, page 23-10
• Enabling IGMP Immediate Leave, page 23-11
• Disabling IGMP Report Suppression, page 23-11
Default IGMP Snooping Configuration
Table 23-3 shows the default IGMP snooping configuration.
Table 23-3 Default IGMP Snooping Configuration
Feature Default Setting
IGMP snooping Enabled globally and per VLAN
Multicast routers None configured
Multicast router learning (snooping) method PIM-DVMRP
IGMP snooping Immediate Leave Disabled
Static groups None configured
IGMP report suppression Enabled
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