24-7
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 24 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 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 contain this configuration information:
• Default IGMP Snooping Configuration, page 24-7
• Enabling or Disabling IGMP Snooping, page 24-8
• Setting the Snooping Method, page 24-9
• Configuring a Multicast Router Port, page 24-10
• Configuring a Host Statically to Join a Group, page 24-11
• Enabling IGMP Immediate Leave, page 24-11
• Configuring the IGMP Leave Timer, page 24-12
• Configuring TCN-Related Commands, page 24-13
• Configuring the IGMP Snooping Querier, page 24-15
• Disabling IGMP Report Suppression, page 24-16
Default IGMP Snooping Configuration
Table 24-3 shows the default IGMP snooping configuration.
Table 24-3 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
TCN
1
flood query count 2
TCN query solicitation Disabled
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