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17-5
Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 17 Configuring IGMP Snooping and MVR
Configuring IGMP Snooping
Note You should only use the Immediate-Leave processing feature on VLANs where a single host is
connected to each port. If Immediate Leave is enabled in VLANs where more than one host is connected
to a port, some hosts might be inadvertently dropped. Immediate Leave is supported with only IGMP
version 2 hosts.
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 17-5
• Enabling or Disabling IGMP Snooping, page 17-5
• Setting the Snooping Method, page 17-6
• Configuring a Multicast Router Port, page 17-7
• Configuring a Host Statically to Join a Group, page 17-8
• Enabling IGMP Immediate-Leave Processing, page 17-9
• Disabling IP Multicast-Source-Only Learning, page 17-9
Default IGMP Snooping Configuration
Table 17-3 shows the default IGMP snooping configuration.
Enabling or Disabling IGMP Snooping
By default, IGMP snooping is globally enabled on the switch. When globally enabled or disabled, it is
also enabled or disabled in all existing VLAN interfaces. IGMP snooping is by default enabled on all
VLANs, but can be enabled and disabled on a per-VLAN basis.
Global IGMP snooping overrides the VLAN IGMP snooping. If global snooping is disabled, you cannot
enable VLAN snooping. If global snooping is enabled, you can enable or disable VLAN snooping.
Table 17-3 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
IP multicast-source-only learning Enabled