11-2
Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 11 Configuring IGMP Snooping and MVR
Understanding and Configuring IGMP Snooping
Layer 2 multicast groups learned through IGMP snooping are dynamic. However, you can statically
configure MAC multicast groups by using the ip igmp snooping vlan static command. If you specify
group membership for a multicast group address statically, your setting supersedes any automatic
manipulation by IGMP snooping. Multicast group membership lists can consist of both user-defined and
IGMP snooping-learned settings.
Catalyst 2950 switches support a maximum of 255 IP multicast groups and support both IGMP version
1 and IGMP version 2.
If a port spanning-tree, a port group, or a VLAN ID change occurs, the IGMP snooping-learned multicast
groups from this port on the VLAN are deleted.
In the IP multicast-source-only environment, the switch learns the IP multicast group from the IP
multicast data stream and only forwards traffic to the multicast router ports.
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. By default, IGMP snooping is enabled on all
VLANs, but it can be enabled and disabled on a per-VLAN basis.
Global IGMP snooping overrides the per-VLAN IGMP snooping capability. If global snooping is
disabled, you cannot enable VLAN snooping. If global snooping is enabled, you can enable or disable
snooping on a VLAN basis.
CLI: Enabling or Disabling IGMP Snooping
Beginning in privileged EXEC mode, follow these steps to globally enable IGMP snooping on the
switch:
To globally disable IGMP snooping on all VLAN interfaces, use the no ip igmp snooping global
command.
Beginning in privileged EXEC mode, follow these steps to enable IGMP snooping on a VLAN interface:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
ip igmp snooping Globally enable IGMP snooping in all existing VLAN interfaces.
Step 3
end Return to privileged EXEC mode.
Step 4
show ip igmp snooping Display snooping configuration.
Step 5
copy running-config startup-config (Optional) Save your configuration to the startup configuration.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
ip igmp snooping vlan vlan-id Enable IGMP snooping on the VLAN interface.
Step 3
end Return to privileged EXEC mode.
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