20-8
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 20 Configuring IGMP Snooping and MVR
Configuring IGMP Snooping
To disable IGMP snooping on a VLAN interface, use the no ip igmp snooping vlan vlan-id global
configuration command for the specified VLAN number.
Setting the Snooping Method
Multicast-capable router ports are added to the forwarding table for every Layer 2 multicast entry. The
switch learns of such ports through one of these methods:
• Snooping on IGMP queries, Protocol Independent Multicast (PIM) packets, and Distance Vector
Multicast Routing Protocol (DVMRP) packets
• Listening to Cisco Group Management Protocol (CGMP) packets from other routers
• Statically connecting to a multicast router port with the ip igmp snooping mrouter global
configuration command
You can configure the switch either to snoop on IGMP queries and PIM/DVMRP packets or to listen to
CGMP self-join or proxy-join packets. By default, the switch snoops on PIM/DVMRP packets on all
VLANs. To learn of multicast router ports through only CGMP packets, use the ip igmp snooping vlan
vlan-id mrouter learn cgmp global configuration command. When this command is entered, the router
listens to only CGMP self-join and CGMP proxy-join packets and no other CGMP packets. To learn of
multicast router ports through only PIM-DVMRP packets, use the ip igmp snooping vlan vlan-id
mrouter learn pim-dvmrp global configuration command.
Beginning in privileged EXEC mode, follow these steps to alter the method in which a VLAN interface
dynamically accesses a multicast router:
This example shows how to configure IGMP snooping to use CGMP packets as the learning method:
Switch# configure terminal
Switch(config)# ip igmp snooping vlan 1 mrouter learn cgmp
Switch(config)# end
Step 3 end Return to privileged EXEC mode.
Step 4 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 ip igmp snooping vlan vlan-id mrouter
learn {cgmp | pim-dvmrp}
Enable IGMP snooping on a VLAN. The VLAN ID range is 1 to 4094.
Specify the multicast router learning method:
• cgmp—Listen for CGMP packets. This method is useful for
reducing control traffic.
• pim-dvmrp—Snoop on IGMP queries and PIM-DVMRP packets.
This is the default.
Step 3 end Return to privileged EXEC mode.
Step 4 show ip igmp snooping Verify the configuration.
Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.