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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter21 Configuring IGMP Snooping and MVR
Configuring IGMP Snooping
Setting the Snooping Method
Multicast-capable router ports are added to the forwarding table for every Layer2 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
Switch# show ip igmp snooping vlan 1
Global IGMP Snooping configuration:
-----------------------------------
IGMP snooping :Enabled
IGMPv3 snooping (minimal) :Enabled
Report suppression :Enabled
TCN solicit query :Disabled
TCN flood query count :2
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 ip igmp snooping vlan vlan-id mrouter
learn {cgmp | pim-dvmrp}Enable IGMP snooping on a VLAN.The VLAN ID range is 1 to 1005
when the standard software image (SI) is installed and 1 to 4094 when
the enhanced software image (EI) is installed.
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.
Step3 end Return to privileged EXEC mode.
Step4 show ip igmp snooping Verify the configuration.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.