15-8
Catalyst 2360 Switch Software Configuration Guide
OL-19808-01
Chapter 15 Configuring IGMP Snooping
Configuring IGMP Snooping
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 to 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.
Note
If you want to use CGMP as the learning method and no multicast routers in the VLAN are CGMP
proxy-enabled, you must enter the
ip cgmp router-only
command to dynamically access the router.
Beginning in privileged EXEC mode, follow these steps to alter the method in which a VLAN interface
dynamically accesses a multicast router:
To return to the default learning method, use the
no
ip igmp snooping vlan
vlan-id
mrouter learn cgmp
global configuration command.
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
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 1001
and 1006 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.
