Setting The Snooping Method - Cisco Catalyst 3120 Software Manual

Chapter 23 Configuring IGMP Snooping and MVR

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:
•
•
•
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.
If you want to use CGMP as the learning method and no multicast routers in the VLAN are CGMP
Note
proxy-enabled, you must enter the ip cgmp router-only command to dynamically access the router. For
more information, see
Beginning in privileged EXEC mode, follow these steps to alter the method in which a VLAN interface
dynamically accesses a multicast router:
Command
Step 1
configure terminal
Step 2
ip igmp snooping vlan vlan-id mrouter
learn {cgmp | pim-dvmrp}
Step 3
end
Step 4 show ip igmp snooping
Step 5
copy running-config startup-config
To return to the default learning method, use the no ip igmp snooping vlan vlan-id mrouter learn cgmp
global configuration command.
OL-12247-01
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
Chapter 44, "Configuring IP Multicast Routing."
Purpose
Enter global configuration mode.
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.
Return to privileged EXEC mode.
Verify the configuration.
(Optional) Save your entries in the configuration file.
Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
Configuring IGMP Snooping
23-9