Cisco Systems 3750E Setting the Snooping Method, Ip igmp snooping vlan vlan-id mrouter, 24-9

Chapter 24 Configuring IGMP Snooping and MVR

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-idmrouter 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-idmrouter learn pim-dvmrpglobal 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-onlycommand to dynamically access the router. For more information, see Chapter 42, “Configuring IP Multicast Routing.”

Beginning in privileged EXEC mode, follow these steps to alter the method in which a VLAN interface dynamically accesses a multicast router:

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2 ip igmp snooping vlan vlan-idmrouter		Enable IGMP snooping on a VLAN. The VLAN ID range is 1 to 1001
	learn {cgmp pim-dvmrp}	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.

To return to the default learning method, use the no ip igmp snooping vlan vlan-idmrouter learn cgmp global configuration command.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

OL-9775-02 24-9