3Com 10014298 manual By default, a router does not join a multicast group

	Configuring IGMP 121
Table 126 Configure a Router to Be a Member of a Group
Operation	Command
Cancel a router’s membership of a multicast	undo igmp host-join group-address
group (VLAN interface group)	port { interface_type
	interface_num interface_name } [ to {
	interface_type interface_num
	interface_name } ]
Configure a router to be a member of a	igmp host-join group-addressvlan
multicast group (Ethernet interface view)	vlanid
Cancel a router’s membership of a multicast	undo igmp host-join group-address
group (Ethernet interface group)	vlan vlanid

By default, a router does not join a multicast group.

Limiting Access to IP Multicast Groups

A multicast router learns whether there are members of a multicast group on the network when it receives an IGMP membership message. A filter can be set on an interface to limit the range of allowed multicast groups.

Perform the following configuration in VLAN-interface view.

Table 127 Limit the Access to IP Multicast Groups

Operation	Command
Limit the range of allowed multicast groups	igmp group-policy acl-number [ 1
on current interface	2 ]
Remove the filter set on the interface	undo igmp group-policy
Limit the range of allowed multicast groups	igmp group policy acl-numbervlan
on current interface (Ethernet port view)	vlanid
Remove the filter set on the interface	undo igmp group policy vlan
(Ethernet port view)	vlanid

By default, no filters are configured. All multicast groups are allowed on the interface.

Configuring the IGMP Query Message Interval

Multicast routers send IGMP query messages to find present multicast groups on other networks. Multicast routers send query messages periodically to refresh their information of members present.

Perform the following configuration in VLAN interface view.

Table 128 Configure the IGMP Query Message Interval

Operation	Command
Configure the IGMP query message interval	igmp	timer query seconds
Restore the IGMP query message interval to	undo	igmp timer query
the default value

When there are multiple multicast routers on a network segment, the querier is responsible for sending IGMP query messages to all hosts on the LAN.

The default interval is 60 seconds.