29-6
Cisco ASA 5500 Series Configuration Guide using ASDM
Chapter29 Configuring Multicast Routing
Customizing Multicast Routing
Configuring IGMP Features
IP hosts use the Internet Group Management Protocol (IGMP) to report their group memberships to
directly connected multicast routers.
IGMP is used to dynamically register individual hosts in a multicast group on a particular LAN. Hosts
identify group memberships by sending IGMP messages to their local multicast router. Under IGMP,
routers listen to IGMP messages and periodically send out queries to discover which groups are active
or inactive on a particular subnet.
IGMP uses group addresses (Class D IP address) as group identifiers. Host group address can be in the
range of 224.0.0.0 to 239.255.255.255. The address 224.0.0.0 is never assigned to any group. The
address 224.0.0.1 is assigned to all systems on a subnet. The address 224.0.0.2 is assigned to all routers
on a subnet.
When you enable multicast routing on the ASA, IGMP Version 2 is automatically enabled on all
interfaces.
Note Only the no igmp command appears in the interface configuration when you use the show run
command. If the multicast-routing command appears in the device configuration, then IGMP is
automatically enabled on all interfaces.
This section describes how to configure optional IGMP setting on a per-interface basis and includes the
following topics:
•Disabling IGMP on an Interface, page29-6
•Configuring IGMP Group Membership, page29-7
•Configuring a Statically Joined IGMP Group, page29-7
•Controlling Access to Multicast Groups, page29-8
•Limiting the Number of IGMP States on an Interface, page29-9
•Modifying the Query Messages to Multicast Groups, page29-9
•Changing the IGMP Version, page29-10

Disabling IGMP on an Interface

You can disable IGMP on specific interfaces. This information is useful if you know that there are no
multicast hosts on a specific interface and you want to prevent the ASA from sending host query
messages on that interface.
To disable IGMP on an interface, perform the following steps:
Step1 In the main ASDM window, choose Configuration > Device Setup > Routing > Multicast > IGMP >
Protocol.
The Protocol pane displays the IGMP parameters for each interface on the ASA.
Step2 Choose the interface that you want to disable and click Edit.
Step3 To disable the specified interface, uncheck the Enable IGMP check box.
Step4 Click OK.