# IGMP Interface Configuration

The Internet Group Management Protocol (IGMP) multicast protocol provides a mechanism for hosts and routers to maintain multicast group memberships. Multicast routing protocols, such as Protocol-Independent Multicast (PIM), then process the membership information from IGMP, create entries in the multicast routing table, and forwards multicast traffic to hosts throughout the network.

On some routers, IGMP is automatically enabled when you enable a multicast routing protocol. On security devices, you must explicitly enable IGMP on interfaces and a multicast routing protocol.

### To Configure IGMP on an Interface

1. Enter the necessary information.

IGMP Mode: Select one of the following:

Router: Enable IGMP in router mode on interfaces that are connected to hosts.

Host: Enable IGMP in host mode on upstream interfaces that are functioning as IGMP proxy interfaces.

Protocol IGMP: Select Enable to enable IGMP on the interface.

Packet Without Router Alert Option: By default, an IGMPv2/v3-enabled router accepts only IGMP packets with a router-alert IP option, and drops packets that do not have this option. IGMPv1 packets do not have this option and consequently, a NetScreen device running IGMPv2/v3 drops IGMPv1 packets by default. Select Permit for the NetScreen device to accept all IGMP packets, allowing backward compatibility with IGMPv1 routers.

Packet From Different Subnet: By default, an IGMP interface accepts IGMP messages from its own subnet only. It ignores IGMP messages from external sources. Select Permit to enable the NetScreen device to accept IGMP messages from sources in other subnets when you run IGMP proxy.

Router Mode only Settings: Configure the following settings when the interface is in router mode.

IGMP Version: When in router mode, the NetScreen device runs IGMPv2 by default. You can change the default and run IGMPv1, IGMPv2 and v3, or only IGMPv3.

Proxy: Select this option to enable IGMP proxy on the router interface.

Always: For a router interface to forward multicast traffic, it must be the querier in the local network. Select this option to allow a non-querier interface to forward multicast traffic.

Accept Group's Access List ID: Select the access list that identifies the multicast groups that hosts can join.

Accept Host's Access List ID: Select the access list that identifies the hosts from which the IGMP router interface can receive IGMP messages

Accept Router's Access List ID: Select the access list that identifies the queriers from which the IGMP router interface can receive IGMP messages

Last Member Query Interval: Specify the interval at which the interface sends a Group-Specific query. If it does not receive a response after the second Group-Specific query, then it assumes there are no more members for that group on its local network. The default is one second.

Leave Interval: Sets the interval (in seconds) between group specific-queries (range 1 - 255 inclusive).

Query Interval: Specify the interval at which the querier interface sends general queries to the “all hosts” group (224.0.0.1). The default is 125 seconds.

Query Maximum Response Time: Specify the maximum time between a general query and a response from the host. The default is 10 seconds.

Static MGroup: Click this option to create a static multicast group. For information on configuring a static multicast group, see Static Multicast Group.

2. Click Apply to save the configuration.