IGMP operating features

In the factory default configuration, IGMP is disabled. If multiple VLANs are not configured, configure IGMP on the default VLAN (DEFAULT_VLAN; VID = 1); if multiple VLANs are configured, configure IGMP on a per-VLAN basis for every VLAN where this feature is needed.

With the CLI, you can also configure the following options:

  • Forward with high priority: Disabling this parameter (the default) causes the switch or VLAN to process IP multicast traffic and other traffic, in the order received (usually normal priority). Enabling this parameter causes the switch or VLAN to give higher priority to IP multicast traffic than to other traffic.

  • Auto/blocked/forward: You can configure individual ports to any of the following states:

    • Auto (the default): Causes the switch to interpret IGMP packets and to filter IP multicast traffic based on the IGMP packet information for ports belonging to a multicast group. Thus IGMP traffic is forwarded on a specific port only if an IGMP host or multicast router is connected to the port.

    • Blocked: Causes the switch to block IGMP joins arriving on the blocked port. A multicast stream will still flood out a blocked port if no active joins have been received.

    • Forward: Causes the switch to forward all IGMP and IP multicast transmissions through the port.

  • Operation with or without IP addressing: Helps conserve IP addresses by enabling IGMP to run on VLANs that do not have an IP address. See Operation with or without IP addressing.

  • Querier capability: The switch performs this function for IGMP on VLANs having an IP address when no other device in the VLAN is acting as querier. See Using the switch as querier.

NOTE:

Whenever IGMP is enabled, the switch generates an Event Log message indicating whether querier functionality is enabled.

IP multicast traffic groups are identified by IP addresses in the range of 224.0.0.0 to 239.255.255.255 and incoming IGMP packets intended for reserved, or “well-known” multicast addresses automatically flood through all ports (except the port on which the packets entered the switch). For more on this topic, see Excluding multicast addresses from IP multicast filtering.