IGMP general operation and features

In a network where IP multicast traffic is transmitted for various multimedia applications, you can use the switch to reduce unnecessary bandwidth usage on a per-port basis by configuring IGMP. In the factory default state (IGMP disabled), the switch simply floods all IP multicast traffic it receives on a given VLAN through all ports on that VLAN (except the port on which it received the traffic.) This can result in significant and unnecessary bandwidth usage in networks where IP multicast traffic is a factor. Enabling IGMP allows the ports to detect IGMP queries and report packets and manage IP multicast traffic through the switch.

IGMP is useful in multimedia applications such as LAN TV, desktop conferencing, and collaborative computing, where there is multipoint communication, that is, communication from one to many hosts, or communication originating from many hosts and destined for many other hosts. In such multipoint applications, IGMP is configured on the hosts, and multicast traffic is generated by one or more servers (inside or outside of the local network.) Switches in the network (that support IGMP) can then be configured to direct the multicast traffic to only the ports where needed. If multiple VLANs are configured, you can configure IGMP on a per-VLAN basis.

Enabling IGMP allows detection of IGMP queries and report packets used to manage IP multicast traffic through the switch. If no other querier is detected, the switch then also functions as the querier. If you need to disable the querier feature, do so through the IGMP configuration MIB, see Configuring the querier function.

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NOTE: IGMP configuration on the switches operates at the VLAN context level. If you are not using VLANs, configure IGMP in VLAN 1 (the default VLAN) context.

IGMP operating features

Basic operation

In the factory default configuration, IGMP is disabled. To enable IGMP

  • 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 to be used.


With the CLI, you can configure these additional options:


You can use the console to configure individual ports to any of the following states:


(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. This means that IGMP traffic will be forwarded on a specific port only if an IGMP host or multicast router is connected to the port.


Causes the switch to drop all IGMP transmissions received from a specific port. Outgoing queries are not blocked on the port.


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

Operation with or without IP addressing

This feature helps to 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 there is no other device in the VLAN acting as querier. See Using the switch as querier.

To configure high priority settings for traffic, see “Quality of Service: managing bandwidth more effectively” in the Advanced Traffic Management Guide.

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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 to Also, 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 Well-known or reserved multicast addresses excluded from IP multicast filtering.

For more information about IGMP, see How IGMP operates.

Number of IP multicast addresses allowed

The number of IGMP filters (addresses) and static multicast filters available is 2,038. Additionally, 16 static multicast filters are allowed, If multiple VLANs are configured, then each filter is counted once per VLAN in which it is used.