Multimedia Traffic Control with IP Multicast (IGMP)

General Operation and Features

IGMP Operating Features

Basic Operation

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

The switches covered in this guide support up to 255 IGMP filters (addresses). If multiple VLANs are confgiured, each filter is counted once per VLAN in which it is used.

Enhancements

With the CLI, you can configure these additional options:

Forward with High Priority. Disabling this parameter (the default) causes the switch or VLAN to process IP multicast traffic, along with other traffic, in the order received (usually, normal priority). Enabling this parameter causes the switch or VLAN to give a higher priority to IP multicast traffic than to other traffic.

Auto/Blocked/Forward: You can use the console to 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. 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.

Blocked: Causes the switch to drop all IGMP transmissions received from a specific port and to block all outgoing IP Multicast packets for that port. This has the effect of preventing IGMP traffic from moving through specific ports.

Forward: 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” on page 4-13.

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 “Querier Operation” on page 4-22.

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