IGMP Group Compatibility

IGMP group compatibility allows devices running higher IGMP versions to communicate with devices running lower IGMP versions.

In IGMP group compatibility mode, a multicast device of a higher IGMP version can also be compatible with the hosts of a lower IGMP version.

For example, the multicast device of the IGMPv2 version can correctly process the joining of hosts in the IGMPv1 version; the multicast device of the IGMPv3 version can correctly process the joining of hosts in the IGMPv1 or IGMPv2 version. When the multicast device operates in IGMP group compatibility mode, and receives IGMP Report messages from the hosts in a lower IGMP version, the multicast device automatically lowers the version of the corresponding multicast group to be the same as that for the hosts and then operates in this version.

For example, when the multicast device of IGMPv2 or IGMPv3 version receives Report messages from the hosts in the IGMPv1 version, the multicast device lowers the version of the corresponding multicast group to IGMPv1. Then, the multicast device ignores the IGMPv2 Leave messages in the multicast group.

In addition, when the multicast device of the IGMPv3 version receives Report messages from the hosts in the IGMPv2 version, the multicast device lowers the version of the corresponding multicast group to IGMPv2. Then, the multicast device ignores the IGMPv3 BLOCK messages, the IGMPv3 TO_IN messages, and the multicast source list in the IGMPv3 TO_EX messages. The multicast source-selecting function of IGMPv3 messages is suppressed.

If the IGMP version of a multicast device is configured higher, the multicast group of the original IGMP version can still function properly as soon as the multicast group contains hosts.

By default, the IGMP version of a multicast device is IGMPv2.