An IGMP version 3 receiver signals EXCLUDE mode report with an empty EXCLUDE list. What does this indicate?

In IGMP version 3, a receiver uses an EXCLUDE mode report to specify sources from which it does not want to receive traffic. The report essentially states, "send me traffic for this group from all sources, except for the ones in this list." When the EXCLUDE list is empty, the receiver is excluding zero sources. This logically means the receiver is willing to accept traffic from any and all sources for that multicast group. This is the standard method for an IGMPv3-capable host to signal a join for an Any-Source Multicast (ASM) group, which is functionally equivalent to a join in IGMPv1 or IGMPv2.

A. The report is a complete state declaration. An empty list is a valid and final state, not an indication that more information will follow in a subsequent message.

C. This report is an explicit request to receive multicast traffic for a group. A host that does not wish to join a group would simply not send a report.

D. Leaving a group in IGMPv3 is typically signaled by sending a report that changes the filter mode to INCLUDE with an empty source list (TOIN {}).

1. IETF RFC 3376, "Internet Group Management Protocol, Version 3", Section 5.2, Paragraph 2: "A MODEISEXCLUDE record with an empty source list indicates that the interface has a filter mode of EXCLUDE for that group, with an empty exclusion list. That is, it is requesting traffic from all sources."

2. Nokia 7750 SR OS Multicast Routing Protocols Guide, Release 21.10.R1, "IGMP", Section: IGMPv3: This guide details the protocol operations, explaining that an EXCLUDE report with a null source set (EXCLUDE {}) is the mechanism for joining an ASM group, indicating a desire to receive from any source.

3. Cain, B., et al. "Internet Group Management Protocol, Version 3 (IGMPv3) and Multicast Listener Discovery, Version 2 (MLDv2) for Source-Specific Multicast (SSM) Address Assignments." IEEE Network, vol. 17, no. 1, 2003, pp. 10-15. DOI: 10.1109/MNET.2003.1174174: This academic paper discusses IGMPv3 mechanics, clarifying that the EXCLUDE {} state is the functional equivalent of an IGMPv2 join, requesting traffic from all potential sources.