RFC 3376, "Internet Group Management Protocol, Version 3", October 2002
Note: This RFC has been updated by RFC 4604Source of RFC: idmr (rtg)
Errata ID: 5562
Status: Held for Document Update
Publication Format(s) : TEXT
Reported By: Wim De Smet
Date Reported: 2018-11-26
Held for Document Update by: Alvaro Retana
Date Held: 2019-02-08
Section 6.2.1 says:
When a router filter-mode for a group is EXCLUDE, the source record list contains two types of sources. The first type is the set which represents conflicts in the desired reception state; this set must be forwarded by some router on the network. The second type is the set of sources which hosts have requested to not be forwarded. Appendix A describes the reasons for keeping this second set when in EXCLUDE mode.
It should say:
Appendix A.3 contains the following:
One of the ways to accomplish this is for routers to keep track of
all sources desired by hosts that are in INCLUDE mode even though the
router itself is in EXCLUDE mode.
Appendix A.3 makes clear that in EXCLUDE mode we need to keep track of the set of hosts that *are* desired (i.e. set A in section 6.4 or the "first type" in this paragraph). The second set (set B in section 6.4) is the set that will be reported to upstream routers, it is not the set which is needed for smooth switching to INCLUDE mode (the behavior described in appendix A). I believe that the intended description may have been "Appendix A describes the reasons for keeping two different sets when in EXCLUDE mode". At the very least, it appears to be set A (the "first set") which is intended in appendix A.