When IGMPv3 router in EXCLUDE(X, Y) state receives TO_IN(A)

Hi,

RFC 3376 Section 6.4.2 change state record handling router state machine
last line mentions about sending a group specific query in addition to the
source specific query.
I am not very sure if I am able to understand the necessity of this group
specific query. Usually a TO_IN(A) message is received from a host that
underwent a state change from EXCLUDE(A) to INCLUDE(A) which means the
router already had a state of EXCLUDE(X,Y) where A is a subset of Y. The
router then tries to find out if there is any host which still has interest
in receiving traffic for the sources already having source timer > 0. I do
not understand what is the use of sending a group specific query in this
case since the group specific query has a wider scoped purpose than the
source specific query.

Could it be that since for other cases no query is sent if sources to be
queried is NULL set, for this case only (since TO_IN(NULL) is the IGMPv3
translation for IGMPv2 Leave when older version host for that group is
present) a group specific query has to be sent regardless of whether the to
be queried source set is NULL or not.

Any help on these lines would be highly appreciated.

-- 
thanks,
Rohan Sen

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