target = "https://www.rfc-editor.org/rfc/rfc8899#section-4.3"

# 4.3.  Black Hole Detection and Reducing the PLPMTU
#
# The description that follows uses the set of constants defined in
# Section 5.1.2 and variables defined in Section 5.1.3.
# 
# Black hole detection is triggered by an indication that the network
# path could be unable to support the current PLPMTU size.
# 
# There are three indicators that can be used to detect black holes:
# 
# *  A validated PTB message can be received that indicates a
#    PL_PTB_SIZE less than the current PLPMTU.  A DPLPMTUD method MUST
#    NOT rely solely on this method.
# 
# *  A PL can use the DPLPMTUD probing mechanism to periodically
#    generate probe packets of the size of the current PLPMTU (e.g.,
#    using the CONFIRMATION_TIMER, Section 5.1.1).  A timer tracks
#    whether acknowledgments are received.  Successive loss of probes
#    is an indication that the current path no longer supports the
#    PLPMTU (e.g., when the number of probe packets sent without
#    receiving an acknowledgment, PROBE_COUNT, becomes greater than
#    MAX_PROBES).
# 
# *  A PL can utilize an event that indicates the network path no
#    longer sustains the sender's PLPMTU size.  This could use a
#    mechanism implemented within the PL to detect excessive loss of
#    data sent with a specific packet size and then conclude that this
#    excessive loss could be a result of an invalid PLPMTU (as in
#    PLPMTUD for TCP [RFC4821]).
# 
# The three methods can result in different transmission patterns for
# packet probes and are expected to result in different responsiveness
# following a change in the actual PMTU.
# 
# A PL MAY inhibit sending probe packets when no application data has
# been sent since the previous probe packet.  A PL that resumes sending
# user data MAY continue PLPMTU discovery for each path.  This allows
# it to use an up-to-date PLPMTU.  However, this could result in
# additional packets being sent.
# 
# When the method detects that the current PLPMTU is not supported,
# DPLPMTUD sets a lower PLPMTU and a lower MPS.  The PL then confirms
# that the new PLPMTU can be successfully used across the path.  A
# probe packet could need to be smaller than the size of the data block
# generated by the application.

[[spec]]
level = "MUST"
quote = '''
A DPLPMTUD method MUST
NOT rely solely on this method.
'''

[[spec]]
level = "MAY"
quote = '''
A PL MAY inhibit sending probe packets when no application data has
been sent since the previous probe packet.
'''

[[spec]]
level = "MAY"
quote = '''
A PL that resumes sending
user data MAY continue PLPMTU discovery for each path.
'''