Why is an SCTP association's MTU not reduced when an ICMP Fragmentation Needed packet is received while Path MTU Discovey is enabled?

Solution In Progress - Updated -

Issue

  • There are a rapid amount of SCTP retransmissions that are far faster than the minimum RTO. Further investigation shows that these are the results of ICMP Fragmentation Needed errors. Why do these retransmissions keep happening?
  • Why is the retransmission of SCTP traffic upon receipt of an ICMP Fragmentation Needed message (due to Path MTU Discovery) not either allowing fragmentation or reducing the frame size to fit the needed MTU?

Environment

  • Red Hat Enterprise Linux (RHEL) 7.4 through 7.6 (version 7.3 does not have this issue)

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