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Appendix B. Changes Since RFC 1981

This document is based on RFC 1981 and has the following changes from RFC 1981:

  • Clarified in Section 1, "Introduction", that the purpose of PMTUD is to reduce the need for IPv6 fragmentation.

  • Added text to Section 1, "Introduction", about the effects on PMTUD when ICMPv6 messages are blocked.

  • Added a "Note" to the introduction to document that this specification doesn't cite RFC 2119 and only uses lower case "should/must" language. Changed all upper case "should/must" to lower case.

  • Added a short summary to Section 1, "Introduction", about PLPMTUD and a reference to RFC 4821 that defines it.

  • Aligned text in Section 2, "Terminology", to match current packetization layer terminology.

  • Added clarification in Section 4, "Protocol Requirements", that nodes should validate the payload of ICMP PTB messages per RFC 4443, and that nodes should detect decreases in PMTU as fast as possible.

  • Removed a "Note" from Section 4, "Protocol Requirements", about a Packet Too Big message reporting a next-hop MTU that is less than the IPv6 minimum link MTU because this was removed from [RFC8200].

  • Added clarification in Section 5.2, "Storing PMTU Information", to discard an ICMPv6 Packet Too Big message if it contains an MTU less than the IPv6 minimum link MTU.

  • Added clarification in Section 5.2, "Storing PMTU Information", that for nodes with multiple interfaces, Path MTU information should be stored for each link.

  • Removed text in Section 5.2, "Storing PMTU Information", about Routing Header type 0 (RH0) because it was deprecated by RFC 5095.

  • Removed text about obsolete security classification from Section 5.2, "Storing PMTU Information".

  • Changed the title of Section 5.4 to "Packetization Layer Actions" and changed the text in the first paragraph to generalize this section to cover all packetization layers, not just TCP.

  • Clarified text in Section 5.4, "Packetization Layer Actions", to use normal packetization layer retransmission methods.

  • Removed text in Section 5.4, "Packetization Layer Actions", that described 4.2 BSD because it is obsolete, and removed reference to TP4.

  • Updated text in Section 5.5, "Issues for Other Transport Protocols", about NFS, including adding a current reference to NFS and removing obsolete text.

  • Added a paragraph to Section 6, "Security Considerations", about black-hole connections if PTB messages are not received and comparison to PLPMTUD.

  • Updated "Acknowledgements".

  • Editorial Changes.

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