Packetization Layer Path MTU Discovery for Datagram Transports
RFC 8899

Document Type RFC - Proposed Standard (September 2020; No errata)
Authors Gorry Fairhurst  , Tom Jones  , Michael Tüxen  , Irene Ruengeler  , Timo Voelker 
Last updated 2020-09-11
Replaces draft-fairhurst-tsvwg-datagram-plpmtud
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Stream WG state Submitted to IESG for Publication (wg milestone: Apr 2020 - Submit 'Packetizatio... )
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IESG IESG state RFC 8899 (Proposed Standard)
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Internet Engineering Task Force (IETF)                      G. Fairhurst
Request for Comments: 8899                                      T. Jones
Updates: 4821, 4960, 6951, 8085, 8261             University of Aberdeen
Category: Standards Track                                       M. Tüxen
ISSN: 2070-1721                                              I. Rüngeler
                                                               T. Völker
                                  Münster University of Applied Sciences
                                                          September 2020

     Packetization Layer Path MTU Discovery for Datagram Transports


   This document specifies Datagram Packetization Layer Path MTU
   Discovery (DPLPMTUD).  This is a robust method for Path MTU Discovery
   (PMTUD) for datagram Packetization Layers (PLs).  It allows a PL, or
   a datagram application that uses a PL, to discover whether a network
   path can support the current size of datagram.  This can be used to
   detect and reduce the message size when a sender encounters a packet
   black hole.  It can also probe a network path to discover whether the
   maximum packet size can be increased.  This provides functionality
   for datagram transports that is equivalent to the PLPMTUD
   specification for TCP, specified in RFC 4821, which it updates.  It
   also updates the UDP Usage Guidelines to refer to this method for use
   with UDP datagrams and updates SCTP.

   The document provides implementation notes for incorporating Datagram
   PMTUD into IETF datagram transports or applications that use datagram

   This specification updates RFC 4960, RFC 4821, RFC 6951, RFC 8085,
   and RFC 8261.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Classical Path MTU Discovery
     1.2.  Packetization Layer Path MTU Discovery
     1.3.  Path MTU Discovery for Datagram Services
   2.  Terminology
   3.  Features Required to Provide Datagram PLPMTUD
   4.  DPLPMTUD Mechanisms
     4.1.  PLPMTU Probe Packets
     4.2.  Confirmation of Probed Packet Size
     4.3.  Black Hole Detection and Reducing the PLPMTU
     4.4.  The Maximum Packet Size (MPS)
     4.5.  Disabling the Effect of PMTUD
     4.6.  Response to PTB Messages
       4.6.1.  Validation of PTB Messages
       4.6.2.  Use of PTB Messages
   5.  Datagram Packetization Layer PMTUD
     5.1.  DPLPMTUD Components
       5.1.1.  Timers
       5.1.2.  Constants
       5.1.3.  Variables
       5.1.4.  Overview of DPLPMTUD Phases
     5.2.  State Machine
     5.3.  Search to Increase the PLPMTU
       5.3.1.  Probing for a Larger PLPMTU
       5.3.2.  Selection of Probe Sizes
       5.3.3.  Resilience to Inconsistent Path Information
     5.4.  Robustness to Inconsistent Paths
   6.  Specification of Protocol-Specific Methods
     6.1.  Application Support for DPLPMTUD with UDP or UDP-Lite
       6.1.1.  Application Request
       6.1.2.  Application Response
       6.1.3.  Sending Application Probe Packets
       6.1.4.  Initial Connectivity
       6.1.5.  Validating the Path
       6.1.6.  Handling of PTB Messages
     6.2.  DPLPMTUD for SCTP
       6.2.1.  SCTP/IPv4 and SCTP/IPv6  Initial Connectivity  Sending SCTP Probe Packets  Validating the Path with SCTP  PTB Message Handling by SCTP
       6.2.2.  DPLPMTUD for SCTP/UDP  Initial Connectivity  Sending SCTP/UDP Probe Packets  Validating the Path with SCTP/UDP  Handling of PTB Messages by SCTP/UDP
       6.2.3.  DPLPMTUD for SCTP/DTLS  Initial Connectivity  Sending SCTP/DTLS Probe Packets
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