Lossless Path MTU Discovery (PMTUD)
draft-bonica-intarea-lossless-pmtud-00

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INTAREA WG                                                     R. Bonica
Internet-Draft                                                  M. Nayak
Intended status: Standards Track                        Juniper Networks
Expires: May 1, 2020                                           B. Newton
                                                                H. Alpan
                                                           R. Rosborough
                                                            M. President
                                                     Harvey Mudd College
                                                        October 29, 2019

                  Lossless Path MTU Discovery (PMTUD)
                 draft-bonica-intarea-lossless-pmtud-00

Abstract

   This document describes alternative IPv4 PMTUD procedures that do not
   prevent IP fragmentation and do no rely on the network's ability to
   deliver ICMP Destination Unreachable messages to the source node.
   This document also defines a new ICMP message.  IPv4 nodes emit this
   new message when they reassemble a fragmented packet.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 1, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

Bonica, et al.             Expires May 1, 2020                  [Page 1]
Internet-Draft               Lossless PMTUD                 October 2019

   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  The ICMP Packet Reassembly Message  . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   For reasons described in [RFC1191], IPv4 source nodes estimate the
   Path MTU (PMTU) between themselves and destination nodes.  An
   extremely conservative source node estimates the PMTU for each path
   to be equal to the IPv4 Minimum Link MTU (See Note 1).  While such
   conservative estimates are guaranteed to be less than or equal to the
   actual PMTU, they are likely to be much less than the actual PMTU.
   This may adversely affect upper-layer protocol performance.

   By executing PMTU Discovery (PMTUD) [RFC1191] procedures, IPv4 source
   nodes can maintain less conservative PMTU estimates.  In PMTUD, the
   source node produces an initial PMTU estimate.  This initial estimate
   is equal to the MTU of the first link along the path to the
   destination node.  It can be greater than the actual PMTU.

   Having produced an initial PMTU estimate, the source node sends non-
   fragmentable packets to the destination node (see NOTE 2).  If one of
   these packets is larger than the actual PMTU, a downstream router
   will not be able to forward the packet through the next link along
   the path.  Therefore, the downstream router drops the packet and
   sends an Internet Control Message Protocol (ICMP) [RFC0792]
   Destination Unreachable message to the source node.  The Code field
   in the ICMP message is set to (4) "fragmentation needed".  The ICMP
   message also indicates the MTU of the link through which the packet
   could not be forwarded.  The source node uses this information to
   refine its PMTU estimate.
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