IPv6 Path MTU Option
draft-kline-6man-pmo-00

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Internet Engineering Task Force                                 E. Kline
Internet-Draft                                                  Loon LLC
Intended status: Standards Track                            July 8, 2019
Expires: January 9, 2020

                          IPv6 Path MTU Option
                        draft-kline-6man-pmo-00

Abstract

   This document describes an IPv6 Neighbor Discovery (ND) Path MTU
   Option (PMO) for inclusion in Router Advertisements (RAs).  This
   allows some environments greater flexibility to support, for example,
   a higher MTU for on-link or intra-administrative-domain
   communications than for broader Internet communications.

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 January 9, 2020.

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1.  Introduction

   This document describes an IPv6 Neighbor Discovery (ND) Path MTU
   Option (PMO) for inclusion in Router Advertisements (RAs).  This
   allows some environments greater flexibility to support, for example,
   a higher MTU for on-link or intra-administrative-domain
   communications than for broader Internet communications.

   TBD: Explain why extending RFC4191 RIOs didn't look easy.

   TBD: more discussion

2.  Terminology

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  Summary of key terms

   For the purposes of this document the following terms are used as
   described here.

2.2.1.  Link MTU

   The MTU of the link ([RFC4861]); alternatively, the MTU as it would
   be determined were no Path MTU Option (Section 2.2.5) present.  This
   may be:

      the value specified in an MTU Option (Section 2.2.4),

      a value specified in a separate document that covers operating IP
      over a particular link type (e.g., [RFC2464]), or

      a value derived by other means (e.g. administrative or a hint from
      a sub-IP layer mechanism).

   The Link MTU MUST be the initial Path MTU used when transmitting to
   any link-local destination.

Kline                    Expires January 9, 2020                [Page 2]
Internet-Draft            IPv6 Path MTU Option                 July 2019

2.2.2.  Path MTU

   TBD: Path MTU

2.2.3.  Path MTU Discovery

   TBD: Path MTU Discovery (cite [RFC8201])

2.2.4.  MTU Option

   The MTU Option is defined in [RFC4861] section 4.6.4.  In this
   documented it may also be referred to as the Link MTU Option, in
   order to disambiguate it from this the Path MTU Option
   (Section 2.2.5).

2.2.5.  Path MTU Option

   The IPv6 ND Path MTU Option is described in this document.  It
   provides more explicit signaling of the best initial Path MTU value
   for a given set of destinations when sending via the advertising
   router.

3.  Path MTU Option Format

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |     MTU #1 (upper 16 bits)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     MTU #1 (lower 16 bits)    | num prefixes  | prefix len #1 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   prefix #1  ...                                              |
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