Network Time Protocol Version 4 (NTPv4) Extension Fields
draft-stenn-ntp-extension-fields-00

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Internet Engineering Task Force                               T. Mizrahi
Internet-Draft                                                   Marvell
Intended status: Standards Track                                D. Mayer
Expires: May 17, 2017                                           H. Stenn
                                                 Network Time Foundation
                                                       November 13, 2016

        Network Time Protocol Version 4 (NTPv4) Extension Fields
                  draft-stenn-ntp-extension-fields-00

Abstract

   Network Time Protocol version 4 (NTPv4) defines the optional usage of
   extension fields.  An extension field, as defined in RFC 5905
   [RFC5905], resides after the end of the NTP header, and supplies
   optional capabilities or information that is not conveyed in the
   standard NTP header.  This document updates RFC 5905 [RFC5905] by
   clarifying some points regarding NTP extension fields and their usage
   with legacy Message Authentication Codes (MACs).

   With the adoption of this update, the authors recommend rescinding
   [Err3627].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on May 17, 2017.

Copyright Notice

   Copyright (c) 2016 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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Terms and Abbreviations . . . . . . . . . . . . . . . . .   3
   3.  NTP Extension Fields - RFC 5905 Update  . . . . . . . . . . .   3
     3.1.  OLD: 7.5 NTP Extension Field Format . . . . . . . . . . .   3
     3.2.  NEW: 7.5 NTP Extension Field Format . . . . . . . . . . .   4
     3.3.  NEW: 7.5.1 Extension Fields and MACs  . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The NTP header format consists of a set of fixed fields that may be
   followed by optional fields.  Two types of optional fields are
   defined: extension fields as defined in Section 7.5 of RFC 5905
   [RFC5905], and legacy Message Authentication Codes (legacy MACs).

   If a legacy MAC is used, it resides at the end of the packet.  This
   field can be either a 4-octet crypto-NAK or data that is usually 20
   or 24 octets long.

   NTP extension fields are defined in RFC 5905 [RFC5905] as a generic
   mechanism that allows the addition of future extensions and features
   without modifying the NTP header format (Section 16 of RFC 5905
   [RFC5905]).

   Section 7.5 of RFC 5905 [RFC5905] clearly states that "one or more
   extension fields can be inserted after the header and before the MAC,
   which is always present when an extension field is present."
   However, the experimental Checksum Complement RFC 7821 [RFC7821]
   cannot be used if the NTP packet contains a MAC.

   To allow for extension fields that do not require a MAC, changes to
   the NTPv4 specification must be made.  [Err3627] was an attempt to

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