



Internet Engineering Task Force (IETF)                           R. Salz
Request for Comments: 9748                           Akamai Technologies
Updates: 5905, 5906, 7821, 7822, 8573                      February 2025
Category: Standards Track                                               
ISSN: 2070-1721


                      Updating the NTP Registries

Abstract

   The Network Time Protocol (NTP) and Network Time Security (NTS)
   documents define a number of registries, collectively called the NTP
   registries.

   Some registries are correct, but some include incorrect assignments
   and some don't follow common practice.  For the sake of completeness,
   this document reviews all NTP and NTS registries, and corrects the
   registries where necessary.

   This document updates RFCs 5905, 5906, 7821, 7822, and 8573.

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
   https://www.rfc-editor.org/info/rfc9748.

Copyright Notice

   Copyright (c) 2025 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
   (https://trustee.ietf.org/license-info) 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 Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Existing Registries
     2.1.  Reference ID and Kiss-o'-Death Registries
     2.2.  Extension Field Types
     2.3.  Network Time Security Registries
   3.  NTP Registry Updates
     3.1.  Designated Experts
   4.  IANA Considerations
     4.1.  NTP Reference Identifier Codes
     4.2.  NTP Kiss-o'-Death Codes
     4.3.  NTP Extension Field Types
   5.  Security Considerations
   6.  Normative References
   Acknowledgements
   Author's Address

1.  Introduction

   The Network Time Protocol (NTP) and Network Time Security (NTS)
   documents define a number of registries, collectively called the NTP
   registries.  The NTP registries can all be found at
   <https://www.iana.org/assignments/ntp-parameters> and the NTS
   registries can all be found at <https://www.iana.org/assignments/
   nts>.

   Some registries are correct, but some include incorrect assignments
   and some don't follow common practice.  For the sake of completeness,
   this document reviews all NTP and NTS registries, and corrects the
   registries where necessary.

   The bulk of this document can be divided into two parts:

   *  a summary of the relevant registries, including syntax
      requirements, registration procedures, and the defining documents.

   *  a revised format and entries for each registry being modified.

2.  Existing Registries

   This section describes the registries and the rules for them.  It is
   intended to be a short summary of the syntax and registration
   requirements for each registry.  The semantics and protocol
   processing rules for each registry -- that is, how an implementation
   acts when sending or receiving any of the fields -- are not described
   here.

2.1.  Reference ID and Kiss-o'-Death Registries

   [RFC5905] defines two registries: "NTP Reference Identifier Codes" in
   Section 7.3 and the "NTP Kiss-o'-Death Codes" in Section 7.4.
   Reference identifiers and kiss codes can be up to four ASCII
   characters, padded on the right with all-bits-zero if necessary.
   Entries that start with 0x58, the ASCII letter uppercase X, are
   reserved for Private or Experimental Use. Both registries are First
   Come First Served.  The registries were created per Section 16 of
   [RFC5905].

2.2.  Extension Field Types

   Section 7.5 of [RFC5905] defines the on-the-wire format of extension
   fields but does not create a registry for them.

   Section 13 of [RFC5906] mentions the "NTP Extension Field Types"
   registry, and defines it indirectly by defining 30 extensions (10
   each for request, response, and error response).  It does not provide
   a formal definition of the columns in the registry.  Section 10 of
   [RFC5906] splits the Field Type into four subfields, only for use
   within the Autokey extensions.

   [RFC7821] adds a new entry, Checksum Complement, to the "NTP
   Extension Field Types" registry.

   [RFC7822] clarifies the processing rules for Extension Field Types,
   particularly around the interaction with the Message Authentication
   Code (MAC) field.  NTPv4 packets may contain a MAC that appears where
   one would expect the next extension field header.

   [RFC8573] changes the cryptography used in the MAC field.

   [RFC8915] adds four new entries to the "NTP Extension Field Types"
   registry.

   The following problems exist with the current registry:

   *  Many of the entries in the "NTP Extension Field Types" registry
      have swapped some of the nibbles; for example, 0x0302 was listed
      for Cookie Message Request instead of 0x0203.  The errors are due
      to documentation errors with the original implementation of
      Autokey.  This document marks the erroneous values as reserved, in
      case there is an implementation using the registered values
      instead of what the original implementation used.  Applications
      that used those values would have realized that they did not
      interoperate with the dominant (if not only) implementation at the
      time.  Marking the values as reserved ensures that any such
      applications continue to work as is.

   *  Some values were mistakenly reused.

2.3.  Network Time Security Registries

   [RFC8915] defines the NTS protocol.  The related registries are
   listed here for completeness, but there are no changes specified in
   this document.

   In [RFC8915]:

   Sections 7.1 through 7.5 (inclusive) added entries to existing
   registries.

   Section 7.6 created the "Network Time Security Key Establishment
   Record Types" registry that partitions the range into three different
   registration policies: IETF Review, Specification Required, and
   Private or Experimental Use.

   Section 7.7 created the "Network Time Security Next Protocols"
   registry that similarly partitions the range.

   Section 7.8 created the "Network Time Security Error Codes" and
   "Network Time Security Warning Codes" registries.  Both registries
   are partitioned the same way.

3.  NTP Registry Updates

   The following general guidelines apply to the NTP registries:

   *  A partition of the "NTP Extension Field Types" registry is
      reserved for Private or Experimental Use.

   *  In the "NTP Reference Identifier Codes" and "NTP Kiss-o'-Death
      Codes" registries, entries with ASCII fields are now limited to
      uppercase letters or digits.  Fields starting with 0x58, the
      uppercase letter "X", are reserved for Private or Experimental
      Use.

   *  The policy for each registry is now Specification Required, as
      defined in [RFC8126], Section 4.6.

3.1.  Designated Experts

   The IESG is requested to choose three designated experts (DEs), with
   approvals from two being required to implement a change.  Guidance
   for the experts is given below.

   The DEs should be familiar with [RFC8126], particularly Section 5.
   As that reference suggests, the DE should ascertain the existence of
   a suitable specification and verify that it is publicly available.
   The DE is also expected to check the clarity of purpose and use of
   the requested code points.

   In addition, the DE is expected to be familiar with this document,
   specifically the history documented here.

4.  IANA Considerations

   Each entry described in the subsections below is intended to
   completely replace the existing entry with the same name.

4.1.  NTP Reference Identifier Codes

   The registration procedure has been changed to Specification Required
   and this document has been added as a reference.

   The Note has been changed to read as follows:

   |  Codes beginning with the character "X" are reserved for
   |  experimentation and development.  IANA cannot assign them.

   The columns are defined as follows:

   ID (required):  a four-byte value padded on the right with all-bits-
      zero.  Each byte other than padding must be ASCII uppercase
      letters or digits.
   Clock source (required):  a brief text description of the ID.
   Reference (required):  the publication defining the ID.

   The existing entries are left unchanged.

4.2.  NTP Kiss-o'-Death Codes

   The registration procedure is changed to Specification Required and
   this document has been added as a reference.

   The Note has been changed to read as follows:

   |  Codes beginning with the character "X" are reserved for
   |  experimentation and development.  IANA cannot assign them.

   The columns are defined as follows:

   ID (required):  a four-byte value padded on the right with all-bits-
      zero.  Each byte other than padding must be ASCII uppercase
      letters or digits.
   Meaning source (required):  a brief text description of the ID.
   Reference (required):  the publication defining the ID.

   The existing entries are left unchanged.

4.3.  NTP Extension Field Types

   The registration procedure has been changed to Specification Required
   and [RFC5906] and this document have been added as references.

   The following two Notes have been added:

   |  Field Types in the range 0xF000 through 0xFFFF, inclusive, are
   |  reserved for experimentation and development.  IANA cannot assign
   |  them.  Both NTS Cookie and Autokey Message Request have the same
   |  Field Type; in practice this is not a problem as the field
   |  semantics will be determined by other parts of the message.

   |  The "Reserved for historic reasons" is for differences between the
   |  original documentation and implementation of Autokey and marks the
   |  erroneous values as reserved, in case there is an implementation
   |  that used the registered values instead of what the original
   |  implementation used.

   The columns are defined as follows:

   Field Type (required):  a two-byte value in hexadecimal.
   Meaning (required):  a brief text description of the field type.
   Reference (required):  the publication defining the field type.

   IANA has updated the registry as shown in Table 1.

   +===============+====================================+=============+
   | Field Type    | Meaning                            | Reference   |
   +===============+====================================+=============+
   | 0x0000        | Crypto-NAK; authentication failure | [RFC5905]   |
   +---------------+------------------------------------+-------------+
   | 0x0002        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0102        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0104        | Unique Identifier                  | [RFC8915],  |
   |               |                                    | Section 5.3 |
   +---------------+------------------------------------+-------------+
   | 0x0200        | No-Operation Request               | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0201        | Association Message Request        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0202        | Certificate Message Request        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0203        | Cookie Message Request             | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0204        | Autokey Message Request            | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0204        | NTS Cookie                         | [RFC8915],  |
   |               |                                    | Section 5.4 |
   +---------------+------------------------------------+-------------+
   | 0x0205        | Leapseconds Message Request        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0206        | Sign Message Request               | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0207        | IFF Identity Message Request       | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0208        | GQ Identity Message Request        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0209        | MV Identity Message Request        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x0302        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0304        | NTS Cookie Placeholder             | [RFC8915],  |
   |               |                                    | Section 5.5 |
   +---------------+------------------------------------+-------------+
   | 0x0402        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0404        | NTS Authenticator and Encrypted    | [RFC8915],  |
   |               | Extension Fields                   | Section 5.6 |
   +---------------+------------------------------------+-------------+
   | 0x0502        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0602        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0702        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0802        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x0902        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x2005        | UDP Checksum Complement            | [RFC7821]   |
   +---------------+------------------------------------+-------------+
   | 0x8002        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8102        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8200        | No-Operation Response              | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8201        | Association Message Response       | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8202        | Certificate Message Response       | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8203        | Cookie Message Response            | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8204        | Autokey Message Response           | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8205        | Leapseconds Message Response       | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8206        | Sign Message Response              | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8207        | IFF Identity Message Response      | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8208        | GQ Identity Message Response       | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8209        | MV Identity Message Response       | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0x8302        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8402        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8502        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8602        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8702        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8802        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0x8902        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC002        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC102        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC200        | No-Operation Error Response        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC201        | Association Message Error Response | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC202        | Certificate Message Error Response | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC203        | Cookie Message Error Response      | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC204        | Autokey Message Error Response     | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC205        | Leapseconds Message Error Response | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC206        | Sign Message Error Response        | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC207        | IFF Identity Message Error         | [RFC5906]   |
   |               | Response                           |             |
   +---------------+------------------------------------+-------------+
   | 0xC208        | GQ Identity Message Error Response | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC209        | MV Identity Message Error Response | [RFC5906]   |
   +---------------+------------------------------------+-------------+
   | 0xC302        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC402        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC502        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC602        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC702        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC802        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xC902        | Reserved for historic reasons      | RFC 9748    |
   +---------------+------------------------------------+-------------+
   | 0xF000-0xFFFF | Reserved for Private or            | RFC 9748    |
   |               | Experimental Use                   |             |
   +---------------+------------------------------------+-------------+

                                 Table 1

5.  Security Considerations

   This document adds no new security considerations, as they are
   defined in the document that defines the extension.  See the
   References column of the appropriate IANA registry.

6.  Normative References

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC5906]  Haberman, B., Ed. and D. Mills, "Network Time Protocol
              Version 4: Autokey Specification", RFC 5906,
              DOI 10.17487/RFC5906, June 2010,
              <https://www.rfc-editor.org/info/rfc5906>.

   [RFC7821]  Mizrahi, T., "UDP Checksum Complement in the Network Time
              Protocol (NTP)", RFC 7821, DOI 10.17487/RFC7821, March
              2016, <https://www.rfc-editor.org/info/rfc7821>.

   [RFC7822]  Mizrahi, T. and D. Mayer, "Network Time Protocol Version 4
              (NTPv4) Extension Fields", RFC 7822, DOI 10.17487/RFC7822,
              March 2016, <https://www.rfc-editor.org/info/rfc7822>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8573]  Malhotra, A. and S. Goldberg, "Message Authentication Code
              for the Network Time Protocol", RFC 8573,
              DOI 10.17487/RFC8573, June 2019,
              <https://www.rfc-editor.org/info/rfc8573>.

   [RFC8915]  Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R.
              Sundblad, "Network Time Security for the Network Time
              Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020,
              <https://www.rfc-editor.org/info/rfc8915>.

Acknowledgements

   The members of the NTP Working Group helped a great deal.  Notable
   contributors include:

   *  Miroslav Lichvar, Red Hat

   *  Daniel Franke, formerly at Akamai Technologies

   *  Danny Mayer, Network Time Foundation

   *  Michelle Cotton, formerly at IANA

   *  Tamme Dittrich, Tweede Golf

Author's Address

   Rich Salz
   Akamai Technologies
   Email: rsalz@akamai.com
