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Internet Engineering Task Force                                 H. Stenn
Internet-Draft                                   Network Time Foundation
Intended status: Standards Track                          March 25, 2019
Expires: September 26, 2019


               Network Time Protocol I-Do Extension Field
                        draft-stenn-ntp-i-do-06

Abstract

   This proposal defines and describes a mechanism by which cooperating
   NTP instances may communicate any optional features they are willing
   to admit they support.

   RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH BEFORE PUBLISHING:

   The source code and issues list for this draft can be found in
   https://github.com/hstenn/ietf-ntp-i-do

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 26, 2019.

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
   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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  The I-Do Extension Field  . . . . . . . . . . . . . . . . . .   2
     2.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  I-DO Packet Format  . . . . . . . . . . . . . . . . . . .   4
     2.3.  Behavior  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The first implementation of NTPv4 was released in 2003, and was
   defined by RFC 5905 [RFC5905].  It contains an optional and now
   obsolete public-key security protocol, Autokey, which is defined by
   RFC 5906 [RFC5906].  Until very recently, Autokey has been the only
   implemented use of NTP packet Extension Fields.  New proposals for
   extension fields are being written and there is currently no
   convenient way to learn if a remote instance of NTP supports any
   extension fields or not.  This proposal contains a method to tell a
   remote instance of NTP what we (are willing to admit we) support, and
   ask what they (are willing to admit they) support.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  The I-Do Extension Field

2.1.  Overview

   The purpose of the I-DO EF is to provide information to the remote
   side about our capabilities.

   If an incoming packet contains an unrecognized extension field, one
   of several things will happen.  While that unrecognized extension



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   field SHOULD be ignored, an implementation MAY choose to drop the
   entire packet.

   If any extension field is present there ordinarily SHOULD be a MAC
   following the extension field.  However, an older conforming NTP
   implementation will require that any EF MUST be followed by a MAC.

   Some extension fields are unable to be "signed" by a MAC, regardless
   of whether or not that MAC is a traditional MAC or an extension field
   MAC.

   In the previous two cases, a conforming legacy system that receives
   these types of packets will interpret the unrecognized EF as a
   missing or legacy MAC, and return a crypto-NAK.

   If the remote system replies with a crypto-NAK, that is a good
   indication that it is running older software that does not recognize
   EFs and thinks we have sent an invalid MAC.  In this case, we SHOULD
   NOT send that system newer EFs.

   If the remote system replies without including an I-DO-RESPONSE EF,
   we at least know they can handle EFs, but they either don't
   understand I-DO or are not willing to tell us anything.  In this
   case, we SHOULD NOT send any newer EFs.

   If the remote system replies with a packet that includes an I-DO-
   RESPONSE EF, then we SHOULD remember what they told us, and use that
   information appropriately.  In other words, we can exchange packets
   containing any new EFs that we agree on, and we should not exchange
   packets containing any new EFs that we have not agreed on.

   In client/server mode, it makes sense for the client to send an I-DO
   to the server, and notice how the server responds.  While the server
   SHOULD respond with an I-DO-RESPONSE EF, it likely does not make
   sense for the server to send an I-DO EF in response to a client
   request.

   In symmetric mode, either side may initiate sending an I-DO EF, and
   the receiving side SHOULD reply with an I-DO-RESPONSE EF.

   In broadcast mode, the broadcast server MAY send broadcast packets
   that include an I-DO EF, but note that if, counter to recommended
   practice, these packets are unauthenticated they MAY cause client
   machines to misinterpret the packet as having invalid authentication.
   In this situation, the broadcast server SHOULD alternate sending
   broadcast server packets with and without an I-DO EF, to insure that
   all clients receive time packets they will accept.  Note that if, as
   recommended, broadcast packets are authenticated, a conforming client



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   SHOULD have no difficulty in receiving a broadcast (mode 5) packet
   from a server that includes an I-DO EF.

2.2.  I-DO Packet Format

   The content of the I-DO extension field is an ordinary four octet
   Extension Field header followed by a payload consisting of an
   appropriate number of two octet I-DO values that use nonzero values
   to indicate a supported feature.  An I-DO value of zero is ignored.
   The payload section must end on a four-octet boundary.

   There are two types of nonzero I-DO values that may be used.  They
   are both defined in the IANA NTP Extension Field Table (Section 4).
   These values are either Extension Field Types, where only the low-
   order values (0x01 thru 0xFE) are used, or I-DO Types, where all 16
   bits are used and the bottom octet is currently always 0xFF.

   The examples below are built using information from the following
   Standards and proposals:

      RFC 5906 [RFC5906]

      NTP-EXTENSION-FIELDS [NTP-EXTENSION-FIELD]

      MAC-LAST-EF [DRAFT-MAC-LAST-EF]

    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
   +---------------+---------------+-------------------------------+
   |          Field Type           |        Field Length           |
   +-------------------------------+-------------------------------+
   |            I-Do 1             |             ...               |
   +-------------------------------+-------------------------------+
   |            I-Do N             |            Padding            |
   +---------------------------------------------------------------+

                   NTP Extension Field: I-DO - Overview

   Field Type: TBD (Recommendation for IANA: 0x0007 (I-Do), 0x8007 (I-Do
   Response))

   Field Length: as needed

   Payload: An enumeration of the supported base Field Types, followed
   by any zero padding (0x0000) needed to fill the payload to the
   desired 32-bit boundary.





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   Example: A system that wants to advertise support for Autokey and
   I-DO, sending to a system that responds with support for I-DO, NTS,
   MAC-EF, and LAST-EF.

    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
   +---------------+---------------+-------------------------------+
   |    Field Type (0x0007)        |   Field Length (0x0008)       |
   +-------------------------------+-------------------------------+
   |            0x0007             |           0x0002              |
   +-------------------------------+-------------------------------+

                    NTP Extension Field: I-Do - Example

    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
   +---------------+---------------+-------------------------------+
   |    Field Type (0x8007)        |   Field Length (0x000a)       |
   +-------------------------------+-------------------------------+
   |            0x0003             |           0x0004              |
   +-------------------------------+-------------------------------+
   |            0x0007             |           0x0008              |
   +-------------------------------+-------------------------------+

               NTP Extension Field: I-Do Response - Example

2.3.  Behavior

   The sender of any I-Do extension field MUST send an extension field
   with a Field Type of 0x0007 (I-Do) and SHOULD include a payload with
   any 0x0000 padding values after enumerating the supported base
   Extension Field Types.  If the responding system recognizes the I-Do
   extension field, its response MUST include an extension field with a
   Field Type of 0x8007 (I-Do Response), and SHOULD include a payload
   with any 0x0000 padding values after enumerating the supported base
   Extension Field Types.

   Any system that receives an I-Do extension field as either an "offer"
   or a "response" SHOULD scan the entire payload looking for nonzero
   values that specify the capabilities of the remote association.

   Any system that receives an I-Do "offer", 0x0007, SHOULD reply with
   an I-Do "response", 0x8007.

   Any system that sends an I-Do "offer" or "response" may send as few
   or as many of its supported Field Types as it chooses.  At any
   subsequent time, either side may re-negotiate the list of supported




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   field types it is prepared to accept from the other system by sending
   a new I-Do extension field.

   The most-recently received I-Do list replaces any previous I-Do list.

3.  Acknowledgements

   The author wishes to acknowledge the contributions of Sam Weiler.

4.  IANA Considerations

   This memo requests IANA to allocate NTP Extension Field Types:

      0x0007 (I-DO)

      0x8007 (I-DO Response)

   and NTP Extension Field I-DO types:

      0x00FF through

      0xFDFF Reserved for future I-DO types

      0xFEFF (I-DO Leap Smear REFIDs)

      0xFFFF (I-DO IPv6 REFID hash)

   for this proposal.

5.  Security Considerations

   No addtional or unusual security considerations are expected if this
   proposal is adopted.

   No feedback has been received suggesting this proposal creates any
   new security considerations.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.






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   [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>.

6.2.  Informative References

   [DRAFT-MAC-LAST-EF]
              Stenn, H., "draft-stenn-ntp-mac-last-ef", 2018.

   [NTP-EXTENSION-FIELD]
              Stenn, H., "draft-stenn-ntp-extension-fields", 2018.

   [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>.

Author's Address

   Harlan Stenn
   Network Time Foundation
   P.O. Box 918
   Talent, OR  97540
   US

   Email: stenn@nwtime.org
























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