Network Time Protocol I-Do Extension Field
draft-stenn-ntp-i-do-03

Internet Engineering Task Force                                 H. Stenn
Internet-Draft                                   Network Time Foundation
Intended status: Standards Track                       November 29, 2017
Expires: June 2, 2018

               Network Time Protocol I-Do Extension Field
                        draft-stenn-ntp-i-do-03

Abstract

   The first implementation of NTPv4 was released in 2003.  NTPv4 is
   defined by RFC 5905 [RFC5905].  It contains a public-key security
   protocol, Autokey, which is defined by RFC 5906 [RFC5906].  Until
   very recently, Autokey has been the only defined "user" 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.

Status of This Memo

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   This Internet-Draft will expire on June 2, 2018.

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  The I-Do Extension Field  . . . . . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The first implementation of NTPv4 was released in 2003.  NTPv4 is
   defined by RFC 5905 [RFC5905].  It contains a public-key security
   protocol, Autokey, which is defined by RFC 5906 [RFC5906].  Until
   very recently, Autokey has been the only defined "user" 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

   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
   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, but an older
   conforming NTP implementation would assume 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

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   or an extension field MAC.  In the final case, the receiving system
   will interpret the unrecognized EF as a 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
   behave accordingly with regard to the remote system.

   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.

   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 client/server mode, it makes sense for the client to send an I-DO
   to the server, and notice how the server responds.  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
   SHOULD have no difficulty in receiving a broadcast (mode 5) packet
   from a server that includes an I-DO 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: REFID Suggestion

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   Field Type: TBD (Recommendation for IANA: 0x0007 (I-Do, MAC
   required), 0x2007 (I-Do, MAC OPTIONAL), 0x8007 (I-Do Response, MAC
   required), 0xA007 I-Do Response, MAC OPTIONAL))

   Field Length: as needed

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

   Example: A system that wants to advertise support for Autokey and
   I-Do, sending to a system that wants to advertise support for I-Do,
   NTS, and MAC-As-Extension-Field

    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 (0x2007)        |   Field Length (0x0008)       |
   +-------------------------------+-------------------------------+
   |            0x0007             |           0x0002              |
   +-------------------------------+-------------------------------+

                         NTP Extension Field: I-Do

    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 (0xA007)        |   Field Length (0x000a)       |
   +-------------------------------+-------------------------------+
   |            0x0003             |           0x0004              |
   +-------------------------------+-------------------------------+
   |            0x0007             |           0x0000              |
   +-------------------------------+-------------------------------+

                    NTP Extension Field: I-Do Response

   The sender of any I-Do extension field MUST send an extension field
   with a Field Type of 0x0007 (I-Do, MAC required) or 0x2007 (I-Do, MAC
   OPTIONAL) 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, MAC required) or 0xA007 (I-Do Response, MAC OPTIONAL), and
   SHOULD include a payload with any 0x0000 padding values after
   enumerating the supported base Extension Field Types.

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   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 or 0x2007, SHOULD
   reply with an I-Do "response", 0x8007 or 0xA007.

   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
   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.  IANA Considerations

   This memo requests IANA to allocate NTP Extension Field Types:

      0x0007 (I-DO)

      0x2007 (I-DO, MAC OPTIONAL)

      0x8007 (I-DO Response)

      0xA007 (I-DO Response, MAC OPTIONAL)

   and I-DO types:

      0xFFFE (I-DO Leap Smear REFIDs)

      0xFFFF (I-DO IPv6 REFID hash)

   for this proposal.

4.  Security Considerations

   Additional information TBD

5.  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>.

   [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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