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 Extended Information Extension Field
draft-stenn-ntp-extended-information-04
Abstract
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-extended-information-ef
The core network packet used by NTP has no spare bits available for
reporting additional state information and no larger data areas
available for larger amounts of information. This proposal offers a
new extension field that would contain this additional information.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. The Extended Information Extension Field . . . . . . . . . . 2
2.1. Version 0 Content Descriptor and Content Data fields . . 3
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The core NTP packet format has changed little since RFC 958 [RFC0958]
was published in 1985. Since then, there has been demonstrated need
to convey additional information about NTP's state in an NTP packet
but no backward-compatible way to usurp the few otherwise potentially
available bits has been found, and no larger data areas are available
in the core packet structure. This proposal offers a new extension
field that would contain this additional information.
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 Extended Information Extension Field
The Field Type of the Extended Information EF includes a version
number field in the low-order bits of the first octet, to make it
easier to evolve this specification. The initial specification for
this proposal uses Version 0, which equates to 0x0009 [ADJUST AS
NEEDED BASED ON IANA, IF AN IANA REGISTRY IS USED]. A future
revision for Version 1 would use 0x0109 [IBID].
The payload for Version 0 is comprised of a two octet Content
Descriptor followed by a two octet Content Data field, as described
below.
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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 |
+-------------------------------+-------------------------------+
| Content Descriptor 1 | Content Data 1 |
+---------------------------------------------------------------+
NTP Extension Field: Extended Information
Field Type: TBD (Recommendation for IANA: 0x0009 (Extended-
Information, Version 0))
Field Length: as needed
2.1. Version 0 Content Descriptor and Content Data fields
There are 16 bits available for state information in the Version 0
Extended Information Content Descriptor. These bits are allocated as
follows:
0x0001: TAI Offset is stored in the low-order 8 bits (the second
octet) of the Content Data.
0x0002: Interleave Mode indicator in the low order bit of the first
octet of the Content Data. [NOTE: this may not be useful, and it
can be removed if desired. It can serve as a belt-and-suspenders
way to identify when a packet contains interleaved timestamps.]
0xFFFD: Reserved for future versions. SHOULD be zeroes for Version
0, and the meaning of any nonzero values is unspecified.
The Content Data field of the Version 0 Extended Information
extension field is comprised of two octets, with the contents
allocated as follows:
0xXXNN: The low-order 8 bits (NNNN) are the TAI Offset. Any data in
the high-order 8 bits (XXXX) are not part of the TAI Offset.
0xX0XX: A value of 0 in the low-order bit of the first octet
indicates that the timestamps in the base packet are not
interleave-mode timestamps.
0xX1XX: A value of 1 in the low-order bit of the first octet
indicates that the timestamps in the base packet are interleave-
mode timestamps.
0xN2XX: thru
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0xNDXX: Any of the seven high-order bits in the first octet are
reserved for future versions and SHOULD be zero for Version 0.
The meaning of any nonzero values is unspecified.
Content Descriptor 1 Content Data 1
0x0001 TAI offset in the low-order 8 bits, 24-31
0x0002 Interleave Mode indicator in Bit 23
0xFFFD Reserved (Zeroes)
Interleave Mode: 1 if the sender is in interleave mode, 0 otherwise
NTP Extension Field: Extended Information, Version 0 Content Fields
Example: A system that wants to convey an offset to TAI of 36
seconds, and show it is in interleave mode.
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 (0x0009) | Field Length (0x0008) |
+-------------------------------+-------------------------------+
| 0x0003 | 0x0124 |
+-------------------------------+-------------------------------+
NTP Extension Field: Extended Information V0, Example
3. Acknowledgements
The author wishes to acknowledge the contributions of Martin Burnicki
and Sam Weiler.
4. IANA Considerations
This memo requests IANA to allocate NTP Extension Field Type
0x0009 (Extended-Information, Version 0)
for this proposal.
5. Security Considerations
No unusual or special security considerations are known to be
associated with this proposal.
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6. Normative References
[RFC0958] Mills, D., "Network Time Protocol (NTP)", RFC 958,
DOI 10.17487/RFC0958, September 1985,
<https://www.rfc-editor.org/info/rfc958>.
[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>.
[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>.
Author's Address
Harlan Stenn
Network Time Foundation
P.O. Box 918
Talent, OR 97540
US
Email: stenn@nwtime.org
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