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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: Note that if an NTP server decides to offer smeared time corrections to clients, it SHOULD only offer this time in response to CLIENT time requests. There is something to be said for further only offering smeared time to CLIENT time requests that show an LI value of 0, and perhaps 3. The reason for this is that if a client knows a leap second is pending, it can be expected to know how to process that leap second. An NTP server that is offering smeared time SHOULD NOT send smeared time in any peer exchanges. Also, CLIENT machines SHOULD not be distributing time (smeared or otherwise) to other systems. -- The document date (October 4, 2018) is 2029 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC0791' is mentioned on line 112, but not defined Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force H. Stenn 3 Internet-Draft Network Time Foundation 4 Intended status: Standards Track October 4, 2018 5 Expires: April 7, 2019 7 Network Time Protocol Leap Smear REFID 8 draft-stenn-ntp-leap-smear-refid-01 10 Abstract 12 Leap Seconds are part of UTC. NTP timestamps are based on POSIX 13 timestamps, which require each day to have exactly 86,400 seconds per 14 day. Some applications and environments choose to "smear" leap 15 second corrections over a period that can last up to 24 hours' time, 16 and implement NTP servers that offer smeared time to clients asking 17 them for the time. 19 Both NTP clients and operators have no current way to tell if an NTP 20 server is offering leap-smeared time or not. This is a problem. 22 This proposal offers a mechanism by which clients (and operators) can 23 trivially detect a server that is offering leap-smeared time. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on April 7, 2019. 42 Copyright Notice 44 Copyright (c) 2018 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 61 2. Leap Smear REFID . . . . . . . . . . . . . . . . . . . . . . 3 62 3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 63 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 65 6. Normative References . . . . . . . . . . . . . . . . . . . . 5 66 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 68 1. Introduction 70 Leap Seconds are applied as needed to UTC in order to keep its time 71 of day close to UT1's mean solar time. 73 RFC 5905 [RFC5905] and earlier versions of NTP are the overwhelming 74 method of distributing time on networks. The timescale used by NTP 75 is based on POSIX which, for better or worse, ignores any instances 76 where there are not 86,400 seconds per day. 78 Leap Seconds will continue to exist for the foreseeable future, and 79 similarly, POSIX can be expected to ignore leap seconds for the 80 foreseeable future. 82 Different applications have different requirements for the stability 83 of time during the application of a leap second. Some applications 84 are tolerant of a fast application of the correction, while other 85 applications prefer to "smear" the leap second over a longer period, 86 where the time reported by leap-second aware servers is gradually 87 applied so there is no abrupt change to time during the processing of 88 a leap second. 90 While leap second processing can be expected to be properly handled 91 by up-to-date software and by time servers, there are large numbers 92 of out-of-date software installations and client systems that are 93 just not able to properly handle a leap second correction. 95 This proposal offers a way for a system to generate a REFID that 96 indicates that the time being supplied in the NTP packet already 97 contains an amount of leap smear correction, and what that amount is. 99 1.1. Requirements Language 101 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 102 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 103 document are to be interpreted as described in RFC 2119 [RFC2119]. 105 2. Leap Smear REFID 107 RFC 5905 [RFC5905] defines the data type of NTP time values in 108 Section 6, "Data Types": 110 All NTP time values are represented in twos-complement format, 111 with bits numbered in big-endian (as described in Appendix A of 112 [RFC0791]) fashion from zero starting at the left, or high-order, 113 position. ... 115 The 32 bit signed integer seconds portion and the 32 bit unsigned 116 fractional seconds portion, or 32:32 format is: 118 0 1 2 3 119 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 1 120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 121 | Seconds | 122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 123 | Fraction | 124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 126 NTP Timestamp Format (32:32) 128 This format provides coverage for 136 years' time to a precision of 129 232 picoseconds. If a leap-second addition is being completely 130 smeared just before before the stroke of the next POSIX second then 131 the smear correction will be (0,1). If this was the only way to 132 apply a leap smear correction then we could simply use an unsigned 133 value to represent the correction. But while the first popular leap 134 smear implementation applied the correction over an appropriate 135 number of hours' time before the actual leap second so the system 136 time was corrected at the stroke of 00:00, that meant that the 137 difference between system time and UTC spent half of the duration of 138 the smear application at [.5,1) "off" of correct time. The second 139 popular implementation of the leap smear applied the first half- 140 second correction before the stroke of 00:00 for a correction range 141 of (0,.5] and the last half-second correction starting at the stroke 142 of 00:00 for a [-.5,0) correction range. This also means we need a 143 signed value to represent the amount of correction. 145 If a system implements the leap-smear REFID, the REFID of a system 146 that is supplying smeared time to client requests while leap-smear 147 correction is active would be 254.b1.b2.b3, where the three octets 148 (b1, b2, and b3) are a 2:22 formatted value, yielding precision to 149 238 nanoseconds, or about a quarter of a microsecond. 151 Note that if an NTP server decides to offer smeared time corrections 152 to clients, it SHOULD only offer this time in response to CLIENT time 153 requests. There is something to be said for further only offering 154 smeared time to CLIENT time requests that show an LI value of 0, and 155 perhaps 3. The reason for this is that if a client knows a leap 156 second is pending, it can be expected to know how to process that 157 leap second. An NTP server that is offering smeared time SHOULD NOT 158 send smeared time in any peer exchanges. Also, CLIENT machines 159 SHOULD not be distributing time (smeared or otherwise) to other 160 systems. 162 We also note that during the application of a leap smear, the REFID 163 from a system offering smeared time cannot provide detection of a 164 timing loop. This is not expected to be a problem because time 165 server systems are not expected to make CLIENT connections with each 166 other, so they should not be receiving smeared time. Moreso, if a 167 time server is configured to make CLIENT connections to a server that 168 offers smeared time, with the mechanism described here it can detect 169 when it is getting smeared time, and either ignore time from that 170 source, or "undo" the leap smear correction and use the corrected 171 time for that sample. 173 This proposal is not an attempt to justify servers offering leap 174 smeared time. Its purpose is to make it easy to identify when a 175 client is receiving smeared time, and provide the client a way to 176 know the amount of smear correction as of the latest successful poll. 178 3. Acknowledgements 180 The author wishes to acknowledge the contributions of Juergen 181 Perlinger. 183 4. IANA Considerations 185 This memo requests that IANA allocate a pseudo Extension Field Type 186 of 0xFFFE so the proposed "I-Do" exchange can report whether or not 187 this server will offer leap smeared time in response to CLIENT time 188 requests, identifying the amount of correction using the above REFID. 190 5. Security Considerations 192 Additional information TBD 194 6. Normative References 196 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 197 Requirement Levels", BCP 14, RFC 2119, 198 DOI 10.17487/RFC2119, March 1997, 199 . 201 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 202 "Network Time Protocol Version 4: Protocol and Algorithms 203 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 204 . 206 Author's Address 208 Harlan Stenn 209 Network Time Foundation 210 P.O. Box 918 211 Talent, OR 97540 212 US 214 Email: stenn@nwtime.org