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Stenn 3 Internet-Draft Network Time Foundation 4 Intended status: Standards Track March 25, 2019 5 Expires: September 26, 2019 7 Network Time Protocol I-Do Extension Field 8 draft-stenn-ntp-i-do-06 10 Abstract 12 This proposal defines and describes a mechanism by which cooperating 13 NTP instances may communicate any optional features they are willing 14 to admit they support. 16 RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH BEFORE PUBLISHING: 18 The source code and issues list for this draft can be found in 19 https://github.com/hstenn/ietf-ntp-i-do 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on September 26, 2019. 38 Copyright Notice 40 Copyright (c) 2019 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 57 2. The I-Do Extension Field . . . . . . . . . . . . . . . . . . 2 58 2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2.2. I-DO Packet Format . . . . . . . . . . . . . . . . . . . 4 60 2.3. Behavior . . . . . . . . . . . . . . . . . . . . . . . . 5 61 3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 62 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 63 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 64 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 65 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 66 6.2. Informative References . . . . . . . . . . . . . . . . . 7 67 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 69 1. Introduction 71 The first implementation of NTPv4 was released in 2003, and was 72 defined by RFC 5905 [RFC5905]. It contains an optional and now 73 obsolete public-key security protocol, Autokey, which is defined by 74 RFC 5906 [RFC5906]. Until very recently, Autokey has been the only 75 implemented use of NTP packet Extension Fields. New proposals for 76 extension fields are being written and there is currently no 77 convenient way to learn if a remote instance of NTP supports any 78 extension fields or not. This proposal contains a method to tell a 79 remote instance of NTP what we (are willing to admit we) support, and 80 ask what they (are willing to admit they) support. 82 1.1. Requirements Language 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 86 document are to be interpreted as described in RFC 2119 [RFC2119]. 88 2. The I-Do Extension Field 90 2.1. Overview 92 The purpose of the I-DO EF is to provide information to the remote 93 side about our capabilities. 95 If an incoming packet contains an unrecognized extension field, one 96 of several things will happen. While that unrecognized extension 97 field SHOULD be ignored, an implementation MAY choose to drop the 98 entire packet. 100 If any extension field is present there ordinarily SHOULD be a MAC 101 following the extension field. However, an older conforming NTP 102 implementation will require that any EF MUST be followed by a MAC. 104 Some extension fields are unable to be "signed" by a MAC, regardless 105 of whether or not that MAC is a traditional MAC or an extension field 106 MAC. 108 In the previous two cases, a conforming legacy system that receives 109 these types of packets will interpret the unrecognized EF as a 110 missing or legacy MAC, and return a crypto-NAK. 112 If the remote system replies with a crypto-NAK, that is a good 113 indication that it is running older software that does not recognize 114 EFs and thinks we have sent an invalid MAC. In this case, we SHOULD 115 NOT send that system newer EFs. 117 If the remote system replies without including an I-DO-RESPONSE EF, 118 we at least know they can handle EFs, but they either don't 119 understand I-DO or are not willing to tell us anything. In this 120 case, we SHOULD NOT send any newer EFs. 122 If the remote system replies with a packet that includes an I-DO- 123 RESPONSE EF, then we SHOULD remember what they told us, and use that 124 information appropriately. In other words, we can exchange packets 125 containing any new EFs that we agree on, and we should not exchange 126 packets containing any new EFs that we have not agreed on. 128 In client/server mode, it makes sense for the client to send an I-DO 129 to the server, and notice how the server responds. While the server 130 SHOULD respond with an I-DO-RESPONSE EF, it likely does not make 131 sense for the server to send an I-DO EF in response to a client 132 request. 134 In symmetric mode, either side may initiate sending an I-DO EF, and 135 the receiving side SHOULD reply with an I-DO-RESPONSE EF. 137 In broadcast mode, the broadcast server MAY send broadcast packets 138 that include an I-DO EF, but note that if, counter to recommended 139 practice, these packets are unauthenticated they MAY cause client 140 machines to misinterpret the packet as having invalid authentication. 141 In this situation, the broadcast server SHOULD alternate sending 142 broadcast server packets with and without an I-DO EF, to insure that 143 all clients receive time packets they will accept. Note that if, as 144 recommended, broadcast packets are authenticated, a conforming client 145 SHOULD have no difficulty in receiving a broadcast (mode 5) packet 146 from a server that includes an I-DO EF. 148 2.2. I-DO Packet Format 150 The content of the I-DO extension field is an ordinary four octet 151 Extension Field header followed by a payload consisting of an 152 appropriate number of two octet I-DO values that use nonzero values 153 to indicate a supported feature. An I-DO value of zero is ignored. 154 The payload section must end on a four-octet boundary. 156 There are two types of nonzero I-DO values that may be used. They 157 are both defined in the IANA NTP Extension Field Table (Section 4). 158 These values are either Extension Field Types, where only the low- 159 order values (0x01 thru 0xFE) are used, or I-DO Types, where all 16 160 bits are used and the bottom octet is currently always 0xFF. 162 The examples below are built using information from the following 163 Standards and proposals: 165 RFC 5906 [RFC5906] 167 NTP-EXTENSION-FIELDS [NTP-EXTENSION-FIELD] 169 MAC-LAST-EF [DRAFT-MAC-LAST-EF] 171 0 1 2 3 172 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 1 173 +---------------+---------------+-------------------------------+ 174 | Field Type | Field Length | 175 +-------------------------------+-------------------------------+ 176 | I-Do 1 | ... | 177 +-------------------------------+-------------------------------+ 178 | I-Do N | Padding | 179 +---------------------------------------------------------------+ 181 NTP Extension Field: I-DO - Overview 183 Field Type: TBD (Recommendation for IANA: 0x0007 (I-Do), 0x8007 (I-Do 184 Response)) 186 Field Length: as needed 188 Payload: An enumeration of the supported base Field Types, followed 189 by any zero padding (0x0000) needed to fill the payload to the 190 desired 32-bit boundary. 192 Example: A system that wants to advertise support for Autokey and 193 I-DO, sending to a system that responds with support for I-DO, NTS, 194 MAC-EF, and LAST-EF. 196 0 1 2 3 197 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 1 198 +---------------+---------------+-------------------------------+ 199 | Field Type (0x0007) | Field Length (0x0008) | 200 +-------------------------------+-------------------------------+ 201 | 0x0007 | 0x0002 | 202 +-------------------------------+-------------------------------+ 204 NTP Extension Field: I-Do - Example 206 0 1 2 3 207 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 1 208 +---------------+---------------+-------------------------------+ 209 | Field Type (0x8007) | Field Length (0x000a) | 210 +-------------------------------+-------------------------------+ 211 | 0x0003 | 0x0004 | 212 +-------------------------------+-------------------------------+ 213 | 0x0007 | 0x0008 | 214 +-------------------------------+-------------------------------+ 216 NTP Extension Field: I-Do Response - Example 218 2.3. Behavior 220 The sender of any I-Do extension field MUST send an extension field 221 with a Field Type of 0x0007 (I-Do) and SHOULD include a payload with 222 any 0x0000 padding values after enumerating the supported base 223 Extension Field Types. If the responding system recognizes the I-Do 224 extension field, its response MUST include an extension field with a 225 Field Type of 0x8007 (I-Do Response), and SHOULD include a payload 226 with any 0x0000 padding values after enumerating the supported base 227 Extension Field Types. 229 Any system that receives an I-Do extension field as either an "offer" 230 or a "response" SHOULD scan the entire payload looking for nonzero 231 values that specify the capabilities of the remote association. 233 Any system that receives an I-Do "offer", 0x0007, SHOULD reply with 234 an I-Do "response", 0x8007. 236 Any system that sends an I-Do "offer" or "response" may send as few 237 or as many of its supported Field Types as it chooses. At any 238 subsequent time, either side may re-negotiate the list of supported 239 field types it is prepared to accept from the other system by sending 240 a new I-Do extension field. 242 The most-recently received I-Do list replaces any previous I-Do list. 244 3. Acknowledgements 246 The author wishes to acknowledge the contributions of Sam Weiler. 248 4. IANA Considerations 250 This memo requests IANA to allocate NTP Extension Field Types: 252 0x0007 (I-DO) 254 0x8007 (I-DO Response) 256 and NTP Extension Field I-DO types: 258 0x00FF through 260 0xFDFF Reserved for future I-DO types 262 0xFEFF (I-DO Leap Smear REFIDs) 264 0xFFFF (I-DO IPv6 REFID hash) 266 for this proposal. 268 5. Security Considerations 270 No addtional or unusual security considerations are expected if this 271 proposal is adopted. 273 No feedback has been received suggesting this proposal creates any 274 new security considerations. 276 6. References 278 6.1. Normative References 280 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 281 Requirement Levels", BCP 14, RFC 2119, 282 DOI 10.17487/RFC2119, March 1997, 283 . 285 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 286 "Network Time Protocol Version 4: Protocol and Algorithms 287 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 288 . 290 6.2. Informative References 292 [DRAFT-MAC-LAST-EF] 293 Stenn, H., "draft-stenn-ntp-mac-last-ef", 2018. 295 [NTP-EXTENSION-FIELD] 296 Stenn, H., "draft-stenn-ntp-extension-fields", 2018. 298 [RFC5906] Haberman, B., Ed. and D. Mills, "Network Time Protocol 299 Version 4: Autokey Specification", RFC 5906, 300 DOI 10.17487/RFC5906, June 2010, 301 . 303 Author's Address 305 Harlan Stenn 306 Network Time Foundation 307 P.O. Box 918 308 Talent, OR 97540 309 US 311 Email: stenn@nwtime.org