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Lourdelet 5 Expires: July 11, 2010 Cisco Systems, Inc. 6 January 7, 2010 8 Network Time Protocol (NTP) Server Option for DHCPv6 9 draft-ietf-ntp-dhcpv6-ntp-opt-06.txt 11 Abstract 13 The NTP Server Option for Dynamic Host Configuration Protocol for 14 IPv6 (DHCPv6) provides NTP (Network Time Protocol version 4) Server 15 location information to DHCPv6 hosts. 17 Status of this Memo 19 This Internet-Draft is submitted to IETF in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 This Internet-Draft will expire on July 11, 2010. 40 Copyright Notice 42 Copyright (c) 2010 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the BSD License. 55 This document may contain material from IETF Documents or IETF 56 Contributions published or made publicly available before November 57 10, 2008. The person(s) controlling the copyright in some of this 58 material may not have granted the IETF Trust the right to allow 59 modifications of such material outside the IETF Standards Process. 60 Without obtaining an adequate license from the person(s) controlling 61 the copyright in such materials, this document may not be modified 62 outside the IETF Standards Process, and derivative works of it may 63 not be created outside the IETF Standards Process, except to format 64 it for publication as an RFC or to translate it into languages other 65 than English. 67 Table of Contents 69 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 71 3. Related Work and Usage Model . . . . . . . . . . . . . . . . . 4 72 4. NTP Server Option for DHCPv6 . . . . . . . . . . . . . . . . . 4 73 4.1. NTP Server Address Suboption . . . . . . . . . . . . . . . 6 74 4.2. NTP Multicast Address Suboption . . . . . . . . . . . . . 6 75 4.3. NTP Server FQDN Suboption . . . . . . . . . . . . . . . . 7 76 5. Appearance of this Option . . . . . . . . . . . . . . . . . . 8 77 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 78 7. RFC 4075 Deprecation . . . . . . . . . . . . . . . . . . . . . 8 79 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 80 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 81 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 82 9.2. Informative References . . . . . . . . . . . . . . . . . . 9 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 85 1. Introduction 87 This document defines a DHCPv6 option and associated suboptions to 88 provide Network Time Protocol version 4 [draft-ntpv4] or greater 89 Server location information to DHCPv6 hosts. 91 2. Requirements notation 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 95 document are to be interpreted as described in [RFC2119]. 97 3. Related Work and Usage Model 99 The NTP service is publicly offered on the Internet by a number of 100 organizations. Those Servers can be used but should not be abused, 101 so any method which is tasked to disseminate locations of NTP Servers 102 must act responsibly in a manner that does not lead to public Server 103 overloading. When using DHCPv6 to offer NTP Server location, and if 104 there is a need to distribute a host with a hardcoded configuration, 105 this configuration MUST NOT include Server location that is not part 106 of the organization that distributes this device. Typical usage of 107 this option is to specify an NTP Server that is part of the 108 organization that operates the DHCPv6 Server. 110 The location of the NTP service, like any other Internet service, can 111 be specified by an IP address or a Fully Qualified Domain Name 112 (FQDN). By design, DHCP offers information to multiple devices and 113 is prone to amplification of mistakes, so great care must be taken to 114 define its configuration. Specification of the NTP service by FQDN 115 offers a level of indirection that works as a possible mitigation 116 tool in case of misconfiguration. DNS can be used to redirect 117 misconfigured clients to an IPv6 address that is not configured on 118 any host instead of having to change the address of the NTP Server 119 itself. 121 While the NTP specification defines a comprehensive set of 122 configuration parameters, modification of those parameters is best 123 left to the decision of the client itself. The DHCPv6 option for NTP 124 is therefore restricted to Server location. 126 4. NTP Server Option for DHCPv6 128 This option serves as a container for Server location information 129 related to one NTP Server or Simple Network Time Protocol (SNTP) 131 [RFC4330] Server. This option can appear multiple times in a DHCPv6 132 message. Each instance of this option is to be considered by the NTP 133 client or SNTP client as a Server to include in its configuration. 135 The option itself does not contain any value. Instead, it contains 136 one or several suboptions that carry NTP Server or SNTP Server Server 137 location. This option MUST include one, and only one, time source 138 suboption. The currently defined time source suboptions are: 139 NTP_OPTION_SRV_ADDR, NTP_OPTION_SRV_MC_ADDR, NTP_OPTION_SRV_FQDN. It 140 carries the NTP Server or SNTP Server location, as a unicast or 141 multicast IPv6 address or as an NTP Server or SNTP Server FQDN. More 142 time source suboptions may be defined in the future. While the FQDN 143 option offers the most deployment flexibility, resiliency as well as 144 security, the IP address options are defined to cover cases where a 145 DNS dependancy is not desirable. 147 If the NTP Server or SNTP Server location is an IPv6 multicast 148 address, the client SHOULD use this address as an NTP multicast group 149 address and listen to messages sent to this group in order to 150 synchronize its clock. 152 The format of the NTP Server Option is: 154 0 1 2 3 155 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 1 156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 157 | OPTION_NTP_SERVER | option-len | 158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 159 | suboption-1 | 160 : : 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | suboption-2 | 163 : : 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 : : 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 | suboption-n | 168 : : 169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 171 option-code: OPTION_NTP_SERVER (TBD_IANA), 173 option-len: Total length of the included suboptions. 175 This document does not define any priority relationship between the 176 client's embedded configuration (if any) and the NTP or SNTP Servers 177 discovered via this option. In particular, the client is allowed to 178 simultaneously use its own configured NTP Servers or SNTP Servers and 179 the Servers discovered via DHCP. 181 4.1. NTP Server Address Suboption 183 This suboption is intended to appear inside the OPTION_NTP_SERVER 184 option. It specifies the IPv6 unicast address of an NTP Server or 185 SNTP Server available to the client. 187 The format of the NTP Server Address Suboption is: 189 0 1 2 3 190 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 1 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 | NTP_SUBOPTION_SRV_ADDR | suboption-len = 16 | 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 | | 195 | | 196 | IPv6 address of NTP Server | 197 | | 198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 IPv6 address of the NTP Server: An IPv6 address, 202 suboption-code: NTP_SUBOPTION_SRV_ADDR (1), 204 suboption-len: 16. 206 4.2. NTP Multicast Address Suboption 208 This suboption is intended to appear inside the OPTION_NTP_SERVER 209 option. It specifies the IPv6 address of the IPv6 multicast group 210 address used by NTP on the local network. 212 The format of the NTP Multicast Address Suboption is: 214 0 1 2 3 215 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 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | NTP_SUBOPTION_MC_ADDR | suboption-len = 16 | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | | 220 | | 221 | Multicast IPv6 address | 222 | | 223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 Multicast IPv6 address: An IPv6 address, 227 suboption-code: NTP_SUBOPTION_MC_ADDR (2), 229 suboption-len: 16. 231 4.3. NTP Server FQDN Suboption 233 This suboption is intended to appear inside the OPTION_NTP_SERVER 234 option. It specifies the FQDN of an NTP Server or SNTP Server 235 available to the client. 237 The format of the NTP Server FQDN Suboption is: 239 0 1 2 3 240 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 1 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | NTP_SUBOPTION_SRV_FQDN | suboption-len | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | | 245 | FQDN of NTP Server | 246 : : 247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 suboption-code: NTP_SUBOPTION_SRV_FQDN (3), 251 suboption-len: Length of the included FQDN field, 253 FQDN: Fully Qualified Domain Name of the NTP Server or SNTP Server. 254 This field MUST be encoded as described in [RFC3315], 255 section 8. Internationalized Domain Name are not allowed 256 in this field. 258 5. Appearance of this Option 260 The OPTION_NTP_SERVER option can appear multiple times in a DHCPv6 261 message. The order in which these options appear is not significant. 262 The client uses its usual algorithms to determine which Server(s) or 263 multicast group(s) should be prefered to synchronize its clock. 265 The OPTION_NTP_SERVER option MUST NOT appear in messages other than 266 the following: Solicit, Advertise, Request, Renew, Rebind, 267 Information-Request, and Reply. If this option appears in messages 268 other than those specified above, the receiver MUST ignore it. 270 The option number for this option MAY appear in the "Option Request" 271 option [RFC3315] in the following messages: Solicit, Request, Renew, 272 Rebind, Information-Request, and Reconfigure. If this option number 273 appears in the "Option Request" option in messages other than those 274 specified above, the receiver SHOULD ignore it. 276 6. Security Considerations 278 This option could be used by an intruder to advertise the address of 279 a malicious NTP Server or SNTP Server and adversely affect the clock 280 of clients on the network. The consequences of such an attack can be 281 critical, because many security protocols depend on time 282 synchronization to run their algorithms. As an example, an attacker 283 could break connectivity between SEND-enabled nodes [RFC3971], simply 284 by affecting the clock on these nodes. 286 To prevent these attacks, it is strongly advisable to secure the use 287 of this option either by: 289 - using the NTPv4 Autokey public key authentication, as defined 290 in [draft-autokey] or, 292 - using authenticated DHCP as described in [RFC3315] section 21. 294 7. RFC 4075 Deprecation 296 [RFC4075] (SNTP Configuration Option for DHCPv6) provides some degree 297 of automatic time Server configuration for IPv6, as it specifies how 298 to transmit SNTP [RFC4330] Servers addresses through DHCPv6. However 299 this approach is not suitable for all NTP deployments. It is not an 300 extensible mechanism and introduces some semantic confusion throught 301 the use of the "SNTP" acronym. Additionally the approach of only 302 offering IPv6 addresses to specify Server location does not meet NTP 303 requirements that make use of a FQDN (Fully Qualified Domain Name) as 304 well. For all the abovementioned reasons, this document makes 305 [RFC4075] deprecated. 307 8. IANA Considerations 309 When this document is published, the IANA is requested to assign an 310 option code from the "DHCPv6 Options Codes" registry for 311 OPTION_NTP_SERVER. 313 IANA is required to maintain a new number space of NTP time source 314 suboptions, located in the BOOTP-DHCP Parameters Registry. The 315 initial suboptions are described in section 4 of this document. IANA 316 assigns future NTP time source suboptions with a "IETF Consensus" 317 policy as described in [RFC5226]. Future proposed suboptions are to 318 be referenced symbolically in the Internet-Drafts that describe them, 319 and shall be assigned numeric codes by IANA when approved for 320 publication as an RFC. 322 9. References 324 9.1. Normative References 326 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 327 and M. Carney, "Dynamic Host Configuration Protocol for 328 IPv6 (DHCPv6)", RFC 3315, July 2003. 330 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 331 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 332 May 2008. 334 [draft-ntpv4] 335 Burbank, J., Kasch, W., Martin, J., and D. Mills, "Network 336 Time Protocol Version 4 Protocol And Algorithms 337 Specification", draft-ietf-ntp-ntpv4-proto-11 (work in 338 progress), September 2008. 340 [draft-autokey] 341 Haberman, B. and D. Mills, "Network Time Protocol Version 342 4 Autokey Specification", draft-ietf-ntp-autokey-06 (work 343 in progress), July 2009. 345 9.2. Informative References 347 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 348 Requirement Levels", BCP 14, RFC 2119, March 1997. 350 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 351 Neighbor Discovery (SEND)", RFC 3971, March 2005. 353 [RFC4075] Kalusivalingam, V., "Simple Network Time Protocol (SNTP) 354 Configuration Option for DHCPv6", RFC 4075, May 2005. 356 [RFC4330] Mills, D., "Simple Network Time Protocol (SNTP) Version 4 357 for IPv4, IPv6 and OSI", RFC 4330, January 2006. 359 Authors' Addresses 361 Richard Gayraud 363 Email: richard.gayraud@free.fr 365 Benoit Lourdelet 366 Cisco Systems, Inc. 367 Village ent. GreenSide, Bat T3, 368 400, Av de Roumanille, 369 06410 BIOT - Sophia-Antipolis Cedex 370 France 372 Phone: +33 4 97 23 26 23 373 Email: blourdel@cisco.com