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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DNSEXT M. Stapp 3 Internet-Draft Cisco Systems, Inc. 4 Expires: September 1, 2006 T. Lemon 5 Nominum, Inc. 6 A. Gustafsson 7 Araneus Information Systems Oy 8 February 28, 2006 10 A DNS RR for Encoding DHCP Information (DHCID RR) 11 13 Status of this Memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt. 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 36 This Internet-Draft will expire on September 1, 2006. 38 Copyright Notice 40 Copyright (C) The Internet Society (2006). 42 Abstract 44 It is possible for DHCP clients to attempt to update the same DNS 45 FQDN or attempt to update a DNS FQDN that has been added to the DNS 46 for another purpose as they obtain DHCP leases. Whether the DHCP 47 server or the clients themselves perform the DNS updates, conflicts 48 can arise. To resolve such conflicts, "Resolution of DNS Name 49 Conflicts" [1] proposes storing client identifiers in the DNS to 50 unambiguously associate domain names with the DHCP clients to which 51 they refer. This memo defines a distinct RR type for this purpose 52 for use by DHCP clients and servers, the "DHCID" RR. 54 Table of Contents 56 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. The DHCID RR . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3.1. DHCID RDATA format . . . . . . . . . . . . . . . . . . . . 3 60 3.2. DHCID Presentation Format . . . . . . . . . . . . . . . . 4 61 3.3. The DHCID RR Identifier Type Codes . . . . . . . . . . . . 4 62 3.4. The DHCID RR Digest Type Code . . . . . . . . . . . . . . 4 63 3.5. Computation of the RDATA . . . . . . . . . . . . . . . . . 5 64 3.5.1. Using the Client's DUID . . . . . . . . . . . . . . . 5 65 3.5.2. Using the Client Identifier Option . . . . . . . . . . 5 66 3.5.3. Using the Client's htype and chaddr . . . . . . . . . 6 67 3.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 3.6.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 6 69 3.6.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 6 70 3.6.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . 7 71 4. Use of the DHCID RR . . . . . . . . . . . . . . . . . . . . . 7 72 5. Updater Behavior . . . . . . . . . . . . . . . . . . . . . . . 8 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 75 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 76 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 77 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 78 9.2. Informative References . . . . . . . . . . . . . . . . . . 10 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 80 Intellectual Property and Copyright Statements . . . . . . . . . . 12 82 1. Terminology 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 [2]. 88 2. Introduction 90 A set of procedures to allow DHCP [6] [10] clients and servers to 91 automatically update the DNS (RFC 1034 [3], RFC 1035 [4]) is proposed 92 in "Resolution of DNS Name Conflicts" [1]. 94 Conflicts can arise if multiple DHCP clients wish to use the same DNS 95 name or a DHCP client attempts to use a name added for another 96 purpose. To resolve such conflicts, "Resolution of DNS Name 97 Conflicts" [1] proposes storing client identifiers in the DNS to 98 unambiguously associate domain names with the DHCP clients using 99 them. In the interest of clarity, it is preferable for this DHCP 100 information to use a distinct RR type. This memo defines a distinct 101 RR for this purpose for use by DHCP clients or servers, the "DHCID" 102 RR. 104 In order to obscure potentially sensitive client identifying 105 information, the data stored is the result of a one-way SHA-256 hash 106 computation. The hash includes information from the DHCP client's 107 message as well as the domain name itself, so that the data stored in 108 the DHCID RR will be dependent on both the client identification used 109 in the DHCP protocol interaction and the domain name. This means 110 that the DHCID RDATA will vary if a single client is associated over 111 time with more than one name. This makes it difficult to 'track' a 112 client as it is associated with various domain names. 114 3. The DHCID RR 116 The DHCID RR is defined with mnemonic DHCID and type code [TBD]. The 117 DHCID RR is only defined in the IN class. DHCID RRs cause no 118 additional section processing. The DHCID RR is not a singleton type. 120 3.1. DHCID RDATA format 122 The RDATA section of a DHCID RR in transmission contains RDLENGTH 123 octets of binary data. The format of this data and its 124 interpretation by DHCP servers and clients are described below. 126 DNS software should consider the RDATA section to be opaque. DHCP 127 clients or servers use the DHCID RR to associate a DHCP client's 128 identity with a DNS name, so that multiple DHCP clients and servers 129 may deterministically perform dynamic DNS updates to the same zone. 130 From the updater's perspective, the DHCID resource record RDATA 131 consists of a 2-octet identifier type, in network byte order, 132 followed by a 1-octet digest type, followed by one or more octets 133 representing the actual identifier: 135 < 2 octets > Identifier type code 136 < 1 octet > Digest type code 137 < n octets > Digest (length depends on digest type) 139 3.2. DHCID Presentation Format 141 In DNS master files, the RDATA is represented as a single block in 142 base 64 encoding identical to that used for representing binary data 143 in RFC 3548 [7]. The data may be divided up into any number of white 144 space separated substrings, down to single base 64 digits, which are 145 concatenated to form the complete RDATA. These substrings can span 146 lines using the standard parentheses. 148 3.3. The DHCID RR Identifier Type Codes 150 The DHCID RR Identifier Type Code specifies what data from the DHCP 151 client's request was used as input into the hash function. The 152 identifier type codes are defined in a registry maintained by IANA, 153 as specified in Section 7. The initial list of assigned values for 154 the identifier type code is: 156 0x0000 = htype, chaddr from a DHCPv4 client's DHCPREQUEST [6]. 157 0x0001 = The data octets (i.e., the Type and Client-Identifier 158 fields) from a DHCPv4 client's Client Identifier option [9]. 159 0x0002 = The client's DUID (i.e., the data octets of a DHCPv6 160 client's Client Identifier option [10] or the DUID field from a 161 DHCPv4 client's Client Identifier option [12]). 163 0x0003 - 0xfffe = Available to be assigned by IANA. 165 0xffff = RESERVED 167 3.4. The DHCID RR Digest Type Code 169 The DHCID RR Digest Type Code is an identifier for the digest 170 algorithm used. The digest is calculated over an identifier and the 171 canonical FQDN as described in the next section. 173 The digest type codes are defined in a registry maintained by IANA, 174 as specified in Section 7. The initial list of assigned values for 175 the digest type codes is: value 0 is reserved and value 1 is SHA-256. 177 Reserving other types requires IETF standards action. Defining new 178 values will also require IETF standards action to document how DNS 179 updaters are to deal with multiple digest types. 181 3.5. Computation of the RDATA 183 The DHCID RDATA is formed by concatenating the 2-octet identifier 184 type code with variable-length data. 186 The RDATA for all type codes other than 0xffff, which is reserved for 187 future expansion, is formed by concatenating the 2-octet identifier 188 type code, the 1-octet digest type code, and the digest value (32 189 octets for SHA-256). 191 < identifier-type > < digest-type > < digest > 193 The input to the digest hash function is defined to be: 195 digest = SHA-256(< identifier > < FQDN >) 197 The FQDN is represented in the buffer in unambiguous canonical form 198 as described in RFC 4034 [8], section 6.1. The identifier type code 199 and the identifier are related as specified in Section 3.3: the 200 identifier type code describes the source of the identifier. 202 A DHCPv4 updater uses the 0x0002 type code if a Client Identifier 203 option is present in the DHCPv4 messages and it is encoded as 204 specified in [12]. Otherwise, the updater uses 0x0001 if a Client 205 Identifier option is present and 0x0000 if not. 207 A DHCPv6 updater always uses the 0x0002 type code. 209 3.5.1. Using the Client's DUID 211 When the updater is using the Client's DUID (either from a DHCPv6 212 Client Identifier option or from a portion of the DHCPv4 Client 213 Identifier option encoded as specified in [12]), the first two octets 214 of the DHCID RR MUST be 0x0002, in network byte order. The third 215 octet is the digest type code (1 for SHA-256). The rest of the DHCID 216 RR MUST contain the results of computing the SHA-256 hash across the 217 octets of the DUID followed by the FQDN. 219 3.5.2. Using the Client Identifier Option 221 When the updater is using the DHCPv4 Client Identifier option sent by 222 the client in its DHCPREQUEST message, the first two octets of the 223 DHCID RR MUST be 0x0001, in network byte order. The third octet is 224 the digest type code (1 for SHA-256). The rest of the DHCID RR MUST 225 contain the results of computing the SHA-256 hash across the data 226 octets (i.e., the Type and Client-Identifier fields) of the option, 227 followed by the FQDN. 229 3.5.3. Using the Client's htype and chaddr 231 When the updater is using the client's link-layer address as the 232 identifier, the first two octets of the DHCID RDATA MUST be zero. 233 The third octet is the digest type code (1 for SHA-256). To generate 234 the rest of the resource record, the updater computes a one-way hash 235 using the SHA-256 algorithm across a buffer containing the client's 236 network hardware type, link-layer address, and the FQDN data. 237 Specifically, the first octet of the buffer contains the network 238 hardware type as it appeared in the DHCP 'htype' field of the 239 client's DHCPREQUEST message. All of the significant octets of the 240 'chaddr' field in the client's DHCPREQUEST message follow, in the 241 same order in which the octets appear in the DHCPREQUEST message. 242 The number of significant octets in the 'chaddr' field is specified 243 in the 'hlen' field of the DHCPREQUEST message. The FQDN data, as 244 specified above, follows. 246 3.6. Examples 248 3.6.1. Example 1 250 A DHCP server allocating the IPv4 address 10.0.0.1 to a client with 251 Ethernet MAC address 01:02:03:04:05:06 using domain name 252 "client.example.com" uses the client's link-layer address to identify 253 the client. The DHCID RDATA is composed by setting the two type 254 octets to zero, the 1-octet digest type to 1 for SHA-256, and 255 performing an SHA-256 hash computation across a buffer containing the 256 Ethernet MAC type octet, 0x01, the six octets of MAC address, and the 257 domain name (represented as specified in Section 3.5). 259 client.example.com. A 10.0.0.1 260 client.example.com. DHCID ( AAABxLmlskllE0MVjd57zHcWmEH3pCQ6V 261 ytcKD//7es/deY= ) 263 If the DHCID RR type is not supported, the RDATA would be encoded 264 [13] as: 266 \# 35 ( 000001c4b9a5b249651343158dde7bcc77169841f7a4243a572b5c283 267 fffedeb3f75e6 ) 269 3.6.2. Example 2 271 A DHCP server allocates the IPv4 address 10.0.12.99 to a client which 272 included the DHCP client-identifier option data 01:07:08:09:0a:0b:0c 273 in its DHCP request. The server updates the name "chi.example.com" 274 on the client's behalf, and uses the DHCP client identifier option 275 data as input in forming a DHCID RR. The DHCID RDATA is formed by 276 setting the two type octets to the value 0x0001, the 1-octet digest 277 type to 1 for SHA-256, and performing a SHA-256 hash computation 278 across a buffer containing the seven octets from the client-id option 279 and the FQDN (represented as specified in Section 3.5). 281 chi.example.com. A 10.0.12.99 282 chi.example.com. DHCID ( AAEBOSD+XR3Os/0LozeXVqcNc7FwCfQdW 283 L3b/NaiUDlW2No= ) 285 If the DHCID RR type is not supported, the RDATA would be encoded 286 [13] as: 288 \# 35 ( 0001013920fe5d1dceb3fd0ba3379756a70d73b17009f41d58bddbfcd 289 6a2503956d8da ) 291 3.6.3. Example 3 293 A DHCP server allocates the IPv6 address 2000::1234:5678 to a client 294 which included the DHCPv6 client-identifier option data 00:01:00:06: 295 41:2d:f1:66:01:02:03:04:05:06 in its DHCPv6 request. The server 296 updates the name "chi6.example.com" on the client's behalf, and uses 297 the DHCP client identifier option data as input in forming a DHCID 298 RR. The DHCID RDATA is formed by setting the two type octets to the 299 value 0x0002, the 1-octet digest type to 1 for SHA-256, and 300 performing a SHA-256 hash computation across a buffer containing the 301 14 octets from the client-id option and the FQDN (represented as 302 specified in Section 3.5). 304 chi6.example.com. AAAA 2000::1234:5678 305 chi6.example.com. DHCID ( AAIBY2/AuCccgoJbsaxcQc9TUapptP69l 306 OjxfNuVAA2kjEA= ) 308 If the DHCID RR type is not supported, the RDATA would be encoded 309 [13] as: 311 \# 35 ( 000201636fc0b8271c82825bb1ac5c41cf5351aa69b4febd94e8f17cd 312 b95000da48c40 ) 314 4. Use of the DHCID RR 316 This RR MUST NOT be used for any purpose other than that detailed in 317 "Resolution of DNS Name Conflicts" [1]. Although this RR contains 318 data that is opaque to DNS servers, the data must be consistent 319 across all entities that update and interpret this record. 321 Therefore, new data formats may only be defined through actions of 322 the DHC Working Group, as a result of revising [1]. 324 5. Updater Behavior 326 The data in the DHCID RR allows updaters to determine whether more 327 than one DHCP client desires to use a particular FQDN. This allows 328 site administrators to establish policy about DNS updates. The DHCID 329 RR does not establish any policy itself. 331 Updaters use data from a DHCP client's request and the domain name 332 that the client desires to use to compute a client identity hash, and 333 then compare that hash to the data in any DHCID RRs on the name that 334 they wish to associate with the client's IP address. If an updater 335 discovers DHCID RRs whose RDATA does not match the client identity 336 that they have computed, the updater SHOULD conclude that a different 337 client is currently associated with the name in question. The 338 updater SHOULD then proceed according to the site's administrative 339 policy. That policy might dictate that a different name be selected, 340 or it might permit the updater to continue. 342 6. Security Considerations 344 The DHCID record as such does not introduce any new security problems 345 into the DNS. In order to obscure the client's identity information, 346 a one-way hash is used. And, in order to make it difficult to 347 'track' a client by examining the names associated with a particular 348 hash value, the FQDN is included in the hash computation. Thus, the 349 RDATA is dependent on both the DHCP client identification data and on 350 each FQDN associated with the client. 352 However, it should be noted that an attacker that has some knowledge, 353 such as of MAC addresses commonly used in DHCP client identification 354 data, may be able to discover the client's DHCP identify by using a 355 brute-force attack. Even without any additional knowledge, the 356 number of unknown bits used in computing the hash is typically only 357 48 to 80. 359 Administrators should be wary of permitting unsecured DNS updates to 360 zones, whether or not they are exposed to the global Internet. Both 361 DHCP clients and servers SHOULD use some form of update 362 authentication (e.g., TSIG [11]) when performing DNS updates. 364 7. IANA Considerations 365 IANA is requested to allocate a DNS RR type number for the DHCID 366 record type. 368 This specification defines a new number-space for the 2-octet 369 identifier type codes associated with the DHCID RR. IANA is 370 requested to establish a registry of the values for this number- 371 space. Three initial values are assigned in Section 3.3, and the 372 value 0xFFFF is reserved for future use. New DHCID RR identifier 373 type codes are assigned through Standards Action, as defined in RFC 374 2434 [5]. 376 This specification defines a new number-space for the 1-octet digest 377 type codes associated with the DHCID RR. IANA is requested to 378 establish a registry of the values for this number-space. Two 379 initial values are assigned in Section 3.4. New DHCID RR digest type 380 codes are assigned through Standards Action, as defined in RFC 2434 381 [5]. 383 8. Acknowledgements 385 Many thanks to Harald Alvestrand, Ralph Droms, Olafur Gudmundsson, 386 Sam Hartman, Josh Littlefield, Pekka Savola, and especially Bernie 387 Volz for their review and suggestions. 389 9. References 391 9.1. Normative References 393 [1] Stapp, M. and B. Volz, "Resolution of DNS Name Conflicts Among 394 DHCP Clients (draft-ietf-dhc-dns-resolution-*)", February 2006. 396 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 397 Levels", BCP 14, RFC 2119, March 1997. 399 [3] Mockapetris, P., "Domain names - concepts and facilities", 400 STD 13, RFC 1034, November 1987. 402 [4] Mockapetris, P., "Domain names - implementation and 403 specification", STD 13, RFC 1035, November 1987. 405 [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 406 Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. 408 9.2. Informative References 410 [6] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, 411 March 1997. 413 [7] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", 414 RFC 3548, July 2003. 416 [8] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, 417 "Resource Records for the DNS Security Extensions", RFC 4034, 418 March 2005. 420 [9] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor 421 Extensions", RFC 2132, March 1997. 423 [10] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. 424 Carney, "Dynamic Host Configuration Protocol for IPv6 425 (DHCPv6)", RFC 3315, July 2003. 427 [11] Vixie, P., Gudmundsson, O., Eastlake, D., and B. Wellington, 428 "Secret Key Transaction Authentication for DNS (TSIG)", 429 RFC 2845, May 2000. 431 [12] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers 432 for Dynamic Host Configuration Protocol Version Four (DHCPv4)", 433 RFC 4361, February 2006. 435 [13] Gustafsson, A., "Handling of Unknown DNS Resource Record (RR) 436 Types", RFC 3597, September 2003. 438 Authors' Addresses 440 Mark Stapp 441 Cisco Systems, Inc. 442 1414 Massachusetts Ave. 443 Boxborough, MA 01719 444 USA 446 Phone: 978.936.1535 447 Email: mjs@cisco.com 449 Ted Lemon 450 Nominum, Inc. 451 950 Charter St. 452 Redwood City, CA 94063 453 USA 455 Email: mellon@nominum.com 457 Andreas Gustafsson 458 Araneus Information Systems Oy 459 Ulappakatu 1 460 02320 Espoo 461 Finland 463 Email: gson@araneus.fi 465 Intellectual Property Statement 467 The IETF takes no position regarding the validity or scope of any 468 Intellectual Property Rights or other rights that might be claimed to 469 pertain to the implementation or use of the technology described in 470 this document or the extent to which any license under such rights 471 might or might not be available; nor does it represent that it has 472 made any independent effort to identify any such rights. 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Please address the information to the IETF at 487 ietf-ipr@ietf.org. 489 Disclaimer of Validity 491 This document and the information contained herein are provided on an 492 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 493 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 494 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 495 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 496 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 497 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 499 Copyright Statement 501 Copyright (C) The Internet Society (2006). This document is subject 502 to the rights, licenses and restrictions contained in BCP 78, and 503 except as set forth therein, the authors retain all their rights. 505 Acknowledgment 507 Funding for the RFC Editor function is currently provided by the 508 Internet Society.