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Jiang 3 Internet-Draft Huawei Technologies Co., Ltd 4 Intended status: Informational S. Krishnan 5 Expires: August 24, 2016 Ericsson 6 T. Mrugalski 7 ISC 8 February 21, 2016 10 Privacy considerations for DHCP 11 draft-ietf-dhc-dhcp-privacy-05 13 Abstract 15 DHCP is a protocol that is used to provide addressing and 16 configuration information to IPv4 hosts. This document discusses the 17 various identifiers used by DHCP and the potential privacy issues. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on August 24, 2016. 36 Copyright Notice 38 Copyright (c) 2016 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Requirements Language and Terminology . . . . . . . . . . . . 3 55 3. DHCP Options Carrying Identifiers . . . . . . . . . . . . . . 3 56 3.1. Client Identifier Option . . . . . . . . . . . . . . . . 4 57 3.2. Address Fields & Options . . . . . . . . . . . . . . . . 4 58 3.3. Client FQDN Option . . . . . . . . . . . . . . . . . . . 5 59 3.4. Parameter Request List Option . . . . . . . . . . . . . . 5 60 3.5. Vendor Class and Vendor-Identifying Vendor Class Options 5 61 3.6. Civic Location Option . . . . . . . . . . . . . . . . . . 5 62 3.7. Coordinate-Based Location Option . . . . . . . . . . . . 6 63 3.8. Client System Architecture Type Option . . . . . . . . . 6 64 3.9. Relay Agent Information Option and Sub-options . . . . . 6 65 4. Existing Mechanisms That Affect Privacy . . . . . . . . . . . 7 66 4.1. DNS Updates . . . . . . . . . . . . . . . . . . . . . . . 7 67 4.2. Allocation strategies . . . . . . . . . . . . . . . . . . 7 68 5. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 5.1. Device type discovery . . . . . . . . . . . . . . . . . . 8 70 5.2. Operating system discovery . . . . . . . . . . . . . . . 8 71 5.3. Finding location information . . . . . . . . . . . . . . 9 72 5.4. Finding previously visited networks . . . . . . . . . . . 9 73 5.5. Finding a stable identity . . . . . . . . . . . . . . . . 9 74 5.6. Pervasive monitoring . . . . . . . . . . . . . . . . . . 9 75 5.7. Finding client's IP address or hostname . . . . . . . . . 10 76 5.8. Correlation of activities over time . . . . . . . . . . . 10 77 5.9. Location tracking . . . . . . . . . . . . . . . . . . . . 10 78 5.10. Leasequery & bulk leasequery . . . . . . . . . . . . . . 10 79 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 80 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11 81 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 82 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 83 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 84 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 85 10.2. Informative References . . . . . . . . . . . . . . . . . 12 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 88 1. Introduction 90 Dynamic Host Configuration Protocol (DHCP) [RFC2131] is a protocol 91 that is used to provide addressing and configuration information to 92 IPv4 hosts. DHCP uses several identifiers that could become a source 93 for gleaning information about the IPv4 host. This information may 94 include device type, operating system information, location(s) that 95 the device may have previously visited, etc. This document discusses 96 the various identifiers used by DHCP and the potential privacy issues 97 [RFC6973]. In particular, it also takes into consideration the 98 problem of pervasive monitoring [RFC7258]. 100 Future works may propose protocol changes to fix the privacy issues 101 that have been analyzed in this document. These changes are out of 102 scope for this document. 104 The primary focus of this document is around privacy considerations 105 for clients to support client mobility and connection to random 106 networks. The privacy of DHCP servers and relay agents are 107 considered less important as they are typically open for public 108 services. And, it is generally assumed that relay agent to server 109 communication is protected from casual snooping, as that 110 communication occurs in the provider's backbone. Nevertheless, the 111 topics involving relay agents and servers are explored to some 112 degree. However, future work may want to further explore privacy of 113 DHCP servers and relay agents. 115 2. Requirements Language and Terminology 117 Naming convention from [RFC2131] and related is used throughout this 118 document. 120 In addition the following terminology is used: 122 Stable identifier - Any property disclosed by a DHCP client that 123 does not change over time or changes very infrequently and is 124 unique for said client in a given context. Examples include 125 MAC address, client-id, and a hostname. Some identifiers may 126 be considered stable only under certain conditions, for 127 example one client implementation may keep its client-id 128 stored in stable storage while another may generate it on the 129 fly and use a different one after each boot. Stable 130 identifiers may or may not be globally unique. 132 3. DHCP Options Carrying Identifiers 134 In DHCP, there are a few options that contain identification 135 information or that can be used to extract identification information 136 about the client. This section enumerates various options and the 137 identifiers conveyed in them, which can be used to disclose client 138 identification. They are targets of various attacks that are 139 analyzed in Section 5. 141 3.1. Client Identifier Option 143 The Client Identifier Option [RFC2131] is used to pass an explicit 144 client identifier to a DHCP server. 146 The client identifier is an opaque key, which must be unique to that 147 client within the subnet to which the client is attached. It 148 typically remains stable after it has been initially generated. It 149 may contain a hardware address, identical to the contents of the 150 'chaddr' field, or another type of identifier, such as a DNS name. 151 [RFC3315] in Section 9.2 specifies DUID-LLT (Link-layer + time) as 152 the recommended DUID (DHCP Unique Identifier) type. [RFC4361], 153 Section 6.1 introduces this concept to DHCP. Those two documents 154 recommend that client identifiers be generated by using the permanent 155 link-layer address of the network interface that the client is trying 156 to configure. [RFC4361] updates the recommendation of Client 157 Identifiers to be "consists of a type field whose value is normally 158 255, followed by a four-byte IA_ID field, followed by the DUID for 159 the client as defined in RFC 3315, section 9". This does not change 160 the lifecycle of the Client Identifiers. Clients are expected to 161 generate their Client Identifiers once (during first operation) and 162 store it in non-volatile storage or use the same deterministic 163 algorithm to generate the same Client Identifier values again. 165 This means that most implementations will use the available link- 166 layer address during its first boot. Even if the administrator 167 enables link-layer address randomization, it is likely that it was 168 not yet enabled during the first device boot. Hence the original, 169 unobfuscated link-layer address will likely end up being announced as 170 the client identifier, even if the link-layer address has changed (or 171 even if it is being changed on a periodic basis). The exposure of 172 the original link-layer address in the client identifier will also 173 undermine other privacy extensions such as [RFC4941]. 175 3.2. Address Fields & Options 177 The 'yiaddr' field [RFC2131] in DHCP message is used to convey an 178 allocated address from the server to the client. 180 The DHCP specification [RFC2131] provides a way to specify the client 181 link-layer address in the DHCP message header. A DHCP message header 182 has 'htype' and 'chaddr' fields to specify the client link-layer 183 address type and the link-layer address, respectively. The 'chaddr' 184 field is used both as a hardware address for transmission of reply 185 messages and as a client identifier. 187 The 'requested IP address' option [RFC2131] is used by a client to 188 suggest that a particular IP address be assigned. 190 3.3. Client FQDN Option 192 The Client Fully Qualified Domain Name (FQDN) option [RFC4702] is 193 used by DHCP clients and servers to exchange information about the 194 client's fully qualified domain name and about who has the 195 responsibility for updating the DNS with the associated A and PTR 196 RRs. 198 A client can use this option to convey all or part of its domain name 199 to a DHCP server for the IP-address-to-FQDN mapping. In most case a 200 client sends its hostname as a hint for the server. The DHCP server 201 MAY be configured to modify the supplied name or to substitute a 202 different name. The server should send its notion of the complete 203 FQDN for the client in the Domain Name field. 205 3.4. Parameter Request List Option 207 The Parameter Request List option [RFC2131] is used to inform the 208 server about options the client wants the server to send to the 209 client. The content of a Parameter Request List option are the 210 option codes for options requested by the client. 212 3.5. Vendor Class and Vendor-Identifying Vendor Class Options 214 The Vendor Class option [RFC2131], the Vendor-Identifying Vendor 215 Class option, and the Vendor-Identifying Vendor Information option 216 [RFC3925] are used by the DHCP client to identify the vendor that 217 manufactured the hardware on which the client is running. 219 The information contained in the data area of this option is 220 contained in one or more opaque fields that identify the details of 221 the hardware configuration of the host on which the client is 222 running, or of industry consortium compliance, for example, the 223 version of the operating system the client is running or the amount 224 of memory installed on the client. 226 3.6. Civic Location Option 228 DHCP servers use the Civic Location Option [RFC4776] to deliver 229 location information (the civic and postal addresses) to DHCP 230 clients. It may refer to three locations: the location of the DHCP 231 server, the location of the network element believed to be closest to 232 the client, or the location of the client, identified by the "what" 233 element within the option. 235 3.7. Coordinate-Based Location Option 237 The GeoConf and GeoLoc options [RFC6225] are used by a DHCP server to 238 provide coordinate-based geographic location information to DHCP 239 clients. They enable a DHCP client to obtain its geographic 240 location. 242 3.8. Client System Architecture Type Option 244 The Client System Architecture Type Option [RFC4578] is used by a 245 DHCP client to send a list of supported architecture types to the 246 DHCP server. It is used by clients that must be booted using the 247 network rather than from local storage, so the server can decide 248 which boot file should be provided to the client. 250 3.9. Relay Agent Information Option and Sub-options 252 A DHCP relay agent includes a Relay Agent Information option[RFC3046] 253 to identify the remote host end of the circuit. It contains a 254 "circuit ID" sub-option for the incoming circuit, which is an agent- 255 local identifier of the circuit from which a DHCP client-to-server 256 packet was received, and a "remote ID" sub-option which provides a 257 trusted identifier for the remote high-speed modem. 259 Possible encoding of "circuit ID" sub-option includes: router 260 interface number, switching hub port number, remote access server 261 port number, frame relay DLCI, ATM virtual circuit number, cable data 262 virtual circuit number, etc. 264 Possible encoding of the "remote ID" sub-option includes: a "caller 265 ID" telephone number for dial-up connection, a "user name" prompted 266 for by a remote access server, a remote caller ATM address, a "modem 267 ID" of a cable data modem, the remote IP address of a point-to-point 268 link, a remote X.25 address for X.25 connections, etc. 270 The link-selection sub-option [RFC3527] is used by any DHCP relay 271 agent that desires to specify a subnet/link for a DHCP client request 272 that it is relaying but needs the subnet/link specification to be 273 different from the IP address the DHCP server should use when 274 communicating with the relay agent. It contains an IP address, which 275 can identify the client's subnet/link. Also, assuming network 276 topology knowledge, it also reveals client location. 278 A DHCP relay includes a Subscriber-ID option [RFC3993] to associate 279 some provider-specific information with clients' DHCP messages that 280 is independent of the physical network configuration through which 281 the subscriber is connected. The "subscriber-id" assigned by the 282 provider is intended to be stable as customers connect through 283 different paths, and as network changes occur. The Subscriber-ID is 284 an ASCII string, which is assigned and configured by the network 285 provider. 287 4. Existing Mechanisms That Affect Privacy 289 This section describes deployed DHCP mechanisms that affect privacy. 291 4.1. DNS Updates 293 The Client FQDN (Fully Qualified Domain Name) Option [RFC4702] used 294 along with DNS Updates [RFC2136] defines a mechanism that allows both 295 clients and server to insert into the DNS domain information about 296 clients. Both forward (A) and reverse (PTR) resource records can be 297 updated. This allows other nodes to conveniently refer to a host, 298 despite the fact that its IP address may be changing. 300 This mechanism exposes two important pieces of information: current 301 address (which can be mapped to current location) and client's 302 hostname. The stable hostname can then be used to correlate the 303 client across different network attachments even when its IP 304 addresses keep changing. 306 4.2. Allocation strategies 308 A DHCP server running in typical, stateful mode is given a task of 309 managing one or more pools of IP address. When a client requests an 310 address, the server must pick an address out of a configured pool. 311 Depending on the server's implementation, various allocation 312 strategies are possible. Choices in this regard may have privacy 313 implications. Note that the constraints in DHCP and DHCPv6 are 314 radically different, but servers that allow allocation strategy 315 configuration may allow configuring them in both DHCP and DHCPv6. 316 Not every allocation strategy is equally suitable for DHCP and for 317 DHCPv6. 319 Iterative allocation - a server may choose to allocate addresses one 320 by one. That strategy has the benefit of being very fast, thus being 321 favored in deployments that prefer performance. However, it makes 322 the allocated addresses very predictable. Also, since the addresses 323 allocated tend to be clustered at the beginning of an available pool, 324 it makes scanning attacks much easier. 326 Identifier-based allocation - some server implementations may choose 327 to allocate an address that is based on one of the available 328 identifiers, e.g., client identifier or MAC address. It is also 329 convenient, as a returning client is very likely to get the same 330 address. Those properties are convenient for system administrators, 331 so DHCP server implementers are often requested to implement it. The 332 downside of such allocation is that the client has a very stable IP 333 address. That means that correlation of activities over time, 334 location tracking, address scanning and OS/vendor discovery apply. 335 This is certainly an issue in DHCPv6, but due to a much smaller 336 address space is almost never a problem in DHCP. 338 Hash allocation - it's an extension of identifier-based allocation. 339 Instead of using the identifier directly, it is hashed first. If the 340 hash is implemented correctly, it removes the flaw of disclosing the 341 identifier, a property that eliminates susceptibility to address 342 scanning and OS/vendor discovery. If the hash is poorly implemented 343 (e.g., it can be reversed), it introduces no improvement over 344 identifier-based allocation. 346 Random allocation - a server can pick a resource randomly out of an 347 available pool. This allocation scheme essentially prevents 348 returning clients from getting the same address again. On the other 349 hand, it is beneficial from a privacy perspective as addresses 350 generated that way are not susceptible to correlation attacks, OS/ 351 vendor discovery attacks, or identity discovery attacks. Note that 352 even though the address itself may be resilient to a given attack, 353 the client may still be susceptible if additional information is 354 disclosed other way, e.g., the client's address may be randomized, 355 but it still can leak its MAC address in the client-id option. 357 Other allocation strategies may be implemented. 359 Given the limited size of most IPv4 public address pools, allocation 360 mechanisms in IPv4 may not provide much privacy protection or leak 361 much useful information, if misused. 363 5. Attacks 365 5.1. Device type discovery 367 The type of device used by the client can be guessed by the attacker 368 using the Vendor Class Option, the 'chaddr' field, and by parsing the 369 Client ID Option. All of those options may contain an 370 Organizationally Unique Identifier (OUI) that represents the device's 371 vendor. That knowledge can be used for device-specific vulnerability 372 exploitation attacks. 374 5.2. Operating system discovery 376 The operating system running on a client can be guessed using the 377 Vendor Class option, the Client System Architecture Type option, or 378 by using fingerprinting techniques on the combination of options 379 requested using the Parameter Request List option. 381 5.3. Finding location information 383 The location information can be obtained by the attacker by many 384 means. The most direct way to obtain this information is by looking 385 into a message originating from the server that contains the Civic 386 Location, GeoConf, or GeoLoc options. It can also be indirectly 387 inferred using the Relay Agent Information option, with the remote ID 388 sub-option, the circuit ID option (e.g., if an access circuit on an 389 Access Node corresponds to a civic location), or the Subscriber ID 390 Option (if the attacker has access to subscriber info). 392 5.4. Finding previously visited networks 394 When DHCP clients connect to a network, they attempt to obtain the 395 same address they had used before they attached to the network. They 396 do this by putting the previously assigned address in the requested 397 IP address option. By observing these addresses, an attacker can 398 identify the network the client had previously visited. 400 5.5. Finding a stable identity 402 An attacker might use a stable identity gleaned from DHCP messages to 403 correlate activities of a given client on unrelated networks. The 404 Client FQDN option, the Subscriber ID option, and the Client ID 405 option can serve as long-lived identifiers of DHCP clients. The 406 Client FQDN option can also provide an identity that can easily be 407 correlated with web server activity logs. 409 5.6. Pervasive monitoring 411 Pervasive Monitoring [RFC7258] is widespread (and often covert) 412 surveillance through intrusive gathering of protocol artefacts, 413 including application content, or protocol metadata such as headers. 414 An operator who controls a non-trivial number of access points or 415 network segments, may use obtained information about a single client 416 and observe the client's habits. Although users may not expect true 417 privacy from their operators, the information that is set up to be 418 monitored by users' service operators may also be gathered by an 419 adversary who monitors a wide range of networks and develops 420 correlations from that information. 422 5.7. Finding client's IP address or hostname 424 Many DHCP deployments use DNS Updates [RFC4702] that put a client's 425 information (current IP address, client's hostname) into the DNS, 426 where it is easily accessible by anyone interested. Client ID is 427 also disclosed, albeit in not easily accessible form (SHA-256 digest 428 of the client-id). As SHA-256 is considered irreversible, DHCP 429 client ID can't be converted back to client-id. However, SHA-256 430 digest can be used as an unique identifier that is accessible by any 431 host. 433 5.8. Correlation of activities over time 435 As with other identifiers, an IP address can be used to correlate the 436 activities of a host for at least as long as the lifetime of the 437 address. If that address was generated from some other, stable 438 identifier and that generation scheme can be deduced by an attacker, 439 the duration of the correlation attack extends to that of the 440 identifier. In many cases, its lifetime is equal to the lifetime of 441 the device itself. 443 5.9. Location tracking 445 If a stable identifier is used for assigning an address and such 446 mapping is discovered by an attacker, it can be used for tracking a 447 user. In particular both passive (a service that the client connects 448 to can log the client's address and draw conclusions regarding its 449 location and movement patterns based on the addresses it is 450 connecting from) and active (an attacker can send ICMP echo requests 451 or other probe packets to networks of suspected client locations) 452 methods can be used. To give specific example, by accessing a social 453 portal from tomek-laptop.coffee.somecity.com.example, tomek- 454 laptop.mycompany.com.example and tomek-laptop.myisp.example.com, the 455 portal administrator can draw conclusions about tomek-laptop's 456 owner's current location and his habits. 458 5.10. Leasequery & bulk leasequery 460 Attackers may pretend to be an access concentrator, either as a DHCP 461 relay agent or as a DHCP client, to obtain location information 462 directly from the DHCP server(s) using the DHCP leasequery [RFC4388] 463 mechanism. 465 Location information is information needed by the access concentrator 466 to forward traffic to a broadband-accessible host. This information 467 includes knowledge of the host hardware address, the port or virtual 468 circuit that leads to the host, and/or the hardware address of the 469 intervening subscriber modem. 471 Furthermore, the attackers may use the DHCP bulk leasequery [RFC6926] 472 mechanism to obtain bulk information about DHCP bindings, even 473 without knowing the target bindings. 475 Additionally, active leasequery [RFC7724] is a mechanism for 476 subscribing to DHCP lease update changes in near real-time. The 477 intent of this mechanism is to update an operator's database, but if 478 misused, an attacker could defeat the server's authentication 479 mechanisms and subscribe to all updates. He then could continue 480 receiving updates, without any need for local presence. 482 6. Security Considerations 484 In current practice, the client privacy and client authentication are 485 mutually exclusive. The client authentication procedure reveals 486 additional client information in their certificates/identifiers. 487 Full privacy for the clients may mean the clients are also anonymous 488 to the server and the network. 490 7. Privacy Considerations 492 This document in its entirety discusses privacy considerations in 493 DHCP. As such, no dedicated discussion is needed. 495 8. IANA Considerations 497 This draft does not request any IANA action. 499 9. Acknowledgements 501 The authors would like to thank the valuable comments made by Stephen 502 Farrell, Ted Lemon, Ines Robles, Russ White, Christian Huitema, 503 Bernie Volz, Jinmei Tatuya, Marcin Siodelski, Christian Schaefer, 504 Robert Sparks, Peter Yee, and other members of DHC WG. 506 This document was produced using the xml2rfc tool [RFC7749]. 508 10. References 510 10.1. Normative References 512 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 513 RFC 2131, DOI 10.17487/RFC2131, March 1997, 514 . 516 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 517 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 518 RFC 2136, DOI 10.17487/RFC2136, April 1997, 519 . 521 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 522 Morris, J., Hansen, M., and R. Smith, "Privacy 523 Considerations for Internet Protocols", RFC 6973, 524 DOI 10.17487/RFC6973, July 2013, 525 . 527 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an 528 Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 529 2014, . 531 10.2. Informative References 533 [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", 534 RFC 3046, DOI 10.17487/RFC3046, January 2001, 535 . 537 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 538 C., and M. Carney, "Dynamic Host Configuration Protocol 539 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 540 2003, . 542 [RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy, 543 "Link Selection sub-option for the Relay Agent Information 544 Option for DHCPv4", RFC 3527, DOI 10.17487/RFC3527, April 545 2003, . 547 [RFC3925] Littlefield, J., "Vendor-Identifying Vendor Options for 548 Dynamic Host Configuration Protocol version 4 (DHCPv4)", 549 RFC 3925, DOI 10.17487/RFC3925, October 2004, 550 . 552 [RFC3993] Johnson, R., Palaniappan, T., and M. Stapp, "Subscriber-ID 553 Suboption for the Dynamic Host Configuration Protocol 554 (DHCP) Relay Agent Option", RFC 3993, 555 DOI 10.17487/RFC3993, March 2005, 556 . 558 [RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client 559 Identifiers for Dynamic Host Configuration Protocol 560 Version Four (DHCPv4)", RFC 4361, DOI 10.17487/RFC4361, 561 February 2006, . 563 [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration 564 Protocol (DHCP) Leasequery", RFC 4388, 565 DOI 10.17487/RFC4388, February 2006, 566 . 568 [RFC4578] Johnston, M. and S. Venaas, Ed., "Dynamic Host 569 Configuration Protocol (DHCP) Options for the Intel 570 Preboot eXecution Environment (PXE)", RFC 4578, 571 DOI 10.17487/RFC4578, November 2006, 572 . 574 [RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host 575 Configuration Protocol (DHCP) Client Fully Qualified 576 Domain Name (FQDN) Option", RFC 4702, 577 DOI 10.17487/RFC4702, October 2006, 578 . 580 [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol 581 (DHCPv4 and DHCPv6) Option for Civic Addresses 582 Configuration Information", RFC 4776, 583 DOI 10.17487/RFC4776, November 2006, 584 . 586 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 587 Extensions for Stateless Address Autoconfiguration in 588 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 589 . 591 [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, Ed., 592 "Dynamic Host Configuration Protocol Options for 593 Coordinate-Based Location Configuration Information", 594 RFC 6225, DOI 10.17487/RFC6225, July 2011, 595 . 597 [RFC6926] Kinnear, K., Stapp, M., Desetti, R., Joshi, B., Russell, 598 N., Kurapati, P., and B. Volz, "DHCPv4 Bulk Leasequery", 599 RFC 6926, DOI 10.17487/RFC6926, April 2013, 600 . 602 [RFC7724] Kinnear, K., Stapp, M., Volz, B., and N. Russell, "Active 603 DHCPv4 Lease Query", RFC 7724, DOI 10.17487/RFC7724, 604 December 2015, . 606 [RFC7749] Reschke, J., "The "xml2rfc" Version 2 Vocabulary", 607 RFC 7749, DOI 10.17487/RFC7749, February 2016, 608 . 610 Authors' Addresses 612 Sheng Jiang 613 Huawei Technologies Co., Ltd 614 Q14, Huawei Campus, No.156 Beiqing Road 615 Hai-Dian District, Beijing, 100095 616 P.R. China 618 Email: jiangsheng@huawei.com 620 Suresh Krishnan 621 Ericsson 622 8400 Decarie Blvd. 623 Town of Mount Royal, QC 624 Canada 626 Phone: +1 514 345 7900 x42871 627 Email: suresh.krishnan@ericsson.com 629 Tomek Mrugalski 630 Internet Systems Consortium, Inc. 631 950 Charter Street 632 Redwood City, CA 94063 633 USA 635 Email: tomasz.mrugalski@gmail.com