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Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) -- Obsolete informational reference (is this intentional?): RFC 4941 (Obsoleted by RFC 8981) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 dhc S. Jiang 3 Internet-Draft Huawei Technologies Co., Ltd 4 Intended status: Informational S. Krishnan 5 Expires: August 17, 2016 Ericsson 6 T. Mrugalski 7 ISC 8 February 14, 2016 10 Privacy considerations for DHCP 11 draft-ietf-dhc-dhcp-privacy-04 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 17, 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 . . . . . . . . . 9 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 . . . . . . . . . . . . . . . . . . . . . . . 13 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 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 118 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 119 document are to be interpreted as described in [RFC2119]. When these 120 words are not in ALL CAPS (such as "should" or "Should"), they have 121 their usual English meanings, and are not to be interpreted as 122 [RFC2119] key words. 124 In addition the following terminology is used: 126 Stable identifier - Any property disclosed by a DHCP client that 127 does not change over time or changes very infrequently and is 128 unique for said client in a given context. Examples include 129 MAC address, client-id, and a hostname. Some identifiers may 130 be considered stable only under certain conditions, for 131 example one client implementation may keep its client-id 132 stored in stable storage while another may generate it on the 133 fly and use a different one after each boot. Stable 134 identifiers may or may not be globally unique. 136 3. DHCP Options Carrying Identifiers 138 In DHCP, there are a few options that contain identification 139 information or that can be used to extract identification information 140 about the client. This section enumerates various options and the 141 identifiers conveyed in them, which can be used to disclose client 142 identification. They are targets of various attacks that are 143 analyzed in Section 5. 145 3.1. Client Identifier Option 147 The Client Identifier Option [RFC2131] is used to pass an explicit 148 client identifier to a DHCP server. 150 The client identifier is an opaque key, which must be unique to that 151 client within the subnet to which the client is attached. It 152 typically remains stable after it has been initially generated. It 153 may contain a hardware address, identical to the contents of the 154 'chaddr' field, or another type of identifier, such as a DNS name. 155 [RFC3315] in Section 9.2 specifies DUID-LLT (Link-layer + time) as 156 the recommended DUID (DHCP Unique Identifier) type. [RFC4361], 157 Section 6.1 introduces this concept to DHCP. Those two documents 158 recommend that client identifiers be generated by using the permanent 159 link-layer address of the network interface that the client is trying 160 to configure. [RFC4361] updates the recommendation of Client 161 Identifiers to be "consists of a type field whose value is normally 162 255, followed by a four-byte IA_ID field, followed by the DUID for 163 the client as defined in RFC 3315, section 9". This does not change 164 the lifecycle of the Client Identifiers. Clients are expected to 165 generate their Client Identifiers once (during first operation) and 166 store it in non-volatile storage or use the same deterministic 167 algorithm to generate the same Client Identifier values again. 169 This means that most implementations will use the available link- 170 layer address during its first boot. Even if the administrator 171 enables link-layer address randomization, it is likely that it was 172 not yet enabled during the first device boot. Hence the original, 173 unobfuscated link-layer address will likely end up being announced as 174 the client identifier, even if the link-layer address has changed (or 175 even if it is being changed on a periodic basis). The exposure of 176 the original link-layer address in the client identifier will also 177 undermine other privacy extensions such as [RFC4941]. 179 3.2. Address Fields & Options 181 The 'yiaddr' field [RFC2131] in DHCP message is used to convey an 182 allocated address from the server to the client. 184 The DHCP specification [RFC2131] provides a way to specify the client 185 link-layer address in the DHCP message header. A DHCP message header 186 has 'htype' and 'chaddr' fields to specify the client link-layer 187 address type and the link-layer address, respectively. The 'chaddr' 188 field is used both as a hardware address for transmission of reply 189 messages and as a client identifier. 191 The 'requested IP address' option [RFC2131] is used by a client to 192 suggest that a particular IP address be assigned. 194 3.3. Client FQDN Option 196 The Client Fully Qualified Domain Name (FQDN) option [RFC4702] is 197 used by DHCP clients and servers to exchange information about the 198 client's fully qualified domain name and about who has the 199 responsibility for updating the DNS with the associated A and PTR 200 RRs. 202 A client can use this option to convey all or part of its domain name 203 to a DHCP server for the IP-address-to-FQDN mapping. In most case a 204 client sends its hostname as a hint for the server. The DHCP server 205 MAY be configured to modify the supplied name or to substitute a 206 different name. The server should send its notion of the complete 207 FQDN for the client in the Domain Name field. 209 3.4. Parameter Request List Option 211 The Parameter Request List option [RFC2131] is used to inform the 212 server about options the client wants the server to send to the 213 client. The content of a Parameter Request List option are the 214 option codes for options requested by the client. 216 3.5. Vendor Class and Vendor-Identifying Vendor Class Options 218 The Vendor Class option [RFC2131], the Vendor-Identifying Vendor 219 Class option, and the Vendor-Identifying Vendor Information option 220 [RFC3925] are used by the DHCP client to identify the vendor that 221 manufactured the hardware on which the client is running. 223 The information contained in the data area of this option is 224 contained in one or more opaque fields that identify the details of 225 the hardware configuration of the host on which the client is 226 running, or of industry consortium compliance, for example, the 227 version of the operating system the client is running or the amount 228 of memory installed on the client. 230 3.6. Civic Location Option 232 DHCP servers use the Civic Location Option [RFC4776] to deliver 233 location information (the civic and postal addresses) to DHCP 234 clients. It may refer to three locations: the location of the DHCP 235 server, the location of the network element believed to be closest to 236 the client, or the location of the client, identified by the "what" 237 element within the option. 239 3.7. Coordinate-Based Location Option 241 The GeoConf and GeoLoc options [RFC6225] are used by a DHCP server to 242 provide coordinate-based geographic location information to DHCP 243 clients. They enable a DHCP client to obtain its geographic 244 location. 246 3.8. Client System Architecture Type Option 248 The Client System Architecture Type Option [RFC4578] is used by a 249 DHCP client to send a list of supported architecture types to the 250 DHCP server. It is used by clients that must be booted using the 251 network rather than from local storage, so the server can decide 252 which boot file should be provided to the client. 254 3.9. Relay Agent Information Option and Sub-options 256 A DHCP relay agent includes a Relay Agent Information option[RFC3046] 257 to identify the remote host end of the circuit. It contains a 258 "circuit ID" sub-option for the incoming circuit, which is an agent- 259 local identifier of the circuit from which a DHCP client-to-server 260 packet was received, and a "remote ID" sub-option which provides a 261 trusted identifier for the remote high-speed modem. 263 Possible encoding of "circuit ID" sub-option includes: router 264 interface number, switching hub port number, remote access server 265 port number, frame relay DLCI, ATM virtual circuit number, cable data 266 virtual circuit number, etc. 268 Possible encoding of the "remote ID" sub-option includes: a "caller 269 ID" telephone number for dial-up connection, a "user name" prompted 270 for by a remote access server, a remote caller ATM address, a "modem 271 ID" of a cable data modem, the remote IP address of a point-to-point 272 link, a remote X.25 address for X.25 connections, etc. 274 The link-selection sub-option [RFC3527] is used by any DHCP relay 275 agent that desires to specify a subnet/link for a DHCP client request 276 that it is relaying but needs the subnet/link specification to be 277 different from the IP address the DHCP server should use when 278 communicating with the relay agent. It contains an IP address, which 279 can identify the client's subnet/link. Also, assuming network 280 topology knowledge, it also reveals client location. 282 A DHCP relay includes a Subscriber-ID option [RFC3993] to associate 283 some provider-specific information with clients' DHCP messages that 284 is independent of the physical network configuration through which 285 the subscriber is connected. The "subscriber-id" assigned by the 286 provider is intended to be stable as customers connect through 287 different paths, and as network changes occur. The Subscriber-ID is 288 an ASCII string, which is assigned and configured by the network 289 provider. 291 4. Existing Mechanisms That Affect Privacy 293 This section describes deployed DHCP mechanisms that affect privacy. 295 4.1. DNS Updates 297 The Client FQDN (Fully Qualified Domain Name) Option [RFC4702] used 298 along with DNS Updates [RFC2136] defines a mechanism that allows both 299 clients and server to insert into the DNS domain information about 300 clients. Both forward (A) and reverse (PTR) resource records can be 301 updated. This allows other nodes to conveniently refer to a host, 302 despite the fact that its IP address may be changing. 304 This mechanism exposes two important pieces of information: current 305 address (which can be mapped to current location) and client's 306 hostname. The stable hostname can then be used to correlate the 307 client across different network attachments even when its IP 308 addresses keep changing. 310 4.2. Allocation strategies 312 A DHCP server running in typical, stateful mode is given a task of 313 managing one or more pools of IP address. When a client requests an 314 address, the server must pick an address out of a configured pool. 315 Depending on the server's implementation, various allocation 316 strategies are possible. Choices in this regard may have privacy 317 implications. Note that the constraints in DHCP and DHCPv6 are 318 radically different, but servers that allow allocation strategy 319 configuration may allow configuring them in both DHCP and DHCPv6. 320 Not every allocation strategy is equally suitable for DHCP and for 321 DHCPv6. 323 Iterative allocation - a server may choose to allocate addresses one 324 by one. That strategy has the benefit of being very fast, thus being 325 favored in deployments that prefer performance. However, it makes 326 the allocated addresses very predictable. Also, since the addresses 327 allocated tend to be clustered at the beginning of an available pool, 328 it makes scanning attacks much easier. 330 Identifier-based allocation - some server implementations may choose 331 to allocate an address that is based on one of the available 332 identifiers, e.g., client identifier or MAC address. It is also 333 convenient, as a returning client is very likely to get the same 334 address. Those properties are convenient for system administrators, 335 so DHCP server implementors are often requested to implement it. The 336 downside of such allocation is that the client has a very stable IP 337 address. That means that correlation of activities over time, 338 location tracking, address scanning and OS/vendor discovery apply. 339 This is certainly an issue in DHCPv6, but due to a much smaller 340 address space is almost never a problem in DHCP. 342 Hash allocation - it's an extension of identifier-based allocation. 343 Instead of using the identifier directly, it is hashed first. If the 344 hash is implemented correctly, it removes the flaw of disclosing the 345 identifier, a property that eliminates susceptibility to address 346 scanning and OS/vendor discovery. If the hash is poorly implemented 347 (e.g., it can be reversed), it introduces no improvement over 348 identifier-based allocation. 350 Random allocation - a server can pick a resource randomly out of an 351 available pool. This allocation scheme essentially prevents 352 returning clients from getting the same address again. On the other 353 hand, it is beneficial from a privacy perspective as addresses 354 generated that way are not susceptible to correlation attacks, OS/ 355 vendor discovery attacks, or identity discovery attacks. Note that 356 even though the address itself may be resilient to a given attack, 357 the client may still be susceptible if additional information is 358 disclosed other way, e.g., the client's address may be randomized, 359 but it still can leak its MAC address in the client-id option. 361 Other allocation strategies may be implemented. 363 Given the limited size of most IPv4 public address pools, allocation 364 mechanisms in IPv4 may not provide much privacy protection or leak 365 much useful information, if misused. 367 5. Attacks 369 5.1. Device type discovery 371 The type of device used by the client can be guessed by the attacker 372 using the Vendor Class Option, the 'chaddr' field, and by parsing the 373 Client ID Option. All of those options may contain an 374 Organizationally Unique Identifier (OUI) that represents the device's 375 vendor. That knowledge can be used for device-specific vulnerability 376 exploitation attacks. 378 5.2. Operating system discovery 380 The operating system running on a client can be guessed using the 381 Vendor Class option, the Client System Architecture Type option, or 382 by using fingerprinting techniques on the combination of options 383 requested using the Parameter Request List option. 385 5.3. Finding location information 387 The location information can be obtained by the attacker by many 388 means. The most direct way to obtain this information is by looking 389 into a message originating from the server that contains the Civic 390 Location, GeoConf, or GeoLoc options. It can also be indirectly 391 inferred using the Relay Agent Information option, with the remote ID 392 sub-option, the circuit ID option (e.g., if an access circuit on an 393 Access Node corresponds to a civic location), or the Subscriber ID 394 Option (if the attacker has access to subscriber info). 396 5.4. Finding previously visited networks 398 When DHCP clients connect to a network, they attempt to obtain the 399 same address they had used before they attached to the network. They 400 do this by putting the previously assigned address in the requested 401 IP address option. By observing these addresses, an attacker can 402 identify the network the client had previously visited. 404 5.5. Finding a stable identity 406 An attacker might use a stable identity gleaned from DHCP messages to 407 correlate activities of a given client on unrelated networks. The 408 Client FQDN option, the Subscriber ID option, and the Client ID 409 option can serve as long-lived identifiers of DHCP clients. The 410 Client FQDN option can also provide an identity that can easily be 411 correlated with web server activity logs. 413 5.6. Pervasive monitoring 415 This is an enhancement, or a combination of most of the 416 aforementioned mechanisms. An operator who controls a non-trivial 417 number of access points or network segments, may use obtained 418 information about a single client and observe the client's habits. 419 Although users may not expect true privacy from their operators, the 420 information that is set up to be monitored by users' service 421 operators may also be gathered by an adversary who monitors a wide 422 range of networks and develops correlations from that information. 424 5.7. Finding client's IP address or hostname 426 Many DHCP deployments use DNS Updates [RFC4702] that put a client's 427 information (current IP address, client's hostname) into the DNS, 428 where it is easily accessible by anyone interested. Client ID is 429 also disclosed, albeit in not easily accessible form (SHA-256 digest 430 of the client-id). Although SHA-256 is considered irreversible, DHCP 431 client ID can't be converted back to client-id. However, SHA-256 432 digest can be used as an unique identifier that is accessible by any 433 host. 435 5.8. Correlation of activities over time 437 As with other identifiers, an IP address can be used to correlate the 438 activities of a host for at least as long as the lifetime of the 439 address. If that address was generated from some other, stable 440 identifier and that generation scheme can be deduced by an attacker, 441 the duration of the correlation attack extends to that of the 442 identifier. In many cases, its lifetime is equal to the lifetime of 443 the device itself. 445 5.9. Location tracking 447 If a stable identifier is used for assigning an address and such 448 mapping is discovered by an attacker, it can be used for tracking a 449 user. In particular both passive (a service that the client connects 450 to can log the client's address and draw conclusions regarding its 451 location and movement patterns based on the addresses it is 452 connecting from) and active (an attacker can send ICMP echo requests 453 or other probe packets to networks of suspected client locations) 454 methods can be used. To give specific example, by accessing a social 455 portal from tomek-laptop.coffee.somecity.com.example, tomek- 456 laptop.mycompany.com.example and tomek-laptop.myisp.example.com, the 457 portal administrator can draw conclusions about tomek-laptop's 458 owner's current location and his habits. 460 5.10. Leasequery & bulk leasequery 462 Attackers may pretend to be an access concentrator, either as a DHCP 463 relay agent or as a DHCP client, to obtain location information 464 directly from the DHCP server(s) using the DHCP leasequery [RFC4388] 465 mechanism. 467 Location information is information needed by the access concentrator 468 to forward traffic to a broadband-accessible host. This information 469 includes knowledge of the host hardware address, the port or virtual 470 circuit that leads to the host, and/or the hardware address of the 471 intervening subscriber modem. 473 Furthermore, the attackers may use the DHCP bulk leasequery [RFC6926] 474 mechanism to obtain bulk information about DHCP bindings, even 475 without knowing the target bindings. 477 Additionally, active leasequery [RFC7724] is a mechanism for 478 subscribing to DHCP lease update changes in near real-time. The 479 intent of this mechanism is to update an operator's database, but if 480 misused, an attacker could defeat the server's authentication 481 mechanisms and subscribe to all updates. He then could continue 482 receiving updates, without any need for local presence. 484 6. Security Considerations 486 In current practice, the client privacy and client authentication are 487 mutually exclusive. The client authentication procedure reveals 488 additional client information in their certificates/identifiers. 489 Full privacy for the clients may mean the clients are also anonymous 490 to the server and the network. 492 7. Privacy Considerations 494 This document in its entirety discusses privacy considerations in 495 DHCP. As such, no dedicated discussion is needed. 497 8. IANA Considerations 499 This draft does not request any IANA action. 501 9. Acknowledgements 503 The authors would like to thank the valuable comments made by Stephen 504 Farrell, Ted Lemon, Ines Robles, Russ White, Christian Huitema, 505 Bernie Volz, Jinmei Tatuya, Marcin Siodelski, Christian Schaefer, and 506 other members of DHC WG. 508 10. References 510 10.1. Normative References 512 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 513 Requirement Levels", BCP 14, RFC 2119, 514 DOI 10.17487/RFC2119, March 1997, 515 . 517 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 518 RFC 2131, DOI 10.17487/RFC2131, March 1997, 519 . 521 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 522 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 523 RFC 2136, DOI 10.17487/RFC2136, April 1997, 524 . 526 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 527 Morris, J., Hansen, M., and R. Smith, "Privacy 528 Considerations for Internet Protocols", RFC 6973, 529 DOI 10.17487/RFC6973, July 2013, 530 . 532 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an 533 Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 534 2014, . 536 10.2. Informative References 538 [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", 539 RFC 3046, DOI 10.17487/RFC3046, January 2001, 540 . 542 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 543 C., and M. Carney, "Dynamic Host Configuration Protocol 544 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 545 2003, . 547 [RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy, 548 "Link Selection sub-option for the Relay Agent Information 549 Option for DHCPv4", RFC 3527, DOI 10.17487/RFC3527, April 550 2003, . 552 [RFC3925] Littlefield, J., "Vendor-Identifying Vendor Options for 553 Dynamic Host Configuration Protocol version 4 (DHCPv4)", 554 RFC 3925, DOI 10.17487/RFC3925, October 2004, 555 . 557 [RFC3993] Johnson, R., Palaniappan, T., and M. Stapp, "Subscriber-ID 558 Suboption for the Dynamic Host Configuration Protocol 559 (DHCP) Relay Agent Option", RFC 3993, 560 DOI 10.17487/RFC3993, March 2005, 561 . 563 [RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client 564 Identifiers for Dynamic Host Configuration Protocol 565 Version Four (DHCPv4)", RFC 4361, DOI 10.17487/RFC4361, 566 February 2006, . 568 [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration 569 Protocol (DHCP) Leasequery", RFC 4388, 570 DOI 10.17487/RFC4388, February 2006, 571 . 573 [RFC4578] Johnston, M. and S. Venaas, Ed., "Dynamic Host 574 Configuration Protocol (DHCP) Options for the Intel 575 Preboot eXecution Environment (PXE)", RFC 4578, 576 DOI 10.17487/RFC4578, November 2006, 577 . 579 [RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host 580 Configuration Protocol (DHCP) Client Fully Qualified 581 Domain Name (FQDN) Option", RFC 4702, 582 DOI 10.17487/RFC4702, October 2006, 583 . 585 [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol 586 (DHCPv4 and DHCPv6) Option for Civic Addresses 587 Configuration Information", RFC 4776, 588 DOI 10.17487/RFC4776, November 2006, 589 . 591 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 592 Extensions for Stateless Address Autoconfiguration in 593 IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, 594 . 596 [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, Ed., 597 "Dynamic Host Configuration Protocol Options for 598 Coordinate-Based Location Configuration Information", 599 RFC 6225, DOI 10.17487/RFC6225, July 2011, 600 . 602 [RFC6926] Kinnear, K., Stapp, M., Desetti, R., Joshi, B., Russell, 603 N., Kurapati, P., and B. Volz, "DHCPv4 Bulk Leasequery", 604 RFC 6926, DOI 10.17487/RFC6926, April 2013, 605 . 607 [RFC7724] Kinnear, K., Stapp, M., Volz, B., and N. Russell, "Active 608 DHCPv4 Lease Query", RFC 7724, DOI 10.17487/RFC7724, 609 December 2015, . 611 Authors' Addresses 613 Sheng Jiang 614 Huawei Technologies Co., Ltd 615 Q14, Huawei Campus, No.156 Beiqing Road 616 Hai-Dian District, Beijing, 100095 617 P.R. China 619 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