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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-07) exists of draft-ietf-dhc-dhcpv4-active-leasequery-05 -- Obsolete informational reference (is this intentional?): RFC 2629 (Obsoleted by RFC 7749) -- Obsolete informational reference (is this intentional?): RFC 3315 (Obsoleted by RFC 8415) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 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: February 27, 2016 Ericsson 6 T. Mrugalski 7 ISC 8 August 26, 2015 10 Privacy considerations for DHCPv4 11 draft-ietf-dhc-dhcp-privacy-01 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 February 27, 2016. 36 Copyright Notice 38 Copyright (c) 2015 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. Identifiers in DHCP . . . . . . . . . . . . . . . . . . . . . 3 56 3.1. Client ID Option . . . . . . . . . . . . . . . . . . . . 4 57 3.2. Address Fields & Options . . . . . . . . . . . . . . . . 4 58 3.3. Client FQDN Option . . . . . . . . . . . . . . . . . . . 4 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 . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . 9 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. The DHCP protocol uses several identifiers that could 93 become a source for gleaning information about the IPv4 host. This 94 information may include device type, operating system information, 95 location(s) that the device may have previously visited, etc. This 96 document discusses the various identifiers used by DHCP and the 97 potential privacy issues [RFC6973]. In particular, it also takes 98 into consideration the 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. It is out of scope for 102 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 or 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 may 129 include MAC address, client-id or a hostname. Some 130 identifiers may be considered stable only under certain 131 conditions, for example one client implementation may keep 132 its client-id stored in stable storage while other may 133 generate it on the fly and use a different one after each 134 boot. Stable identifier may or may not be globally unique. 136 3. Identifiers in DHCP 138 There are several identifiers used in DHCP. This section provides an 139 introduction to the various options that will be used further in the 140 document. 142 3.1. Client ID Option 144 The Client Identifier Option [RFC2131] is used to pass an explicit 145 client identifier to a DHCP server. 147 The client identifier is an opaque key, which must be unique to that 148 client within the subnet to which the client is attached. It 149 typically remains stable after it has been initially generated. It 150 may contain a hardware address, identical to the contents of the 151 'chaddr' field, or another type of identifier, such as a DNS name. 152 [RFC3315] in Section 9.2 specifies DUID-LLT (Link-layer + time) as 153 the recommended DUID type. [RFC4361], Section 6.1 introduces this 154 concept to DHCPv4. Those two document recommend that client 155 identifiers be generated by using the permanent link-layer address of 156 the network interface that the client is trying to configure. 157 [RFC4361] updates the recommendation of Client Identifiers to be 158 "consists of a type field whose value is normally 255, followed by a 159 four-byte IA_ID field, followed by the DUID for the client as defined 160 in RFC 3315, section 9". This does not change the lifecycle of the 161 Client Identifiers. Clients are expected to generate their Client 162 Identifiers once (during first operation) and store it in a non- 163 volatile storage or use the same deterministic algorithm to generate 164 the same Client Identifier values again. 166 3.2. Address Fields & Options 168 The 'yiaddr' field [RFC2131] in DHCP message is used to allocate 169 address from the server to the client. 171 The DHCPv4 specification [RFC2131] provides a way to specify the 172 client link-layer address in the DHCPv4 message header. A DHCPv4 173 message header has 'htype' and 'chaddr' fields to specify the client 174 link-layer address type and the link-layer address, respectively. 175 The 'chaddr' field is used both as a hardware address for 176 transmission of reply messages and as a client identifier. 178 The 'requested IP address' option [RFC2131] is used by client to 179 suggest that a particular IP address be assigned. 181 3.3. Client FQDN Option 183 The Client Fully Qualified Domain Name (FQDN) option [RFC4702] is 184 used by DHCP clients and servers to exchange information about the 185 client's fully qualified domain name and about who has the 186 responsibility for updating the DNS with the associated AAAA and PTR 187 RRs. 189 A client can use this option to convey all or part of its domain name 190 to a DHCP server for the IP-address-to-FQDN mapping. In most case a 191 client sends its hostname as a hint for the server. The DHCP server 192 MAY be configured to modify the supplied name or to substitute a 193 different name. The server should send its notion of the complete 194 FQDN for the client in the Domain Name field. 196 3.4. Parameter Request List Option 198 The Parameter Request List option [RFC2131] is used to inform the 199 server about options the client wants the server to send to the 200 client. The content of a Parameter Request List option are the 201 option codes for an option requested by the client. 203 3.5. Vendor Class and Vendor-Identifying Vendor Class Options 205 The Vendor Class option [RFC2131], the Vendor-Identifying Vendor 206 Class option and Vendor-Identifying Vendor Information option 207 [RFC3925] are used by the DHCP client to identify the vendor that 208 manufactured the hardware on which the client is running. 210 The information contained in the data area of this option is 211 contained in one or more opaque fields that identify the details of 212 the hardware configuration of the host on which the client is 213 running, or of industry consortium compliance, for example, the 214 version of the operating system the client is running or the amount 215 of memory installed on the client. 217 3.6. Civic Location Option 219 DHCP servers use the Civic Location Option [RFC4776] to delivery of 220 the location information (the civic and postal addresses) to the DHCP 221 clients. It may refer to three locations: the location of the DHCP 222 server, the location of the network element believed to be closest to 223 the client, or the location of the client, identified by the "what" 224 element within the option. 226 3.7. Coordinate-Based Location Option 228 The GeoConf and GeoLoc options [RFC6225] is used by DHCP server to 229 provide the coordinate-based geographic location information to the 230 DHCP clients. It enables a DHCP client to obtain its geographic 231 location. 233 After the relevant DHCP exchanges have taken place, the location 234 information is stored on the end device rather than somewhere else, 235 where retrieving it might be difficult in practice. 237 3.8. Client System Architecture Type Option 239 The Client System Architecture Type Option [RFC4578] is used by DHCP 240 client to send a list of supported architecture types to the DHCP 241 server. It is used to provide configuration information for a node 242 that must be booted using the network rather than from local storage. 244 3.9. Relay Agent Information Option and Sub-options 246 A DHCP relay agent includes a Relay Agent Information [RFC3046] to 247 identify the remote host end of the circuit. It contains a "circuit 248 ID" sub-option for the incoming circuit, which is an agent-local 249 identifier of the circuit from which a DHCP client-to-server packet 250 was received, and a "remote ID" sub-option which provides a trusted 251 identifier for the remote high-speed modem. 253 Possible encoding of "circuit ID" sub-option includes: router 254 interface number, switching hub port number, remote access server 255 port number, frame relay DLCI, ATM virtual circuit number, cable data 256 virtual circuit number, etc. 258 Possible encoding of the "remote ID" sub-option includes: a "caller 259 ID" telephone number for dial-up connection, a "user name" prompted 260 for by a remote access server, a remote caller ATM address, a "modem 261 ID" of a cable data modem, the remote IP address of a point-to-point 262 link, a remote X.25 address for X.25 connections, etc. 264 The link-selection sub-option [RFC3527] is used by any DHCP relay 265 agent that desires to specify a subnet/link for a DHCP client request 266 that it is relaying but needs the subnet/link specification to be 267 different from the IP address the DHCP server should use when 268 communicating with the relay agent. It contains an IP address, which 269 can identify the client's subnet/link. Also, assuming network 270 topology knowledge, it also reveals client location. 272 A DHCP relay includes a Subscriber-ID option [RFC3993] to associate 273 some provider-specific information with clients' DHCP messages that 274 is independent of the physical network configuration through which 275 the subscriber is connected. The "subscriber-id" assigned by the 276 provider is intended to be stable as customers connect through 277 different paths, and as network changes occur. The Subscriber-ID is 278 an ASCII string, which is assigned and configured by the network 279 provider. 281 4. Existing Mechanisms That Affect Privacy 283 This section describes available DHCP mechanisms that one can use to 284 protect or enhance one's privacy. 286 4.1. DNS Updates 288 DNS Updates [RFC4702] defines a mechanism that allows both clients 289 and server to insert into DNS domain information about clients. Both 290 forward (A) and reverse (PTR) resource records can be updated. This 291 allows other nodes to conveniently refer to a host, despite the fact 292 that its IP address may be changing. 294 This mechanism exposes two important pieces of information: current 295 address (which can be mapped to current location) and client's 296 hostname. The stable hostname can then be used to correlate the 297 client across different network attachments even when its IP 298 addresses keep changing. 300 4.2. Allocation strategies 302 A DHCP server running in typical, stateful mode is given a task of 303 managing one or more pools of IP address. When a client requests an 304 address, the server must pick an address out of configured pool. 305 Depending on the server's implementation, various allocation 306 strategies are possible. Choices in this regard may have privacy 307 implications. Note that the constraints in DHCPv4 and DHCPv6 are 308 radically different, but servers that allow allocation strategy 309 configuration may allow configuring them in both DHCPv4 and DHCPv6. 310 Not every allocation strategy is equally suitable for DHCPv4 and for 311 DHCPv6. 313 Iterative allocation - a server may choose to allocate addresses one 314 by one. That strategy has the benefit of being very fast, thus can 315 be favored in deployments that prefer performance. However, it makes 316 the allocated addresses very predictable. Also, since the addresses 317 allocated tend to be clustered at the beginning of available pool, it 318 makes scanning attacks much easier. 320 Identifier-based allocation - a server may choose to allocate an 321 address that is based on one of available identifiers, e.g. client 322 identifier or MAC address. It is also convenient, as returning 323 client is very likely to get the same address. Those properties are 324 convenient for system administrators, so DHCP server implementors are 325 often requested to implement it. On the other hand, the downside of 326 such allocation is that the client has a very stable IP address. 327 That means that correlation of activities over time, location 328 tracking, address scanning and OS/vendor discovery apply. This is 329 certainly an issue in DHCPv6, but due to much smaller address space 330 is almost never a problem in DHCPv4. 332 Hash allocation - it's an extension of identifier based allocation. 333 Instead of using the identifier directly, it is being hashed first. 334 If the hash is implemented correctly, it removes the flaw of 335 disclosing the identifier, a property that eliminates susceptibility 336 to address scanning and OS/vendor discovery. If the hash is poorly 337 implemented (e.g. can be reverted), it introduces no improvement over 338 identifier-based allocation. 340 Random allocation - a server can pick a resource randomly out of 341 available pool. That strategy works well in scenarios where pool 342 utilization is small, as the likelihood of collision (resulting in 343 the server needing to repeat randomization) is small. With the pool 344 allocation increasing, the collision is disproportionally large, due 345 to birthday paradox. With high pool utilization (e.g. when 90% of 346 available resources being allocated already), the server will use 347 most computational resources to repeatedly pick a random resource, 348 which will degrade its performance. This allocation scheme 349 essentially prevents returning clients from getting the same address 350 again. On the other hand, it is beneficial from privacy perspective 351 as addresses generated that way are not susceptible to correlation 352 attacks, OS/vendor discovery attacks or identity discovery attacks. 353 Note that even though the address itself may be resilient to a given 354 attack, the client may still be susceptible if additional information 355 is disclosed other way, e.g. client's address can be randomized, but 356 it still can leak its MAC address in client-id option. 358 Other allocation strategies may be implemented. 360 Given the limited size of most IPv4 public address pools, allocation 361 mechanisms in IPv4 may not provide much privacy protection or leak 362 much useful information, if misused. 364 5. Attacks 366 5.1. Device type discovery 368 The type of device used by the client can be guessed by the attacker 369 using the Vendor Class Option, the 'chaddr' field, and by parsing the 370 Client ID Option. All of those options may contain an 371 Organizationally Unique Identifier (OUI) that represents the device's 372 vendor. That knowledge can be used for device-specific vulnerability 373 exploitation attacks. 375 5.2. Operating system discovery 377 The operating system running on a client can be guessed using the 378 Vendor Class option, the Client System Architecture Type option, or 379 by using fingerprinting techniques on the combination of options 380 requested using the Parameter Request List option. 382 5.3. Finding location information 384 The location information can be obtained by the attacker by many 385 means. The most direct way to obtain this information is by looking 386 into a message originating from the server that contains the Civic 387 Location, GeoConf, or GeoLoc options. It can also be indirectly 388 inferred using the Relay Agent Information option, with the remote ID 389 sub-option, the circuit ID option (e.g. if an access circuit on an 390 Access Node corresponds to a civic location), or the Subscriber ID 391 Option (if the attacker has access to subscriber info). 393 5.4. Finding previously visited networks 395 When DHCP clients connect to a network, they attempt to obtain the 396 same address they had used before they attached to the network. They 397 do this by putting the previously assigned address in the requested 398 IP address option. By observing these addresses, an attacker can 399 identify the network the client had previously visited. 401 5.5. Finding a stable identity 403 An attacker might use a stable identity gleaned from DHCP messages to 404 correlate activities of a given client on unrelated networks. The 405 Client FQDN option, the Subscriber ID Option and the Client ID 406 options can serve as long lived identifiers of DHCP clients. The 407 Client FQDN option can also provide an identity that can easily be 408 correlated with web server activity logs. 410 5.6. Pervasive monitoring 412 This is an enhancement, or a combination of most aforementioned 413 mechanisms. Operator who controls non-trivial number of access 414 points or network segments, may use obtained information about a 415 single client and observer client's habits. 417 5.7. Finding client's IP address or hostname 419 Many DHCP deployments use DNS Updates [RFC4702] that put client's 420 information (current IP address, client's hostname) into DNS, where 421 it is easily accessible by anyone interested. Client ID is also 422 disclosed, albeit in not easily accessible form (SHA-256 digest of 423 the client-id). As SHA-256 is considered irreversible, DHCID can't 424 be converted back to client-id. However, SHA-256 digest can be used 425 as an unique identifier that is accessible by any host. 427 5.8. Correlation of activities over time 429 As with other identifiers, an IP address can be used to correlate the 430 activities of a host for at least as long as the lifetime of the 431 address. If that address was generated from some other, stable 432 identifier and that generation scheme can be deducted by an attacker, 433 the duration of correlation attack extends to that identifier. In 434 many cases, its lifetime is equal to the lifetime of the device 435 itself. 437 5.9. Location tracking 439 If a stable identifier is used for assigning an address and such 440 mapping is discovered by an attacker, e.g. a hostname being put into 441 DNS, it can be used for tracking user. In particular both passive (a 442 service that the client connects to can log client's address and draw 443 conclusions regarding its location and movement patterns based on 444 address it is connecting from) and active (attacker can send ICMP 445 echo requests or other probe packets to networks of suspected client 446 locations) methods can be used. To give specific example, by 447 accessing a social portal from tomek- 448 laptop.coffee.somecity.com.example, tomek- 449 laptop.mycompany.com.example and tomek-laptop.myisp.example.com, the 450 portal administrator can draw conclusions about tomek-laptop's owner 451 current location and his habits. 453 5.10. Leasequery & bulk leasequery 455 Attackers may pretend as an access concentrator, either DHCP relay 456 agent or DHCP client, to obtain location information directly from 457 the DHCP server(s) using the DHCP leasequery [RFC4388] mechanism. 459 Location information is information needed by the access concentrator 460 to forward traffic to a broadband-accessible host. This information 461 includes knowledge of the host hardware address, the port or virtual 462 circuit that leads to the host, and/or the hardware address of the 463 intervening subscriber modem. 465 Furthermore, the attackers may use DHCP bulk leasequery [RFC6926] 466 mechanism to obtain bulk information about DHCP bindings, even 467 without knowing the target bindings. 469 Additionally, active leasequery 470 [I-D.ietf-dhc-dhcpv4-active-leasequery] is a mechanism for 471 subscribing to DHCPv4 lease update changes in near real-time. The 472 intent of this mechanism is to update operator's database, but if 473 misused, an attacker could defeat server's authentication mechanisms 474 and subscribe to all updates. He then could continue receiving 475 updates, without any need for local presence. 477 6. Security Considerations 479 In current practice, the client privacy and the client authentication 480 are mutually exclusive. The client authentication procedure reveals 481 additional client information in their certificates/identifiers. 482 Full privacy for the clients may mean the clients are also anonymous 483 for the server and the network. 485 7. Privacy Considerations 487 This document at its entirety discusses privacy considerations in 488 DHCP. As such, no dedicated section about this is needed. 490 8. IANA Considerations 492 This draft does not request any IANA action. 494 9. Acknowledgements 496 The authors would like to thanks the valuable comments made by 497 Stephen Farrell, Ted Lemon, Ines Robles, Russ White, Christian 498 Huitema, Bernie Volz and other members of DHC WG. 500 This document was produced using the xml2rfc tool [RFC2629]. 502 10. References 504 10.1. Normative References 506 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 507 Requirement Levels", BCP 14, RFC 2119, 508 DOI 10.17487/RFC2119, March 1997, 509 . 511 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 512 RFC 2131, DOI 10.17487/RFC2131, March 1997, 513 . 515 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 516 Morris, J., Hansen, M., and R. Smith, "Privacy 517 Considerations for Internet Protocols", RFC 6973, 518 DOI 10.17487/RFC6973, July 2013, 519 . 521 [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an 522 Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 523 2014, . 525 10.2. Informative References 527 [I-D.ietf-dhc-dhcpv4-active-leasequery] 528 Kinnear, K., Stapp, M., Volz, B., and N. Russell, "Active 529 DHCPv4 Lease Query", draft-ietf-dhc-dhcpv4-active- 530 leasequery-05 (work in progress), August 2015. 532 [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, 533 DOI 10.17487/RFC2629, June 1999, 534 . 536 [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", 537 RFC 3046, DOI 10.17487/RFC3046, January 2001, 538 . 540 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 541 C., and M. Carney, "Dynamic Host Configuration Protocol 542 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 543 2003, . 545 [RFC3527] Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy, 546 "Link Selection sub-option for the Relay Agent Information 547 Option for DHCPv4", RFC 3527, DOI 10.17487/RFC3527, April 548 2003, . 550 [RFC3925] Littlefield, J., "Vendor-Identifying Vendor Options for 551 Dynamic Host Configuration Protocol version 4 (DHCPv4)", 552 RFC 3925, DOI 10.17487/RFC3925, October 2004, 553 . 555 [RFC3993] Johnson, R., Palaniappan, T., and M. Stapp, "Subscriber-ID 556 Suboption for the Dynamic Host Configuration Protocol 557 (DHCP) Relay Agent Option", RFC 3993, 558 DOI 10.17487/RFC3993, March 2005, 559 . 561 [RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client 562 Identifiers for Dynamic Host Configuration Protocol 563 Version Four (DHCPv4)", RFC 4361, DOI 10.17487/RFC4361, 564 February 2006, . 566 [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration 567 Protocol (DHCP) Leasequery", RFC 4388, 568 DOI 10.17487/RFC4388, February 2006, 569 . 571 [RFC4578] Johnston, M. and S. Venaas, Ed., "Dynamic Host 572 Configuration Protocol (DHCP) Options for the Intel 573 Preboot eXecution Environment (PXE)", RFC 4578, 574 DOI 10.17487/RFC4578, November 2006, 575 . 577 [RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host 578 Configuration Protocol (DHCP) Client Fully Qualified 579 Domain Name (FQDN) Option", RFC 4702, 580 DOI 10.17487/RFC4702, October 2006, 581 . 583 [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol 584 (DHCPv4 and DHCPv6) Option for Civic Addresses 585 Configuration Information", RFC 4776, 586 DOI 10.17487/RFC4776, November 2006, 587 . 589 [RFC6225] Polk, J., Linsner, M., Thomson, M., and B. Aboba, Ed., 590 "Dynamic Host Configuration Protocol Options for 591 Coordinate-Based Location Configuration Information", 592 RFC 6225, DOI 10.17487/RFC6225, July 2011, 593 . 595 [RFC6926] Kinnear, K., Stapp, M., Desetti, R., Joshi, B., Russell, 596 N., Kurapati, P., and B. Volz, "DHCPv4 Bulk Leasequery", 597 RFC 6926, DOI 10.17487/RFC6926, April 2013, 598 . 600 Authors' Addresses 602 Sheng Jiang 603 Huawei Technologies Co., Ltd 604 Q14, Huawei Campus, No.156 Beiqing Road 605 Hai-Dian District, Beijing, 100095 606 P.R. China 608 Email: jiangsheng@huawei.com 609 Suresh Krishnan 610 Ericsson 611 8400 Decarie Blvd. 612 Town of Mount Royal, QC 613 Canada 615 Phone: +1 514 345 7900 x42871 616 Email: suresh.krishnan@ericsson.com 618 Tomek Mrugalski 619 Internet Systems Consortium, Inc. 620 950 Charter Street 621 Redwood City, CA 94063 622 USA 624 Email: tomasz.mrugalski@gmail.com