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Huitema 3 Internet-Draft Microsoft 4 Updates: 4361 (if approved) February 20, 2015 5 Intended status: Informational 6 Expires: August 24, 2015 8 Anonymity profile for DHCP clients 9 draft-huitema-dhc-anonymity-profile-00.txt 11 Abstract 13 Some DHCP options carry unique identifiers. These identifiers can 14 enable device tracking even if the device administrator takes care of 15 randomizing other potential identifications like link-layer addresses 16 or IPv6 addresses. The anonymity profile is designed for clients 17 that wish to remain anonymous to the visited network. The profile 18 provides guidelines on the composition of DHCP or DHCPv6 requests, 19 designed to minimize disclosure of identifying information. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on August 24, 2015. 38 Copyright Notice 40 Copyright (c) 2015 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Application domain . . . . . . . . . . . . . . . . . . . . . 3 58 3. Anonymity profile for DHCPv4 . . . . . . . . . . . . . . . . 4 59 3.1. Client IP address field . . . . . . . . . . . . . . . . . 5 60 3.2. Requested IP address option . . . . . . . . . . . . . . . 6 61 3.3. Client hardware address . . . . . . . . . . . . . . . . . 6 62 3.4. Client Identifier Option . . . . . . . . . . . . . . . . 6 63 3.5. Host Name Option . . . . . . . . . . . . . . . . . . . . 7 64 3.6. Client FQDN Option . . . . . . . . . . . . . . . . . . . 7 65 3.7. UUID/GUID-based Client Identifier Option . . . . . . . . 8 66 3.8. User and Vendor Class DHCP options . . . . . . . . . . . 8 67 4. Anonymity profile for DHCPv6 . . . . . . . . . . . . . . . . 9 68 4.1. Client Identifier DHCPv6 Option . . . . . . . . . . . . . 9 69 4.2. Server Identifier Option . . . . . . . . . . . . . . . . 9 70 4.3. Address assignment options . . . . . . . . . . . . . . . 10 71 4.4. Option Request Option . . . . . . . . . . . . . . . . . . 10 72 4.4.1. Previous option values . . . . . . . . . . . . . . . 10 73 4.5. Authentication Option . . . . . . . . . . . . . . . . . . 10 74 4.6. User and Vendor Class DHCPv6 options . . . . . . . . . . 11 75 4.7. Client FQDN Option . . . . . . . . . . . . . . . . . . . 11 76 5. Management considerations . . . . . . . . . . . . . . . . . . 11 77 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 78 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 79 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 80 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 81 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 82 9.2. Informative References . . . . . . . . . . . . . . . . . 12 83 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13 85 1. Introduction 87 Reports surfaced recently of systems that would monitor the wireless 88 connections of passengers at Canadian airports [CNBC]. We can assume 89 that these are either fragments or trial runs of a wider system that 90 would attempt to monitor Internet users as they roam through wireless 91 access points and other temporary network attachments. We can also 92 assume that privacy conscious users will attempt to evade this 93 monitoring, for example by ensuring that low level identifiers such 94 as link-layer addresses are "randomized," so that the devices do not 95 broadcast a unique identifier in every location that they visit. 97 Of course, link layer "MAC" addresses are not the only way to 98 identify a device. As soon as it connects to a remote network, the 99 device may use DHCP and DHCPv6 to obtain network parameters. The 100 analysis of DHCP and DHCPv6 options shows that parameters of these 101 protocols can reveal identifiers of the device, negating the benefits 102 of link-layer address randomization. The natural reaction is to 103 restrict the number and values of such parameters in order to 104 minimize disclosure. 106 In the absence of a common standard, different system developers are 107 likely to implement this minimization of disclosure in different 108 ways. Monitoring entities could then use the differences to identify 109 the software version running on the device. The proposed anonymity 110 profile provides a common standard that minimizes information 111 disclosure, including the disclosure of implementation identifiers. 113 1.1. Requirements 115 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, 116 SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this 117 document, are to be interpreted as described in [RFC2026]. 119 2. Application domain 121 Mobile nodes can be tracked using multiple identifiers, the most 122 prominent being MAC addresses. For example, when devices use Wi-Fi 123 connectivity, they place the MAC address in the header of all the 124 packets that they transmit. Standard implementation of Wi-Fi use 125 unique 48 bit MAC addresses, assigned to the devices according to 126 procedures defined by IEEE 802. Even when the Wi-Fi packets are 127 encrypted, the portion of the header containing the addresses will be 128 sent in clear text. Tracking devices can "listen to the airwaves" to 129 find out what devices are transmitting near them. 131 We can easily imagine that the MAC addresses can be correlated with 132 other data, e.g., clear text names and cookies, to build a registry 133 linking MAC addresses to the identity of devices' owners. Once that 134 correlation is done, tracking the MAC address is sufficient to track 135 individual people, even when all application data sent from the 136 devices is encrypted. MAC addresses can also be correlated with IP 137 addresses of devices, negating potential privacy benefits of IPv6 138 "privacy" addresses. Privacy advocates have some reason to be 139 concerned. 141 The obvious solution is to "randomize" the MAC address. Before 142 connecting to a particular network, the device replaces the MAC 143 address with a randomly drawn 48 bit value. MAC address 144 randomization was successfully tried at the IETF in Honolulu in 145 November 2014 [IETFMACRandom]. However, we have to consider the 146 linkage between MAC addresses, DHCP identifiers and IP addresses. 148 From a privacy point of view, it is clear that MAC Addresses, IP 149 addresses and DHCP identifiers shall evolve in synchrony. For 150 example, if the MAC address changes and the DHCP identifier stays 151 constant, then it is really easy to correlate old and new MAC 152 addresses, either by listening to DHCP traffic or by observing that 153 the IP address remains constant, since it is tied to the DHCP 154 identifier. Conversely, if the DHCP identifier changes but the MAC 155 address remains constant, the old and new identifiers and addresses 156 can be correlated by listening to L2 traffic. The procedures 157 documented in the following sections construct DHCP identifiers from 158 the current MAC address, automatically providing for this 159 synchronization. 161 Of course, there are downsides to randomizing MAC addresses and DHCP 162 identifiers. By definition, randomization will break management 163 procedures that rely on tracking MAC addresses. Even if this is not 164 too much of a concern, we have to be worried about the frequency of 165 MAC address randomization. Suppose for example that many devices 166 would get new random MAC addresses at short intervals, maybe every 167 few minutes. This would generate new DHCP requests in rapid 168 succession, with a high risk of exhausting DHCPv4 address pools. 169 Even with IPv6, there would still be a risk of increased neighbor 170 discovery traffic, and bloating of various address tables. 171 Implementers will have to be cautious when programming devices to use 172 randomized MAC addresses. They will have to carefully chose the 173 frequency with which such addresses will be renewed. 175 This document only provides guidelines for using DHCP when privacy is 176 considered more important than network management. We assume that 177 the request for anonymity is materialized by the assignment of a 178 randomized MAC address to the network interface. Once that decision 179 is made, the following guidelines will avoid leakage of identity in 180 DHCP parameters or in assigned addresses. 182 There may be rare situations where the clients want anonymity to 183 attackers but not to their DHCP server. These clients should still 184 use MAC Address randomization to hide from observers, and some form 185 of encrypted communication to the DHCP server. This document does 186 not study this scenario. 188 3. Anonymity profile for DHCPv4 190 Clients using the DHCPv4 anonymity profile limit the disclosure of 191 information by controlling the header parameters and by limiting the 192 number and values of options. The number of options depend on the 193 specific DHCP message: 195 DISCOVER: The anonymized DISCOVER messages MUST contain the Message 196 Type, Client Identifier, Host name, and Parameter Request List 197 options. It SHOULD NOT contain any other option. 199 REQUEST: The anonymized REQUEST messages SHOULD contain the Message 200 Type, Client Identifier, Host name, and Parameter Request List 201 options. If the message is in response to an OFFER, it SHOULD 202 contain the corresponding Server Identifier option. It SHOULD NOT 203 contain any other option. 205 DECLINE: The anonymized DECLINE messages SHOULD contain the Message 206 Type, Client Identifier and Server Identifier options. 208 RELEASE: The anonymized RELEASE messages SHOULD contain the Message 209 Type, Client Identifier and Server Identifier options. 211 INFORM: The anonymized INFORM messages MUST contain the Message 212 Type, Client Id, Host name, and Parameter Request List options. 213 It SHOULD NOT contain any other option. 215 Header fields and option values SHOULD be set in accordance with the 216 DHCP specification, but some header fields and option values SHOULD 217 be constructed per the following guidelines. 219 3.1. Client IP address field 221 Four bytes in the header of the DHCP messages carry the "Client IP 222 address" (ciaddr) as defined in [RFC2131]. In DHCP, this field is 223 used by the clients to indicate the address that they used 224 previously, so that as much as possible the server can allocate them 225 the same address. 227 There is very little privacy implication of sending this address in 228 the DHCP messages, except in one case, when connecting to a different 229 network than the last network connected. If the DHCP client somehow 230 repeated the address used in a previous network attachment, 231 monitoring services might use the information to tie the two network 232 locations. DHCP clients should ensure that the field is cleared when 233 they know that the network attachment has changed, and in particular 234 of the link layer address is reset by the device's administrator. 236 3.2. Requested IP address option 238 The Requested IP address option (code 50) allows the client to 239 request that a particular IP address be assigned. The option is 240 mandatory in some protocol messages per [RFC2131], for example when a 241 client selects to use an address offered by a server. However, this 242 option is not mandatory in the DHCPDISCOVER message. It is simply a 243 convenience, an attempt to regain the same IP address that was used 244 in a previous connection. Doing so entails the risk of disclosing an 245 IP address used by the client at a previous location, or with a 246 different MAC Address. 248 When using the anonymity profile, clients SHOULD NOT use the 249 Requested IP address option in DHCPDISCOVER Messages. 251 3.3. Client hardware address 253 Sixteen bytes in the header of the DHCP messages carry the "Client 254 hardware address" (chaddr) as defined in [RFC2131]. The presence of 255 this address is necessary for the proper operation of the DHCP 256 service. 258 Hardware addresses, called "link layer address" in many RFCs, can be 259 used to uniquely identify a device, especially if they follow the 260 IEEE 802 recommendations. These unique identifiers can be used by 261 monitoring services to track the location of the device and its user. 262 The only plausible defense is to somehow reset the hardware address 263 to a random value when visiting an untrusted location, before 264 transmitting anything at that location with the hardware address. If 265 the hardware address is reset to a new value, or randomized, the DHCP 266 client SHOULD use the new randomized value in the DHCP messages. 268 3.4. Client Identifier Option 270 The client identifier option is defined in [RFC2132] with option code 271 61. It is discussed in details in [RFC4361]. The purpose of the 272 client identifier option is to identify the client in a manner 273 independent of the link layer address. This is particularly useful 274 if the DHCP server is expected to assign the same address to the 275 client after a network attachment is swapped and the link layer 276 address changes. It is also useful when the same node issues 277 requests through several interfaces, and expects the DHCP server to 278 provide consistent configuration data over multiple interfaces. 280 The considerations for hardware independence and strong client 281 identity have an adverse effect on the privacy of mobile clients, 282 because the hardware-independent unique identifier obviously enables 283 very efficient tracking of the client's movements. 285 The recommendations in [RFC4361] are very strong, stating for example 286 that "DHCPv4 clients MUST NOT use client identifiers based solely on 287 layer two addresses that are hard-wired to the layer two device 288 (e.g., the Ethernet MAC address)." These strong recommendations are 289 in fact a tradeoff between ease of management and privacy, and the 290 tradeoff should depend on the circumstances. 292 In contradiction to [RFC4361], when privacy considerations trump 293 management considerations, DHCP clients MUST use client identifiers 294 based solely on the link layer address that will be used in the 295 underlying connection. This will ensure that the DHCP client 296 identifier does not leak any information that is not already 297 available to entities monitoring the network connection. It will 298 also ensure that a strategy of randomizing the link layer address 299 will not be nullified by DHCP options. 301 3.5. Host Name Option 303 The Host Name option is defined in [RFC2132] with option code 12. 304 Depending on implementations, the option value can carry either a 305 fully qualified domain name such as "node1984.example.com," or a 306 simple host name such as "node1984." The host name is commonly used 307 by the DHCP server to identify the host, and also to automatically 308 update the address of the host in local name services. 310 Fully qualified domain names are obviously unique identifiers, but 311 even simple host names can provide a significant amount of 312 information on the identity of the device. They are typically chosen 313 to be unique in the context where the device is most often used. If 314 that context is wide enough, in a large company or in a big 315 university, the host name will be a pretty good identifier of the 316 device. Monitoring services could use that information in 317 conjunction with traffic analysis and quickly derive the identity of 318 the device's owner. 320 When privacy considerations trump management considerations, DHCP 321 clients MUST always send a non-qualified host name instead of a fully 322 qualified domain name, and SHOULD obfuscate the host name value, so 323 it could not be linked to anything other than the link layer address. 324 A simple solution would be to set the host name value to a 325 hexadecimal representation of the link layer address that will be 326 used in the underlying connection. 328 3.6. Client FQDN Option 330 The Client FQDN option is defined in [RFC4702] with option code 81. 331 The option allows the DHCP clients to advertise to the DHCP server 332 their fully qualified domain name (FQDN) such as 333 "mobile.example.com." This would allow the DHCP server to update in 334 the DNS the PTR record for the IP address allocated to the client. 335 Depending on circumstances, either the DHCP client or the DHCP server 336 could update in the DNS the A record for the FQDN of the client. 338 Obviously, this option uniquely identifies the client, exposing it to 339 the DHCP server or to anyone listening to DHCP traffic. In fact, if 340 the DNS record is updated, the location of the client becomes visible 341 to anyone with DNS lookup capabilities. 343 When privacy considerations trump management considerations, DHCP 344 clients SHOULD NOT include the Client FQDN option in their DHCP 345 requests. Alternatively, they MAY include a special purpose FQDN 346 using the same hostname as in the Host Name Option, with a suffix 347 matching the connection-specific DNS suffix being advertised by that 348 DHCP server. Having a name in the DNS allows working with legacy 349 systems that require one to be there, e.g., by verifying a forward 350 and reverse lookup succeeds with the same result. 352 3.7. UUID/GUID-based Client Identifier Option 354 The UUID/GUID-based Client Machine Identifier option is defined in 355 [RFC4578], with option code 97. The option is part of a set of 356 options for Intel Preboot eXecution Environment (PXE). The purpose 357 of the PXE system is to perform management functions on a device 358 before its main OS is operational. The Client Machine Identifier 359 carries a 16-octet Globally Unique Identifier (GUID), which uniquely 360 identifies the device. 362 The PXE system is clearly designed for devices operating in a 363 controlled environment, and its functions are not meant to be used by 364 mobile nodes visiting untrusted networks. If only for privacy 365 reasons, nodes visiting untrusted networks MUST disable the PXE 366 functions, and MUST NOT send the corresponding options. 368 3.8. User and Vendor Class DHCP options 370 Vendor identifying options are defined in [RFC2132] and [RFC3925]. 371 When using the anonymity profile, DHCP clients SHOULD NOT use the 372 Vendor Specific Information option (code 43), the Vendor Class 373 Identifier Option (60), the Vendor Class option (code 124), or the 374 Vendor Specific Information option (code 125) as these options 375 potentially reveal identifying information. 377 4. Anonymity profile for DHCPv6 379 DHCPv6 is typically used by clients in one of two scenarios: stateful 380 and stateless configuration. In the stateful scenario, clients use a 381 combination of SOLICIT, REQUEST, CONFIRM, RENEW, REBIND and RELEASE 382 messages to obtain addresses, and manage these addresses. 384 In the stateless scenario, clients configure addresses using a 385 combination of client managed identifiers and router-advertised 386 prefixes, without involving the DHCPv6 services. Different ways of 387 constructing these prefixes have different implications on privacy, 388 which are discussed in [I-D.ietf-6man-default-iids] and 389 [I-D.ietf-6man-ipv6-address-generation-privacy]. In the stateless 390 scenario, clients use DHCPv6 to obtain network configuration 391 parameters, through the INFORMATION-REQUEST message. 393 When using the anonymity profile, DHCPv6 clients carefully select 394 DHCPv6 options used in the various messages that they sent. The list 395 of options that are mandatory or optional for each message is 396 specified in [RFC3315]. Some of these options have specific 397 implications on anonymity. The following sections provide guidance 398 on the choice of option values when using the anonymity profile. 400 4.1. Client Identifier DHCPv6 Option 402 The client identifier option is defined in [RFC3315] with option code 403 1. The purpose of the client identifier option is to identify the 404 client to the server. The content of the option is a DHCP User ID 405 (DUID) for which three formats are specified: Link-layer address plus 406 time, Vendor-assigned unique ID based on Enterprise Number, Link- 407 layer address. 409 When using the anonymity profile, DHCPv6 clients MUST use the DUID 410 format number 3, Link-layer address. The value of the Link-layer 411 address should be that currently assigned to the interface. 413 4.2. Server Identifier Option 415 When using the anonymity profile, DHCPv6 clients SHOULD use the 416 Server Identifier Option (code 2) as specified in [RFC3315]. Clients 417 MUST only include server identifier values that were received with 418 the current MAC address, because reuse of old values discloses 419 information that can be used to identify the client. 421 4.3. Address assignment options 423 When using the anonymity profile, DHCPv6 clients might have to use 424 SOLICIT or REQUEST messages to obtain IPv6 addresses through the DHCP 425 server. The clients SHOULD only use the options necessary to perform 426 the requested DHCPv6 transactions, such as Identity Association for 427 Non-temporary Addresses Option (code 3) or Identity Association for 428 Temporary Addresses Option (code 4). 430 The clients MAY use the IA Address Option (code 5) but need to 431 balance the potential advantage of "address continuity" versus the 432 potential risk of "previous address disclosure." A potential 433 solution is to remove all stored addresses when a MAC address 434 changes, and to only use the IA Address option with addresses that 435 have been explicitly assigned through the current MAC address. 437 4.4. Option Request Option 439 When using the anonymity profile, DHCPv6 clients SHOULD use the 440 Option Request Option (code 6) as specified in [RFC3315]. 442 4.4.1. Previous option values 444 According to [RFC3315], the client that includes an Option Request 445 Option in a Solicit or Request message MAY additionally include 446 instances of those options that are identified in the Option Request 447 option, with data values as hints to the server about parameter 448 values the client would like to have returned. 450 When using the anonymity profile, clients SHOULD NOT include such 451 instances of options because old values might be used to identify the 452 client. 454 4.5. Authentication Option 456 The purpose of the Authentication option (code 11) is to authenticate 457 the identity of clients and servers and the contents of DHCP 458 messages. As such, the option can be used to identify the client, 459 and is incompatible with the stated goal of "client anonymity." 460 DHCPv6 clients that use the anonymity profile SHOULD NOT use the 461 authentication option. They MAY use it if they recognize that they 462 are operating in a trusted environment, e.g., in a work place 463 network. 465 4.6. User and Vendor Class DHCPv6 options 467 When using the anonymity profile, DHCPv6 clients SHOULD NOT use the 468 User Class option (code 15) or the Vendor Class option (code 16), as 469 these options potentially reveal identifying information. 471 4.7. Client FQDN Option 473 The Client FQDN option is defined in [RFC4704] with option code 29. 474 The option allows the DHCP clients to advertize to the DHCP their 475 fully qualified domain name (FQDN) such as "mobile.example.com." 476 When using the anonymity profile, DHCPv6 clients SHOULD NOT include 477 the Client FQDN option in their DHCPv6 messages because it identifies 478 the client. As explained in Section 3.6 they MAY use a local-only 479 FQDN by combining a host name derived from the link layer address and 480 a suffix advertised by the local DHCP server. 482 5. Management considerations 484 The anonymity profile has the effect of hiding the client identity 485 from the DHCP server. This is not always desirable. Some DHCP 486 servers provide facilities like publishing names and addresses in the 487 DNS, or ensuring that returning clients get reassigned the same 488 address. Implementers should be careful to only use the anonymity 489 profile when privacy trumps management considerations. 491 6. Security Considerations 493 The use of the anonymity profile does not change the security 494 considerations of the DHCPv4 or DHCPv6 protocols. 496 7. IANA Considerations 498 This draft does not require any IANA action. 500 8. Acknowledgments 502 The inspiration for this draft came from discussions in the Perpass 503 mailing list. Several people provided feedback on early versions of 504 this draft, notably Noel Anderson, Tushar Gupta, Gabriel Montenegro, 505 Dave Thaler and Jun Wu. 507 9. References 508 9.1. Normative References 510 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 511 3", BCP 9, RFC 2026, October 1996. 513 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 514 2131, March 1997. 516 [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor 517 Extensions", RFC 2132, March 1997. 519 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 520 and M. Carney, "Dynamic Host Configuration Protocol for 521 IPv6 (DHCPv6)", RFC 3315, July 2003. 523 [RFC3925] Littlefield, J., "Vendor-Identifying Vendor Options for 524 Dynamic Host Configuration Protocol version 4 (DHCPv4)", 525 RFC 3925, October 2004. 527 [RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client 528 Identifiers for Dynamic Host Configuration Protocol 529 Version Four (DHCPv4)", RFC 4361, February 2006. 531 [RFC4578] Johnston, M. and S. Venaas, "Dynamic Host Configuration 532 Protocol (DHCP) Options for the Intel Preboot eXecution 533 Environment (PXE)", RFC 4578, November 2006. 535 [RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host 536 Configuration Protocol (DHCP) Client Fully Qualified 537 Domain Name (FQDN) Option", RFC 4702, October 2006. 539 [RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for 540 IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN) 541 Option", RFC 4704, October 2006. 543 9.2. Informative References 545 [CNBC] Weston, G., Greenwald, G., and R. Gallagher, "CBC News: 546 CSEC used airport Wi-Fi to track Canadian travellers", Jan 547 2014, . 551 [I-D.ietf-6man-default-iids] 552 Gont, F., Cooper, A., Thaler, D., and W. Will, 553 "Recommendation on Stable IPv6 Interface Identifiers", 554 draft-ietf-6man-default-iids-02 (work in progress), 555 January 2015. 557 [I-D.ietf-6man-ipv6-address-generation-privacy] 558 Cooper, A., Gont, F., and D. Thaler, "Privacy 559 Considerations for IPv6 Address Generation Mechanisms", 560 draft-ietf-6man-ipv6-address-generation-privacy-03 (work 561 in progress), January 2015. 563 [IETFMACRandom] 564 Zuniga, JC., "MAC Privacy", November 2014, 565 . 567 Author's Address 569 Christian Huitema 570 Microsoft 571 Redmond, WA 98052 572 U.S.A. 574 Email: huitema@microsoft.com