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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC2486bis' is mentioned on line 134, but not defined ** Obsolete undefined reference: RFC 2486 (Obsoleted by RFC 4282) ** Obsolete normative reference: RFC 2234 (Obsoleted by RFC 4234) ** Downref: Normative reference to an Informational RFC: RFC 2607 -- Obsolete informational reference (is this intentional?): RFC 3588 (Obsoleted by RFC 6733) Summary: 8 errors (**), 0 flaws (~~), 4 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Adrangi 3 Internet-Draft V. Lortz 4 Expires: February 12, 2006 Intel 5 F. Bari 6 Cingular Wireless 7 P. Eronen 8 Nokia 9 August 11, 2005 11 Identity selection hints for Extensible Authentication Protocol (EAP) 12 draft-adrangi-eap-network-discovery-14 14 Status of this Memo 16 By submitting this Internet-Draft, each author represents that any 17 applicable patent or other IPR claims of which he or she is aware 18 have been or will be disclosed, and any of which he or she becomes 19 aware will be disclosed, in accordance with Section 6 of BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF), its areas, and its working groups. Note that 23 other groups may also distribute working documents as Internet- 24 Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 This Internet-Draft will expire on February 12, 2006. 39 Copyright Notice 41 Copyright (C) The Internet Society (2005). 43 Abstract 45 The Extensible Authentication Protocol (EAP) is defined in [RFC3748]. 46 This document defines a mechanism that allows an access network to 47 provide identity selection hints to an EAP peer - the end of the link 48 that responds to the authenticator. The purpose is to assist the EAP 49 peer in selecting an appropriate Network Access Identifier (NAI). 50 This is useful in situations where the peer does not receive a lower 51 layer indication of what network it is connecting to, or when there 52 is no direct roaming relationship between the access network and the 53 peer's home network. In the latter case, authentication is typically 54 accomplished via a mediating network such as a roaming consortium or 55 broker. 57 The mechanism defined in this document is limited in its scalability. 58 It is intended for access networks that have a small to moderate 59 number of direct roaming partners. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 1.1 Relationship with other specifications . . . . . . . . . . 3 65 1.2 Applicability . . . . . . . . . . . . . . . . . . . . . . 3 66 1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 67 2. Implementation requirements . . . . . . . . . . . . . . . . . 5 68 2.1 Packet format . . . . . . . . . . . . . . . . . . . . . . 6 69 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 70 4. Security considerations . . . . . . . . . . . . . . . . . . . 7 71 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 72 6. Appendix - Delivery Options . . . . . . . . . . . . . . . . . 8 73 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 74 7.1 Normative references . . . . . . . . . . . . . . . . . . . 12 75 7.2 Informative references . . . . . . . . . . . . . . . . . . 12 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13 77 Intellectual Property and Copyright Statements . . . . . . . . 14 79 1. Introduction 81 The Extensible Authentication Protocol (EAP) is defined in [RFC3748]. 82 An EAP peer (hereafter, also referred to as the peer) may have 83 multiple credentials. Where the lower layer does not provide an 84 indication of which network it is connecting to, or where its home 85 network may have roaming relationships with several mediating 86 networks, the peer may be uncertain which Network Access Identity 87 (NAI) to include in an EAP-Response/Identity. 89 This document defines a mechanism that allows the access network to 90 provide an EAP peer with identity selection hints, including 91 information about its roaming relationships. This information is 92 sent to the peer in an EAP-Request/Identity message by appending it 93 after the displayable message and a NUL character. 95 This mechanism may assist the peer in selecting a credential and 96 associated NAI, or in formatting the NAI [rfc2486bis] to facilitate 97 routing of AAA messages to the home AAA server. If there are several 98 mediating networks available, the peer can influence which one is 99 used. 101 Exactly how the selection is made by the peer depends largely on the 102 peer's local policy and configuration, and is outside the scope of 103 this document. For example, the peer could decide to use one of its 104 other identities, decide to switch to another access network, or 105 attempt to reformat its NAI [rfc2486bis] to assist in proper AAA 106 routing. The exact client behaviour is described by standard bodies 107 using this specification such as 3GPP [TS 24.234]. 109 Section 2 describes the required behavior of implementations, 110 including the format for identity hints. 112 1.1 Relationship with other specifications 114 This document specifies behavior of RADIUS proxies that handle EAP 115 messages. This includes the specification of the behavior of proxies 116 in response to an unknown realm within the User-Name(1) attribute of 117 an Access-Request containing one or EAP-Message attributes. This 118 document, if used in a scenario requiring NAI "decoration" specified 119 in [rfc2486bis], assumes a source routing model for determination of 120 the roaming relationship path, and therefore affects the behavior of 121 RADIUS proxies in roaming situations. 123 1.2 Applicability 125 Identity hints are useful in situations where the peer cannot 126 determine which credentials to use, or where there may be multiple 127 alternative routes by which an access network can reach a home 128 network. This can occur when access networks support multiple 129 roaming consortiums but do not have a full list of the home networks 130 reachable through them. 132 In such scenarios, identity hints (e.g., a list of roaming partners 133 of the access network) can be provided to enable the EAP peer to 134 influence route selection, using the NAI [RFC2486bis] to specify the 135 desired source route. The immediate application of the proposed 136 mechanism is in 3GPP systems interworking with WLANs [TS 23.234] and 137 [TS 24.234]. 139 The number of hints that can be provided by this mechanism is limited 140 by the EAP MTU. For example, assuming 20 octets per hint and an EAP 141 MTU of 1096, a maximum of 50 roaming partners can be advertised. 142 Scaling limitations imposed by the EAP MTU should be taken into 143 account when deploying this solution. 145 Since this mechanism relies on information provided in the EAP- 146 Request/Identity packet, it is necessary for the peer to select a 147 point of attachment prior to obtaining identity hints. Where there 148 are multiple point of attachment available, the mechanism defined in 149 this specification does not allow the peer to utilize the identity 150 hints in making a decision about which point of attachment to select. 151 In roaming situations, this can require the peer to try multiple 152 points of attachment before it finds a compatible one, increasing 153 handoff latency. 155 This document is related to the general network discovery and 156 selection problem described in [netsel-problem]. The proposed 157 mechanism described in this document solves only a part of the 158 problem in [netsel-problem]. IEEE 802.11 is also looking into more 159 comprehensive and long-term solutions for network discovery and 160 selection. 162 1.3 Terminology 164 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 165 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 166 document are to be interpreted as described in [RFC2119]. 168 NAI Network Address Identifier [rfc2486bis]. 170 Decorated NAI An NAI specifying a source route. See [rfc2486bis] 171 section 2.7 for more information. 173 NAI Realm Realm portion of an NAI [rfc2486bis]. 175 2. Implementation requirements 177 The EAP authenticator MAY send an identity hint to the peer in the 178 initial EAP-Request/Identity. If the identity hint is not sent 179 initially (such as when the authenticator does not support this 180 specification), then the EAP peer may select the wrong NAI. If the 181 local AAA proxy does not have a default route configured, then it may 182 find that the User-Name(1) attribute in the request contains a realm 183 for which there is no corresponding route. 185 As noted in [RFC2607], Section 5.1: 187 "Proxies are frequently used to implement policy in roaming 188 situations. Proxies implementing policy MAY reply directly to 189 Access-Requests without forwarding the request. When replying 190 directly to an Access-Request, the proxy MUST reply either with an 191 Access-Reject or an Access-Challenge packet. A proxy MUST NOT reply 192 directly with an Access-Accept." 194 Where no route is found, existing AAA proxies will typically send an 195 Access-Reject. However, where the request contains an EAP-Message 196 attribute, AAA proxies implementing this specification should instead 197 reply with a challenge including an identity hint. 199 For example, if a RADIUS proxy receives an Access-Request with an 200 EAP-Message attribute and a User-Name(1) attribute containing an 201 unknown realm, it SHOULD reply with an Access-Challenge with an EAP- 202 Message attribute encapsulating an EAP-Request/Identity packet 203 containing an identity hint, rather than an Access-Reject. See 204 "option 3" in the appendix for the message flow diagram. 206 If the peer responds with an EAP-Response/Identity containing an 207 unknown realm after the local AAA proxy sends an identity hint, then 208 a local AAA proxy/server implementing this specification MUST 209 eventually send an Access-Reject containing an EAP-Failure. Prior to 210 doing so it MAY send an Access-Challenge containing an EAP- 211 Notification, in order to provide an explanation for the failure. In 212 order to determine whether an identity hint had been previously sent, 213 the State(24) attribute defined in [RFC2865] can be used. 215 As noted in [RFC3748], Section 3.1, the minimum EAP MTU size is 1020 216 octets. EAP does not support fragmentation of EAP-Request/Identity 217 messages, so the maximum length of the identity hint information is 218 limited by the link MTU. 220 2.1 Packet format 222 The Identity hint information is placed after the displayable string 223 and a NUL character in the EAP-Request/Identity. The following ABNF 224 [RFC2234] defines an NAIRealms attribute for presenting the identity 225 hint information. The attribute's value consists of a set of realm 226 names separated by a semicolon. 228 identity-request-data = [ displayable-string ] "%x00" [ Network-Info ] 230 displayable-string = *CHAR 232 Network-Info = "NAIRealms=" realm-list 233 Network-Info =/ 1*OCTET ",NAIRealms=" realm-list 234 Network-Info =/ "NAIRealms=" realm-list "," 1*OCTET 235 Network-Info =/ 1*OCTET ",NAIRealms=" realm-list "," 1*OCTET 237 realm-list = realm / 238 ( realm-list ";" realm ) 240 The "OCTET" and "CHAR" rules are defined in [RFC2234] and the "realm" 241 rule is defined in [rfc2486bis]. 243 A sample hex dump of an EAP-Request/Identity packet is shown below. 245 01 ; Code: Request 246 00 ; Identifier: 0 247 00 43 ; Length: 67 octets 248 01 ; Type: Identity 249 48 65 6c 6c 6f 21 00 4e ; "Hello!\0NAIRealms=example.com;mnc014. 250 41 49 52 65 61 6c 6d 73 ; mcc310.3gppnetwork.org" 251 3d 69 73 70 2e 65 78 61 252 6d 70 6c 65 2e 63 6f 6d 253 3b 6d 6e 63 30 31 34 2e 254 6d 63 63 33 31 30 2e 33 255 67 70 70 6e 65 74 77 6f 256 72 6b 2e 6f 72 67 258 The Network-Info can contain a NAIRealms list in addition to 259 proprietary information. The proprietary information can be placed 260 before or after NAIRealms list. To extract NAIRealms list, an 261 implementation can either find the "NAIRealms=" immediately after the 262 NUL or seek forward to find ",NAIRealms" somewhere in the string. 263 The realms data ends either at the first "," or at the end of the 264 string, whichever comes first. 266 3. IANA Considerations 268 This document does not define any new namespaces to be managed by 269 IANA, and does not require any assignments in existing namespaces. 271 4. Security considerations 273 Identity hint information is delivered inside an EAP-Request/Identity 274 before the authentication conversation begins. Therefore, it can be 275 modified by an attacker. The NAIRealms attribute therefore MUST be 276 treated as a hint by the peer. That is, the peer must treat the hint 277 as an unreliable indication 279 Unauthenticated hints may result in peers inadvertently revealing 280 additional identities, thus compromising privacy. Since the EAP- 281 Response/Identity is sent in the clear, this vulnerability already 282 exists. This vulnerability can be addressed via method-specific 283 identity exchanges. 285 Similarly, in a situation where the peer has multiple identities to 286 choose from, an attacker can use a forged hint to convince the peer 287 to choose an identity bound to a weak EAP method. Requiring the use 288 of strong EAP methods can protect against this. A similar issue 289 already exists with respect to unprotected link layer advertisements 290 such as 802.11 SSIDs. 292 If the identity hint is used to select a mediating network, existing 293 EAP methods may not provide a way for the home AAA server to verify 294 that the mediating network selected by the peer was actually used. 296 Any information revealed either from the network or client sides 297 before authentication has occurred can be seen as a security risk. 298 For instance, revealing the existence of a network that uses a weak 299 authentication method can make it easier for attackers to discover 300 that such network is accessible. Therefore, the consent of the 301 network being advertised in the hints is required before such hints 302 can be sent. 304 5. Acknowledgements 306 The authors would specially like to thank Jari Arkko, Bernard Aboba, 307 and Glen Zorn for their help in scoping the problem, for reviewing 308 the draft work in progress and for suggesting improvements to it. 310 The authors would also like to acknowledge and thank Adrian Buckley, 311 Blair Bullock, Jose Puthenkulam, Johanna Wild, Joe Salowey, Marco 312 Spini, Simone Ruffino, Mark Grayson, Mark Watson, and Avi Lior for 313 their support, feedback and guidance during the various stages of 314 this work. 316 6. Appendix - Delivery Options 318 Although the delivery options are described in the context of IEEE 319 802.11 access networks, they are also applicable to other access 320 networks that use EAP [RFC3748] for authentication and use the NAI 321 format [rfc2486bis] for identifying users. 323 The options assume that the AAA protocol in use is RADIUS [RFC2865]. 324 However, Diameter [RFC3588] could also be used instead of RADIUS 325 without introducing significant architectural differences. 327 The main difference amongst the options is which entity in the access 328 network creates the EAP-Request/Identity. For example, the role of 329 EAP server may be played by the EAP authenticator (where an initial 330 EAP-Request/Identity is sent with an identity hint) or a RADIUS 331 proxy/server (where the NAI Realm is used for forwarding). 333 The RADIUS proxy/server acts only on the RADIUS UserName(1) attribute 334 and does not have to parse the EAP-Message attribute. 336 Option 1: Initial EAP-Request/Identity from access point 338 In typical IEEE 802.11 wireless LANs, the initial EAP-Request/ 339 Identity is sent by the access point (i.e., EAP authenticator). In 340 the simplest case, the identity hint information is simply included 341 in this request, as shown below. 343 EAP Access Point local RADIUS home RADIUS 344 Peer proxy/server server 345 | 1. EAP | | | 346 | Request/Identity | | | 347 | (NAIRealms) | | | 348 |<------------------| | | 349 | 2. EAP | | | 350 | Response/Identity| | | 351 |------------------>| | | 352 | | 3. Access-Request | | 353 | | (EAP | | 354 | | Response/Identity)| | 355 | |------------------->| | 356 | | | 4.Access-Request | 357 | | | (EAP | 358 | | | Response/Identity) | 359 | | |------------------->| 360 | | | | 361 |<-------------------EAP conversation ----------------------->| 363 Current access points do not support this mechanism, so other options 364 may be preferable. This option can also require configuring the 365 identity hint information in a potentially large number of access 366 points, which may be problematic if the information changes often. 368 Option 2: Initial EAP-Request/Identity from local RADIUS proxy/server 370 This is similar to Option 1, but the initial EAP-Request/Identity is 371 created by the local RADIUS proxy/server instead of the access point. 372 Once a peer associates with an access network AP using IEEE 802.11 373 procedures, the AP sends an EAP-Start message [RFC3579] within a 374 RADIUS Access-Request. The access network RADIUS server can then 375 send the EAP-Request/Identity containing the identity hint 376 information. 378 EAP Access Point local RADIUS home RADIUS 379 Peer proxy/server server 380 | | 1. Access-Request | | 381 | | (EAP-Start) | | 382 | |------------------->| | 383 | | 2.Access-Challenge | | 384 | | (EAP | | 385 | | Request/Identity | | 386 | | with NAIRealms) | | 387 | |<-------------------| | 388 | 3. EAP | | | 389 | Request/Identity | | | 390 | (NAIRealms) | | | 391 |<------------------| | | 392 | 4. EAP | | | 393 | Response/Identity | | | 394 |------------------>| | | 395 | | 5. Access-Request | | 396 | | (EAP | | 397 | | Response/Identity) | | 398 | |------------------->| | 399 | | | 6. Access-Request | 400 | | | (EAP | 401 | | | Response/Identity) | 402 | | |------------------->| 403 | | | | 404 |<------------------- EAP conversation ---------------------->| 406 This option can work with current access points if they support the 407 EAP-Start message. 409 Option 3: Subsequent EAP-Request/Identity from local RADIUS proxy/ 410 server 412 In the third option, the access point sends the initial EAP-Request/ 413 Identity without any hint information. The peer then responds with 414 an EAP-Response/Identity, which is forwarded to the local RADIUS 415 proxy/server. If the RADIUS proxy/server cannot route the message 416 based on the identity provided by the peer, it sends a second EAP- 417 Request/Identity containing the identity hint information. 419 EAP Access Point local RADIUS home RADIUS 420 Peer Proxy/Server server 421 | | | | 422 | 1. EAP | | | 423 | Request/Identity | | | 424 | (w/o NAIRealms) | | | 425 |<------------------| | | 426 | 2. EAP | | | 427 | Response/Identity | | | 428 |------------------>| | | 429 | | 3. Access-Request | | 430 | | (EAP | | 431 | | Response/Identity) | | 432 | |------------------->| | 433 | | 4.Access-Challenge | | 434 | | (EAP | | 435 | | Request/Identity | | 436 | | with NAIRealms) | | 437 | |<-------------------| | 438 | 5. EAP | | | 439 | Request/Identity | | | 440 | (NAIRealms) | | | 441 |<------------------| | | 442 | 6. EAP | | | 443 | Response/Identity | | | 444 |------------------>| | | 445 | | 7. Access-Request | | 446 | | (EAP | | 447 | | Response/Identity) | | 448 | |------------------->| | 449 | | | | 450 ======================Failure due to unknown realm============= 451 | | | | 452 | | 7a.Access-Reject | | 453 | | (EAP-Failure) | | 454 | |<-------------------| | 455 | 7b. EAP | | | 456 | Failure | | | 457 |<------------------| | | 458 ================================================================ 459 | | | | 460 | | | 8. Access-Request | 461 | | | (EAP | 462 | | | Response/Identity) | 463 | | |------------------->| 464 | | | | 465 |<-------------------- EAP conversation --------------------->| 467 This option does not require changes to existing NASes, so it may be 468 preferable in many environments. 470 7. References 472 7.1 Normative references 474 [rfc2486bis] 475 Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The 476 Network Access Identifier", 477 draft-ietf-radext-rfc2486bis-05 (work in progress), 478 July 2004. 480 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. 481 Levkowetz, "Extensible Authentication Protocol (EAP)", 482 RFC 3748, June 2004. 484 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 485 Requirement Levels", BCP 14, RFC 2119, March 1997. 487 [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 488 Specifications: ABNF", RFC 2234, November 1997. 490 [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy 491 Implementation in Roaming", RFC 2607, June 1999. 493 7.2 Informative references 495 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication 496 Dial In User Service) Support For Extensible 497 Authentication Protocol (EAP)", RFC 3579, September 2003. 499 [netsel-problem] 500 Arkko, J. and B. Aboba, "Network Discovery and Selection 501 Problem", draft-ietf-eap-netsel-problem-02 (work in 502 progress), July 2004. 504 [TS 23.234] 505 "3GPP System to Wireless Local Area Network (WLAN) 506 interworking. Stage 2. (www.3gpp.org)", Release 6 3GPP/ 507 WLAN Stage 2 Specification TS 23.234. 509 [TS 24.234] 510 "3GPP System to Wireless Local Area Network (WLAN) 511 interworking. Stage 3. (www.3gpp.org)", Release 6 3GPP/ 512 WLAN Stage 2 Specification TS 24.234. 514 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 516 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 518 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 519 "Remote Authentication Dial In User Service (RADIUS)", 520 RFC 2865, June 2000. 522 Authors' Addresses 524 Farid Adrangi 525 Intel Corporation 526 2111 N.E. 25th Avenue 527 Hillsboro, OR 97124 528 USA 530 Phone: +1 503-712-1791 531 Email: farid.adrangi@intel.com 533 Victor Lortz 534 Intel Corporation 535 2111 N.E. 25th Avenue 536 Hillsboro, OR 97124 537 USA 539 Phone: +1 503-264-3253 540 Email: victor.lortz@intel.com 542 Farooq Bari 543 Cingular Wireless 544 7277 164th Avenue N.E. 545 Redmond, WA 98052 546 USA 548 Phone: +1 425-580-5526 549 Email: farooq.bari@cingular.com 551 Pasi Eronen 552 Nokia Research Center 553 P.O. Box 407 554 FIN-00045 Nokia Group 555 Finland 557 Email: pasi.eronen@nokia.com 559 Intellectual Property Statement 561 The IETF takes no position regarding the validity or scope of any 562 Intellectual Property Rights or other rights that might be claimed to 563 pertain to the implementation or use of the technology described in 564 this document or the extent to which any license under such rights 565 might or might not be available; nor does it represent that it has 566 made any independent effort to identify any such rights. 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