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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group David Nelson 3 INTERNET-DRAFT Elbrys Networks, Inc 4 Updates: 2865, 2866, 2869, 3579 Alan DeKok 5 Category: Proposed Standard FreeRADIUS 6 7 Expires: March 1, 2007 8 4 September 2007 10 Common Remote Authentication Dial In User Service (RADIUS) 11 Implementation Issues and Suggested Fixes 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on September 10, 2007. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2007). 40 Abstract 42 This document describes common issues seen in RADIUS implementations 43 and suggests some fixes. Where applicable, ambiguities and errors in 44 previous RADIUS specifications are clarified. 46 Table of Contents 48 1. Introduction ............................................. 3 49 1.1. Terminology ......................................... 3 50 1.2. Requirements Language ............................... 3 51 2. Issues ................................................... 4 52 2.1. Session Definition .................................. 4 53 2.1.1. State Attribute ................................ 4 54 2.1.2. Request-ID Supplementation ..................... 6 55 2.2. Overload Conditions ................................. 7 56 2.2.1. Retransmission Behavior ........................ 7 57 2.2.2. Duplicate detection and orderly delivery. ...... 9 58 2.2.3. Server Response to Overload .................... 11 59 2.3. Accounting Issues ................................... 12 60 2.3.1. Attributes allowed in an Interim Update ........ 12 61 2.3.2. Acct-Session-Id and Acct-Multi-Session-Id ...... 12 62 2.3.3. Request Authenticator .......................... 13 63 2.3.4. Interim-Accounting-Interval .................... 13 64 2.3.5. Counter values in the RADIUS Management Informat 14 65 2.4. Multiple Filter-ID Attributes ....................... 15 66 2.5. Mandatory and Optional Attributes ................... 16 67 2.6. Interpretation of Access-Reject ..................... 17 68 2.6.1. Improper Use of Access-Reject .................. 17 69 2.6.2. Service Request Denial ......................... 19 70 2.7. Addressing .......................................... 19 71 2.7.1. Link-Local Addresses ........................... 20 72 2.7.2. Multiple Addresses ............................. 20 73 2.8. Idle-Timeout ........................................ 20 74 2.9. Unknown Identity .................................... 21 75 2.10. Responses after retransmissions .................... 22 76 2.11. Framed-IPv6-Prefix ................................. 23 77 3. IANA Considerations ...................................... 24 78 4. Security Considerations .................................. 24 79 5. References ............................................... 24 80 5.1. Normative references ................................ 24 81 5.2. Informative references .............................. 25 82 Intellectual Property Statement .............................. 26 83 Disclaimer of Validity ....................................... 28 84 Full Copyright Statement ..................................... 28 85 1. Introduction 87 The last few years have seen an increase in the deployment of RADIUS 88 clients and servers. This document describes common issues seen in 89 RADIUS implementations and suggests some fixes. Where applicable, 90 ambiguities and errors in previous RADIUS specifications are 91 clarified. 93 1.1. Terminology 95 This document uses the following terms: 97 Network Access Server (NAS) 98 The device providing access to the network. Also known as the 99 Authenticator in IEEE 802.1X or Extensible Authentication Protocol 100 (EAP) terminology, or RADIUS client. 102 service 103 The NAS provides a service to the user, such as network access via 104 802.11 or Point to Point Protocol (PPP). 106 session 107 Each service provided by the NAS to a peer constitutes a session, 108 with the beginning of the session defined as the point where 109 service is first provided and the end of the session defined as the 110 point where service is ended. A peer may have multiple sessions in 111 parallel or series if the NAS supports that, with each session 112 generating a separate start and stop accounting record. 114 silently discard 115 This means the implementation discards the packet without further 116 processing. The implementation SHOULD provide the capability of 117 logging the error, including the contents of the silently discarded 118 packet, and SHOULD record the event in a statistics counter. 120 1.2. Requirements Language 122 In this document, several words are used to signify the requirements 123 of the specification. The key words "MUST", "MUST NOT", "REQUIRED", 124 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 125 and "OPTIONAL" in this document are to be interpreted as described in 126 [RFC2119]. 128 2. Issues 130 2.1. Session Definition 132 2.1.1. State Attribute 134 Regarding the State attribute, [RFC2865] Section 5.24 states: 136 This Attribute is available to be sent by the server to the client 137 in an Access-Challenge and MUST be sent unmodified from the client 138 to the server in the new Access-Request reply to that challenge, 139 if any. 141 This Attribute is available to be sent by the server to the client 142 in an Access-Accept that also includes a Termination-Action 143 Attribute with the value of RADIUS-Request. If the NAS performs 144 the Termination-Action by sending a new Access-Request upon 145 termination of the current session, it MUST include the State 146 attribute unchanged in that Access-Request. 148 Some RADIUS client implementations do not properly use the State 149 attribute in order to distinguish a restarted EAP authentication 150 process from the continuation of an ongoing process (by the same user 151 on the same NAS and port). Where an EAP-Message attribute is 152 included in an Access-Challenge or Access-Accept attribute, RADIUS 153 servers SHOULD also include a State attribute. See Section 2.1.2 on 154 Request ID supplementation for additional benefits to using the State 155 attribute in this fashion. 157 As defined in [RFC2865] Table 5.44, Access-Request packets may 158 contain a State attribute. The table does not qualify this 159 statement, while the text in Section 5.24 quoted above adds other 160 requirements not specified in that table. 162 We extend the requirements of [RFC2865] to say that Access-Requests 163 which are part of an ongoing Access-Request / Access-Challenge 164 authentication process SHOULD contain a State attribute. It is the 165 responsibility of the server to send a State attribute in an Access- 166 Challenge packet, if that server needs a State attribute in a 167 subsequent Access-Request to tie multiple Access-Requests togther 168 into one authentication session. As defined in [RFC2865] Section 169 5.24, the State MUST be sent unmodified from the client to the server 170 in the new Access-Request reply to that challenge, if any. 172 While most server implementations require the presence of a State 173 attribute in an Access-Challenge packet, some challenge-response 174 systems can distinguish the initial request from the response to the 175 challenge without using a State attribute to track an authentication 176 session. The Access-Challenge and subsequent Access-Request packets 177 for those systems do not need to contain a State attribute. 179 Other authentication mechanisms need to tie a sequence of Access- 180 Request / Access-Challenge packets together into one ongoing 181 authentication session. Servers implementing those authentication 182 mechanisms SHOULD include a State attribute in Access-Challenge 183 packets. 185 In general, if the authentication process involves one or more 186 Access-Request / Access-Challenge sequences, the State attribute 187 SHOULD be sent by the server in the Access-Challenge packets. Using 188 the State attribute to create a multi-packet session is the simplest 189 method available in RADIUS today. While other methods of creating 190 multi-packet sessions are possible (e.g. [RFC3579] Section 2.6.1), 191 those methods are NOT RECOMMENDED. 193 The only permissible values for a State attribute are values provided 194 in an Access-Accept, Access-Challenge, CoA-Request or Disconnect- 195 Request packet. A RADIUS client MUST use only those values for the 196 State attribute that it has previously received from a server. An 197 Access-Request sent as a result of a new or restarted authentication 198 run MUST NOT include the State attribute, even if a State attribute 199 has previously been received in an Access-Challenge for the same user 200 and port. 202 In contrast, Access-Requests which are intended to perform 203 authorization checks MUST contain a State attribute in order to tie 204 the authorization check to a previous authentication session. This 205 last requirement often means that an Access-Accept needs to contain a 206 State attribute, which is then used in a later Access-Request that 207 performs authorization checks. 209 Access-Request packets that contain a Service-Type attribute with 210 value Authorize Only (17) MUST contain a State attribute. Access- 211 Request packets that contain a Service-Type attribute with value Call 212 Check (10) SHOULD NOT contain a State attribute. Any other Access- 213 Request packet that performs authorization checks MUST contain a 214 State attribute. 216 The standard use case for Call-Check is pre-screening authentication 217 based solely on the end-point identifier information, such as phone 218 number or MAC address in Calling-Station-ID and optionally Called- 219 Station-ID. In that use case there is no source of the State 220 attribute in the NAS. Other, non-standard, uses of Call-Check may 221 require or permit the use of a State Attribute, but are beyond the 222 scope of this document. 224 Implementing Call Check functionality via requests where the User- 225 Name and User-Password contain the same information (e.g. MAC 226 address) is NOT RECOMMENDED. This practice gives an attacker both 227 the clear-text and cipher-text of the User-Password field, which 228 permits many additional attacks on the security of the RADIUS 229 protocol. For example, if the Request Authenticator does not satisfy 230 the [RFC2865] requirements on global and temporal uniqueness, the 231 practice described above may lead to the compromise of the User- 232 Password attribute in other Access-Requests for unrelated users. 233 Access to the cipher-text also greatly simplifies offline dictionary 234 attacks, potentially exposing the shared secret, and compromising the 235 entire RADIUS protocol. 237 Any Access-Request packet that performs authorization checks, 238 including Call Check, MUST contain a Message-Authenticator attribute. 239 Any response to an Access-Request performing an authorization check 240 MUST NOT contain confidential information about any user (such as 241 Tunnel-Password), unless that Access-Request contains a State 242 attribute. The use of State here permits the authorization check to 243 be tied to an earlier user authentication. In that case, the server 244 MAY respond to the NAS with confidential information about that user. 245 The server MUST NOT respond to that authorization check with 246 confidential information about any other user. 248 2.1.2. Request-ID Supplementation 250 [RFC3579] Section 2.6.1 states: 252 In EAP, each session has its own unique Identifier space. RADIUS 253 server implementations MUST be able to distinguish between EAP 254 packets with the same Identifier existing within distinct 255 sessions, originating on the same NAS. For this purpose, sessions 256 can be distinguished based on NAS and session identification 257 attributes. NAS identification attributes include NAS-Identifier, 258 NAS-IPv6-Address and NAS-IPv4-Address. Session identification 259 attributes include User-Name, NAS-Port, NAS-Port-Type, NAS-Port- 260 Id, Called-Station-Id, Calling-Station-Id and Originating-Line- 261 Info. 263 There are issues with the suggested algorithm. Since proxies may 264 modify Access-Request attributes such as NAS-IP-Address, depending on 265 any attribute under control of the NAS to distinguish request 266 identifiers can result in deployment problems. 268 The FreeRADIUS implementation does not track EAP identifiers by NAS- 269 IP-Address or other non-EAP attributes sent by the NAS. Instead, it 270 uses the EAP identifier, source Internet Protocol (IP) address, and 271 the State attribute as a "key" to uniquely identify each EAP session. 273 Since the State attribute is under the control of the RADIUS server, 274 this means that the uniqueness of each session is controlled by the 275 server, not the NAS. The algorithm used in FreeRADIUS is as follows: 277 if (EAP start, or EAP identity) { 278 allocate unique State Attribute 279 insert session into "active session" table with 280 key=(EAP identifier, State, source IP) 281 } else { 282 look up active session in table, with above key 283 } 285 This algorithm appears to work well in variety of situations, 286 including situations where home servers receive messages via 287 intermediate RADIUS proxies. 289 Implementations that do not use this algorithm are often restricted 290 to having an EAP Identifier space per NAS, or perhaps one that is 291 global to the implementation. These restrictions are unnecessary 292 when the above algorithm is used, which gives each session a unique 293 EAP Identifier space. The above algorithm SHOULD be used to track 294 EAP sessions in preference to any other method. 296 2.2. Overload Conditions 298 2.2.1. Retransmission Behavior 300 [RFC2865] Section 2.4 describes the retransmission requirements for 301 RADIUS clients: 303 At one extreme, RADIUS does not require a "responsive" detection 304 of lost data. The user is willing to wait several seconds for the 305 authentication to complete. The generally aggressive Transmission 306 Control Protocol (TCP) retransmission (based on average round trip 307 time) is not required, nor is the acknowledgment overhead of TCP. 309 At the other extreme, the user is not willing to wait several 310 minutes for authentication. Therefore the reliable delivery of 311 TCP data two minutes later is not useful. The faster use of an 312 alternate server allows the user to gain access before giving up. 314 Some existing RADIUS clients implement excessively aggressive 315 retransmission behavior, utilizing default retransmission timeouts of 316 one second or less without support for congestive backoff. When 317 deployed at large scale, these implementations are susceptible to 318 congestive collapse. For example, as the result of a power failure, 319 a network with 3000 NAS devices with a fixed retransmission timer of 320 one second will continuously generate 3000 RADIUS Access-Requests per 321 second. This is sufficient to overwhelm most RADIUS servers. 323 Suggested solutions include: 325 [a] Jitter. To avoid synchronization, a RADIUS client SHOULD 326 incorporate induced jitter within its retransmission algorithm, as 327 specified below. 329 [b] Congestive backoff. While it is not necessary for RADIUS client 330 implementations to implement complex retransmission algorithms, 331 implementations SHOULD support congestive backoff. 333 RADIUS retransmission timers are based on the model used in DHCPv6 334 [RFC3315]. Variables used here are also borrowed from this 335 specification. RADIUS is a request/response-based protocol. The 336 message exchange terminates when the requester successfully receives 337 the answer or the message exchange is considered to have failed 338 according to the RECOMMENDED retransmission mechanism described 339 below. Other retransmission mechanisms are possible, so long as they 340 satisfy the requirements on jitter and congestive backoff. 342 The following algorithms apply to any client that originates RADIUS 343 packets, including but not limited to Access-Request, Accounting- 344 Request, Disconnect-Request, and CoA-Request [RFC3576]. 346 The retransmission behavior is controlled and described by the 347 following variables: 349 RT Retransmission timeout 351 IRT Initial retransmission time (default 2 seconds) 353 MRC Maximum retransmission count (default 10 attempts) 355 MRT Maximum retransmission time (default 16 seconds) 357 MRD Maximum retransmission duration (default 30 seconds) 359 RAND Randomization factor 361 With each message transmission or retransmission, the sender sets RT 362 according to the rules given below. If RT expires before the message 363 exchange terminates, the sender recomputes RT and retransmits the 364 message. 366 Each of the computations of a new RT include a randomization factor 367 (RAND), which is a random number chosen with a uniform distribution 368 between -0.1 and +0.1. The randomization factor is included to 369 minimize synchronization of messages. 371 The algorithm for choosing a random number does not need to be 372 cryptographically sound. The algorithm SHOULD produce a different 373 sequence of random numbers from each invocation. 375 RT for the first message transmission is based on IRT: 377 RT = IRT + RAND*IRT 379 RT for each subsequent message retransmission is based on the 380 previous value of RT: 382 RT = 2*RTprev + RAND*RTprev 384 MRT specifies an upper bound on the value of RT (disregarding the 385 randomization added by the use of RAND). If MRT has a value of 0, 386 there is no upper limit on the value of RT. Otherwise: 388 if (RT > MRT) 389 RT = MRT + RAND*MRT 391 MRD specifies an upper bound on the length of time a sender may 392 retransmit a message. The message exchange fails once MRD seconds 393 have elapsed since the client first transmitted the message. MRD 394 MUST be set, and SHOULD have a value between 5 and 30 seconds. These 395 values mirror the values for a servers duplicate detection cache, as 396 described in the next section. 398 MRC specifies an upper bound on the number of times a sender may 399 retransmit a message. if MRC is zero, the message exchange fails 400 once MRD seconds have elapsed since the client first transmitted the 401 message. If MRC is non-zero, the message exchange fails when the 402 either the sender has transmitted the message MRC times, or when MRD 403 seconds have elapsed since the client first transmitted the message. 405 For Accounting-Request packets, the default values for MRC, MRD, and 406 MRT SHOULD be zero. These settings will enable a RADIUS client to 407 continue sending accounting requests to a RADIUS server until the 408 request is acknowledged. If any of MRC, MRD, or MRT are non-zero, 409 then the accounting information could potentially be discarded 410 without being recorded. 412 2.2.2. Duplicate detection and orderly delivery. 414 When packets are retransmitted by a client, the server may receive 415 duplicate requests. The limitations of the transport protocol used 416 by RADIUS, the User Datagram Protocol (UDP), means that the Access- 417 Request packets may be received, and potentially processed, in an 418 order different from the order in which the packets were sent. 419 However, the discussion of the Identifier field in Section 3 of 420 [RFC2865] says: 422 The RADIUS server can detect a duplicate request if it has the 423 same client source IP address and source UDP port and Identifier 424 within a short span of time. 426 Also, Section 7 of [RFC4669] defines a 427 radiusAuthServDupAccessRequests object, as 429 The number of duplicate Access-Request packets received. 431 This text has a number of implications. First, without duplicate 432 detection, a RADIUS server may process an authentication request 433 twice, leading to an erroneous conclusion that a user has logged in 434 twice. That behavior is undesirable, so duplicate detection is 435 desirable. Second, the server may track not only the duplicate 436 request, but also the replies to those requests. This behavior 437 permits the server to send duplicate replies in response to duplicate 438 requests, increasing network stability. 440 Since Access-Request packets may also be sent by the client in 441 response to an Access-Challenge from the server, those packets form a 442 logically ordered stream, and therefore have additional ordering 443 requirements over Access-Request packets for different sessions. 444 Implementing duplicate detection results in new packets being 445 processed only once, ensuring order. 447 RADIUS servers MUST therefore implement duplicate detection for 448 Access-Request packets, as described in Section 3 of [RFC2865]. 449 Implementations MUST also cache the Responses (Access-Accept, Access- 450 Challenge, or Access-Reject) that they send in response to Access- 451 Request packets. If a server receives a valid duplicate Access- 452 Request for which is already has sent a Response, it MUST resend its 453 original Response without reprocessing the request. The server MUST 454 silently discard any duplicate Access-Requests for which a Response 455 has not been sent yet. 457 Each cache entry SHOULD be purged after a period of time. This time 458 SHOULD be no less than 5 seconds, and no more than 30 seconds. After 459 about 30 seconds, most RADIUS clients and end users will have given 460 up on the authentication request. Therefore, there is little value 461 in having a larger cache timeout. 463 Cache entries MUST also be purged if the server receives a valid 464 Access-Request packet that matches a cached Access-Request packet in 465 source address, source port, RADIUS Identifier, and receiving socket, 466 but where the Request Authenticator field is different from the one 467 in the cached packet. If the request contains a Message- 468 Authenticator attribute, the request MUST be processed as described 469 in [RFC3580] Section 3.2. Packets with invalid Message- 470 Authenticators MUST NOT affect the cache in any way. 472 However, Access-Request packets not containing a Message- 473 Authenticator attribute always affect the cache, even though they may 474 be trivially forged. To avoid this issue, server implementations may 475 be configured to require the presence of a Message-Authenticator 476 attribute in Access-Request packets. Requests not containing a 477 Message-Authenticator attribute MAY then be silently discarded. 479 Client implementations SHOULD include a Message-Authenticator 480 attribute in every Access-Request, to further help mitigate this 481 issue. 483 When sending requests, RADIUS clients MUST NOT re-use Identifiers for 484 a source IP address and source UDP port until either a valid response 485 has been received, or the request has timed out. Clients SHOULD 486 allocate Identifiers via a least-recently-used (LRU) method for a 487 particular source IP address and source UDP port 489 RADIUS clients do not have to perform duplicate detection. When a 490 client sends a request, it processes the first response that has a 491 valid Response Authenticator as defined in [RFC2865] Section 3. Any 492 later responses MUST be silently discarded, as they do not match a 493 pending request. That is, later responses are treated exactly the 494 same as unsolicited responses, and are silently discarded. 496 2.2.3. Server Response to Overload 498 Some RADIUS server implementations are not robust in response to 499 overload, dropping packets with even probability across multiple 500 sessions. In an overload situation, this results in a high failure 501 rate for multi-round authentication protocols such as EAP [RFC3579]. 502 Typically, users will continually retry in an attempt to gain access, 503 increasing the load even further. 505 A more sensible approach is for a RADIUS server to preferentially 506 accept RADIUS Access-Request packets containing a valid State 507 attribute, so that multi-round authentication conversations, once 508 begun, will be more likely to succeed. Similarly, a server that is 509 proxying requests should preferentially process Access-Accept, 510 Access-Challenge, or Access-Reject packets from home servers, before 511 processing new requests from a NAS. 513 These methods will allow some users to gain access to the network, 514 reducing the load created by ongoing access attempts. 516 2.3. Accounting Issues 518 2.3.1. Attributes allowed in an Interim Update 520 [RFC2866] indicates that Acct-Input-Octets, Acct-Output-Octets, Acct- 521 Session-Time, Acct-Input-Packets, Acct-Output-Packets and Acct- 522 Terminate-Cause attributes "can only be present in Accounting-Request 523 records where the Acct-Status-Type is set to Stop." 525 However [RFC2869] Section 2.1 states: 527 It is envisioned that an Interim Accounting record (with Acct- 528 Status-Type = Interim-Update (3)) would contain all of the 529 attributes normally found in an Accounting Stop message with the 530 exception of the Acct-Term-Cause attribute. 532 Although [RFC2869] does not indicate that it updates [RFC2866], this 533 is an oversight, and the above attributes are allowable in an Interim 534 Accounting record. 536 2.3.2. Acct-Session-Id and Acct-Multi-Session-Id 538 [RFC2866] Section 5.5 describes Acct-Session-Id as Text within the 539 figure summarizing the attribute format, but then goes to state that 540 "The String field SHOULD be a string of UTF-8 encoded 10646 541 characters." 543 [RFC2865] defines the "Text" type as "containing UTF-8 encoded 10646 544 characters", which is compatible with the description of Acct- 545 Session-Id. Since other attributes are consistently described as 546 "Text" within both the figure summarizing the attribute format, and 547 the following attribute definition, it appears that this is a 548 typographical error, and that Acct-Session-Id is of type Text, and 549 not of type String. 551 The definition of the Acct-Multi-Session-Id attribute also has 552 typographical errors. It says 554 A summary of the Acct-Session-Id attribute format ... 556 This text should read 558 A summary of the Acct-Multi-Session-Id attribute format ... 560 The Acct-Multi-Session-Id attribute is also defined as being of type 561 "String". However, the language in the text strongly recommends that 562 implementors consider the attribute as being of type "Text". It is 563 unclear why the type "String" was chosen for this attribute when the 564 type "Text" would be sufficient. This attribute SHOULD be treated as 565 "Text". 567 2.3.3. Request Authenticator 569 [RFC2866] Section 4.1 states: 571 The Request Authenticator of an Accounting-Request contains a 572 16-octet MD5 hash value calculated according to the method 573 described in "Request Authenticator" above. 575 However, the text does not indicate any action to take when an 576 Accounting-Request packet contains an invalid Request Authenticator. 577 The following text should be considered to be part of the above 578 description: 580 The Request Authenticator field MUST contain the correct data, as 581 given by the above calculation. Invalid packets are silently 582 discarded. Note that some early implementations always set the 583 Request Authenticator to all zeros. New implementations of RADIUS 584 clients MUST use the above algorithm to calculate the Request 585 Authenticator field. New RADIUS server implementations MUST 586 silently discard invalid packets. 588 2.3.4. Interim-Accounting-Interval 590 [RFC2869] Section 2.1 states: 592 It is also possible to statically configure an interim value on 593 the NAS itself. Note that a locally configured value on the NAS 594 MUST override the value found in an Access-Accept. 596 This requirement may be phrased too strongly. It is conceivable that 597 a NAS implementation has a setting for a "minimum" value of Interim- 598 Accounting-Interval, based on resource constraints in the NAS, and 599 network loading in the local environment of the NAS. In such cases, 600 the value administratively provisioned in the NAS should not be over- 601 ridden by a smaller value from an Access-Accept message. The NAS's 602 value could be over-ridden by a larger one, however. The intent is 603 that the NAS sends accounting information at fixed intervals, short 604 enough such that the potential loss of billable revenue is limited, 605 but also that the accounting updates are infrequent enough such that 606 the NAS, network, and RADIUS server are not overloaded. 608 2.3.5. Counter values in the RADIUS Management Information Base (MIB) 610 The RADIUS Authentication and Authorization Client MIB module 611 [RFC2618], [RFC4668] includes counters of packet statistics. In the 612 descriptive text of the MIB module, formulas are provided for certain 613 counter objects. Implementors have noted apparent inconsistencies in 614 the formulas, which could result in negative values. 616 Since the original MIB module specified in [RFC2618] had been widely 617 implemented, the RADEXT WG chose not to change the object definitions 618 or to create new ones within the revised MIB module [RFC4668]. 619 However, this section explains the issues and provides guidance for 620 implementors regarding the interpretation of the textual description 621 and comments for certain MIB objects. 623 The issues raised can be summarized as follows: 625 Issue (1): 627 -- TotalIncomingPackets = Accepts + Rejects + Challenges + 628 UnknownTypes 629 -- 630 -- TotalIncomingPackets - MalformedResponses - BadAuthenticators - 631 -- UnknownTypes - PacketsDropped = Successfully received 632 -- 633 -- AccessRequests + PendingRequests + ClientTimeouts = 634 -- Successfully Received 636 It appears that the value of "Successfully Received" could be 637 negative, since various counters are subtracted from 638 TotalIncomingPackets that are not included in the calculation of 639 TotalIncomingPackets. 641 It also appears that "AccessRequests + PendingRequests + 642 ClientTimeouts = Successfully Received" should read "AccessRequests + 643 PendingRequests + ClientTimeouts = Successfully Transmitted". 645 "TotalIncomingPackets" and "Successfully Received" are temporary 646 variables, i.e. not objects within the MIB module. The comment text 647 in the MIB modules is intended, therefore, to aid in understanding. 648 What's of consequence is the consistency of values of the objects in 649 the MIB module, and that does not appear to be impacted by the 650 inconsistencies noted above. It does appear, however, that the 651 "Successfully Received" variable should be labeled "Successfully 652 Transmitted". 654 In addition, the definition of Accept, Reject or Challenge counters 655 indicates that they MUST be incremented before the message is 656 validated. If the message is invalid, one of MalformedResponses, 657 BadAuthenticators or PacketsDropped counters will be additionally 658 incremented. In that case the first two equations are consistent, 659 i.e. "Successfully Received" could not be negative. 661 Issue (2): 663 It appears that the radiusAuthClientPendingRequests counter is 664 decremented upon retransmission. That would mean a retransmitted 665 packet is not considered as being as pending, although such 666 retransmissions can still be considered as being pending requests. 668 The definition of this MIB object in [RFC2618] is as follows: 670 The number of RADIUS Access-Request packets destined for this 671 server that have not yet timed out or received a response. This 672 variable is incremented when an Access-Request is sent and 673 decremented due to receipt of an Access-Accept, Access-Reject or 674 Access-Challenge, a timeout or retransmission. 676 This object purports to count the number of pending request packets. 677 It is open to interpretation whether or not retransmissions of a 678 request are to be counted as additional pending packets. In either 679 event, it seems appropriate to treat retransmissions consistently 680 with respect to incrementing and decrementing this counter. 682 2.4. Multiple Filter-ID Attributes 684 [RFC2865] Section 5.11 states: 686 Zero or more Filter-Id attributes MAY be sent in an Access-Accept 687 packet. 689 In practice the behavior of a RADIUS client receiving multiple 690 Filter-ID attributes is implementation dependent. For example, some 691 implementations treat multiple instances of the Filter-ID attribute 692 as alternative filters; the first Filter-ID attribute having a name 693 matching a locally defined filter is used, and the remaining ones are 694 discarded. Other implementations may combine matching filters. 696 As a result, the interpretation of multiple Filter-ID attributes is 697 undefined within RADIUS. The sending of multiple Filter-ID 698 attributes within an Access-Accept SHOULD be avoided within 699 heterogeneous deployments and roaming scenarios, where it is likely 700 to produce unpredictable results. 702 2.5. Mandatory and Optional Attributes 704 RADIUS attributes do not explicitly state whether they are optional 705 or mandatory. Nevertheless there are instances where RADIUS 706 attributes need to be treated as mandatory. 708 [RFC2865] Section 1.1 states: 710 A NAS that does not implement a given service MUST NOT implement 711 the RADIUS attributes for that service. For example, a NAS that 712 is unable to offer Apple Remote Access Protocol (ARAP) service 713 MUST NOT implement the RADIUS attributes for ARAP. A NAS MUST 714 treat a RADIUS access-accept authorizing an unavailable service as 715 an access-reject instead. 717 With respect to the Service-Type attribute, [RFC2865] Section 5.6 718 says: 720 This Attribute indicates the type of service the user has 721 requested, or the type of service to be provided. It MAY be used 722 in both Access-Request and Access-Accept packets. A NAS is not 723 required to implement all of these service types, and MUST treat 724 unknown or unsupported Service-Types as though an Access-Reject 725 had been received instead. 727 [RFC2865] Section 5 states: 729 A RADIUS server MAY ignore Attributes with an unknown Type. 731 A RADIUS client MAY ignore Attributes with an unknown Type. 733 With respect to Vendor-Specific Attributes (VSAs), [RFC2865] Section 734 5.26 states: 736 Servers not equipped to interpret the vendor-specific information 737 sent by a client MUST ignore it (although it may be reported). 738 Clients which do not receive desired vendor-specific information 739 SHOULD make an attempt to operate without it, although they may do 740 so (and report they are doing so) in a degraded mode. 742 It is possible for either a standard attribute or VSA to represent a 743 request for an unavailable service. However, where the Type, Vendor- 744 ID, or Vendor-Type is unknown, a RADIUS client will not know whether 745 the attribute defines a service or not. 747 In general, it is best for a RADIUS clients to err on the side of 748 caution. On receiving an Access-Accept including an attribute of 749 known Type for an unimplemented service, a RADIUS client MUST treat 750 it as an Access-Reject, as directed in [RFC2865] Section 1.1. On 751 receiving an Access-Accept including an attribute of unknown Type, a 752 RADIUS client SHOULD assume that it is a potential service 753 definition, and treat it as an Access-Reject. Unknown VSAs SHOULD be 754 ignored by RADIUS clients. 756 In order to avoid introducing changes in default behavior, existing 757 implementations that do not obey this recommendation should make the 758 behavior configurable, with the legacy behavior being enabled by 759 default. A configuration flag such as "treat unknown attributes as 760 reject" can be exposed to the system administrator. If the flag is 761 set to true, then Access-Accepts containing unknown attributes are 762 treated as Access-Rejects. If the flag is set to false, then unknown 763 attributes in Access-Accepts are be silently ignored. 765 On receiving a packet including an attribute of unknown type, RADIUS 766 authentication server implementations SHOULD ignore such attributes. 767 However, RADIUS accounting server implementations typically do not 768 need to understand attributes in order to write them to stable 769 storage or pass them to the billing engine. Therefore, accounting 770 server implementations SHOULD be equipped to handle unknown 771 attributes. 773 To avoid misinterpretation of service requests encoded within VSAs, 774 RADIUS servers SHOULD NOT send VSAs containing service requests to 775 RADIUS clients that are not known to understand them. For example, a 776 RADIUS server should not send a VSA encoding a filter without 777 knowledge that the RADIUS client supports the VSA. 779 2.6. Interpretation of Access-Reject 781 2.6.1. Improper Use of Access-Reject 783 The intent of an Access-Reject is to deny access to the requested 784 service. [RFC2865] Section 2 states: 786 If any condition is not met, the RADIUS server sends an "Access- 787 Reject" response indicating that this user request is invalid. If 788 desired, the server MAY include a text message in the Access- 789 Reject which MAY be displayed by the client to the user. No other 790 Attributes (except Proxy-State) are permitted in an Access-Reject. 792 This text makes it clear that RADIUS does not allow the provisioning 793 of services within an Access-Reject. If the desire is to allow 794 limited access, then an Access-Accept can be sent with attributes 795 provisioning limited access. Attributes within an Access-Reject are 796 restricted to those necessary to route the message (e.g. Proxy- 797 State), attributes providing the user with an indication that access 798 has been denied (e.g. an EAP-Message attribute containing an EAP- 799 Failure) or attributes conveying an error message (e.g. a Reply- 800 Message or Error-Cause attribute). 802 Unfortunately, there are examples where this requirement has been 803 misunderstood. [RFC2869] Section 2.2 states: 805 If that authentication fails, the RADIUS server should return an 806 Access-Reject packet to the NAS, with optional Password-Retry and 807 Reply-Messages attributes. The presence of Password-Retry 808 indicates the ARAP NAS MAY choose to initiate another challenge- 809 response cycle, 811 This paragraph is problematic from two perspectives. Firstly, a 812 Password-Retry attribute is being returned in an Access-Reject; this 813 attribute does not fit into the categories established in [RFC2865]. 814 Secondly, an Access-Reject packet is being sent in the context of a 815 continuing authentication conversation; [RFC2865] requires use of an 816 Access-Challenge for this. [RFC2869] uses the phrase "challenge- 817 response" to describe this use of Access-Reject, indicating that the 818 semantics of Access-Challenge are being used. 820 [RFC2865] Section 4.4, addresses the semantics of Access-Challenge 821 being equivalent to Access-Reject in some cases: 823 If the NAS does not support challenge/response, it MUST treat an 824 Access-Challenge as though it had received an Access-Reject 825 instead. 827 While it is difficult to correct existing deployments of [RFC2869], 828 we make the following recommendations: 830 [1] New RADIUS specifications and implementations MUST NOT use Access- 831 Reject where the semantics of Access-Challenge are intended. 833 [2] Access-Reject MUST mean denial of access to the requested service. 834 In response to an Access-Reject, the NAS MUST NOT send any 835 additional Access-Request packets for that user session. 837 [3] New deployments of ARAP [RFC2869] SHOULD use Access-Challenge 838 instead of Access-Reject packets in the conversations described in 839 [RFC2869] Section 2.2. 841 We also note that the table of attributes [RFC2869] Section 5.19 has 842 an error for the Password-Retry attribute. It says: 844 Request Accept Reject Challenge # Attribute 845 0 0 0-1 0 75 Password-Retry 846 However, the text in [RFC2869] Section 2.3.2 says that Password-Retry 847 can be included within an Access-Challenge packet, for EAP 848 authentication sessions. We recommend a correction to the table, 849 which removes the "0-1" from the Reject column, moves it to the 850 Challenge column. We also add a "Note 2" to follow the existing 851 "Note 1" in the document, to clarify the use of this attribute. 853 Request Accept Reject Challenge # Attribute 854 0 0 0 0-1 75 Password-Retry [Note 2] 856 [Note 2] As per RFC 3579, the use of the Password-Retry in EAP 857 authentications is deprecated. The Password-Retry attribute can be 858 used only for ARAP authentication. 860 2.6.2. Service Request Denial 862 RADIUS has been deployed for purposes outside network access 863 authentication, authorization and accounting. For example, RADIUS 864 has been deployed as a "back-end" for authenticating Voice Over IP 865 (VOIP) connections, Hypertext Transfer Protocol (HTTP) sessions (e.g. 866 Apache), File Transfer Protocol (FTP) sessions (e.g. proftpd), and 867 machine logins for multiple operating systems (e.g. bsdi, pam, gina). 868 In those contexts, an Access-Reject sent to the RADIUS client MUST be 869 interpreted as a rejection of the request for service, and the RADIUS 870 client MUST NOT offer that service to the user. 872 For example, when an authentication failure occurs in the context of 873 an FTP session, the normal semantics for rejecting FTP services 874 apply. The rejection does not necessarily cause the FTP server to 875 terminate the underlying TCP connection, but the FTP server MUST NOT 876 offer any services protected by user authentication. 878 Users may request multiple services from the NAS. Where those 879 services are independent, the deployment MUST treat the RADIUS 880 sessions as being independent. 882 For example, a NAS may offer multi-link services, where a user may 883 have multiple simultaneous network connections. In that case, an 884 Access-Reject for a later multi-link connection request does not 885 necessarily mean that earlier multi-link connections are torn down. 886 Similarly, if a NAS offers both dialup and VOIP services, the 887 rejection of a VOIP attempt does not mean that the dialup session is 888 torn down. 890 2.7. Addressing 891 2.7.1. Link-Local Addresses 893 Since Link-Local addresses are unique only on the local link, if the 894 NAS and RADIUS server are not on the same link, then an IPv6 Link- 895 Local address [RFC2462] or an IPv4 Link-Local Address [RFC3927] 896 cannot be used to uniquely identify the NAS. A NAS SHOULD NOT 897 utilize a link-scope address within a NAS-IPv6-Address or NAS-IP- 898 Address attributes. A RADIUS server receiving a NAS-IPv6-Address or 899 NAS-IP-Address attribute containing a Link-Local address SHOULD NOT 900 count such an attribute toward satisfying the requirements of 901 [RFC3162] Section 2.1: 903 NAS-IPv6-Address and/or NAS-IP-Address MAY be present in an 904 Access-Request packet; however, if neither attribute is present 905 then NAS-Identifier MUST be present. 907 2.7.2. Multiple Addresses 909 There are situations in which a RADIUS client or server may have 910 multiple addresses. For example, a dual stack host can have both 911 IPv4 and IPv6 addresses; a host that is a member of multiple VLANs 912 could have IPv4 and/or IPv6 addresses on each VLAN; a host can have 913 multiple IPv4 or IPv6 addresses on a single interface. However, 914 [RFC2865] Section 5.44 only permits zero or one NAS-IP-Address 915 attribute within an Access-Request and [RFC3162] Section 3 only 916 permits zero or one NAS-IPv6-Address attribute within an Access- 917 Request. When a NAS has more than one global address and no ability 918 to determine which is used for identification in a particular 919 request, it is RECOMMENDED that the NAS include the NAS-Identifier 920 attribute in an Access-Request in order to identify itself to the 921 RADIUS server. 923 [RFC2865] Section 3 states: 925 A RADIUS server MUST use the source IP address of the RADIUS 926 UDP packet to decide which shared secret to use, so that 927 RADIUS requests can be proxied. 929 Therefore if a RADIUS client sends packets from more than one source 930 address, a shared secret will need to be configured on both the 931 client and server for each source address. 933 2.8. Idle-Timeout 935 With respect to the Idle-Timeout attribute, [RFC2865] Section 5.28 936 states: 938 This Attribute sets the maximum number of consecutive seconds of 939 idle connection allowed to the user before termination of the 940 session or prompt. This Attribute is available to be sent by the 941 server to the client in an Access-Accept or Access-Challenge. 943 [RFC3580] Section 3.12 states: 945 The Idle-Timeout attribute is described in [RFC2865]. For IEEE 946 802 media other than 802.11 the media are always on. As a result 947 the Idle-Timeout attribute is typically only used with wireless 948 media such as IEEE 802.11. It is possible for a wireless device 949 to wander out of range of all Access Points. In this case, the 950 Idle-Timeout attribute indicates the maximum time that a wireless 951 device may remain idle. 953 In the above paragraphs "idle" may not necessarily mean "no traffic"; 954 the NAS may support filters defining what traffic is included in the 955 idle time determination. As a result, an "idle connection" is 956 defined by local policy in the absence of other attributes. 958 2.9. Unknown Identity 960 [RFC3748] Section 5.1 states: 962 If the Identity is unknown, the Identity Response field 963 should be zero bytes in length. 965 However, [RFC2865] Section 5.1 describes the User-Name attribute as 966 follows: 968 The String field is one or more octets. 970 How should the RADIUS client behave if it receives an EAP- 971 Response/Identity that is zero octets in length? 973 [RFC2865] Section 5.1 states: 975 This Attribute indicates the name of the user to be authenticated. 976 It MUST be sent in Access-Request packets if available. 978 This suggests that the User-Name attribute may be ommitted if it is 979 unavailable. 981 However, [RFC3579] Section 2.1 states: 983 In order to permit non-EAP aware RADIUS proxies to forward the 984 Access-Request packet, if the NAS initially sends an 985 EAP-Request/Identity message to the peer, the NAS MUST copy the 986 contents of the Type-Data field of the EAP-Response/Identity 987 received from the peer into the User-Name attribute and MUST 988 include the Type-Data field of the EAP-Response/Identity in the 989 User-Name attribute in every subsequent Access-Request. 991 This suggests that the User-Name attribute should contain the 992 contents of the Type-Data field of the EAP-Response/Identity, even if 993 it is zero octets in length. 995 Note that [RFC4282] does not permit a Network Access Identifier (NAI) 996 of zero octets, so that an EAP-Response/Identity with a Type-Data 997 field of zero octets MUST NOT be construed as a request for privacy 998 (e.g. anonymous NAI). 1000 When a NAS receives an EAP-Response/Identity with a Type-Data field 1001 that is zero octets in length, it is RECOMMENDED that it either omit 1002 the User-Name attribute in the Access-Request or include the Calling- 1003 Station-Id in the User-Name attribute, along with a Calling-Station- 1004 Id attribute. 1006 2.10. Responses after retransmissions 1008 Some implementations do not correctly handle the receipt of RADIUS 1009 responses after retransmissions. [RFC2865] Section 2.5 states 1011 If the NAS is retransmitting a RADIUS request to the same server 1012 as before, and the attributes haven't changed, you MUST use the 1013 same Request Authenticator, ID, and source port. If any 1014 attributes have changed, you MUST use a new Request Authenticator 1015 and ID. 1017 Note that changing the Request ID for a retransmission may have 1018 undesirable side effects. Since RADIUS does not have a clear 1019 definition of a "session", it is perfectly valid for a RADIUS server 1020 to treat a retransmission as a new session request, and to reject it 1021 due to (say) multiple simultaneous login restrictions are enforced. 1022 In that situation, the NAS may receive a belated Access-Accept for 1023 the first request, and an Access-Reject for the retransmitted 1024 request, both of which apply to the same "session". 1026 We suggest that the contents of Access-Request packets SHOULD NOT be 1027 changed during retransmissions. If they must be changed due to the 1028 inclusion of an Event-Timestampt attribute, for example, then 1029 responses to earlier transmissions MUST be silently discarded. Any 1030 response to the current request MUST be treated as the definitive 1031 response, even if as noted above, it disagrees with earlier 1032 responses. 1034 This problem can be made worse by implementations that use a fixed 1035 retransmission timeout (30 seconds is common). We reiterate the 1036 suggestions above in Section 2.1 about using congestive backoff. In 1037 that case, responses to earlier transmissions MAY be used as data 1038 points for congestive backoff, even if their contents are discarded. 1040 2.11. Framed-IPv6-Prefix 1042 [RFC3162] Section 2.3 says 1044 This Attribute indicates an IPv6 prefix (and corresponding route) 1045 to be configured for the user. It MAY be used in Access-Accept 1046 packets, and can appear multiple times. It MAY be used in an 1047 Access-Request packet as a hint by the NAS to the server that it 1048 would prefer these prefix(es), but the server is not required to 1049 honor the hint. Since it is assumed that the NAS will plumb a 1050 route corresponding to the prefix, it is not necessary for the 1051 server to also send a Framed-IPv6-Route attribute for the same 1052 prefix. 1054 An Internet Service Provider (ISP) may desire to support Prefix 1055 Delegation [RFC4818] at the same time that it would like to assign a 1056 prefix for the link between the NAS and the user. The intent of the 1057 paragraph was to enable the NAS to advertise the prefix (such as via 1058 a Router Advertisement). If the Framed-Routing attribute is used, it 1059 is also possible that the prefix would be advertised in a routing 1060 protocol such as RIPNG. RFC 2865 Section 5.10 describes the purpose 1061 of Framed-Routing: 1063 This Attribute indicates the routing method for the user, when the 1064 user is a router to a network. It is only used in Access-Accept 1065 packets. 1067 The description of the Prefix-Length field in RFC 3162 indicates 1068 excessively wide latitude: 1070 The length of the prefix, in bits. At least 0 and no larger than 1071 128. 1073 This length appears too broad, because it is not clear what a NAS 1074 should do with a prefix of greater granularity than /64. For example, 1075 the Framed-IPv6-Prefix may contain a /128. This does not imply that 1076 the NAS should assign an IPv6 address to the end user, because RFC 1077 3162 already defines a Framed-IPv6-Identifier attribute to handle the 1078 Identifier portion. 1080 It appears that the Framed-IPv6-Prefix is used for the link between 1081 the NAS and CPE only if a /64 prefix is assigned. When a /64 or 1082 larger prefix is sent, the intent is for the NAS to send a routing 1083 advertisement containing the information present in the Framed- 1084 IPv6-Prefix attribute. 1086 The CPE may also require a delegated prefix for its own use, if it is 1087 decrementing the Time To Live (TTL) field of IP headers. In that 1088 case, it should be delegated a prefix by the NAS via the Delegated- 1089 IPv6-Prefix attribute. [RFC4818]. If the CPE is not decrementing 1090 TTL, it does not require a delegated prefix. 1092 3. IANA Considerations 1094 This specification does not create any new registries, nor does it 1095 require assignment of any protocol parameters. 1097 4. Security Considerations 1099 The contents of the State attribute are available to both the RADIUS 1100 client and observers of the RADIUS protocol. RADIUS server 1101 implementations should ensure that the state attribute does not 1102 disclose sensitive information to a RADIUS client or third parties 1103 observing the RADIUS protocol. 1105 The cache mechanism described in Section 2.2.2 is vulnerable to 1106 attacks when Access-Request packets do not contain a Message- 1107 Authenticator attribute. If the server accepts requests without a 1108 Message-Authenticator, then RADIUS packets can be trivially forged by 1109 an attacker. Cache entries can then be forcibly expired, negating 1110 the utility of the cache. This attack can be mitigated by following 1111 the suggestions in [RFC3579] Section 4, or by requiring the presence 1112 of Message-Authenticator, as described in Sections 2.1.1 and 2.2.2. 1114 Since this document describes the use of RADIUS for purposes of 1115 authentication, authorization, and accounting in a wide variety of 1116 networks, applications using these specifications are vulnerable to 1117 all of the threats that are present in other RADIUS applications. 1118 For a discussion of these threats, see [RFC2865], [RFC2607], 1119 [RFC3162], [RFC3579], and [RFC3580]. 1121 5. References 1123 5.1. Normative references 1125 [RFC2865] 1126 Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote 1127 Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. 1129 [RFC4818] 1130 Salowey, J., Droms., R, "RADIUS Delegated-IPv6-Prefix Attribute", 1131 RFC 4818, April 2007. 1133 5.2. Informative references 1135 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1136 Requirement Levels", RFC 2119, March, 1997. 1138 [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address 1139 Autoconfiguration", RFC 2462, December 1998. 1141 [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy 1142 Implementation in Roaming", RFC 2607, June 1999. 1144 [RFC2618] Aboba, B. and G. Zorn, "RADIUS Authentication Client MIB", RFC 1145 2618, June 1999. 1147 [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. 1149 [RFC2869] Rigney, C., Willats, W. and P. Calhoun, "RADIUS Extensions", 1150 RFC 2869, June 2000. 1152 [RFC3162] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 1153 3162, August 2001. 1155 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. 1156 Carney, "Dynamic Host Configuration Protocol for IPv6 1157 (DHCPv6)", RFC 3315, July 2003. 1159 [RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba, 1160 "Dynamic Authorization Extensions to Remote Authentication 1161 Dial In User Service (RADIUS)", RFC 3576, July 2003. 1163 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS Support for Extensible 1164 Authentication Protocol (EAP)", RFC 3579, September 2003. 1166 [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese, 1167 "IEEE 802.1X Remote Authentication Dial In User Service 1168 (RADIUS) Usage Guidelines", RFC 3580, September 2003. 1170 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. 1171 Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 1172 3748, June 2004. 1174 [RFC3927] Cheshire, S., Aboba, B. and E. Guttman, "Dynamic Configuration 1175 of IPv4 Link-Local Addresses", RFC 3927, May 2005. 1177 [RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network 1178 Access Identifier", RFC 4282, December 2005. 1180 [RFC4668] Nelson, D, "RADIUS Authentication Client MIB for IPv6", RFC 1181 4668, August 2006. 1183 [RFC4669] Nelson, D, "RADIUS Authentication Server MIB for IPv6", RFC 1184 4669, August 2006. 1186 Acknowledgments 1188 The authors would like to acknowledge Glen Zorn and Bernard Aboba for 1189 contributions to this document. 1191 The alternate algorithm to [RFC3579] Section 2.6.1 that is described 1192 in section 2.1.2 of this document was designed by Raghu Dendukuri. 1194 The text discussing retransmissions in Section 2.2.1 is taken with 1195 minor edits from Section 9 of draft-ietf-pana-pana-17.txt 1197 Alan DeKok wishes to acknowledge the support of Quiconnect Inc., 1198 where he was employed during much of the work on this document. 1200 David Nelson wishes to acknowledge the support of Enterasys Networks, 1201 where he was employed during much of the work on this document. 1203 Authors' Addresses 1205 David B. Nelson 1206 Elbrys Networks, Inc. 1207 75 Rochester Ave., Unit 3 1208 Portsmouth N.H. 03801 USA 1210 Phone: +1.603.570.2636 1212 Email: d.b.nelson@comcast.net 1214 Alan DeKok 1215 The FreeRADIUS Server Project 1216 http://freeradius.org/ 1218 Email: aland@freeradius.org 1220 Intellectual Property Statement 1222 The IETF takes no position regarding the validity or scope of any 1223 Intellectual Property Rights or other rights that might be claimed to 1224 pertain to the implementation or use of the technology described in 1225 this document or the extent to which any license under such rights 1226 might or might not be available; nor does it represent that it has 1227 made any independent effort to identify any such rights. 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Please address the information to the IETF at ietf- 1242 ipr@ietf.org. 1244 Disclaimer of Validity 1246 This document and the information contained herein are provided on an 1247 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1248 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1249 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1250 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1251 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1252 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1254 Full Copyright Statement 1256 Copyright (C) The IETF Trust (2007). 1258 This document is subject to the rights, licenses and restrictions 1259 contained in BCP 78, and except as set forth therein, the authors 1260 retain all their rights. 1262 Acknowledgment 1264 Funding for the RFC Editor function is currently provided by the 1265 Internet Society. 1267 Open issues 1269 Open issues relating to this specification are tracked on the 1270 following web site: 1272 http://www.drizzle.com/~aboba/RADEXT/