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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: February 27, 2007 8 27 August 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 within the limits 332 suggested by [RFC2865] Section 2.4. 334 RADIUS retransmission timers are based on the model used in DHCPv6 335 [RFC3315]. Variables used here are also borrowed from this 336 specification. RADIUS is a request/response-based protocol. The 337 message exchange terminates when the requester successfully receives 338 the answer or the message exchange is considered to have failed 339 according to the RECOMMENDED retransmission mechanism described 340 below. Other retransmission mechanisms are possible, so long as they 341 satisfy the requirements on jitter and congestive backoff. 343 The following algorithms apply to any client that originates RADIUS 344 packets, including but not limited to Access-Request, Accounting- 345 Request, Disconnect-Request, and CoA-Request [RFC3576]. 347 The retransmission behavior is controlled and described by the 348 following variables: 350 RT Retransmission timeout 352 IRT Initial retransmission time (default 2 seconds) 354 MRC Maximum retransmission count (default 10 attempts) 356 MRT Maximum retransmission time (default 16 seconds) 358 MRD Maximum retransmission duration (default 30 seconds) 360 RAND Randomization factor 362 With each message transmission or retransmission, the sender sets RT 363 according to the rules given below. If RT expires before the message 364 exchange terminates, the sender recomputes RT and retransmits the 365 message. 367 Each of the computations of a new RT include a randomization factor 368 (RAND), which is a random number chosen with a uniform distribution 369 between -0.1 and +0.1. The randomization factor is included to 370 minimize synchronization of messages. 372 The algorithm for choosing a random number does not need to be 373 cryptographically sound. The algorithm SHOULD produce a different 374 sequence of random numbers from each invocation. 376 RT for the first message transmission is based on IRT: 378 RT = IRT + RAND*IRT 380 RT for each subsequent message retransmission is based on the 381 previous value of RT: 383 RT = 2*RTprev + RAND*RTprev 385 MRT specifies an upper bound on the value of RT (disregarding the 386 randomization added by the use of RAND). If MRT has a value of 0, 387 there is no upper limit on the value of RT. Otherwise: 389 if (RT > MRT) 390 RT = MRT + RAND*MRT 392 MRD specifies an upper bound on the length of time a sender may 393 retransmit a message. The message exchange fails once MRD seconds 394 have elapsed since the client first transmitted the message. MRD 395 MUST be set, and SHOULD have a value between 5 and 30 seconds. These 396 values mirror the values for a servers duplicate detection cache, as 397 described in the next section. 399 MRC specifies an upper bound on the number of times a sender may 400 retransmit a message. if MRC is zero, the message exchange fails 401 once MRD seconds have elapsed since the client first transmitted the 402 message. If MRC is non-zero, the message exchange fails when the 403 either the sender has transmitted the message MRC times, or when MRD 404 seconds have elapsed since the client first transmitted the message. 406 For Accounting-Request packets, the default values for MRC, MRD, and 407 MRT SHOULD be zero. These settings will enable a RADIUS client to 408 continue sending accounting requests to a RADIUS server until the 409 request is acknowledged. If any of MRC, MRD, or MRT are non-zero, 410 then the accounting information could potentially be discarded 411 without being recorded. 413 2.2.2. Duplicate detection and orderly delivery. 415 When packets are retransmitted by a client, the server may receive 416 duplicate requests. The limitations of the transport protocol used 417 by RADIUS, the User Datagram Protocol (UDP), means that the Access- 418 Request packets may be received, and potentially processed, in an 419 order different from the order in which the packets were sent. 420 However, the discussion of the Identifier field in Section 3 of 421 [RFC2865] says: 423 The RADIUS server can detect a duplicate request if it has the 424 same client source IP address and source UDP port and Identifier 425 within a short span of time. 427 Also, Section 7 of [RFC4669] defines a 428 radiusAuthServDupAccessRequests object, as 430 The number of duplicate Access-Request packets received. 432 This text has a number of implications. First, without duplicate 433 detection, a RADIUS server may process an authentication request 434 twice, leading to an erroneous conclusion that a user has logged in 435 twice. That behavior is undesirable, so duplicate detection is 436 desirable. Second, the server may track not only the duplicate 437 request, but also the replies to those requests. This behavior 438 permits the server to send duplicate replies in response to duplicate 439 requests, increasing network stability. 441 Since Access-Request packets may also be sent by the client in 442 response to an Access-Challenge from the server, those packets form a 443 logically ordered stream, and therefore have additional ordering 444 requirements over Access-Request packets for different sessions. 445 Implementing duplicate detection results in new packets being 446 processed only once, ensuring order. 448 RADIUS servers MUST therefore implement duplicate detection for 449 Access-Request packets, as described in Section 3 of [RFC2865]. 450 Implementations MUST also cache the Responses (Access-Accept, Access- 451 Challenge, or Access-Reject) that they send in response to Access- 452 Request packets. If a server receives a valid duplicate Access- 453 Request for which is already has sent a Response, it MUST resend its 454 original Response without reprocessing the request. The server MUST 455 silently discard any duplicate Access-Requests for which a Response 456 has not been sent yet. 458 Each cache entry SHOULD be purged after a period of time. This time 459 SHOULD be no less than 5 seconds, and no more than 30 seconds. 461 Cache entries MUST also be purged if the server receives a valid 462 Access-Request packet that matches a cached Access-Request packet in 463 source address, source port, RADIUS Identifier, and receiving socket, 464 but where the Request Authenticator field is different from the one 465 in the cached packet. If the request contains a Message- 466 Authenticator attribute, the request MUST be processed as described 467 in [RFC3580] Section 3.2. Packets with invalid Message- 468 Authenticators MUST NOT affect the cache in any way. 470 However, Access-Request packets not containing a Message- 471 Authenticator attribute always affect the cache, even though they may 472 be trivially forged. To avoid this issue, server implementations may 473 be configured to require the presence of a Message-Authenticator 474 attribute in Access-Request packets. Requests not containing a 475 Message-Authenticator attribute MAY then be silently discarded. 477 Client implementations SHOULD include a Message-Authenticator 478 attribute in every Access-Request, to further help mitigate this 479 issue. 481 When sending requests, RADIUS clients MUST NOT re-use Identifiers for 482 a source IP address and source UDP port until either a valid response 483 has been received, or the request has timed out. Clients SHOULD 484 allocate Identifiers via a least-recently-used (LRU) method for a 485 particular source IP address and source UDP port 487 RADIUS clients do not have to perform duplicate detection. When a 488 client sends a request, it processes the first response that has a 489 valid Response Authenticator as defined in [RFC2865] Section 3. Any 490 later responses MUST be silently discarded. 492 2.2.3. Server Response to Overload 494 Some RADIUS server implementations are not robust in response to 495 overload, dropping packets with even probability across multiple 496 sessions. In an overload situation, this results in a high failure 497 rate for multi-round authentication protocols such as EAP [RFC3579]. 498 Typically, users will continually retry in an attempt to gain access, 499 increasing the load even further. 501 A more sensible approach is for a RADIUS server to preferentially 502 accept RADIUS Access-Request packets containing a valid State 503 attribute, so that multi-round authentication conversations, once 504 begun, will be more likely to succeed. Similarly, a server that is 505 proxying requests should preferentially process Access-Accept, 506 Access-Challenge, or Access-Reject packets from home servers, before 507 processing new requests from a NAS. 509 These methods will allow some users to gain access to the network, 510 reducing the load created by ongoing access attempts. 512 2.3. Accounting Issues 514 2.3.1. Attributes allowed in an Interim Update 516 [RFC2866] indicates that Acct-Input-Octets, Acct-Output-Octets, Acct- 517 Session-Time, Acct-Input-Packets, Acct-Output-Packets and Acct- 518 Terminate-Cause attributes "can only be present in Accounting-Request 519 records where the Acct-Status-Type is set to Stop." 521 However [RFC2869] Section 2.1 states: 523 It is envisioned that an Interim Accounting record (with Acct- 524 Status-Type = Interim-Update (3)) would contain all of the 525 attributes normally found in an Accounting Stop message with the 526 exception of the Acct-Term-Cause attribute. 528 Although [RFC2869] does not indicate that it updates [RFC2866], this 529 is an oversight, and the above attributes are allowable in an Interim 530 Accounting record. 532 2.3.2. Acct-Session-Id and Acct-Multi-Session-Id 534 [RFC2866] Section 5.5 describes Acct-Session-Id as Text within the 535 figure summarizing the attribute format, but then goes to state that 536 "The String field SHOULD be a string of UTF-8 encoded 10646 537 characters." 539 [RFC2865] defines the "Text" type as "containing UTF-8 encoded 10646 540 characters", which is compatible with the description of Acct- 541 Session-Id. Since other attributes are consistently described as 542 "Text" within both the figure summarizing the attribute format, and 543 the following attribute definition, it appears that this is a 544 typographical error, and that Acct-Session-Id is of type Text, and 545 not of type String. 547 The definition of the Acct-Multi-Session-Id attribute also has 548 typographical errors. It says 550 A summary of the Acct-Session-Id attribute format ... 552 This text should read 554 A summary of the Acct-Multi-Session-Id attribute format ... 556 The Acct-Multi-Session-Id attribute is also defined as being of type 557 "String". However, the language in the text strongly recommends that 558 implementors consider the attribute as being of type "Text". It is 559 unclear why the type "String" was chosen for this attribute when the 560 type "Text" would be sufficient. This attribute SHOULD be treated as 561 "Text". 563 2.3.3. Request Authenticator 565 [RFC2866] Section 4.1 states: 567 The Request Authenticator of an Accounting-Request contains a 568 16-octet MD5 hash value calculated according to the method 569 described in "Request Authenticator" above. 571 However, the text does not indicate any action to take when an 572 Accounting-Request packet contains an invalid Request Authenticator. 573 The following text should be considered to be part of the above 574 description: 576 The Request Authenticator field MUST contain the correct data, as 577 given by the above calculation. Invalid packets are silently 578 discarded. Note that some early implementations always set the 579 Request Authenticator to all zeros. New implementations of RADIUS 580 clients MUST use the above algorithm to calculate the Request 581 Authenticator field. New RADIUS server implementations MUST 582 silently discard invalid packets. 584 2.3.4. Interim-Accounting-Interval 586 [RFC2869] Section 2.1 states: 588 It is also possible to statically configure an interim value on 589 the NAS itself. Note that a locally configured value on the NAS 590 MUST override the value found in an Access-Accept. 592 This requirement may be phrased too strongly. It is conceivable that 593 a NAS implementation has a setting for a "minimum" value of Interim- 594 Accounting-Interval, based on resource constraints in the NAS, and 595 network loading in the local environment of the NAS. In such cases, 596 the value administratively provisioned in the NAS should not be over- 597 ridden by a smaller value from an Access-Accept message. The NAS's 598 value could be over-ridden by a larger one, however. The intent is 599 that the NAS sends accounting information at fixed intervals, short 600 enough such that the potential loss of billable revenue is limited, 601 but also that the accounting updates are infrequent enough such that 602 the NAS, network, and RADIUS server are not overloaded. 604 2.3.5. Counter values in the RADIUS Management Information Base (MIB) 606 The RADIUS Authentication and Authorization Client MIB module 607 [RFC2618], [RFC4668] includes counters of packet statistics. In the 608 descriptive text of the MIB module, formulas are provided for certain 609 counter objects. Implementors have noted apparent inconsistencies in 610 the formulas, which could result in negative values. 612 Since the original MIB module specified in [RFC2618] had been widely 613 implemented, the RADEXT WG chose not to change the object definitions 614 or to create new ones within the revised MIB module [RFC4668]. 615 However, this section explains the issues and provides guidance for 616 implementors regarding the interpretation of the textual description 617 and comments for certain MIB objects. 619 The issues raised can be summarized as follows: 621 Issue (1): 623 -- TotalIncomingPackets = Accepts + Rejects + Challenges + 624 UnknownTypes 625 -- 626 -- TotalIncomingPackets - MalformedResponses - BadAuthenticators - 627 -- UnknownTypes - PacketsDropped = Successfully received 628 -- 629 -- AccessRequests + PendingRequests + ClientTimeouts = 630 -- Successfully Received 632 It appears that the value of "Successfully Received" could be 633 negative, since various counters are subtracted from 634 TotalIncomingPackets that are not included in the calculation of 635 TotalIncomingPackets. 637 It also appears that "AccessRequests + PendingRequests + 638 ClientTimeouts = Successfully Received" should read "AccessRequests + 639 PendingRequests + ClientTimeouts = Successfully Transmitted". 641 "TotalIncomingPackets" and "Successfully Received" are temporary 642 variables, i.e. not objects within the MIB module. The comment text 643 in the MIB modules is intended, therefore, to aid in understanding. 644 What's of consequence is the consistency of values of the objects in 645 the MIB module, and that does not appear to be impacted by the 646 inconsistencies noted above. It does appear, however, that the 647 "Successfully Received" variable should be labeled "Successfully 648 Transmitted". 650 In addition, the definition of Accept, Reject or Challenge counters 651 indicates that they MUST be incremented before the message is 652 validated. If the message is invalid, one of MalformedResponses, 653 BadAuthenticators or PacketsDropped counters will be additionally 654 incremented. In that case the first two equations are consistent, 655 i.e. "Successfully Received" could not be negative. 657 Issue (2): 659 It appears that the radiusAuthClientPendingRequests counter is 660 decremented upon retransmission. That would mean a retransmitted 661 packet is not considered as being as pending, although such 662 retransmissions can still be considered as being pending requests. 664 The definition of this MIB object in [RFC2618] is as follows: 666 The number of RADIUS Access-Request packets destined for this 667 server that have not yet timed out or received a response. This 668 variable is incremented when an Access-Request is sent and 669 decremented due to receipt of an Access-Accept, Access-Reject or 670 Access-Challenge, a timeout or retransmission. 672 This object purports to count the number of pending request packets. 673 It is open to interpretation whether or not retransmissions of a 674 request are to be counted as additional pending packets. In either 675 event, it seems appropriate to treat retransmissions consistently 676 with respect to incrementing and decrementing this counter. 678 2.4. Multiple Filter-ID Attributes 680 [RFC2865] Section 5.11 states: 682 Zero or more Filter-Id attributes MAY be sent in an Access-Accept 683 packet. 685 In practice the behavior of a RADIUS client receiving multiple 686 Filter-ID attributes is implementation dependent. For example, some 687 implementations treat multiple instances of the Filter-ID attribute 688 as alternative filters; the first Filter-ID attribute having a name 689 matching a locally defined filter is used, and the remaining ones are 690 discarded. Other implementations may combine matching filters. 692 As a result, the interpretation of multiple Filter-ID attributes is 693 undefined within RADIUS. The sending of multiple Filter-ID 694 attributes within an Access-Accept SHOULD be avoided within 695 heterogeneous deployments and roaming scenarios, where it is likely 696 to produce unpredictable results. 698 2.5. Mandatory and Optional Attributes 700 RADIUS attributes do not explicitly state whether they are optional 701 or mandatory. Nevertheless there are instances where RADIUS 702 attributes need to be treated as mandatory. 704 [RFC2865] Section 1.1 states: 706 A NAS that does not implement a given service MUST NOT implement 707 the RADIUS attributes for that service. For example, a NAS that 708 is unable to offer Apple Remote Access Protocol (ARAP) service 709 MUST NOT implement the RADIUS attributes for ARAP. A NAS MUST 710 treat a RADIUS access-accept authorizing an unavailable service as 711 an access-reject instead. 713 With respect to the Service-Type attribute, [RFC2865] Section 5.6 714 says: 716 This Attribute indicates the type of service the user has 717 requested, or the type of service to be provided. It MAY be used 718 in both Access-Request and Access-Accept packets. A NAS is not 719 required to implement all of these service types, and MUST treat 720 unknown or unsupported Service-Types as though an Access-Reject 721 had been received instead. 723 [RFC2865] Section 5 states: 725 A RADIUS server MAY ignore Attributes with an unknown Type. 727 A RADIUS client MAY ignore Attributes with an unknown Type. 729 With respect to Vendor-Specific Attributes (VSAs), [RFC2865] Section 730 5.26 states: 732 Servers not equipped to interpret the vendor-specific information 733 sent by a client MUST ignore it (although it may be reported). 734 Clients which do not receive desired vendor-specific information 735 SHOULD make an attempt to operate without it, although they may do 736 so (and report they are doing so) in a degraded mode. 738 It is possible for either a standard attribute or VSA to represent a 739 request for an unavailable service. However, where the Type, Vendor- 740 ID, or Vendor-Type is unknown, a RADIUS client will not know whether 741 the attribute defines a service or not. 743 In general, it is best for a RADIUS clients to err on the side of 744 caution. On receiving an Access-Accept including an attribute of 745 known Type for an unimplemented service, a RADIUS client MUST treat 746 it as an Access-Reject, as directed in [RFC2865] Section 1.1. On 747 receiving an Access-Accept including an attribute of unknown Type, a 748 RADIUS client SHOULD assume that it is a potential service 749 definition, and treat it as an Access-Reject. Unknown VSAs SHOULD be 750 ignored by RADIUS clients. 752 In order to avoid introducing changes in default behavior, existing 753 implementations that do not obey this recommendation should make the 754 behavior configurable, with the legacy behavior being enabled by 755 default. A configuration flag such as "treat unknown attributes as 756 reject" can be exposed to the system administrator. If the flag is 757 set to true, then Access-Accepts containing unknown attributes are 758 treated as Access-Rejects. If the flag is set to false, then unknown 759 attributes in Access-Accepts are be silently ignored. 761 On receiving a packet including an attribute of unknown type, RADIUS 762 authentication server implementations SHOULD ignore such attributes. 763 However, RADIUS accounting server implementations typically do not 764 need to understand attributes in order to write them to stable 765 storage or pass them to the billing engine. Therefore, accounting 766 server implementations SHOULD be equipped to handle unknown 767 attributes. 769 To avoid misinterpretation of service requests encoded within VSAs, 770 RADIUS servers SHOULD NOT send VSAs containing service requests to 771 RADIUS clients that are not known to understand them. For example, a 772 RADIUS server should not send a VSA encoding a filter without 773 knowledge that the RADIUS client supports the VSA. 775 2.6. Interpretation of Access-Reject 777 2.6.1. Improper Use of Access-Reject 779 The intent of an Access-Reject is to deny access to the requested 780 service. [RFC2865] Section 2 states: 782 If any condition is not met, the RADIUS server sends an "Access- 783 Reject" response indicating that this user request is invalid. If 784 desired, the server MAY include a text message in the Access- 785 Reject which MAY be displayed by the client to the user. No other 786 Attributes (except Proxy-State) are permitted in an Access-Reject. 788 This text makes it clear that RADIUS does not allow the provisioning 789 of services within an Access-Reject. If the desire is to allow 790 limited access, then an Access-Accept can be sent with attributes 791 provisioning limited access. Attributes within an Access-Reject are 792 restricted to those necessary to route the message (e.g. Proxy- 793 State), attributes providing the user with an indication that access 794 has been denied (e.g. an EAP-Message attribute containing an EAP- 795 Failure) or attributes conveying an error message (e.g. a Reply- 796 Message or Error-Cause attribute). 798 Unfortunately, there are examples where this requirement has been 799 misunderstood. [RFC2869] Section 2.2 states: 801 If that authentication fails, the RADIUS server should return an 802 Access-Reject packet to the NAS, with optional Password-Retry and 803 Reply-Messages attributes. The presence of Password-Retry 804 indicates the ARAP NAS MAY choose to initiate another challenge- 805 response cycle, 807 This paragraph is problematic from two perspectives. Firstly, a 808 Password-Retry attribute is being returned in an Access-Reject; this 809 attribute does not fit into the categories established in [RFC2865]. 810 Secondly, an Access-Reject packet is being sent in the context of a 811 continuing authentication conversation; [RFC2865] requires use of an 812 Access-Challenge for this. [RFC2869] uses the phrase "challenge- 813 response" to describe this use of Access-Reject, indicating that the 814 semantics of Access-Challenge are being used. 816 [RFC2865] Section 4.4, addresses the semantics of Access-Challenge 817 being equivalent to Access-Reject in some cases: 819 If the NAS does not support challenge/response, it MUST treat an 820 Access-Challenge as though it had received an Access-Reject 821 instead. 823 While it is difficult to correct existing deployments of [RFC2869], 824 we make the following recommendations: 826 [1] New RADIUS specifications and implementations MUST NOT use Access- 827 Reject where the semantics of Access-Challenge are intended. 829 [2] Access-Reject MUST mean denial of access to the requested service. 830 In response to an Access-Reject, the NAS MUST NOT send any 831 additional Access-Request packets for that user session. 833 [3] New deployments of ARAP [RFC2869] SHOULD use Access-Challenge 834 instead of Access-Reject packets in the conversations described in 835 [RFC2869] Section 2.2. 837 We also note that the table of attributes [RFC2869] Section 5.19 has 838 an error for the Password-Retry attribute. It says: 840 Request Accept Reject Challenge # Attribute 841 0 0 0-1 0 75 Password-Retry 842 However, the text in [RFC2869] Section 2.3.2 says that Password-Retry 843 can be included within an Access-Challenge packet, for EAP 844 authentication sessions. We recommend a correction to the table, 845 which removes the "0-1" from the Reject column, moves it to the 846 Challenge column. We also add a "Note 2" to follow the existing 847 "Note 1" in the document, to clarify the use of this attribute. 849 Request Accept Reject Challenge # Attribute 850 0 0 0 0-1 75 Password-Retry [Note 2] 852 [Note 2] As per RFC 3579, the use of the Password-Retry in EAP 853 authentications is deprecated. The Password-Retry attribute can be 854 used only for ARAP authentication. 856 2.6.2. Service Request Denial 858 RADIUS has been deployed for purposes outside network access 859 authentication, authorization and accounting. For example, RADIUS 860 has been deployed as a "back-end" for authenticating Voice Over IP 861 (VOIP) connections, Hypertext Transfer Protocol (HTTP) sessions (e.g. 862 Apache), File Transfer Protocol (FTP) sessions (e.g. proftpd), and 863 machine logins for multiple operating systems (e.g. bsdi, pam, gina). 864 In those contexts, an Access-Reject sent to the RADIUS client MUST be 865 interpreted as a rejection of the request for service, and the RADIUS 866 client MUST NOT offer that service to the user. 868 For example, when an authentication failure occurs in the context of 869 an FTP session, the normal semantics for rejecting FTP services 870 apply. The rejection does not necessarily cause the FTP server to 871 terminate the underlying TCP connection, but the FTP server MUST NOT 872 offer any services protected by user authentication. 874 Users may request multiple services from the NAS. Where those 875 services are independent, the deployment MUST treat the RADIUS 876 sessions as being independent. 878 For example, a NAS may offer multi-link services, where a user may 879 have multiple simultaneous network connections. In that case, an 880 Access-Reject for a later multi-link connection request does not 881 necessarily mean that earlier multi-link connections are torn down. 882 Similarly, if a NAS offers both dialup and VOIP services, the 883 rejection of a VOIP attempt does not mean that the dialup session is 884 torn down. 886 2.7. Addressing 887 2.7.1. Link-Local Addresses 889 Since Link-Local addresses are unique only on the local link, if the 890 NAS and RADIUS server are not on the same link, then an IPv6 Link- 891 Local address [RFC2462] or an IPv4 Link-Local Address [RFC3927] 892 cannot be used to uniquely identify the NAS. A NAS SHOULD NOT 893 utilize a link-scope address within a NAS-IPv6-Address or NAS-IP- 894 Address attributes. A RADIUS server receiving a NAS-IPv6-Address or 895 NAS-IP-Address attribute containing a Link-Local address SHOULD NOT 896 count such an attribute toward satisfying the requirements of 897 [RFC3162] Section 2.1: 899 NAS-IPv6-Address and/or NAS-IP-Address MAY be present in an 900 Access-Request packet; however, if neither attribute is present 901 then NAS-Identifier MUST be present. 903 2.7.2. Multiple Addresses 905 There are situations in which a RADIUS client or server may have 906 multiple addresses. For example, a dual stack host can have both 907 IPv4 and IPv6 addresses; a host that is a member of multiple VLANs 908 could have IPv4 and/or IPv6 addresses on each VLAN; a host can have 909 multiple IPv4 or IPv6 addresses on a single interface. However, 910 [RFC2865] Section 5.44 only permits zero or one NAS-IP-Address 911 attribute within an Access-Request and [RFC3162] Section 3 only 912 permits zero or one NAS-IPv6-Address attribute within an Access- 913 Request. When a NAS has more than one global address and no ability 914 to determine which is used for identification in a particular 915 request, it is RECOMMENDED that the NAS include the NAS-Identifier 916 attribute in an Access-Request in order to identify itself to the 917 RADIUS server. 919 [RFC2865] Section 3 states: 921 A RADIUS server MUST use the source IP address of the RADIUS 922 UDP packet to decide which shared secret to use, so that 923 RADIUS requests can be proxied. 925 Therefore if a RADIUS client sends packets from more than one source 926 address, a shared secret will need to be configured on both the 927 client and server for each source address. 929 2.8. Idle-Timeout 931 With respect to the Idle-Timeout attribute, [RFC2865] Section 5.28 932 states: 934 This Attribute sets the maximum number of consecutive seconds of 935 idle connection allowed to the user before termination of the 936 session or prompt. This Attribute is available to be sent by the 937 server to the client in an Access-Accept or Access-Challenge. 939 [RFC3580] Section 3.12 states: 941 The Idle-Timeout attribute is described in [RFC2865]. For IEEE 942 802 media other than 802.11 the media are always on. As a result 943 the Idle-Timeout attribute is typically only used with wireless 944 media such as IEEE 802.11. It is possible for a wireless device 945 to wander out of range of all Access Points. In this case, the 946 Idle-Timeout attribute indicates the maximum time that a wireless 947 device may remain idle. 949 In the above paragraphs "idle" may not necessarily mean "no traffic"; 950 the NAS may support filters defining what traffic is included in the 951 idle time determination. As a result, an "idle connection" is 952 defined by local policy in the absence of other attributes. 954 2.9. Unknown Identity 956 [RFC3748] Section 5.1 states: 958 If the Identity is unknown, the Identity Response field 959 should be zero bytes in length. 961 However, [RFC2865] Section 5.1 describes the User-Name attribute as 962 follows: 964 The String field is one or more octets. 966 How should the RADIUS client behave if it receives an EAP- 967 Response/Identity that is zero octets in length? 969 [RFC2865] Section 5.1 states: 971 This Attribute indicates the name of the user to be authenticated. 972 It MUST be sent in Access-Request packets if available. 974 This suggests that the User-Name attribute may be ommitted if it is 975 unavailable. 977 However, [RFC3579] Section 2.1 states: 979 In order to permit non-EAP aware RADIUS proxies to forward the 980 Access-Request packet, if the NAS initially sends an 981 EAP-Request/Identity message to the peer, the NAS MUST copy the 982 contents of the Type-Data field of the EAP-Response/Identity 983 received from the peer into the User-Name attribute and MUST 984 include the Type-Data field of the EAP-Response/Identity in the 985 User-Name attribute in every subsequent Access-Request. 987 This suggests that the User-Name attribute should contain the 988 contents of the Type-Data field of the EAP-Response/Identity, even if 989 it is zero octets in length. 991 Note that [RFC4282] does not permit a Network Access Identifier (NAI) 992 of zero octets, so that an EAP-Response/Identity with a Type-Data 993 field of zero octets MUST NOT be construed as a request for privacy 994 (e.g. anonymous NAI). 996 When a NAS receives an EAP-Response/Identity with a Type-Data field 997 that is zero octets in length, it is RECOMMENDED that it either omit 998 the User-Name attribute in the Access-Request or include the Calling- 999 Station-Id in the User-Name attribute, along with a Calling-Station- 1000 Id attribute. 1002 2.10. Responses after retransmissions 1004 Some implementations do not correctly handle the receipt of RADIUS 1005 responses after retransmissions. [RFC2865] Section 2.5 states 1007 If the NAS is retransmitting a RADIUS request to the same server 1008 as before, and the attributes haven't changed, you MUST use the 1009 same Request Authenticator, ID, and source port. If any 1010 attributes have changed, you MUST use a new Request Authenticator 1011 and ID. 1013 Note that changing the Request ID for a retransmission may have 1014 undesirable side effects. Since RADIUS does not have a clear 1015 definition of a "session", it is perfectly valid for a RADIUS server 1016 to treat a retransmission as a new session request, and to reject it 1017 due to (say) multiple simultaneous login restrictions are enforced. 1018 In that situation, the NAS may receive a belated Access-Accept for 1019 the first request, and an Access-Reject for the retransmitted 1020 request, both of which apply to the same "session". 1022 We suggest that the contents of Access-Request packets SHOULD NOT be 1023 changed during retransmissions. If they must be changed due to the 1024 inclusion of an Event-Timestampt attribute, for example, then 1025 responses to earlier transmissions MUST be silently discarded. Any 1026 response to the current request MUST be treated as the definitive 1027 response, even if as noted above, it disagrees with earlier 1028 responses. 1030 This problem can be made worse by implementations that use a fixed 1031 retransmission timeout (30 seconds is common). We reiterate the 1032 suggestions above in Section 2.1 about using congestive backoff. In 1033 that case, responses to earlier transmissions MAY be used as data 1034 points for congestive backoff, even if their contents are discarded. 1036 2.11. Framed-IPv6-Prefix 1038 [RFC3162] Section 2.3 says 1040 This Attribute indicates an IPv6 prefix (and corresponding route) 1041 to be configured for the user. It MAY be used in Access-Accept 1042 packets, and can appear multiple times. It MAY be used in an 1043 Access-Request packet as a hint by the NAS to the server that it 1044 would prefer these prefix(es), but the server is not required to 1045 honor the hint. Since it is assumed that the NAS will plumb a 1046 route corresponding to the prefix, it is not necessary for the 1047 server to also send a Framed-IPv6-Route attribute for the same 1048 prefix. 1050 An Internet Service Provider (ISP) may desire to support Prefix 1051 Delegation [RFC4818] at the same time that it would like to assign a 1052 prefix for the link between the NAS and the user. The intent of the 1053 paragraph was to enable the NAS to advertise the prefix (such as via 1054 a Router Advertisement). If the Framed-Routing attribute is used, it 1055 is also possible that the prefix would be advertised in a routing 1056 protocol such as RIPNG. RFC 2865 Section 5.10 describes the purpose 1057 of Framed-Routing: 1059 This Attribute indicates the routing method for the user, when the 1060 user is a router to a network. It is only used in Access-Accept 1061 packets. 1063 The description of the Prefix-Length field in RFC 3162 indicates 1064 excessively wide latitude: 1066 The length of the prefix, in bits. At least 0 and no larger than 1067 128. 1069 This length appears too broad, because it is not clear what a NAS 1070 should do with a prefix of greater granularity than /64. For example, 1071 the Framed-IPv6-Prefix may contain a /128. This does not imply that 1072 the NAS should assign an IPv6 address to the end user, because RFC 1073 3162 already defines a Framed-IPv6-Identifier attribute to handle the 1074 Identifier portion. 1076 It appears that the Framed-IPv6-Prefix is used for the link between 1077 the NAS and CPE only if a /64 prefix is assigned. When a /64 or 1078 larger prefix is sent, the intent is for the NAS to send a routing 1079 advertisement containing the information present in the Framed- 1080 IPv6-Prefix attribute. 1082 The CPE may also require a delegated prefix for its own use, if it is 1083 decrementing the Time To Live (TTL) field of IP headers. In that 1084 case, it should be delegated a prefix by the NAS via the Delegated- 1085 IPv6-Prefix attribute. [RFC4818]. If the CPE is not decrementing 1086 TTL, it does not require a delegated prefix. 1088 3. IANA Considerations 1090 This specification does not create any new registries, nor does it 1091 require assignment of any protocol parameters. 1093 4. Security Considerations 1095 The contents of the State attribute are available to both the RADIUS 1096 client and observers of the RADIUS protocol. RADIUS server 1097 implementations should ensure that the state attribute does not 1098 disclose sensitive information to a RADIUS client or third parties 1099 observing the RADIUS protocol. 1101 The cache mechanism described in Section 2.2.2 is vulnerable to 1102 attacks when Access-Request packets do not contain a Message- 1103 Authenticator attribute. If the server accepts requests without a 1104 Message-Authenticator, then RADIUS packets can be trivially forged by 1105 an attacker. Cache entries can then be forcibly expired, negating 1106 the utility of the cache. This attack can be mitigated by following 1107 the suggestions in [RFC3579] Section 4, or by requiring the presence 1108 of Message-Authenticator, as described in Sections 2.1.1 and 2.2.2. 1110 Since this document describes the use of RADIUS for purposes of 1111 authentication, authorization, and accounting in a wide variety of 1112 networks, applications using these specifications are vulnerable to 1113 all of the threats that are present in other RADIUS applications. 1114 For a discussion of these threats, see [RFC2865], [RFC2607], 1115 [RFC3162], [RFC3579], and [RFC3580]. 1117 5. References 1119 5.1. Normative references 1121 [RFC2865] 1122 Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote 1123 Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. 1125 [RFC4818] 1126 Salowey, J., Droms., R, "RADIUS Delegated-IPv6-Prefix Attribute", 1127 RFC 4818, April 2007. 1129 5.2. Informative references 1131 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1132 Requirement Levels", RFC 2119, March, 1997. 1134 [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address 1135 Autoconfiguration", RFC 2462, December 1998. 1137 [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy 1138 Implementation in Roaming", RFC 2607, June 1999. 1140 [RFC2618] Aboba, B. and G. Zorn, "RADIUS Authentication Client MIB", RFC 1141 2618, June 1999. 1143 [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. 1145 [RFC2869] Rigney, C., Willats, W. and P. Calhoun, "RADIUS Extensions", 1146 RFC 2869, June 2000. 1148 [RFC3162] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 1149 3162, August 2001. 1151 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. 1152 Carney, "Dynamic Host Configuration Protocol for IPv6 1153 (DHCPv6)", RFC 3315, July 2003. 1155 [RFC3576] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba, 1156 "Dynamic Authorization Extensions to Remote Authentication 1157 Dial In User Service (RADIUS)", RFC 3576, July 2003. 1159 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS Support for Extensible 1160 Authentication Protocol (EAP)", RFC 3579, September 2003. 1162 [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese, 1163 "IEEE 802.1X Remote Authentication Dial In User Service 1164 (RADIUS) Usage Guidelines", RFC 3580, September 2003. 1166 [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. 1167 Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 1168 3748, June 2004. 1170 [RFC3927] Cheshire, S., Aboba, B. and E. Guttman, "Dynamic Configuration 1171 of IPv4 Link-Local Addresses", RFC 3927, May 2005. 1173 [RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network 1174 Access Identifier", RFC 4282, December 2005. 1176 [RFC4668] Nelson, D, "RADIUS Authentication Client MIB for IPv6", RFC 1177 4668, August 2006. 1179 [RFC4669] Nelson, D, "RADIUS Authentication Server MIB for IPv6", RFC 1180 4669, August 2006. 1182 Acknowledgments 1184 The authors would like to acknowledge Glen Zorn and Bernard Aboba for 1185 contributions to this document. 1187 The alternate algorithm to [RFC3579] Section 2.6.1 that is described 1188 in section 2.1.2 of this document was designed by Raghu Dendukuri. 1190 The text discussing retransmissions in Section 2.2.1 is taken with 1191 minor edits from Section 9 of draft-ietf-pana-pana-17.txt 1193 Alan DeKok wishes to acknowledge the support of Quiconnect Inc., 1194 where he was employed during much of the work on this document. 1196 David Nelson wishes to acknowledge the support of Enterasys Networks, 1197 where he was employed during much of the work on this document. 1199 Authors' Addresses 1201 David B. Nelson 1202 Elbrys Networks, Inc. 1203 75 Rochester Ave., Unit 3 1204 Portsmouth N.H. 03801 USA 1206 Phone: +1.603.570.2636 1208 Email: d.b.nelson@comcast.net 1210 Alan DeKok 1211 The FreeRADIUS Server Project 1212 http://freeradius.org/ 1214 Email: aland@freeradius.org 1216 Intellectual Property Statement 1218 The IETF takes no position regarding the validity or scope of any 1219 Intellectual Property Rights or other rights that might be claimed to 1220 pertain to the implementation or use of the technology described in 1221 this document or the extent to which any license under such rights 1222 might or might not be available; nor does it represent that it has 1223 made any independent effort to identify any such rights. 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Please address the information to the IETF at ietf- 1238 ipr@ietf.org. 1240 Disclaimer of Validity 1242 This document and the information contained herein are provided on an 1243 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1244 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1245 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1246 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1247 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1248 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1250 Full Copyright Statement 1252 Copyright (C) The IETF Trust (2007). 1254 This document is subject to the rights, licenses and restrictions 1255 contained in BCP 78, and except as set forth therein, the authors 1256 retain all their rights. 1258 Acknowledgment 1260 Funding for the RFC Editor function is currently provided by the 1261 Internet Society. 1263 Open issues 1265 Open issues relating to this specification are tracked on the 1266 following web site: 1268 http://www.drizzle.com/~aboba/RADEXT/