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Weber 5 Individual Contributor 6 Expires: January 7, 2011 7 7 June 2010 9 RADIUS Design Guidelines 10 draft-ietf-radext-design-14 12 Abstract 14 This document provides guidelines for the design of attributes used 15 by the Remote Authentication Dial In User Service (RADIUS) protocol. 16 It is expected that these guidelines will prove useful to authors and 17 reviewers of future RADIUS attribute specifications, both within the 18 IETF as well as other Standards Development Organizations (SDOs). 20 Status of this Memo 22 This Internet-Draft is submitted to IETF in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF), its areas, and its working groups. Note that 27 other groups may also distribute working documents as Internet- 28 Drafts. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 The list of current Internet-Drafts can be accessed at 36 http://www.ietf.org/ietf/1id-abstracts.txt. 38 The list of Internet-Draft Shadow Directories can be accessed at 39 http://www.ietf.org/shadow.html. 41 This Internet-Draft will expire on January 7, 2011. 43 Copyright Notice 45 Copyright (c) 2010 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info/) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 This document may contain material from IETF Documents or IETF 59 Contributions published or made publicly available before November 60 10, 2008. The person(s) controlling the copyright in some of this 61 material may not have granted the IETF Trust the right to allow 62 modifications of such material outside the IETF Standards Process. 63 Without obtaining an adequate license from the person(s) controlling 64 the copyright in such materials, this document may not be modified 65 outside the IETF Standards Process, and derivative works of it may 66 not be created outside the IETF Standards Process, except to format 67 it for publication as an RFC or to translate it into languages other 68 than English. 70 Table of Contents 72 1. Introduction ............................................. 5 73 1.1. Terminology ......................................... 5 74 1.2. Requirements Language ............................... 6 75 1.3. Applicability ....................................... 6 76 2. Guidelines ............................................... 7 77 2.1. Data Types .......................................... 8 78 2.2. Vendor-Specific Attribute Space ..................... 9 79 2.3. Service definitions and RADIUS ...................... 10 80 2.4. Translation of Vendor Specifications ................ 11 81 3. Rationale ................................................ 11 82 3.1. RADIUS Operational Model ............................ 11 83 3.2. Data Model Issues ................................... 14 84 3.2.1. Basic Data Types ............................... 15 85 3.2.2. Tagging Mechanism .............................. 16 86 3.2.3. Complex Data Types ............................. 17 87 3.3. Vendor Space ........................................ 20 88 3.3.1. Interoperability Considerations ................ 21 89 3.3.2. Vendor Allocations ............................. 21 90 3.3.3. SDO Allocations ................................ 22 91 3.3.4. Publication of specifications .................. 22 92 3.4. Polymorphic Attributes .............................. 23 93 4. IANA Considerations ...................................... 24 94 5. Security Considerations .................................. 24 95 5.1. New Data Types and Complex Attributes ............... 25 96 6. References ............................................... 26 97 6.1. Normative References ................................ 26 98 6.2. Informative References .............................. 26 99 Appendix A - Design Guidelines ............................... 29 100 A.1. Types matching the RADIUS data model ................. 29 101 A.1.1. Transport of basic data types ................... 29 102 A.1.2. Transport of Authentication and Security Data ... 30 103 A.1.3. Opaque data types ............................... 30 104 A.1.4. Pre-existing data types ......................... 30 105 A.2. Improper Data Types .................................. 31 106 A.2.1. Basic Data Types ................................ 31 107 A.2.2. Complex Data Types .............................. 32 108 A.3. Vendor-Specific formats .............................. 32 109 A.4. Changes to the RADIUS Operational Model .............. 33 110 A.5. Allocation of attributes ............................. 34 111 Appendix B - Complex Attributes .............................. 35 112 B.1. CHAP-Password ........................................ 35 113 B.2. CHAP-Challenge ....................................... 35 114 B.3. Tunnel-Password ...................................... 35 115 B.4. ARAP-Password ........................................ 36 116 B.5. ARAP-Features ........................................ 36 117 B.6. Connect-Info ......................................... 37 118 B.7. Framed-IPv6-Prefix ................................... 38 119 B.8. Egress-VLANID ........................................ 38 120 B.9. Egress-VLAN-Name ..................................... 39 121 B.9. Digest-* ............................................. 39 123 1. Introduction 125 This document provides guidelines for the design of RADIUS attributes 126 both within the IETF as well as within other SDOs. By articulating 127 RADIUS design guidelines, it is hoped that this document will 128 encourage the development and publication of high quality RADIUS 129 attribute specifications. 131 However, the advice in this document will not be helpful unless it is 132 put to use. As with "Guidelines for Authors and Reviewers of MIB 133 Documents" [RFC4181], it is expected that this document will be used 134 by authors to check their document against the guidelines prior to 135 publication, or requesting review (such as an "Expert Review" 136 described in [RFC3575]). Similarly, it is expected that this 137 document will used by reviewers (such as WG participants or the AAA 138 Doctors [DOCTORS]), resulting in an improvement in the consistency of 139 reviews. 141 In order to meet these objectives, this document needs to cover not 142 only the science of attribute design, but also the art. Therefore, 143 in addition to covering the most frequently encountered issues, this 144 document explains some of the considerations motivating the 145 guidelines. These considerations include complexity trade-offs that 146 make it difficult to provide "hard and fast" rules for attribute 147 design. This document explains those trade-offs through reviews of 148 current attribute usage. 150 1.1. Terminology 152 This document uses the following terms: 154 Network Access Server (NAS) 155 A device that provides an access service for a user to a network. 157 RADIUS server 158 A RADIUS authentication, authorization, and/or accounting (AAA) 159 server is an entity that provides one or more AAA services to a 160 NAS. 162 standard space 163 The 256 possible attributes that follow the format defined in 164 [RFC2865] Section 5. 166 vendor space 167 The contents of the "String" field of a Vendor-Specific Attribute 168 (VSA) ([RFC2865] Section 5.26). 170 1.2. Requirements Language 172 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 173 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 174 document are to be interpreted as described in [RFC2119]. 176 We emphasize that the uses of "MUST" and "MUST NOT" in this document 177 are limited to requirements to follow the IETF process for IETF 178 standards, and quotes from other documents. As a result, the uses of 179 "MUST" and "MUST NOT" in this document do not prescribe new mandatory 180 behavior within implementations. 182 1.3. Applicability 184 The reviews and advice in this document applies to attributes used to 185 encode service-provisioning, authentication, or accounting data, 186 based on the attribute encodings and data formats defined in RFC 2865 187 and subsequent RADIUS RFCs. It is RECOMMENDED that these guidelines 188 be followed for all new RADIUS specifications, whether they originate 189 from a vendor, an SDO, or the IETF. Doing so will ensure the widest 190 possible applicability and interoperability of the specifications, 191 while requiring minimal changes to existing systems. 193 When new attributes are defined, they can be classified into one of 194 three broad categories: 196 * Attributes that are of interest to a single vendor, e.g., for a 197 product or product line. Minimal cross-vendor interoperability 198 is needed. 200 Vendor-Specific Attributes (VSAs) MUST be used. Code-point 201 allocation is managed by the vendor with the number space 202 defined by their Private Enterprise Number (PEN). 204 * Attributes that are of interest to an industry segment, where an 205 SDO defines the attributes for that industry. Multi-vendor 206 interoperability within an industry segment is expected. 208 Vendor-Specific Attributes (VSAs) MUST be used. Code-point 209 allocation is managed by the SDO with the number space defined 210 by the SDOs PEN, rather then the PEN of an individual vendor. 212 * Attributes that are of broad interest to the Internet Community. 213 Global Internet multi-vendor interoperability is expected. 215 Standard (i.e. non-VSA) Attributes SHOULD be used. All code- 216 point allocation for Standard Attributes MUST be done via IANA, 217 and MUST follow "IETF consensus", as discussed in [RFC3575]. 219 Strict conformance with the design guidelines is expected, 220 unless a good case can be made for an exception. Those tasked 221 with reviewing the proposals SHOULD use the design guidelines as 222 a review checklist. 224 IETF review is RECOMMENDED for all RADIUS specifications, as 225 experience has shown that attributes not originally designed for 226 general usage can subsequently garner wide-spread deployment. An 227 example is the vendor-specific attributes defined in [RFC2548], which 228 have been widely implemented within IEEE 802.11 Access Points. See 229 Section 3.3.4 for instructions on the review process. 231 IETF review of a specification MAY be avoided when it satisfies all 232 of the following criteria: 234 * it is not intended for publication as an IETF RFC; 236 * it references pre-existing attributes from IETF or SDO 237 specifications; 239 * it defines new attributes only in the VSA space; 241 * it uses only the "basic data types" (see Section 2.1) for all 242 VSAs; 244 * it follows the guidelines given in this document. 246 We recognize that SDOs and vendors may still choose to create 247 specifications not following these guidelines. We do not forbid that 248 practice, though it is NOT RECOMMENDED. 250 RADIUS protocol changes, or specification of attributes (such as 251 Service-Type) that can, in effect, provide new RADIUS commands 252 require greater expertise and deeper review, as do changes to the 253 RADIUS operational model. As a result, such changes are outside the 254 scope of this document and MUST NOT be undertaken outside the IETF. 256 2. Guidelines 258 The Remote Authentication Dial In User Service (RADIUS) defined in 259 [RFC2865] and [RFC2866] uses elements known as attributes in order to 260 represent authentication, authorization and accounting data. 262 Unlike SNMP, first defined in [RFC1157] and [RFC1155], RADIUS does 263 not define a formal data definition language. The data type of 264 RADIUS attributes is not transported on the wire. Rather, the data 265 type of a RADIUS attribute is fixed when an attribute is defined. 266 Based on the RADIUS attribute type code, RADIUS clients and servers 267 can determine the data type based on preconfigured entries within a 268 data dictionary. 270 To explain the implications of this early RADIUS design decision we 271 distinguish two types of data types, namely "basic" and "complex". 272 Basic data types use one of the existing RADIUS data types as defined 273 below, encapsulated in a [RFC2865] RADIUS attribute, or in a 274 [RFC2865] RADIUS VSA. All other data formats are "complex types". 276 RADIUS attributes are also divided into two distinct attribute 277 spaces: the "standard space", and a "Vendor-Specific Attribute 278 space". Attributes in the "standard space" follow the [RFC2865] 279 attribute encoding, with allocation managed by the Internet Assigned 280 Number Authority (IANA). Vendors MUST NOT "self-allocate" attributes 281 in this space, as they are not authoritative for it. 283 The VSA space is defined to be the contents of the "String" field of 284 the Vendor-Specific Attribute ([RFC2865] Section 5.26). Allocation 285 in this space is managed independently by each vendor. See Section 286 2.2, below, for a more in-depth discussion. 288 2.1. Data Types 290 RADIUS defines a limited set of data types, defined as "basic data 291 types". The following data qualifies as "basic data types": 293 * 32-bit unsigned integer, in network byte order. 295 * Enumerated data types, represented as a 32-bit unsigned integer 296 with a list of name to value mappings. (e.g. Service-Type) 298 * IPv4 address in network byte order. 300 * time as 32 bit unsigned value, in network byte order, and in 301 seconds since 00:00:00 UTC, January 1, 1970. 303 * IPv6 address in network byte order. 305 * Interface-Id (8 octet string in network byte order) 307 * IPv6 prefix. 309 * string (i.e., binary data), totalling 253 octets or less in 310 length. This includes the opaque encapsulation of data 311 structures defined outside of RADIUS. See also Appendix A.1.3, 312 below, for additional discussion. 314 * UTF-8 text, totalling 253 octets or less in length. 316 Note that the length limitations for VSAs of type String and Text are 317 less than 253 octets, due to the additional overhead of the Vendor- 318 Specific encoding. 320 The following data also qualifies as "basic data types": 322 * Attributes grouped into a logical container, using the 323 [RFC2868] tagging mechanism. This approach is NOT RECOMMENDED, 324 but is permissible where the alternatives are worse. 326 * Attributes requiring the transport of more than 253 octets of 327 Text or String data. This includes the opaque encapsulation 328 of data structures defined outside of RADIUS. 329 (e.g. EAP-Message) 331 All other data formats are defined to be "complex data types", and 332 are NOT RECOMMENDED for normal use. Nested attributes, or attributes 333 grouped via methods other than defined in [RFC2868] do not qualify as 334 "basic data types", and SHOULD NOT be used. 336 There may be situations where complex attributes are acceptable 337 because they reduce complexity in non-RADIUS systems, or because 338 leveraging the basic data types would be awkward. Unfortunately, 339 there are no "hard and fast" rules for where the complexity would 340 best be located. Each situation has to be decided on a case-by-case 341 basis. The cost-benefit trade-off may result in a "complex data 342 type" being defined in RADIUS, as discussed in Appendix B. When this 343 is done, an explanation SHOULD be offered as to why the complex data 344 type was used. 346 2.2. Vendor-Specific Attribute Space 348 The Vendor-Specific Attribute space is defined to be the contents of 349 the "String" field of the Vendor-Specific Attribute ([RFC2865] 350 Section 5.26). As discussed there, it is intended for vendors and 351 SDOs to support their own Attributes not suitable for general use. 352 It is RECOMMENDED that vendors and SDOs follow the guidelines 353 outlined here, which are intended to enable maximum interoperability 354 with minimal changes to existing systems. 356 Following these guidelines means that RADIUS servers can be updated 357 to support a new attribute by editing a RADIUS dictionary. If these 358 guidelines are not followed, then the new attribute can only be 359 supported via code changes in RADIUS server implementations. Such 360 code changes add complexity and delays to implementations. 362 Vendor RADIUS Attribute specifications SHOULD self-allocate 363 attributes from the vendor space, rather than asking the IETF and 364 IANA for an allocation from the RADIUS standard attribute space. 366 All data formats other than described above as "basic data types" are 367 NOT RECOMMENDED. These non-standard formats will typically not be 368 implementable without RADIUS server code changes. 370 All VSA encodings that do not follow the [RFC2865] Section 5.26 371 scheme are NOT RECOMMENDED. Although [RFC2865] does not mandate it, 372 implementations commonly assume that the Vendor Id can be used as a 373 key to determine the on-the-wire encoding of a VSA. Vendors 374 therefore SHOULD NOT use multiple encodings for VSAs that are 375 associated with a particular Vendor Id. A vendor wishing to use 376 multiple VSA encodings SHOULD request one Vendor Id for each VSA 377 encoding that they will use. 379 Notwithstanding the above recommendations, the encoding of the vendor 380 space is under the complete control of individual vendors and SDOs. 381 The guidelines outlined here are recommendations, and therefore do 382 not define any requirements or restrictions on the vendor space. 384 2.3. Service definitions and RADIUS 386 RADIUS specifications define how an existing service or protocol can 387 be provisioned using RADIUS. Therefore, it is expected that a RADIUS 388 attribute specification will reference documents defining the 389 protocol or service to be provisioned. Within the IETF, a RADIUS 390 attribute specification SHOULD NOT be used to define the protocol or 391 service being provisioned. New services using RADIUS for 392 provisioning SHOULD be defined elsewhere and referenced in the RADIUS 393 specification. 395 New attributes, or new values of existing attributes, SHOULD NOT be 396 used to define new RADIUS commands. RADIUS attributes are intended 397 to: 399 * authenticate users 401 * authorize users (i.e., service provisioning or changes to 402 provisioning) 404 * account for user activity (i.e., logging of session activity) 406 New commands (i.e., the Code field in the packet header) and new 407 attributes in the standard space are allocated only through "IETF 408 Consensus" as noted in [RFC3575] Section 2.1. 410 2.4. Translation of Vendor Specifications 412 The limitation on changes to the RADIUS protocol effectively 413 prohibits VSAs from changing fundamental aspects of RADIUS operation, 414 such as modifying RADIUS packet sequences, or adding new commands. 415 However, the requirement for clients and servers to be able to 416 operate in the absence of VSAs has proven to be less of a constraint, 417 since it is still possible for a RADIUS client and server to mutually 418 indicate support for VSAs, after which behavior expectations can be 419 reset. 421 Therefore, RFC 2865 provides considerable latitude for development of 422 new attributes within the vendor space, while prohibiting development 423 of protocol variants. This flexibility implies that RADIUS 424 attributes can often be developed within the vendor space without 425 loss (and possibly even with gain) in functionality. 427 As a result, translation of RADIUS attributes developed within the 428 vendor space into the standard space may provide only modest 429 benefits, while accelerating the exhaustion of the standard attribute 430 space. We do not expect that all RADIUS attribute specifications 431 requiring interoperability will be developed within the IETF, and 432 allocated from the standards space. A more scalable approach is to 433 recognize the flexibility of the vendor space, while working toward 434 improvements in the quality and availability of RADIUS attribute 435 specifications, regardless of where they are developed. 437 It is therefore NOT RECOMMENDED that specifications intended solely 438 for use by a vendor or SDO use be translated into the standard space. 440 3. Rationale 442 This section outlines the rationale behind the above recommendations. 444 3.1. RADIUS Operational Model 446 The RADIUS operational model includes several assumptions: 448 * The RADIUS protocol is stateless; 450 * Provisioning of services is not possible within an 451 Access-Reject; 453 * There is a distinction between authorization checks and user 454 authentication; 456 * The protocol provides for authentication and integrity 457 protection of packets; 459 * The RADIUS protocol is a Request/Response protocol; 461 * The protocol defines packet length restrictions. 463 While RADIUS server implementations may keep state, the RADIUS 464 protocol is stateless, although information may be passed from one 465 protocol transaction to another via the State Attribute. As a 466 result, documents which require stateful protocol behavior without 467 use of the State Attribute are inherently incompatible with RADIUS as 468 defined in [RFC2865], and SHOULD be redesigned. See [RFC5080] 469 Section 2.1.1 for additional discussion surrounding the use of the 470 State Attribute. 472 As noted in [RFC5080] Section 2.6, the intent of an Access-Reject is 473 to deny access to the requested service. As a result, RADIUS does 474 not allow the provisioning of services within an Access-Reject. 475 Documents which include provisioning of services within an Access- 476 Reject are inherently incompatible with RADIUS, and SHOULD be 477 redesigned. 479 As noted in [RFC5080] Section 2.1.1, a RADIUS Access-Request may not 480 contain user authentication attributes or a State Attribute linking 481 the Access-Request to an earlier user authentication. Such an 482 Access-Request, known as an authorization check, provides no 483 assurance that it corresponds to a live user. RADIUS specifications 484 defining attributes containing confidential information (such as 485 Tunnel-Password) should be careful to prohibit such attributes from 486 being returned in response to an authorization check. Also, 487 [RFC5080] Section 2.1.1 notes that authentication mechanisms need to 488 tie a sequence of Access-Request/Access-Challenge packets together 489 into one authentication session. The State Attribute is RECOMMENDED 490 for this purpose. 492 While [RFC2865] did not require authentication and integrity 493 protection of RADIUS Access-Request packets, subsequent 494 authentication mechanism specifications such as RADIUS/EAP [RFC3579] 495 and Digest Authentication [RFC5090] have mandated authentication and 496 integrity protection for certain RADIUS packets. [RFC5080] Section 497 2.1.1 makes this behavior RECOMMENDED for all Access-Request packets, 498 including Access-Request packets performing authorization checks. It 499 is expected that specifications for new RADIUS authentication 500 mechanisms will continue this practice. 502 The RADIUS protocol as defined in [RFC2865] is a request-response 503 protocol spoken between RADIUS clients and servers. A single RADIUS 504 Access-Request packet will solicit in response at most a single 505 Access-Accept, Access-Reject or Access-Challenge packet, sent to the 506 IP address and port of the RADIUS Client that originated the Access- 507 Request. Similarly, a single Change-of-Authorization (CoA)-Request 508 packet [RFC5176] will solicit in response at most a single CoA-ACK or 509 CoA-NAK packet, sent to the IP address and port of the Dynamic 510 Authorization Client (DAC) that originated the CoA-Request. A single 511 Disconnect-Request packet will solicit in response at most a single 512 Disconnect-ACK or Disconnect-NAK packet, sent to the IP address and 513 port of the Dynamic Authorization Client (DAC) that originated the 514 Disconnect-Request. Changes to this model are likely to require 515 major revisions to existing implementations and so this practice is 516 NOT RECOMMENDED. 518 The Length field in the RADIUS packet header is defined in [RFC2865] 519 Section 3. It is noted there that the maximum length of a RADIUS 520 packet is 4096 octets. As a result, attribute designers SHOULD NOT 521 assume that a RADIUS implementation can successfully process RADIUS 522 packets larger than 4096 octets. 524 Even when packets are less than 4096 octets, they may be larger than 525 the Path Maximum Transmission Unit (PMTU). Any packet larger than 526 the PMTU will be fragmented, making communications more brittle as 527 firewalls and filtering devices often discard fragments. Transport 528 of fragmented UDP packets appears to be a poorly tested code path on 529 network devices. Some devices appear to be incapable of transporting 530 fragmented UDP packets, making it difficult to deploy RADIUS in a 531 network where those devices are deployed. We RECOMMEND that RADIUS 532 messages be kept as small possible. 534 If a situation is envisaged where it may be necessary to carry 535 authentication, authorization or accounting data in a packet larger 536 than 4096 octets, then one of the following approaches is 537 RECOMMENDED: 539 1. Utilization of a sequence of packets. 540 For RADIUS authentication, a sequence of Access-Request/ Access- 541 Challenge packets would be used. For this to be feasible, 542 attribute designers need to enable inclusion of attributes that 543 can consume considerable space within Access-Challenge packets. 544 To maintain compatibility with existing NASes, either the use of 545 Access-Challenge packets needs to be permissible (as with 546 RADIUS/EAP, defined in [RFC3579]), or support for receipt of an 547 Access-Challenge needs to be indicated by the NAS (as in RADIUS 548 Location [RFC5580]). Also, the specification needs to clearly 549 describe how attribute splitting is to be signalled and how 550 attributes included within the sequence are to be interpreted, 551 without requiring stateful operation. Unfortunately, previous 552 specifications have not always exhibited the required foresight. 553 For example, even though very large filter rules are 554 conceivable, the NAS-Filter-Rule Attribute defined in [RFC4849] 555 is not permitted in an Access-Challenge packet, nor is a 556 mechanism specified to allow a set of NAS-Filter-Rule attributes 557 to be split across an Access-Request/Access-Challenge sequence. 559 In the case of RADIUS accounting, transporting large amounts of 560 data would require a sequence of Accounting-Request packets. 561 This is a non-trivial change to RADIUS, since RADIUS accounting 562 clients would need to be modified to split the attribute stream 563 across multiple Accounting-Requests, and billing servers would 564 need to be modified to re-assemble and interpret the attribute 565 stream. 567 2. Utilization of names rather than values. 568 Where an attribute relates to a policy that could conceivably be 569 pre-provisioned on the NAS, then the name of the pre-provisioned 570 policy can be transmitted in an attribute, rather than the 571 policy itself, which could be quite large. An example of this 572 is the Filter-Id Attribute defined in [RFC2865] Section 5.11, 573 which enables a set of pre-provisioned filter rules to be 574 referenced by name. 576 3. Utilization of Packetization Layer Path MTU Discovery 577 techniques, as specified in [RFC4821]. As a last resort, where 578 the above techniques cannot be made to work, it may be possible 579 to apply the techniques described in [RFC4821] to discover the 580 maximum supported RADIUS packet size on the path between a 581 RADIUS client and a home server. While such an approach can 582 avoid the complexity of utilization of a sequence of packets, 583 dynamic discovery is likely to be time consuming and cannot be 584 guaranteed to work with existing RADIUS implementations. As a 585 result, this technique is not generally applicable. 587 3.2. Data Model Issues 589 The RADIUS data types are poorly defined. While [RFC2865] Section 5 590 defines basic data types, later specifications did not follow this 591 practice. This problem has led implementations to define their own 592 names for data types, resulting in non-standard names for those 593 types. 595 In addition, the number of vendors and SDOs creating new attributes 596 within the Vendor-Specific attribute space has grown, and this has 597 lead to some divergence in approaches to RADIUS attribute design. 598 For example, vendors and SDOs have evolved the data model to support 599 functions such as new data types, along with attribute grouping and 600 attribute fragmentation, with different groups taking different 601 approaches. These approaches are often incompatible, leading to 602 additional complexity in RADIUS implementations. 604 In order to avoid repeating old mistakes, this section describes the 605 history of the RADIUS data model, and attempts to codify existing 606 practices. 608 3.2.1. Basic Data Types 610 [RFC2865] and [RFC2866] utilize data types defined in [RFC2865] 611 Section 5, which states the following: 613 The format of the value field is one of five data types. Note 614 that type "text" is a subset of type "string". 616 text 1-253 octets containing UTF-8 encoded 10646 [RFC3629] 617 characters. Text of length zero (0) MUST NOT be sent; 618 omit the entire attribute instead. 620 string 1-253 octets containing binary data (values 0 through 621 255 decimal, inclusive). Strings of length zero (0) 622 MUST NOT be sent; omit the entire attribute instead. 624 address 32 bit value, most significant octet first. 626 integer 32 bit unsigned value, most significant octet first. 628 time 32 bit unsigned value, most significant octet first -- 629 seconds since 00:00:00 UTC, January 1, 1970. The 630 standard Attributes do not use this data type but it is 631 presented here for possible use in future attributes. 633 Subsequent RADIUS specifications also defined attributes using new 634 data types. These specifications did not explicitly define those 635 data types as was done in [RFC2865]. They did not consistently 636 indicate the format of the value field using the same conventions as 637 [RFC2865]. As a result, the data type is ambiguous in some cases, 638 and may not be consistent among different implementations. 640 It is out of the scope of this document to resolve all potential 641 ambiguities within existing RADIUS specifications. However in order 642 to prevent future ambiguities, it is recommended that future RADIUS 643 attribute specifications explicitly define newly created data types 644 at the beginning of the document, and indicate clearly the data type 645 to be used for each attribute. 647 For example, [RFC3162] utilizes but does not explicitly define the 648 following data types: 650 IPv6 address 128 bit value, in network byte order. 652 IPv6 prefix 8 bits of reserved, 8 bits of prefix length, up to 653 128 bits of value, in network byte order. 655 The IPv6 address type is used for the NAS-IPv6-Address defined in 656 [RFC3162] Section 2.1 and the Login-IPv6-Host defined in [RFC3162] 657 Section 2.4. The IPv6 prefix type is used in [RFC3162] Section 2.3, 658 and in [RFC4818] Section 3. 660 While the Framed-Interface-Id attribute defined in [RFC3162] Section 661 2.2 included a value field of 8 octets, the data type was not 662 explicitly indicated, and therefore there is controversy over whether 663 the format of the data was intended to be an 8 octet String or 664 whether a special Interface-Id type was intended. 666 Given that attributes of type "IPv6 address" and "IPv6 prefix" are 667 already in use, it is RECOMMENDED that RADIUS server implementations 668 include support for these additional basic types, in addition to the 669 types defined in [RFC2865]. Where the intent is to represent a 670 specific IPv6 address, the "IPv6 address" type SHOULD be used. 671 Although it is possible to use the "IPv6 Prefix" type with a prefix 672 length of 128 to represent an IPv6 address, this usage is NOT 673 RECOMMENDED. Implementations supporting the Framed-Interface-Id 674 attribute may select a data type of their choosing (most likely an 8 675 octet String or a special Interface-Id data type). 677 It is worth noting that since RADIUS only supports unsigned integers 678 of 32 bits, attributes using signed integer data types or unsigned 679 integer types of other sizes will require code changes, and SHOULD be 680 avoided. 682 For [RFC2865] RADIUS VSAs, the length limitation of the String and 683 Text types is 247 octets instead of 253 octets, due to the additional 684 overhead of the Vendor-Specific Attribute. 686 3.2.2. Tagging Mechanism 688 [RFC2868] defines an attribute grouping mechanism based on the use of 689 a one octet tag value. Tunnel attributes that refer to the same 690 tunnel are grouped together by virtue of using the same tag value. 692 This tagging mechanism has some drawbacks. There are a limited 693 number of unique tags (31). The tags are not well suited for use 694 with arbitrary binary data values, because it is not always possible 695 to tell if the first byte after the Length is the tag or the first 696 byte of the untagged value (assuming the tag is optional). 698 Other limitations of the tagging mechanism are that when integer 699 values are tagged, the value portion is reduced to three bytes 700 meaning only 24-bit numbers can be represented. The tagging 701 mechanism does not offer an ability to create nested groups of 702 attributes. Some RADIUS implementations treat tagged attributes as 703 having additional data types tagged-string and tagged-integer. These 704 types increase the complexity of implementing and managing RADIUS 705 systems. 707 For these reasons, the tagging scheme described in RFC 2868 is NOT 708 RECOMMENDED for use as a generic grouping mechanism. 710 3.2.3. Complex Data Types 712 The RADIUS attribute encoding is summarized in [RFC2865]: 714 0 1 2 715 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 717 | Type | Length | Value ... 718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 720 However, some standard attributes do not follow this encoding. 721 Attributes that use an encoding other than the basic data types as 722 discussed above are defined to be "complex types". As described 723 below in this section, the creation of complex types can lead to 724 interoperability and deployment issues, so they need to be introduced 725 with care. 727 In general, complex types containing multiple sub-fields can be 728 supported by concatenating the sub-fields into a String data type 729 field. However, separating these sub-fields into different 730 attributes, each with its own type and length, would have the 731 following benefits: 733 * it is easier for the user to enter the data as well-known 734 types, rather than complex structures; 736 * it enables additional error checking by leveraging the 737 parsing and validation routines for well-known types; 739 * it simplifies implementations by eliminating special-case 740 attribute-specific parsing. 742 One of the fundamental goals of the RADIUS protocol design was to 743 allow RADIUS servers to be configured to support new attributes 744 without requiring server code changes. RADIUS server implementations 745 typically provide support for basic data types, and define attributes 746 in a data dictionary. This architecture enables a new attribute to 747 be supported by the addition of a dictionary entry, without requiring 748 other RADIUS server code changes. 750 On the RADIUS client, code changes are typically required in order to 751 implement a new attribute. The RADIUS client typically has to 752 compose the attribute dynamically when sending. When receiving, a 753 RADIUS client needs to be able to parse the attribute and carry out 754 the requested service. As a result, a detailed understanding of the 755 new attribute is required on clients, and data dictionaries are less 756 useful on clients than on servers. 758 Given these considerations, the introduction of a new basic or 759 complex attribute will typically require code changes on the RADIUS 760 client. The magnitude of changes for the complex attribute could be 761 greater, due to the potential need for custom parsing logic. 763 The RADIUS server can be configured to send a new static attribute by 764 entering its type and data format in the RADIUS server dictionary, 765 and then filling in the value within a policy based on the attribute 766 name, data type and type-specific value. For data types not 767 supported by current RADIUS server dictionaries, changes to the 768 dictionary code can be required in order to allow the new type to be 769 supported by and configured on the RADIUS server. 771 Code changes can also be required in policy management and in the 772 RADIUS server's receive path. These changes are due to limitations 773 in RADIUS server policy languages, which typically only provide for 774 limited operations (such as comparisons or arithmetic operations) on 775 the existing data types. Many existing RADIUS policy languages 776 typically are not capable of parsing sub-elements, or providing 777 sophisticated matching functionality. 779 Given these limitations, the introduction of new types can require 780 code changes on the RADIUS server which would be unnecessary if basic 781 data types had been used instead. In addition if "ad-hoc" types are 782 used, attribute-specific parsing means more complex software to 783 develop and maintain. More complexity can lead to more error prone 784 implementations, interoperability problems, and even security 785 vulnerabilities. These issues can increase costs to network 786 administrators as well as reducing reliability and introducing 787 deployment barriers. We therefore RECOMMEND that the introduction of 788 new types and complex data types within RADIUS attribute 789 specifications be avoided. A potential exception to this 790 recommendation occurs for attributes that inherently require code 791 changes on both the client and server. For example, as described in 792 Appendix B, complex attributes have been used in situations involving 793 authentication and security attributes that need to be dynamically 794 computed and verified. 796 As can be seen in Appendix B, most of the existing complex attributes 797 involve authentication or security functionality. Supporting this 798 functionality requires code changes on both the RADIUS client and 799 server, regardless of the attribute format. As a result, in most 800 cases, the use of complex attributes to represent these methods is 801 acceptable, and does not create additional interoperability or 802 deployment issues. 804 The only other exception to the recommendation against complex types 805 is for types that can be treated as opaque data by the RADIUS server. 806 For example, the EAP-Message attribute, defined in [RFC3579] Section 807 3.1 contains a complex data type that is an EAP packet. Since these 808 complex types do not need to be parsed by the RADIUS server, the 809 issues arising from policy language limitations do not arise. 810 Similarly, since attributes of these complex types can be configured 811 on the server using a data type of String, dictionary limitations are 812 also not encountered. Appendix A.1 below includes a series of 813 checklists that may be used to analyze a design for RECOMMENDED and 814 NOT RECOMMENDED behavior in relation to complex types. 816 If the RADIUS Server simply passes the contents of an attribute to 817 some non-RADIUS portion of the network, then the data is opaque, and 818 SHOULD be defined to be of type String. A concrete way of judging 819 this requirement is whether or not the attribute definition in the 820 RADIUS document contains delineated fields for sub-parts of the data. 821 If those fields need to be delineated in RADIUS, then the data is not 822 opaque, and it SHOULD be separated into individual RADIUS attributes. 824 An examination of existing RADIUS RFCs discloses a number of complex 825 attributes that have already been defined. Appendix B includes a 826 listing of complex attributes used within [RFC2865], [RFC2868], 827 [RFC2869], [RFC3162], [RFC4818], and [RFC4675]. The discussion of 828 these attributes includes reasons why a complex type is acceptable, 829 or suggestions for how the attribute could have been defined to 830 follow the RADIUS data model. 832 In other cases, the data in the complex type are described textually. 833 This is possible because the data types are not sent within the 834 attributes, but are a matter for endpoint interpretation. An 835 implementation can define additional data types, and use these data 836 types today by matching them to the attribute's textual description. 838 Despite the above caveats, there may be situations where complex 839 attributes are beneficial because they reduce complexity in the non- 840 RADIUS systems. Unfortunately, there are no "hard and fast" rules 841 for where the complexity would best be located. Each situation has 842 to be decided on a case-by-case basis. 844 3.3. Vendor Space 846 The usage model for RADIUS VSAs is described in [RFC2865] Section 847 6.2: 849 Note that RADIUS defines a mechanism for Vendor-Specific 850 extensions (Attribute 26) and the use of that should be encouraged 851 instead of allocation of global attribute types, for functions 852 specific only to one vendor's implementation of RADIUS, where no 853 interoperability is deemed useful. 855 Nevertheless, many new attributes have been defined in the vendor 856 specific space in situations where interoperability is not only 857 useful, but is required. For example, SDOs outside the IETF (such as 858 the IEEE 802 and the 3rd Generation Partnership Project (3GPP)) have 859 been assigned Vendor-Ids, enabling them to define their own VSA 860 encoding and assign Vendor types within their own space. 862 The use of VSAs by SDOs outside the IETF has gained in popularity for 863 several reasons: 865 Efficiency 866 As with SNMP, which defines an "Enterprise" Object Identifier (OID) 867 space suitable for use by vendors as well as other SDOs, the 868 definition of Vendor-Specific RADIUS attributes has become a common 869 occurrence as part of standards activity outside the IETF. For 870 reasons of efficiency, it is easiest if the RADIUS attributes 871 required to manage a standard are developed within the same SDO 872 that develops the standard itself. As noted in "Transferring MIB 873 Work from IETF Bridge MIB WG to IEEE 802.1 WG" [RFC4663], today few 874 vendors are willing to simultaneously fund individuals to 875 participate within an SDO to complete a standard, as well as to 876 participate in the IETF in order to complete the associated RADIUS 877 attributes specification. 879 Attribute scarcity 880 The standard RADIUS attribute space is limited to 255 unique 881 attributes. Of these, only about half remain available for 882 allocation. In the vendor space, the number of attributes 883 available is a function of the encoding of the attribute (the size 884 of the Vendor type field). 886 Along with these advantages, some limitations of VSA usage are noted 887 in [RFC2865] Section 5.26: 889 This Attribute is available to allow vendors to support their own 890 extended Attributes not suitable for general usage. It MUST NOT 891 affect the operation of the RADIUS protocol. 893 Servers not equipped to interpret the vendor-specific information 894 sent by a client MUST ignore it (although it may be reported). 895 Clients which do not receive desired vendor-specific information 896 SHOULD make an attempt to operate without it, although they may do 897 so (and report they are doing so) in a degraded mode. 899 3.3.1. Interoperability Considerations 901 Vendors and SDOs are reminded that the standard RADIUS attribute 902 space, and the enumerated value space for enumerated attributes, are 903 reserved for allocation through work published via the IETF, as noted 904 in [RFC3575] Section 2.1. Some vendors and SDOs have in the past 905 performed self-allocation by assigning vendor-specific meaning to 906 "unused" values from the standard RADIUS attribute ID or enumerated 907 value space. This self-allocation results in interoperability 908 issues, and is counter-productive. Similarly, the Vendor-Specific 909 enumeration practice discussed in [RFC2882] Section 2.2.1 is NOT 910 RECOMMENDED. 912 If it is not possible to follow the IETF process, vendors and SDOs 913 SHOULD self-allocate an attribute, which MUST be in vendor space, as 914 discussed in Sections 3.3.2 and 3.3.3, below. 916 The design and specification of VSAs for multi-vendor usage SHOULD be 917 undertaken with the same level of care as standard RADIUS attributes. 918 Specifically, the provisions of this document that apply to standard 919 RADIUS attributes also apply to VSAs for multi-vendor usage. 921 3.3.2. Vendor Allocations 923 As noted in [RFC3575] Section 2.1, vendors are encouraged to utilize 924 VSAs to define functions "specific only to one vendor's 925 implementation of RADIUS, where no interoperability is deemed useful. 926 For functions specific only to one vendor's implementation of RADIUS, 927 the use of that should be encouraged instead of the allocation of 928 global attribute types." 930 The recommendation for vendors to allocate attributes from a vendor 931 space rather than via the IETF process is a recognition that vendors 932 desire to assert change control over their own RADIUS specifications. 933 This change control can be obtained by requesting a PEC from the 934 Internet Assigned Number Authority (IANA), for use as a Vendor-Id 935 within a Vendor-Specific attribute. The vendor can then allocate 936 attributes within the VSA space defined by that Vendor-Id, at their 937 sole discretion. Similarly, the use of data types (complex or 938 otherwise) within that VSA space is solely under the discretion of 939 the vendor. 941 Nevertheless, following the guidelines outlined within this document 942 has many advantages. Following these guidelines means that RADIUS 943 servers can be updated to support the vendor's equipment by editing a 944 RADIUS dictionary. It is therefore RECOMMENDED that vendors follow 945 the guidelines outlined here, which are intended to enable maximum 946 interoperability with minimal changes to existing systems. If these 947 guidelines are not followed, then the vendor's equipment can only be 948 supported via code changes in RADIUS server implementations. Such 949 code changes add complexity and delay to implementations. 951 3.3.3. SDO Allocations 953 Given the expanded utilization of RADIUS, it has become apparent that 954 requiring SDOs to accomplish all their RADIUS work within the IETF is 955 inherently inefficient and unscalable. Is is therefore RECOMMENDED 956 that SDO RADIUS Attribute specifications allocate attributes from the 957 vendor space, rather than requesting an allocation from the RADIUS 958 standard attribute space, for attributes matching any of the 959 following criteria: 961 * attributes relying on data types not defined within RADIUS 963 * attributes intended primarily for use within an SDO 965 * attributes intended primarily for use within a group of SDOs. 967 Any new RADIUS attributes or values intended for interoperable use 968 across a broad spectrum of the Internet Community SHOULD follow the 969 allocation process defined in [RFC3575]. 971 The recommendation for SDOs to allocate attributes from a vendor 972 space rather than via the IETF process is a recognition that SDOs 973 desire to assert change control over their own RADIUS specifications. 974 This change control can be obtained by requesting a PEC from the 975 Internet Assigned Number Authority (IANA), for use as a Vendor-Id 976 within a Vendor-Specific attribute. The SDO can then allocate 977 attributes within the VSA space defined by that Vendor-Id, at their 978 sole discretion. Similarly, the use of data types (complex or 979 otherwise) within that VSA space is solely under the discretion of 980 the SDO. 982 3.3.4. Publication of specifications 984 SDOs or vendors desiring review of their RADIUS specifications by the 985 IETF are encouraged to seek review as early as possible, so as to 986 avoid potential delays. Since reviews are handled by volunteers, 987 responses are provided on a best-effort basis, with no service level 988 guarantees. In order to provide reviewers with access to the 989 specification, vendors and SDOs are encouraged to make them publicly 990 available. 992 Where the RADIUS specification is embedded within a larger document 993 which cannot be made public, the RADIUS attribute and value 994 definitions can be made available on a public web site or can be 995 published as an Informational RFC, as with [RFC4679]. 997 Review can be requested by sending email to the AAA Doctors [DOCTORS] 998 or equivalent mailing list. The IETF Operations & Management Area 999 Directors will then arrange for the review to be completed and posted 1000 to the AAA Doctors mailing list [DOCTORS], RADEXT WG mailing list, or 1001 other IETF mailing list. 1003 The review process requires neither allocation of attributes within 1004 the IETF standard attribute space nor publication of an IETF RFC. 1005 Requiring SDOs or vendors to rehost VSAs into the IETF standards 1006 attribute space solely for the purpose of obtaining review would put 1007 pressure on the standards space, and may be harmful to 1008 interoperability, since would create two ways to provision the same 1009 service. Rehosting may also require changes to the RADIUS data model 1010 which will affect implementations that do not intend to support the 1011 SDO or vendor specifications. 1013 Similarly, vendors are encouraged to make their specifications 1014 publicly available, for maximum interoperability. However, it is not 1015 necessary for a vendor to request publication of a VSA specification 1016 as an Informational RFC by the IETF. 1018 All other specifications, including new authentication, 1019 authorization, and/or security mechanisms SHOULD follow the 1020 allocation process defined in [RFC3575], as they are likely to have 1021 impact on the Internet Community. 1023 3.4. Polymorphic Attributes 1025 A polymorphic attribute is one whose format or meaning is dynamic. 1026 For example, rather than using a fixed data format, an attribute's 1027 format might change based on the contents of another attribute. Or, 1028 the meaning of an attribute may depend on earlier packets in a 1029 sequence. 1031 RADIUS server dictionary entries are typically static, enabling the 1032 user to enter the contents of an attribute without support for 1033 changing the format based on dynamic conditions. However, this 1034 limitation on static types does not prevent implementations from 1035 implementing policies that return different attributes based on the 1036 contents of received attributes; this is a common feature of existing 1037 RADIUS implementations. 1039 In general, polymorphism is NOT RECOMMENDED. Polymorphism rarely 1040 enables capabilities that would not be available through use of 1041 multiple attributes. Polymorphism requires code changes in the 1042 RADIUS server in situations where attributes with fixed formats would 1043 not require such changes. Thus, polymorphism increases complexity 1044 while decreasing generality, without delivering any corresponding 1045 benefits. 1047 Note that changing an attribute's format dynamically is not the same 1048 thing as using a fixed format and computing the attribute itself 1049 dynamically. RADIUS authentication attributes such as User-Password, 1050 EAP-Message, etc. while being computed dynamically, use a fixed 1051 format. 1053 4. IANA Considerations 1055 This document does not require that the IANA update any existing 1056 registry or create any new registry, but includes information that 1057 affects the IANA, which: 1059 * includes specific guidelines for Expert Reviewers appointed 1060 under the IANA considerations of [RFC3575] 1062 * includes guidelines that recommend against self allocation from 1063 the RADIUS standard attribute space in other SDO RADIUS 1064 Attribute specifications. 1066 * recommends that SDOs request a Private Enterprise Code (PEC) 1067 from the IANA, for use as a Vendor-Id within a Vendor-Specific 1068 attribute. 1070 5. Security Considerations 1072 This specification provides guidelines for the design of RADIUS 1073 attributes used in authentication, authorization and accounting. 1074 Threats and security issues for this application are described in 1075 [RFC3579] and [RFC3580]; security issues encountered in roaming are 1076 described in [RFC2607]. 1078 Obfuscation of RADIUS attributes on a per-attribute basis is 1079 necessary in some cases. The current standard mechanism for this is 1080 described in [RFC2865] Section 5.2 (for obscuring User-Password 1081 values) and is based on the MD5 algorithm specified in [RFC1321]. 1082 The MD5 and SHA-1 algorithms have recently become a focus of scrutiny 1083 and concern in security circles, and as a result, the use of these 1084 algorithms in new attributes is NOT RECOMMENDED. In addition, 1085 previous documents referred to this method as generating "encrypted" 1086 data. This terminology is no longer accepted within the 1087 cryptographic community. 1089 Where new RADIUS attributes use cryptographic algorithms, algorithm 1090 negotiation SHOULD be supported. Specification of a mandatory-to- 1091 implement algorithm is REQUIRED, and it is RECOMMENDED that the 1092 mandatory-to-implement algorithm be certifiable under FIPS 140 1093 [FIPS]. 1095 Where new RADIUS attributes encapsulate complex data types, or 1096 transport opaque data, the security considerations discussed in 1097 Section 5.1 SHOULD be addressed. 1099 Message authentication in RADIUS is provided largely via the Message- 1100 Authenticator attribute. See [RFC3579] Section 3.2, and also 1101 [RFC5080] 2.2.2, which says that client implementations SHOULD 1102 include a Message-Authenticator attribute in every Access-Request. 1104 In general, the security of the RADIUS protocol is poor. Robust 1105 deployments SHOULD support a secure communications protocol such as 1106 IPSec. See [RFC3579] Section 4, and [RFC3580] Section 5 for a more 1107 in-depth explanation of these issues. 1109 Implementations not following the suggestions outlined in this 1110 document may be subject to a problems such as ambiguous protocol 1111 decoding, packet loss leading to loss of billing information, and 1112 denial of service attacks. 1114 5.1. New Data Types and Complex Attributes 1116 The introduction of complex data types brings the potential for the 1117 introduction of new security vulnerabilities. Experience shows that 1118 the common data types have few security vulnerabilities, or else that 1119 all known issues have been found and fixed. New data types require 1120 new code, which may introduce new bugs, and therefore new attack 1121 vectors. 1123 Some systems permit complex attributes to be defined via a method 1124 that is more capable than traditional RADIUS dictionaries. These 1125 systems can reduce the security threat of new types significantly, 1126 but they do not remove it entirely. 1128 RADIUS servers are highly valued targets, as they control network 1129 access and interact with databases that store usernames and 1130 passwords. An extreme outcome of a vulnerability due to a new, 1131 complex type would be that an attacker is capable of taking complete 1132 control over the RADIUS server. 1134 The use of attributes representing opaque data does not reduce this 1135 threat. The threat merely moves from the RADIUS server to the system 1136 that consumes that opaque data. 1138 The threat is particularly severe when the opaque data originates 1139 from the user, and is not validated by the NAS. In those cases, the 1140 RADIUS server is potentially exposed to attack by malware residing on 1141 an unauthenticated host. 1143 Any system consuming opaque data that originates from a RADIUS system 1144 SHOULD be properly isolated from that RADIUS system, and SHOULD run 1145 with minimal privileges. Any potential vulnerabilities in the non- 1146 RADIUS system will then have minimal impact on the security of the 1147 system as a whole. 1149 6. References 1151 6.1. Normative References 1153 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1154 Requirement Levels", BCP 14, RFC 2119, March 1997. 1156 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote 1157 Authentication Dial In User Service (RADIUS)", RFC 2865, June 1158 2000. 1160 [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote 1161 Authentication Dial In User Service)", RFC 3575, July 2003. 1163 6.2. Informative References 1165 [RFC1155] Rose, M. and K. McCloghrie, "Structure and identification of 1166 management information for TCP/IP-based internets", STD 16, 1167 RFC 1155, May 1990. 1169 [RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple 1170 Network Management Protocol (SNMP)", STD 15, RFC 1157, May 1171 1990. 1173 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, 1174 April 1992. 1176 [RFC2548] Zorn, Glen, "Microsoft Vendor-specific RADIUS Attributes", RFC 1177 2548, March 1999. 1179 [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy 1180 Implementation in Roaming", RFC 2607, June 1999. 1182 [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. 1184 [RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M., 1185 and I. Goyret, "RADIUS Attributes for Tunnel Protocol 1186 Support", RFC 2868, June 2000. 1188 [RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RADIUS Extensions", 1189 RFC 2869, June 2000. 1191 [RFC2882] Mitton, D, "Network Access Servers Requirements: Extended 1192 RADIUS Practices", RFC 2882, July 2000. 1194 [RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 1195 3162, August 2001. 1197 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial 1198 In User Service) Support For Extensible Authentication 1199 Protocol (EAP)", RFC 3579, September 2003. 1201 [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., Roese, J., "IEEE 1202 802.1X Remote Authentication Dial In User Service (RADIUS) 1203 Usage Guidelines", RFC3580, September 2003. 1205 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 1206 RFC 3629, November 2003. 1208 [RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB 1209 Documents", RFC 4181, September 2005. 1211 [RFC4663] Harrington, D., "Transferring MIB Work from IETF Bridge MIB WG 1212 to IEEE 802.1 WG", RFC 4663, September 2006. 1214 [RFC4675] Congdon, P., Sanchez, M. and B. Aboba, "RADIUS Attributes for 1215 Virtual LAN and Priority Support", RFC 4675, September 2006. 1217 [RFC4679] Mammoliti, V., et al., "DSL Forum Vendor-Specific RADIUS 1218 Attributes", RFC 4679, September 2006. 1220 [RFC4818] Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix 1221 Attribute", RFC 4818, April 2007. 1223 [RFC4821] Mathis, M. and Heffner, J, "Packetization Layer Path MTU 1224 Discovery", RFC 4821, March 2007. 1226 [RFC4849] Congdon, P. et al, "RADIUS Filter-Rule Attribute", RFC 4849, 1227 April 2007. 1229 [RFC5080] Nelson, D. and DeKok, A, "Common Remote Authentication Dial In 1230 User Service (RADIUS) Implementation Issues and Suggested 1231 Fixes", RFC 5080, December 2007. 1233 [RFC5090] Sterman, B. et al., "RADIUS Extension for Digest 1234 Authentication", RFC 5090, February 2008. 1236 [RFC5176] Chiba, M. et al., "Dynamic Authorization Extensions to Remote 1237 Authentication Dial In User Service (RADIUS)", RFC 5176, 1238 January 2008. 1240 [DOCTORS] AAA Doctors Mailing list 1242 [FIPS] FIPS 140-3 (DRAFT), "Security Requirements for Cryptographic 1243 Modules", http://csrc.nist.gov/publications/fips/fips140-3/ 1245 [IEEE-802.1Q] 1246 IEEE Standards for Local and Metropolitan Area Networks: Draft 1247 Standard for Virtual Bridged Local Area Networks, 1248 P802.1Q-2003, January 2003. 1250 [RFC5580] Tschofenig, H. (Ed.), "Carrying Location Objects in RADIUS and 1251 Diameter", RFC 5580, August 2009. 1253 [AAA-SIP] Sterman, B. et al., "RADIUS Extension for Digest 1254 Authentication", draft-sterman-sip-aaa-00.txt, November 2001 1255 (expired). 1257 Appendix A - Design Guidelines 1259 The following text provides guidelines for the design of attributes 1260 used by the RADIUS protocol. Specifications that follow these 1261 guidelines are expected to achieve maximum interoperability with 1262 minimal changes to existing systems. 1264 A.1. Types matching the RADIUS data model 1266 A.1.1. Transport of basic data types 1268 Does the data fit within the basic data types described in Section 1269 2.1.1, as outlined below? If so, it SHOULD be encapsulated in a 1270 [RFC2865] format RADIUS attribute, or in a [RFC2865] format RADIUS 1271 VSA that uses one of the existing RADIUS data types: 1273 * 32-bit unsigned integer, in network byte order. 1275 * Enumerated data types, represented as a 32-bit unsigned integer 1276 with a list of name to value mappings. (e.g. Service-Type) 1278 * IPv4 address in network byte order. 1280 * time as 32 bit unsigned value, in network byte order, and in 1281 seconds since 00:00:00 UTC, January 1, 1970. 1283 * IPv6 address in network byte order. 1285 * Interface-Id (8 octet string in network byte order) 1287 * IPv6 prefix. 1289 * string (i.e., binary data), totalling 253 octets or less in 1290 length. This includes the opaque encapsulation of data 1291 structures defined outside of RADIUS. See also Appendix A.1.3, 1292 below. 1294 * UTF-8 text, totalling 253 octets or less in length. 1296 Note that the length limitations for VSAs of type String and Text are 1297 less than 253 octets, due to the additional overhead of the Vendor- 1298 Specific format. 1300 The following data also qualifies as "basic data types": 1302 * Attributes grouped into a logical container, using the 1303 [RFC2868] tagging mechanism. This approach is NOT 1304 RECOMMENDED (see Section 2.1.2), but is permissible where 1305 the alternatives are worse. 1307 * Attributes requiring the transport of more than 247 octets of 1308 Text or String data. This includes the opaque encapsulation 1309 of data structures defined outside of RADIUS. See also Section 1310 A.1.3, below. 1312 Nested groups or attributes do not qualify as "basic data types", and 1313 SHOULD NOT be used. 1315 A.1.2. Transport of Authentication and Security Data 1317 Does the data provide authentication and/or security capabilities for 1318 the RADIUS protocol, as outlined below? If so, it SHOULD be 1319 allocated from the standard space via "IETF consensus", and SHOULD 1320 NOT be allocated from the vendor space. 1322 * Complex data types that carry authentication methods which 1323 RADIUS servers are expected to parse and verify as part of 1324 an authentication process. 1326 * Complex data types that carry security information intended 1327 to increase the security of the RADIUS protocol itself. 1329 Any data type carrying authentication and/or security data that is 1330 not meant to be parsed by a RADIUS server is an "opaque data type", 1331 as defined below. 1333 A.1.3. Opaque data types 1335 Does the attribute encapsulate an existing data structure defined 1336 outside of the RADIUS specifications? Can the attribute be treated 1337 as opaque data by RADIUS servers (including proxies?) If both 1338 questions can be answered affirmatively, a complex structure MAY be 1339 used in a RADIUS specification. 1341 The specification of the attribute SHOULD define the encapsulating 1342 attribute to be of type String. The specification SHOULD refer to an 1343 external document defining the structure. The specification SHOULD 1344 NOT define or describe the structure, for reasons discussed above in 1345 Section 2.1.3. 1347 A.1.4. Pre-existing data types 1349 There is a trade-off in design between re-using existing formats for 1350 historical compatibility, or choosing new formats for a "better" 1351 design. This trade-off does not always require the "better" design 1352 to be used. As a result. pre-existing complex data types described 1353 in Appendix B MAY be used, though this practice is NOT RECOMMENDED. 1355 A.2. Improper Data Types 1357 All data types other than the ones described above in Appendix A.1 1358 and Appendix B SHOULD NOT be used. This section describes in detail 1359 a number of data types that are NOT RECOMMENDED in new RADIUS 1360 specifications. Where possible, replacement data types are 1361 suggested. 1363 A.2.1. Basic Data Types 1365 Does the attribute use any of the following data types? If so, the 1366 data type SHOULD be replaced with the suggested alternatives, or it 1367 SHOULD NOT be used at all. 1369 * Signed integers of any size. 1370 SHOULD NOT be used. SHOULD be replaced with one or more 1371 unsigned integer attributes. The definition of the attribute 1372 can contain information that would otherwise go into the sign 1373 value of the integer. 1375 * 8 bit unsigned integers. 1376 SHOULD be replaced with 32-bit unsigned integer. There is 1377 insufficient justification to save three bytes. 1379 * 16 bit unsigned integers. 1380 SHOULD be replaced with 32-bit unsigned integer. There is 1381 insufficient justification to save two bytes. 1383 * Unsigned integers of size other than 32 bits. 1384 SHOULD be replaced by an unsigned integer of 32 bits. 1385 There is insufficient justification to define a new size of 1386 integer. 1388 * Integers of any size in non-network byte order 1389 SHOULD be replaced by unsigned integer of 32 bits in network 1390 There is no reason to transport integers in any format other 1391 than network byte order. 1393 * Multi-field text strings. 1394 Each field SHOULD be encapsulated in a separate attribute. 1396 * Polymorphic attributes. 1397 Multiple attributes, each with a static data type SHOULD be 1398 defined instead. 1400 * Nested AVPs. 1402 Attributes should be defined in a flat typespace. 1404 A.2.2. Complex Data Types 1406 Does the attribute: 1408 * define a complex data type not described in Appendix B, 1410 * that a RADIUS server and/or client is expected to parse, 1411 validate, or create the contents of via a dynamic computation? 1412 i.e. A type that cannot be treated as opaque data (Section A.1.3) 1414 * involve functionality that could be implemented without code 1415 changes on both the client and server? (i.e. a type that doesn't 1416 require dynamic computation and verification, such as those 1417 performed for authentication or security attributes) 1419 If so, this data type SHOULD be replaced with simpler types, as 1420 discussed above in Appendix A.2.1. See also Section 2.1.3 for a 1421 discussion of why complex types are problematic. 1423 A.3. Vendor-Specific formats 1425 Does the specification contain Vendor-Specific attributes that match 1426 any of the following criteria? If so, the VSA encoding should be 1427 replaced with the [RFC2865] Section 5.26 encoding, or should not be 1428 used at all. 1430 * Vendor types of more than 8 bits. 1431 SHOULD NOT be used. Vendor types of 8 bits SHOULD be used 1432 instead. 1434 * Vendor lengths of less than 8 bits. (i.e., zero bits) 1435 SHOULD NOT be used. Vendor lengths of 8 bits SHOULD be used 1436 instead. 1438 * Vendor lengths of more than 8 bits. 1439 SHOULD NOT be used. Vendor lengths of 8 bits SHOULD be used 1440 instead. 1442 * Vendor-Specific contents that are not in Type-Length-Value 1443 format. 1444 SHOULD NOT be used. Vendor-Specific attributes SHOULD be in 1445 Type-Length-Value format. 1447 In general, Vendor-Specific attributes SHOULD follow the [RFC2865] 1448 Section 5.26 suggested encoding. Vendor extensions to non-standard 1449 encodings are NOT RECOMMENDED as they can negatively affect 1450 interoperability. 1452 A.4. Changes to the RADIUS Operational Model 1454 Does the specification change the RADIUS operation model, as outlined 1455 in the list below? If so, then another method of achieving the 1456 design objectives SHOULD be used. Potential problem areas include: 1458 * Defining new commands in RADIUS using attributes. 1459 The addition of new commands to RADIUS MUST be handled via 1460 allocation of a new Code, and not by the use of an attribute. 1461 This restriction includes new commands created by overloading 1462 the Service-Type attribute to define new values that modify 1463 the functionality of Access-Request packets. 1465 * Using RADIUS as a transport protocol for data unrelated to 1466 authentication, authorization, or accounting. Using RADIUS to 1467 transport authentication methods such as EAP is explicitly 1468 permitted, even if those methods require the transport of 1469 relatively large amounts of data. Transport of opaque data 1470 relating to AAA is also permitted, as discussed above in 1471 Section 2.1.3. However, if the specification does not relate 1472 to AAA, then RADIUS SHOULD NOT be used. 1474 * Assuming support for packet lengths greater than 4096 octets. 1475 Attribute designers cannot assume that RADIUS implementations 1476 can successfully handle packets larger than 4096 octets. 1477 If a specification could lead to a RADIUS packet larger than 1478 4096 octets, then the alternatives described in Section 3.3 1479 SHOULD be considered. 1481 * Stateless operation. The RADIUS protocol is stateless, and 1482 documents which require stateful protocol behavior without the 1483 use of the State Attribute need to be redesigned. 1485 * Provisioning of service in an Access-Reject. Such provisioning 1486 is not permitted, and MUST NOT be used. If limited access needs 1487 to be provided, then an Access-Accept with appropriate 1488 authorizations can be used instead. 1490 * Lack of user authentication or authorization restrictions. 1491 In an authorization check, where there is no demonstration of a 1492 live user, confidential data cannot be returned. Where there 1493 is a link to a previous user authentication, the State attribute 1494 SHOULD be present. 1496 * Lack of per-packet integrity and authentication. 1497 It is expected that documents will support per-packet 1498 integrity and authentication. 1500 * Modification of RADIUS packet sequences. 1501 In RADIUS, each request is encapsulated in its own packet, and 1502 elicits a single response that is sent to the requester. Since 1503 changes to this paradigm are likely to require major 1504 modifications to RADIUS client and server implementations, they 1505 SHOULD be avoided if possible. 1506 For further details, see Section 3.3. 1508 A.5. Allocation of attributes 1510 Does the attribute have a limited scope of applicability, as outlined 1511 below? If so, then the attributes SHOULD be allocated from the 1512 vendor space, rather than requesting allocation from the standard 1513 space. 1515 * attributes intended for a vendor to support their own systems, 1516 and not suitable for general usage 1518 * attributes relying on data types not defined within RADIUS 1520 * attributes intended primarily for use within an SDO 1522 * attributes intended primarily for use within a group of SDOs. 1524 Note that the points listed above do not relax the recommendations 1525 discussed in this document. Instead, they recognize that the RADIUS 1526 data model has limitations. In certain situations where 1527 interoperability can be strongly constrained by the SDO or vendor, an 1528 expanded data model MAY be used. It is RECOMMENDED, however, that 1529 the RADIUS data model be used, even when it is marginally less 1530 efficient than alternatives. 1532 When attributes are used primarily within a group of SDOs, and are 1533 not applicable to the wider Internet community, we expect that one 1534 SDO will be responsible for allocation from their own private space. 1536 Appendix B - Complex Attributes 1538 This section summarizes RADIUS attributes with complex data types 1539 that are defined in existing RFCs. 1541 This appendix is published for informational purposes only, and 1542 reflects the usage of attributes with complex data types at the time 1543 of the publication of this document. 1545 B.1. CHAP-Password 1547 [RFC2865] Section 5.3 defines the CHAP-Password Attribute which is 1548 sent from the RADIUS client to the RADIUS server in an Access- 1549 Request. The data type of the CHAP Identifier is not given, only the 1550 one octet length: 1552 0 1 2 1553 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 1554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1555 | Type | Length | CHAP Ident | String ... 1556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1558 Since this is an authentication attribute, code changes are required 1559 on the RADIUS client and server to support it, regardless of the 1560 attribute format. Therefore, this complex data type is acceptable in 1561 this situation. 1563 B.2. CHAP-Challenge 1565 [RFC2865] Section 5.40 defines the CHAP-Challenge Attribute which is 1566 sent from the RADIUS client to the RADIUS server in an Access- 1567 Request. While the data type of the CHAP Identifier is given, the 1568 text also says: 1570 If the CHAP challenge value is 16 octets long it MAY be placed in 1571 the Request Authenticator field instead of using this attribute. 1573 Defining attributes to contain values taken from the RADIUS packet 1574 header is NOT RECOMMENDED. Attributes should have values that are 1575 packed into a RADIUS AVP. 1577 B.3. Tunnel-Password 1579 [RFC2868] Section 3.5 defines the Tunnel-Password Attribute, which is 1580 sent from the RADIUS server to the client in an Access-Accept. This 1581 attribute includes Tag and Salt fields, as well as a string field 1582 which consists of three logical sub-fields: the Data-Length (one 1583 octet) and Password sub-fields (both of which are required), and the 1584 optional Padding sub-field. The attribute appears as follows: 1586 0 1 2 3 1587 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1589 | Type | Length | Tag | Salt 1590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1591 Salt (cont) | String ... 1592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1594 Since this is a security attribute and is encrypted, code changes are 1595 required on the RADIUS client and server to support it, regardless of 1596 the attribute format. Therefore, this complex data type is 1597 acceptable in this situation. 1599 B.4. ARAP-Password 1601 [RFC2869] Section 5.4 defines the ARAP-Password attribute, which is 1602 sent from the RADIUS client to the server in an Access-Request. It 1603 contains four 4 octet values, instead of having a single Value field: 1605 0 1 2 3 1606 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1607 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1608 | Type | Length | Value1 1609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1610 | Value2 1611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1612 | Value3 1613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1614 | Value4 1615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1616 | 1617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1619 As with the CHAP-Password attribute, this is an authentication 1620 attribute which would have required code changes on the RADIUS client 1621 and server regardless of format. 1623 B.5. ARAP-Features 1625 [RFC2869] Section 5.5 defines the ARAP-Features Attribute, which is 1626 sent from the RADIUS server to the client in an Access-Accept or 1627 Access-Challenge. It contains a compound string of two single octet 1628 values, plus three 4-octet values, which the RADIUS client 1629 encapsulates in a feature flags packet in the ARAP protocol: 1631 0 1 2 3 1632 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1634 | Type | Length | Value1 | Value2 | 1635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1636 | Value3 | 1637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1638 | Value4 | 1639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1640 | Value5 | 1641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1643 Unlike the previous attributes, this attribute contains no encrypted 1644 component, nor is it directly involved in authentication. The 1645 individual sub-fields therefore could have been encapsulated in 1646 separate attributes. 1648 While the contents of this attribute is intended to be placed in an 1649 ARAP packet, the fields need to be set by the RADIUS server. Using 1650 standard RADIUS data types would have simplified RADIUS server 1651 implementations, and subsequent management. The current form of the 1652 attribute requires either the RADIUS server implementation, or the 1653 RADIUS server administrator, to understand the internals of the ARAP 1654 protocol. 1656 B.6. Connect-Info 1658 [RFC2869] Section 5.11 defines the Connect-Info attribute, which is 1659 used to indicate the nature of the connection. 1661 0 1 2 1662 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1664 | Type | Length | Text... 1665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1667 Even though the type is Text, the rest of the description indicates 1668 that it is a complex attribute: 1670 The Text field consists of UTF-8 encoded 10646 _8_ characters. 1671 The connection speed SHOULD be included at the beginning of the 1672 first Connect-Info attribute in the packet. If the transmit and 1673 receive connection speeds differ, they may both be included in the 1674 first attribute with the transmit speed first (the speed the NAS 1675 modem transmits at), a slash (/), the receive speed, then 1676 optionally other information. 1677 For example, "28800 V42BIS/LAPM" or "52000/31200 V90" 1679 More than one Connect-Info attribute may be present in an 1680 Accounting-Request packet to accommodate expected efforts by ITU 1681 to have modems report more connection information in a standard 1682 format that might exceed 252 octets. 1684 This attribute contains no encrypted component, and is it not 1685 directly involved in authentication. The individual sub-fields could 1686 therefore have been encapsulated in separate attributes. 1688 Since the form of the text string is well defined, there is no 1689 benefit in using a text string. Instead, an integer attribute should 1690 have been assigned for each of the transmit speed and the receive 1691 speed. A separate enumerated integer should have been assigned for 1692 the additional information, as was done with the NAS-Port-Type 1693 attribute. 1695 B.7. Framed-IPv6-Prefix 1697 [RFC3162] Section 2.3 defines the Framed-IPv6-Prefix Attribute and 1698 [RFC4818] Section 3 reuses this format for the Delegated-IPv6-Prefix 1699 Attribute; these attributes are sent from the RADIUS server to the 1700 client in an Access-Accept. 1702 0 1 2 3 1703 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1705 | Type | Length | Reserved | Prefix-Length | 1706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1707 Prefix 1708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1709 Prefix 1710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1711 Prefix 1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1713 Prefix | 1714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1716 The sub-fields encoded in these attributes are strongly related, and 1717 there was no previous definition of this data structure that could be 1718 referenced. Support for this attribute requires code changes on both 1719 the client and server, due to a new data type being defined. In this 1720 case it appears to be acceptable to encode them in one attribute. 1722 B.8. Egress-VLANID 1724 [RFC4675] Section 2.1 defines the Egress-VLANID Attribute which can 1725 be sent by a RADIUS client or server. 1727 0 1 2 3 1728 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1730 | Type | Length | Value 1731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1732 Value (cont) | 1733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1735 While it appears superficially to be of type Integer, the Value field 1736 is actually a packed structure, as follows: 1738 0 1 2 3 1739 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1741 | Tag Indic. | Pad | VLANID | 1742 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1744 The length of the VLANID field is defined by the [IEEE-802.1Q] 1745 specification. The Tag indicator field is either 0x31 or 0x32, for 1746 compatibility with the Egress-VLAN-Name, as discussed below. The 1747 complex structure of Egress-VLANID overlaps with that of the base 1748 Integer data type, meaning that no code changes are required for a 1749 RADIUS server to support this attribute. Code changes are required 1750 on the NAS, if only to implement the VLAN ID enforcement. 1752 Given the IEEE VLAN requirements and the limited data model of 1753 RADIUS, the chosen method is likely the best of the possible 1754 alternatives. 1756 B.9. Egress-VLAN-Name 1758 [RFC4675] Section 2.3 defines the Egress-VLAN-Name Attribute which 1759 can be sent by a RADIUS client or server. 1761 0 1 2 3 1762 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1763 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1764 | Type | Length | Tag Indic. | String... 1765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1767 The Tag Indicator is either the character '1' or '2', which in ASCII 1768 map to the identical values for Tag Indicator in Egress-VLANID, 1769 above. The complex structure of this attribute is acceptable for 1770 reasons identical to those given for Egress-VLANID. 1771 B.9. Digest-* 1773 [RFC5090] attempts to standardize the functionality provided by an 1774 expired internet-draft [AAA-SIP] which improperly used two attributes 1775 from the standard space without being assigned them by IANA. This 1776 self-allocation is forbidden, as described above in Section 1.3 and 1777 in Section 2. In addition, the draft uses nested attributes, which 1778 are discouraged in Section 2.1. The updated document uses basic data 1779 types, and allocates nearly 20 attributes in the process. 1781 However, the draft has seen wide-spread implementation, where 1782 [RFC5090] has not. While there are a number of factors involved, one 1783 factor may be that implementors disagreed with the trade-offs made in 1784 the updated specification. It may have been better to simply 1785 document the existing format, and request IANA allocation of two 1786 attributes. The resulting design would have used nested attributes, 1787 but may have gained more wide-spread implementation. 1789 It is difficult to know which choice is optimal. Given the 1790 complexity of the protocols and implementations, it is impossible to 1791 define "hard and fast" rules for RADIUS design guidelines. 1793 Acknowledgments 1795 We would like to acknowledge David Nelson, Bernard Aboba, Emile van 1796 Bergen, Barney Wolff, Glen Zorn, Avi Lior, and Hannes Tschofenig for 1797 contributions to this document. 1799 Authors' Addresses 1801 Greg Weber 1802 Knoxville, TN 37932 1803 USA 1805 Email: gdweber@gmail.com 1807 Alan DeKok 1808 The FreeRADIUS Server Project 1809 http://freeradius.org/ 1811 Email: aland@freeradius.org