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Weber 3 INTERNET-DRAFT Individual Contributor 4 Category: Best Current Practice Alan DeKok (ed.) 5 FreeRADIUS 6 Expires: December 25, 2008 7 25 June 2008 9 RADIUS Design Guidelines 10 draft-ietf-radext-design-03.txt 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on June 5, 2008. 35 Copyright Notice 37 Copyright (C) The IETF Trust (2008). 39 Abstract 41 This document provides guidelines for the design of attributes used 42 by the Remote Authentication Dial In User Service (RADIUS) protocol. 43 It is expected that these guidelines will prove useful to authors and 44 reviewers of future RADIUS attribute specifications, both within the 45 IETF as well as other Standards Development Organizations (SDOs). 47 Table of Contents 49 1. Introduction ............................................. 3 50 1.1. Applicability ....................................... 3 51 1.2. Terminology ......................................... 4 52 1.3. Requirements Language ............................... 4 53 2. RADIUS Data Model ........................................ 4 54 2.1. Standard Space ...................................... 5 55 2.1.1. Basic Data Types ............................... 5 56 2.1.2. Tagging Mechanism .............................. 6 57 2.1.3. Complex Attribute Usage ........................ 7 58 2.1.4. Complex Attributes and Security ................ 9 59 2.1.5. Service definitions and RADIUS ................. 10 60 2.2. Vendor Space ........................................ 10 61 3. Data Model Issues ........................................ 12 62 3.1. Vendor Space ........................................ 13 63 3.1.1. Interoperability Considerations ................ 14 64 3.1.2. Vendor Allocations ............................. 15 65 3.1.3. SDO Allocations ................................ 15 66 3.1.4. Publication of specifications .................. 16 67 3.2. Polymorphic Attributes .............................. 16 68 4. IANA Considerations ...................................... 17 69 5. Security Considerations .................................. 17 70 6. References ............................................... 18 71 6.1. Normative References ................................ 18 72 6.2. Informative References .............................. 18 73 Appendix A - Design Guidelines ............................... 20 74 A.1. Types matching the RADIUS data model ................. 20 75 A.1.1. Transport of simple data ........................ 20 76 A.1.2. Extended data types ............................. 20 77 A.1.3. Complex data types .............................. 21 78 A.2. Improper Data Types .................................. 21 79 A.2.1. Simple Data Types ............................... 21 80 A.2.2. Complex Data Types .............................. 22 81 A.3. Vendor-Specific formats .............................. 22 82 A.4. New functionality in RADIUS. ......................... 23 83 A.5. Allocation of attributes ............................. 23 84 Appendix B - Complex Attributes .............................. 25 85 B.1. CHAP-Password ........................................ 25 86 B.2. CHAP-Challenge ....................................... 25 87 B.3. Tunnel-Password ...................................... 25 88 B.4. ARAP-Password ........................................ 26 89 B.5. ARAP-Features ........................................ 26 90 B.6. Connect-Info ......................................... 27 91 B.7. Framed-IPv6-Prefix ................................... 27 92 B.8. Egress-VLANID ........................................ 28 93 B.9. Egress-VLAN-Name ..................................... 29 94 Full Copyright Statement ..................................... 30 95 1. Introduction 97 This document provides guidelines for the design of RADIUS attributes 98 both within the IETF as well as within other Standards Development 99 Organizations (SDOs). By articulating RADIUS design guidelines, it 100 is hoped that this document will encourage the development and 101 publication of high quality RADIUS attribute specifications. 103 However, the advice in this document will not be helpful unless it is 104 put to use. As with "Guidelines for Authors and Reviewers of MIB 105 Documents [RFC4181], it is expected that this document will be used 106 by authors to check their document against the guidelines prior to 107 requesting review (such an "Expert Review" described in [RFC3575]). 108 Similarly, it is expected that this document will used by reviewers 109 (such as WG participants or the AAA Doctors), resulting in an 110 improvement in the consistency of reviews. 112 In order to meet these objectives, this document needs to cover not 113 only the science of attribute design, but also the art. As a result, 114 in addition to covering the most frequently encountered issues, this 115 document attempts to provide some of the considerations motivating 116 the guidelines. 118 In order to characterize current attribute usage, both the basic and 119 complex data types defined in the existing RADIUS RFCs are reviewed, 120 together with the ad-hoc extensions to that data model that have been 121 used in Vendor-Specific Attributes. 123 1.1. Applicability 125 As RADIUS has become more widely accepted as a management protocol, 126 its usage has become more prevalent, both within the IETF as well as 127 within other SDOs. Given the expanded utilization of RADIUS, it has 128 become apparent that requiring SDOs to accomplish all their RADIUS 129 work within the IETF is inherently inefficient and unscalable. By 130 articulating guidelines for RADIUS attribute design, this document 131 enables SDOs to design their own RADIUS attributes within the Vendor- 132 Specific Attribute (VSA) space, seeking review from the IETF. In 133 order enable IETF review of SDO RADIUS attribute specifications, the 134 authors recommend: 136 * Development of a program to encourage SDOs to make their RADIUS 137 attribute specifications publicly available; 139 * Review of IETF and SDO specifications according to the 140 guidelines proposed in this document; 142 The advice in this document applies to attributes used to encode 143 service-provisioning or authentication data. RADIUS protocol 144 changes, or specification of attributes that can be used to, in 145 effect, provide new RADIUS commands (such as Service-Type) are out of 146 scope. Since protocol changes require greater expertise and deeper 147 review, such changes should not be undertaken outside the IETF and 148 when handled within the IETF require "IETF Consensus" for adoption, 149 as noted in [RFC3575] Section 2.1. 151 As with protocol changes, this document does not provide guidance to 152 document authors seeking to change the RADIUS operational model. 153 While RADIUS server implementations may keep state, the RADIUS 154 protocol is stateless, although information may be passed from one 155 protocol transaction to another via the State Attribute. As a 156 result, documents which require stateful protocol behavior without 157 use of the State Attribute are inherently incompatible with RADIUS as 158 defined in [RFC2865], and need to be redesigned. 160 See [RFC5080] Section 2.1.1 for a more in-depth discussion of the use 161 of the State Attribute. 163 1.2. Terminology 165 This document uses the following terms: 167 Network Access Server (NAS) 168 A device that provides an access service for a user to a network. 170 RADIUS server 171 A RADIUS authentication, authorization, and/or accounting (AAA) 172 server is an entity that provides one or more AAA services to a 173 NAS. 175 RADIUS proxy 176 A RADIUS proxy acts as a RADIUS server to the NAS, and a RADIUS 177 client to the RADIUS server. 179 1.3. Requirements Language 181 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 182 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 183 document are to be interpreted as described in [RFC2119]. 185 2. RADIUS Data Model 187 The Remote Authentication Dial In User Service (RADIUS) defined in 188 [RFC2865] and [RFC2866] uses elements known as attributes in order to 189 represent authentication, authorization and accounting data. 191 Unlike SNMP, first defined in [RFC1157] and [RFC1155], RADIUS does 192 not define a formal data definition language. A handful of basic 193 data types are provided, and a data type is associated with an 194 attribute when the attribute is defined. 196 Two distinct attribute spaces are defined: the standard space, and a 197 Vendor-Specific space. Attributes in the standard space generally 198 are composed of a type, length, value (TLV) triplet, although complex 199 attributes have also been defined. The Vendor-Specific space is 200 encapsulated within a single attribute type (Vendor-Specific 201 Attribute). The format of this space is defined by individual 202 vendors, but the same TLV encoding used by the standard space is 203 recommended in [RFC2865] Section 5.26. The similarity between 204 attribute formats has enabled implementations to leverage common 205 parsing functionality, although in some cases the attributes in the 206 Vendor-Specific space have begun to diverge from the common format. 208 2.1. Standard Space 210 The following subsections describe common data types and formats 211 within the RADIUS standard attribute space. Common exceptions are 212 identified. 214 2.1.1. Basic Data Types 216 The data type of RADIUS attributes is not transported on the wire. 217 Rather, the data type of a RADIUS attribute is fixed when that 218 attribute is defined. Based on the RADIUS attribute type code, 219 RADIUS clients and servers can determine the data type based on pre- 220 configured entries within a data dictionary. 222 [RFC2865] defines the following data types: 224 text 1-253 octets containing UTF-8 encoded 10646 [RFC3629] 225 characters. Text of length zero (0) MUST NOT be sent; 226 omit the entire attribute instead. 227 string 1-253 octets containing binary data (values 0 through 228 255 decimal, inclusive). Strings of length zero (0) 229 MUST NOT be sent; omit the entire attribute instead. 230 IPv4 address 32 bit value, most significant octet first. 231 integer 32 bit unsigned value, most significant octet first. 232 time 32 bit unsigned value, most significant octet first 233 -- seconds since 00:00:00 UTC, January 1, 1970. 235 In addition to these data types, follow-on RADIUS specifications 236 define attributes using the following additional types: 238 IPv6 address 128 bit value, most significant octet first. 240 IPv6 prefix 8 bits of reserved, 8 bits of prefix length, up to 241 128 bits of value, most significant octet first. 242 integer64 64 bit unsigned value, most significant octet first. 243 This type has also been used to represent an IPv6 244 interface identifier. 246 Examples of the IPv6 address type include NAS-IPv6-Address defined in 247 [RFC3162] Section 2.1 and Login-IPv6-Host defined in [RFC3162] 248 Section 2.4. The IPv6 prefix type is used in [RFC3162] Section 2.3, 249 and in [RFC4818] Section 3. The integer64 type is used for the ARAP- 250 Challenge-Response Attribute defined in [RFC2869] Section 5.15, and 251 the Framed-Interface-Id Attribute defined in [RFC3162] Section 2.2. 252 [RFC4675] Section 2.4 defines User-Priority-Table as 64-bits in 253 length, but denotes it as type String. 255 Given that attributes of type IPv6 address, IPv6 prefix, and 256 integer64 are already in use, it is RECOMMENDED that RADIUS server 257 implementations include support for these additional basic types, in 258 addition to the types defined in [RFC2865]. 260 Where the intent is to represent a specific IPv6 address, the IPv6 261 address type SHOULD be used. Although it is possible to use the IPv6 262 IPv6 Prefix type with a prefix length of 128 to represent an IPv6 263 address, this usage is NOT RECOMMENDED 265 It is worth noting that since RADIUS only supports unsigned integers 266 of 32 or 64 bits, attributes using signed integer data types or 267 unsigned integer types of other sizes will require code changes, and 268 SHOULD be avoided. 270 For [RFC2865] RADIUS VSAs, the length limitation of the String and 271 Text types is 247 octets instead of 253 octets, due to the additional 272 overhead of the Vendor-Specific Attribute. 274 2.1.2. Tagging Mechanism 276 [RFC2868] defines an attribute grouping mechanism based on the use of 277 a one octet tag value. Tunnel attributes that refer to the same 278 tunnel are grouped together by virtue of using the same tag value. 280 This tagging mechanism has some drawbacks. There are a limited 281 number of unique tags (31). The tags are not well suited for use 282 with arbitrary binary data values, because it is not always possible 283 to tell if the first byte after the Length is the tag or the first 284 byte of the untagged value (assuming the tag is optional). 286 Other limitations of the tagging mechaism are that when integer 287 values are tagged, the value portion is reduced to three bytes 288 meaning only 24-bit numbers can be represented. The tagging 289 mechanism does not offer an ability to create nested groups of 290 attributes. Some RADIUS implementations treat tagged attributes as 291 having additional data types tagged-string and tagged-integer. These 292 types increase the complexity of implementing and managing RADIUS 293 systems. 295 New attributes SHOULD NOT use this tagging method because of the 296 limitations described above. New attributes SHOULD use the grouping 297 method described in [EXTEN]. 299 2.1.3. Complex Attribute Usage 301 The RADIUS attribute encoding is summarized in [RFC2865]: 303 0 1 2 304 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 306 | Type | Length | Value ... 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 309 However, some standard attributes do not follow this format. 310 Attributes that use sub-fields instead of using a basic data type are 311 known as "complex attributes". As described below, the definition of 312 complex attributes can lead to interoperability and deployment 313 issues, so they need to be introduced with care. 315 In general, complex attributes sent from the RADIUS server to the 316 client can be supported by concatenating the values into a String 317 data type field. However, separating these values into different 318 attributes, each with its own type and length, would have the 319 following benefits: 321 * it is easier for the user to enter the data as well-known 322 types, rather than complex structures 323 * it enables additional error checking by leveraging the 324 parsing and validation routines for well-known types 325 * it simplifies implementations by eliminating special-case 326 attribute-specific parsing. 328 One of the fundamental goals of the RADIUS protocol design was to 329 allow RADIUS servers to be configured to support new attributes 330 without requiring server code changes. RADIUS server implementations 331 typically use provide support for basic data types, and define 332 attributes in a data dictionary. This architecture enables a new 333 attribute to be supported by the addition of a dictionary entry, 334 without requiring RADIUS server code changes. 336 On the RADIUS client, code changes are typically required in order to 337 implement a new attribute, as the RADIUS client typically has to 338 compose the attribute dynamically when sending. When receiving, a 339 RADIUS client needs to be able to parse the attribute and carry out 340 the requested service. As a result, a detailed understanding of the 341 new attribute is required on clients, and data dictionaries are less 342 useful on clients than on servers. 344 Given these considerations, the introduction of a new basic or 345 complex attribute will typically require code changes on the RADIUS 346 client. The magnitude of changes for the complex attribute could be 347 greater, due to the potential need for custom parsing logic. 349 The RADIUS server can be configured to send a new attribute by 350 entering its type and data format in the RADIUS server dictionary, 351 and then filling in the value within a policy based on the attribute 352 name, data type and type-specific value. For complex attribute types 353 not supported by RADIUS server dictionaries, changes to the 354 dictionary and policy management code can be required in order to 355 allow the new attribute to be supported by and configured on the 356 RADIUS server. 358 Code changes can also be required in the RADIUS server's receive 359 path, due to limitations in RADIUS server policy languages, which 360 typically only provide for limited operations (such as comparisons or 361 arithmetic operations) on the basic data types. Many existing RADIUS 362 policy languages typically are not capable of parsing sub-elements, 363 or providing sophisticated matching functionality. 365 Given these limitations, the introduction of complex attributes can 366 require code changes on the RADIUS server which would be unnecessary 367 if basic data types had been used instead. In addition, attribute- 368 specific parsing means more complex software to develop and maintain. 369 More complexity can lead to more error prone implementations, and 370 interoperatibility problems. These issues can increase costs to 371 network administrators as well as reducing reliability and 372 introducing deployment barriers. As a result, the introduction of 373 new complex data types within RADIUS attribute specifications SHOULD 374 be avoided, except in the case of complex attributes involving 375 authentication or security functionality. 377 As can be seen in Appendix B, most of the complex attributes involve 378 authentication or security functionality. Supporting this 379 functionality requires code changes on both the RADIUS client and 380 server, regardless of the attribute format. As a result, in most 381 cases, the use of complex attributes to represent these methods is 382 acceptable, and does not create additional interoperability or 383 deployment issues. 385 The only other exception to the recommendation against complex types 386 is for types that can be treated as opaque data by the RADIUS server. 387 For example, the EAP-Message attribute, defined in [RFC3579] Section 388 3.1 contains a complex data type that is an EAP packet. Since these 389 complex types do not need to be parsed by the RADIUS server, the 390 issues arising from policy language limitations do not arise. 391 Similarly, since attributes of these complex types can be configured 392 on the server using a data type of String, dictionary limitations are 393 also not encountered. Section A.1 below includes a series of 394 checklists that may be used to analyze a design for RECOMMENDED and 395 NOT RECOMMENDED behavior in relation to complex types. 397 If the RADIUS Server simply passes the contents of an attribute to 398 some non-RADIUS portion of the network, then the data is opaque, and 399 SHOULD be defined to be of type String. A concrete way of judging 400 this requirement is whether or not the attribute definition in the 401 RADIUS document contains delineated fields for sub-parts of the data. 402 If those fields need to be delineated in RADIUS, then the data is not 403 opaque, and it SHOULD be separated into individual RADIUS attributes. 405 An examination of existing RADIUS RFCs discloses a number of complex 406 attributes that have already been defined. Appendix B includes a 407 listing of complex attributes used within [RFC2865], [RFC2868], 408 [RFC2869], [RFC3162], [RFC4818], and [RFC4675]. The discussion of 409 these attributes includes reasons why a complex type is acceptable, 410 or suggestions for how the attribute could have been defined to 411 follow the RADIUS data model. 413 In other cases, the data in the complex type are described textually. 414 This is possible because the data types are not sent within the 415 attributes, but are a matter for endpoint interpretation. An 416 implementation can define additional data types, and use these data 417 types today by matching them to the attribute's textual description. 419 2.1.4. Complex Attributes and Security 421 The introduction of complex data types brings the potential for the 422 introduction of new security vulnerabilities. Experience shows that 423 the common data types have few security vulnerabilities, or else that 424 all known issues have been found and fixed. New data types require 425 new code, which may introduce new bugs, and therefore new attack 426 vectors. 428 RADIUS servers are highly valued targets, as they control network 429 access and interact with databases that store usernames and 430 passwords. An extreme outcome of a vulnerability due to a new, 431 complex type would be that an attacker is capable of taking complete 432 control over the RADIUS server. 434 The use of attributes representing opaque data does not reduce this 435 threat. The threat merely moves from the RADIUS server to the 436 application that consumes that opaque data. 438 The threat is particularly severe when the opaque data does not 439 originate from, or is checked by the NAS. In those cases, the RADIUS 440 server is potentially exposed to attack by malware residing on an 441 unauthenticated host. Applications consuming opaque data that reside 442 on the RADIUS server SHOULD be properly isolated from the RADIUS 443 server, and SHOULD run with minimal privileges. Any potential 444 vulnerabilities in that application will then have minimal impact on 445 the security of the system as a whole. 447 2.1.5. Service definitions and RADIUS 449 RADIUS specifications define how an existing service or protocol can 450 be provisioned using RADIUS. Therefore, it is expected that a RADIUS 451 attribute specification will reference documents defining the 452 protocol or service to be provisioned. Within the IETF, a RADIUS 453 attribute specification SHOULD NOT be used to define the protocol or 454 service being provisioned. New services using RADIUS for 455 provisioning SHOULD be defined elsewhere and referenced in the RADIUS 456 specification. 458 RADIUS also SHOULD NOT be extended to new commands via attributes. 459 RADIUS attributes are intended to: 461 * authenticate users 462 * authorize users (i.e., service provisioning or changes to 463 provisioning) 464 * account for user activity (i.e., logging of session activity) 466 New commands (i.e., the Code field in the packet header) are 467 allocated only through "IETF Consensus" as noted in [RFC3575] Section 468 2.1. Specifications SHOULD NOT use new attributes to modify the 469 interpretation of existing RADIUS commands. 471 2.2. Vendor Space 473 As noted in [RFC2865] Section 5.26, the VSA format is defined as 474 follows: 476 0 1 2 3 477 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 1 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 479 | Type | Length | Vendor-Id 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 Vendor-Id (cont) | String... 483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 485 The high-order octet of the Vendor-Id field is 0 and the low-order 3 486 octets are the Structure of Management Information (SMI) Network 487 Management Private Enterprise Code (PEC) of the Vendor in network 488 byte order. 490 While the format of the String field is defined by the vendor, 491 [RFC2865] Section 5.26 notes: 493 It SHOULD be encoded as a sequence of vendor type / vendor length 494 / value fields, as follows. The Attribute-Specific field is 495 dependent on the vendor's definition of that attribute. An 496 example encoding of the Vendor-Specific attribute using this 497 method follows: 499 0 1 2 3 500 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 1 501 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 502 | Type | Length | Vendor-Id 503 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 504 Vendor-Id (cont) | Vendor type | Vendor length | 505 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 506 | Attribute-Specific... 507 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 509 Multiple sub-attributes MAY be encoded within a single Vendor- 510 Specific attribute, although they do not have to be. 512 Note that the Vendor type field in the recommended VSA format is only 513 a single octet, like the RADIUS type field. While this limitation 514 results in an efficient encoding, there are situations in which a 515 vendor or SDO will eventually wish to define more than 255 516 attributes. Also, an SDO can be comprised of multiple subgroups, 517 each of whom can desire autonomy over the definition of attributes 518 within their group. In such a situation, a 16-bit Vendor type field 519 would be more appropriate: 521 0 1 2 3 522 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 1 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 | Type | Length | Vendor-Id 525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 Vendor-Id (cont) | Vendor type | 527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 528 | Vendor length | Attribute-Specific... 529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 Other attribute formats are NOT RECOMMENDED. Examples of NOT 531 RECOMMENDED formats include Vendor types of more than 16 bits, Vendor 532 lengths of less than 8 bits, Vendor lengths of more than 8 bits, and 533 Vendor-Specific contents that are not in Type-Length-Value format. 535 In order to be compatible with the above recommendations for 536 attribute definitions, it is RECOMMENDED that RADIUS servers support 537 attributes using a 16-bit Vendor type field. 539 3. Data Model Issues 541 Since the closure of the RADIUS Working Group, the popularity and 542 prevalence of RADIUS has continued to grow. In addition to 543 increasing demand for allocation of attributes within the RADIUS 544 standard attribute space, the number of vendors and SDOs creating new 545 attributes within the Vendor-Specific attribute space has grown, and 546 this has lead to some divergence in approaches to RADIUS attribute 547 design. 549 In general, standard RADIUS attributes have a more constrained data 550 model than attributes within the vendor space. For example, vendors 551 and SDOs have evolved the data model to support new functions such as 552 attribute grouping and attribute fragmentation, with different groups 553 taking different approaches. 555 Given these enhancements, it has become difficult for vendors or SDOs 556 to translate attributes from the vendor space to the more stringent 557 standards space. For example, a Vendor-Specific attribute using sub- 558 elements could require allocation of several standard space 559 attributes using basic data types. In this case not only would 560 translation require substantial additional work, it would further 561 deplete the RADIUS standard attribute space. Given these 562 limitations, translation of vendor attributes to the standards space 563 is not necessarily desirable, particularly if the VSA specification 564 is publicly available and can be implemented within existing RADIUS 565 clients and servers. In such situations, the costs may substantially 566 outweigh the benefits. It is possible that some of the enhancements 567 made within the vendor space may eventually become available within 568 the standard attribute space. However, the divergence of the 569 standard and vendor attribute spaces is most likely a permanent 570 feature, and should be recognized as such. 572 Recent extensions to the RADIUS data model such as [EXTEN] make it 573 possible to minimize the use of complex attributes. New 574 specifications seeking to extend the standard RADIUS data model 575 SHOULD examine [EXTEN] to see if their needs fit within the extended 576 RADIUS data model. 578 3.1. Vendor Space 580 The usage model for RADIUS VSAs is described in [RFC2865] Section 581 6.2: 583 Note that RADIUS defines a mechanism for Vendor-Specific 584 extensions (Attribute 26) and the use of that should be encouraged 585 instead of allocation of global attribute types, for functions 586 specific only to one vendor's implementation of RADIUS, where no 587 interoperability is deemed useful. 589 Nevertheless, many new attributes have been defined in the vendor 590 specific space in situations where interoperability is not only 591 useful, but is required. For example, Standards Development 592 Organizations (SDOs) outside the IETF (such as the IEEE 802 and the 593 3rd Generation Partnership Project (3GPP)) have been assigned Vendor- 594 Ids, enabling them to define their own VSA format and assign Vendor 595 types within their own space. 597 The use of VSAs by SDOs outside the IETF has gained in popularity for 598 several reasons: 600 Efficiency 601 As with SNMP, which defines an "Enterprise" Object Identifier (OID) 602 space suitable for use by vendors as well as other SDOs, the 603 definition of Vendor-Specific RADIUS attributes has become a common 604 occurrence as part of standards activity outside the IETF. For 605 reasons of efficiency, it is easiest if the RADIUS attributes 606 required to manage a standard are developed within the same SDO 607 that develops the standard itself. As noted in "Transferring MIB 608 Work from IETF Bridge MIB WG to IEEE 802.1 WG" [RFC4663], today few 609 vendors are willing to simultaneously fund individuals to 610 participate within an SDO to complete a standard, as well as to 611 participate in IETF in order to complete the associated RADIUS 612 attributes specification. 614 Attribute scarcity 615 The standard RADIUS attribute space is limited to 255 unique 616 attributes. Of these, only about half remain available for 617 allocation. In the Vendor-Specific space, the number of attributes 618 available is a function of the format of the attribute (the size of 619 the Vendor type field). 621 Along with these advantages, some limitations of VSA usage are noted 622 in [RFC2865] Section 5.26: 624 This Attribute is available to allow vendors to support their own 625 extended Attributes not suitable for general usage. It MUST NOT 626 affect the operation of the RADIUS protocol. 628 Servers not equipped to interpret the vendor-specific information 629 sent by a client MUST ignore it (although it may be reported). 630 Clients which do not receive desired vendor-specific information 631 SHOULD make an attempt to operate without it, although they may do 632 so (and report they are doing so) in a degraded mode. 634 The limitation on changes to the RADIUS protocol effectively 635 prohibits VSAs from changing fundamental aspects of RADIUS operation, 636 such as modifying RADIUS packet sequences, or adding new commands. 637 However, the requirement for clients and servers to be able to 638 operate in the absence of VSAs has proven to be less of a constraint, 639 since it is still possible for a RADIUS client and server to mutually 640 indicate support for VSAs, after which behavior expectations can be 641 reset. 643 Therefore, RFC 2865 provides considerable latitude for development of 644 new attributes within the vendor space, while prohibiting development 645 of protocol variants. This flexibility implies that RADIUS 646 attributes can often be developed within the vendor space without 647 loss (and possibly even gain) in functionality. 649 As a result, translation of RADIUS attributes developed within the 650 vendor space into the standard space may provide only modest 651 benefits, while accelerating the exhaustion of the standard attribute 652 space. We do not expect that all RADIUS attribute specifications 653 requiring interoperability will be developed within the IETF, and 654 allocated from the standards space. A more scalable approach is to 655 recognize the flexibility of the vendor space, while working toward 656 improvements in the quality and availability of RADIUS attribute 657 specifications, regardless of where they are developed. 659 3.1.1. Interoperability Considerations 661 Vendors and SDOs are reminded that the standard RADIUS attribute ID 662 space, and the enumerated value space for enumerated attributes, are 663 reserved for allocation through work published via the IETF, as noted 664 in [RFC3575] Section 2.1. Some vendors and SDOs have in the past 665 performed self-allocation by assigning vendor-specific meaning to 666 "unused" values from the standard RADIUS attribute ID or enumerated 667 value space. This self-allocation results in interoperability 668 issues, and is counter-productive. Similarly, the Vendor-Specific 669 enumeration practice discussed in [RFC2882] Section 2.2.1 is NOT 670 RECOMMENDED. 672 If it is not possible to follow the above procedure, vendors and SDOs 673 SHOULD self-allocate an attribute from their Vendor-Specific space, 674 and define an appropriate value for it. 676 As a side note, [RFC2865] Section 5.26 uses the term "Vendor-Specific 677 Attribute" to refer to an encoding format which can be used by 678 individual vendors to define attributes not suitable for general 679 usage. However, since then VSAs have also become widely used by SDOs 680 defining attributes intended for multi-vendor interoperability. As 681 such, these attributes are not specific to any single vendor, and the 682 term "Vendor-Specific" may be misleading. An alternate term which 683 better describes this use case is SDO-Specific Attribute (SSA). 685 The design and specification of VSAs for multi-vendor usage SHOULD be 686 undertaken with the same level of care as standard RADIUS attributes. 687 Specifically, the provisions of this document that apply to standard 688 RADIUS attributes also apply to SSAs or VSAs for multi-vendor usage. 690 3.1.2. Vendor Allocations 692 Vendor RADIUS Attribute specifications SHOULD allocate attributes 693 from the vendor space, rather than requesting an allocation from the 694 RADIUS standard attribute space. 696 As discussed in [RFC2865] Section 5.26, the vendor space is intended 697 for vendors to support their own extended attributes not suitable for 698 general use. However, it is RECOMMENDED that vendors follow the 699 guidelines outlined here, which are intended to enable maximum 700 interoperability with minimal changes to existing systems. 702 Following these guidelines means that RADIUS servers can be updated 703 to support the vendor's equipment by editing a RADIUS dictionary. If 704 these guidelines are not followed, then the vendor's equipment can 705 only be supported via code changes in RADIUS server implementations. 706 Such code changes add complexity and delay to implementations. 708 3.1.3. SDO Allocations 710 SDO RADIUS Attribute specifications SHOULD allocate attributes from 711 the vendor space, rather than requesting an allocation from the 712 RADIUS standard attribute space, for attributes matching any of the 713 following criteria: 715 * attributes relying on data types not defined within RADIUS 716 * attributes intended primarily for use within an SDO 717 * attributes intended primarily for use within a group of SDOs. 719 The recommendation for SDOs to allocate attributes from a vendor 720 space rather than via IETF process is a recognition that SDOs may 721 desire to assert change control over their own RADIUS specifications. 723 This change control can be obtained by requesting a PEC from the 724 Internet Assigned Number Authority (IANA), for use as a Vendor-Id 725 within a Vendor-Specific attribute. Further allocation of attributes 726 inside of the VSA space defined by that Vendor-Id is subject solely 727 to the discretion of the SDO. Similarly, the use of data types 728 (complex or not) within that VSA space is solely under the discretion 729 of the SDO. It is RECOMMENDED that SDOs follow the guidelines 730 outlined here, which are intended to enable maximum interoperability 731 with minimal changes to existing systems. 733 It should be understood that SDOs do not have to rehost VSAs into the 734 standards space solely for the purpose of obtaining IETF review. 735 Rehosting puts pressure on the standards space, and may be harmful to 736 interoperability, since it can create two ways to provision the same 737 service. Rehosting may also require changes to the RADIUS data model 738 which will affect implementations that do not intend to support the 739 SDO specifications 741 3.1.4. Publication of specifications 743 SDOs are encouraged to seek early review of SSA specifications by the 744 IETF. This review may be initiated by sending mail to the AAA 745 Doctors list (aaa-doctors@ops.ietf.org). Since the IETF is not a 746 membership organization, in order to enable the RADIUS SSA 747 specification to be reviewed, it is RECOMMENDED that it be made 748 publicly available; this also encourages interoperability. Where the 749 RADIUS SSA specification is embedded within a larger document which 750 cannot be made public, the RADIUS attribute and value definitions 751 SHOULD be published instead as an Informational RFC, as with 752 [RFC4679]. This process SHOULD be followed instead of requesting 753 IANA allocations from within the standard RADIUS attribute space. 755 Similarly, vendors are encouraged to make their specifications 756 publicly available, for maximum interoperability. However, it is not 757 necessary for them to request publication of their VSA specifications 758 as Informational RFCs by the IETF. 760 All other specifications, including new authentication and/or 761 security mechanisms SHOULD be allocated via the standard RADIUS 762 space, as noted in [RFC3575] Section 2.1. 764 3.2. Polymorphic Attributes 766 A polymorphic attribute is one whose format or meaning is dynamic. 767 For example, rather than using a fixed data format, an attribute's 768 format might change based on the contents of another attribute. Or, 769 the meaning of an attribute may depend on earlier packets in a 770 sequence. 772 RADIUS server dictionary entries are typically static, enabling the 773 user to enter the contents of an attribute without support for 774 changing the format based on dynamic conditions. However, this 775 limitation on static types does not prevent implementations from 776 implementing policies that return different attributes based on the 777 contents of received attributes; this is a common feature of existing 778 RADIUS implementations. 780 In general, polymorphism is NOT RECOMMENDED. Polymorphism rarely 781 enables capabilities that would not be available through use of 782 multiple attributes. Polymorphism requires code changes in the 783 RADIUS server in situations where attributes with fixed formats would 784 not require such changes. Thus, polymorphism increases complexity 785 while decreasing generality, without delivering any corresponding 786 benefits. 788 Note that changing an attribute's format dynamically is not the same 789 thing as using a fixed format and computing the attribute itself 790 dynamically. RADIUS authentication attributes such as User-Password, 791 EAP-Message, etc. while being computed dynamically, use a fixed 792 format. 794 4. IANA Considerations 796 This document requires no action by IANA. 798 5. Security Considerations 800 This specification provides guidelines for the design of RADIUS 801 attributes used in authentication, authorization and accounting. 802 Threats and security issues for this application are described in 803 [RFC3579] and [RFC3580]; security issues encountered in roaming are 804 described in [RFC2607]. 806 Encryption of RADIUS attributes on a per-attribute basis is necessary 807 in some cases. The current standard mechanism for this is described 808 in [RFC2865] Section 5.2 (for obscuring User-Password values) and is 809 based on the MD5 algorithm specified in [RFC1321]. The MD5 and SHA-1 810 algorithms have recently become a focus of scrutiny and concern in 811 security circles, and as a result, the use of these algorithms in new 812 attributes is NOT RECOMMENDED. 814 Where new RADIUS attributes use cryptographic algorithms, algorithm 815 negotiation SHOULD be supported. Specification of a mandatory-to- 816 implement algorithm is REQUIRED, and it is RECOMMENDED that the 817 mandatory-to-implement algorithm be certifiable under FIPS 140 818 [FIPS]. 820 Where new RADIUS attributes encapsulate complex data types, or 821 transport opaque data, the security considerations discussed in 822 Section 2.1.4 SHOULD be addressed. 824 6. References 826 6.1. Normative References 828 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 829 Requirement Levels", BCP 14, RFC 2119, March 1997. 831 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote 832 Authentication Dial In User Service (RADIUS)", RFC 2865, June 833 2000. 835 [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote 836 Authentication Dial In User Service)", RFC 3575, July 2003. 838 6.2. Informative References 840 [RFC1155] Rose, M. and K. McCloghrie, "Structure and identification of 841 management information for TCP/IP-based internets", STD 16, 842 RFC 1155, May 1990. 844 [RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple 845 Network Management Protocol (SNMP)", STD 15, RFC 1157, May 846 1990. 848 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, 849 April 1992. 851 [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy 852 Implementation in Roaming", RFC 2607, June 1999. 854 [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. 856 [RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M., 857 and I. Goyret, "RADIUS Attributes for Tunnel Protocol 858 Support", RFC 2868, June 2000. 860 [RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RADIUS Extensions", 861 RFC 2869, June 2000. 863 [RFC2882] Mitton, D, "Network Access Servers Requirements: Extended 864 RADIUS Practices", RFC 2882, July 2000. 866 [RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 867 3162, August 2001. 869 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial 870 In User Service) Support For Extensible Authentication 871 Protocol (EAP)", RFC 3579, September 2003. 873 [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., Roese, J., "IEEE 874 802.1X Remote Authentication Dial In User Service (RADIUS) 875 Usage Guidelines", RFC3580, September 2003. 877 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 878 RFC 3629, November 2003. 880 [RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB 881 Documents", RFC 4181, September 2005. 883 [RFC4663] Harrington, D., "Transferring MIB Work from IETF Bridge MIB WG 884 to IEEE 802.1 WG", RFC 4663, September 2006. 886 [RFC4675] Congdon, P., Sanchez, M. and B. Aboba, "RADIUS Attributes for 887 Virtual LAN and Priority Support", RFC 4675, September 2006. 889 [RFC4679] Mammoliti, V., et al., "DSL Forum Vendor-Specific RADIUS 890 Attributes", RFC 4679, September 2006. 892 [RFC4818] Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix 893 Attribute", RFC 4818, April 2007. 895 [RFC5080] Nelson, D. and DeKok, A, "Common Remote Authentication Dial In 896 User Service (RADIUS) Implementation Issues and Suggested 897 Fixes", RFC 5080, December 2007. 899 [IEEE-802.1Q] 900 IEEE Standards for Local and Metropolitan Area Networks: Draft 901 Standard for Virtual Bridged Local Area Networks, 902 P802.1Q-2003, January 2003. 904 [EXTEN] Li, Y., et al., "Extended Remote Authentication Dial In User 905 Service (RADIUS) Attributes", draft-ietf-radext-extended- 906 attributes-03.txt (work in progress). 908 [FIPS] FIPS 140-3 (DRAFT), "Security Requirements for Cryptographic 909 Modules", http://csrc.nist.gov/publications/fips/fips140-3/ 911 Appendix A - Design Guidelines 913 The following text provides guidelines for the design of attributes 914 used by the RADIUS protocol. Specifications that follow these 915 guidelines are expected to achieve maximum interoperability with 916 minimal changes to existing systems. 918 A.1. Types matching the RADIUS data model 920 A.1.1. Transport of simple data 922 Does the data fit within the existing RADIUS data model, as outlined 923 below? If so, it SHOULD be encapsulated in a [RFC2865] format RADIUS 924 attribute, or in a [RFC2865] format RADIUS VSA. 926 * 32-bit unsigned integer, most significant octet first. 927 * Enumerated data types, represented as a 32-bit unsigned integer 928 with a list of name to value mappings. (e.g., Service-Type) 929 * 64-bit unsigned integer, most significant octet first. 930 * IPv4 address in network byte order. 931 * IPv6 address in network byte order. 932 * IPv6 prefix. 933 * time as 32 bit unsigned value, most significant octet first, in 934 seconds since 00:00:00 UTC, January 1, 1970. 935 * string (i.e., binary data), totalling 253 octets or less in 936 length. This includes the opaque encapsulation of data 937 structures defined outside of RADIUS. See also Section A.1.3, 938 below. 939 * UTF-8 text, totalling 253 octets or less in length. 940 * Complex data types for authentication and/or security. 941 These attributes SHOULD be defined only within the RADIUS 942 attribute space, and SHOULD NOT be defined within the VSA space. 944 Note that the length limitations for VSAs of type String and Text are 945 less than 253 octets, due to the additional overhead of the Vendor- 946 Specific format. 948 A.1.2. Extended data types 950 Where possible, the data types defined above in Section A.1.2 SHOULD 951 be used. The extended data types SHOULD be used only where there is 952 no clear method of expressing the data using existing types. 954 Does the data fit within the extended RADIUS data model, as outlined 955 below? If so, it SHOULD be encapsulated in a [EXTEN] format RADIUS 956 VSA. 958 * Attributes grouped into a logical container. 960 This does not include nested groups. 961 * Attributes requiring the transport of more than 247 octets of 962 Text or String data. This includes the opaque encapsulation 963 of data structures defined outside of RADIUS. See also Section 964 A.1.3, below. 966 A.1.3. Complex data types 968 Does the attribute encapsulate an existing data structure defined 969 outside of the RADIUS specifications? Can the attribute be treated 970 as opaque data by RADIUS servers (including proxies?) If both 971 questions can be answered affirmatively, a complex structure MAY be 972 used in a RADIUS specification. 974 The specification of the attribute SHOULD define the encapsulating 975 attribute to be of type String. The specification SHOULD refer to an 976 external document defining the structure. The specification SHOULD 977 NOT define or describe the structure, as discussed above in Section 978 2.1.3. 980 A.2. Improper Data Types 982 All data types other than the ones described above in Section A.1 983 SHOULD NOT be used. This section describes in detail a number of 984 data types that are NOT RECOMMENDED in new RADIUS specifications. 985 Where possible, replacement data types are suggested. 987 A.2.1. Simple Data Types 989 Does the attribute use any of the following data types? If so, the 990 data type SHOULD be replaced with the suggested alternatives, or 991 SHOULD NOT be used at all. 993 * Signed integers of any size. 994 SHOULD NOT be used. SHOULD be replaced with one or more 995 unsigned integer attributes. The definition of the attribute 996 can contain information that would otherwise go into the sign 997 value of the integer. 998 * 8 bit unsigned integers. 999 SHOULD be replaced with 32-bit unsigned integer. There is 1000 insufficient justification to save three bytes. 1001 * 16 bit unsigned integers. 1002 SHOULD be replaced with 32-bit unsigned integer. There is 1003 insufficient justification to save two bytes. 1004 * Unsigned integers of size other than 32 or 64. 1005 SHOULD be replaced by an unsigned integer of 32 or 64 bits. 1006 There is insufficient justification to define a new size of 1007 integer. 1009 * Integers of any size in non-network byte order 1010 SHOULD be replaced by unsigned integer of 32 or 64 bits, 1011 in network byte order. There is no reason to transport integers 1012 in any format other than network byte order. 1013 * Tagged data types as described in [RFC2868]. 1014 These data types SHOULD NOT be used in new specifications. The 1015 attribute grouping method defined in [EXTEN] SHOULD be used 1016 instead. 1017 * Complex data structures defined only within RADIUS. 1018 The additional functionality defined in [EXTEN] SHOULD be used 1019 instead. This recommendation does not apply to new attributes 1020 for authentication or security, as described below in Section 1021 A.2.2. 1022 * Multi-field text strings. 1023 Each field SHOULD be encapsulated in a separate attribute. 1024 Where grouping of fields is desired, the additional 1025 functionality defined in [EXTEN] SHOULD be used instead. 1026 * Polymorphic attributes. 1027 Multiple attributes, each with a static data type SHOULD be 1028 defined instead. 1030 A.2.2. Complex Data Types 1032 Does the attribute define a complex data type for purposes other than 1033 authentication or security? If so, this data type SHOULD be replaced 1034 with simpler types, as discussed above in Section A.2.1. Also see 1035 Section 2.1.3 for a discussion of why complex types are problematic. 1037 A.3. Vendor-Specific formats 1039 Does the specification contain Vendor-Specific attributes that match 1040 any of the following criteria? If so, the data type should be 1041 replaced with the suggested alternatives, or should not be used at 1042 all. 1044 * Vendor types of more than 16 bits. 1045 SHOULD NOT be used. Vendor types of 8 or 16 bits SHOULD be used 1046 instead. 1047 * Vendor lengths of less than 8 bits. (i.e., zero bits) 1048 SHOULD NOT be used. Vendor types of 8 or 16 bits SHOULD be used 1049 instead. 1050 * Vendor lengths of more than 8 bits. 1051 SHOULD NOT be used. Vendor lengths of 8 bits SHOULD be used 1052 instead. 1053 * Vendor-Specific contents that are not in Type-Length-Value 1054 format. 1055 SHOULD NOT be used. Vendor-Specific attributes SHOULD be in 1056 Type-Length-Value format. 1058 We recognize that SDOs may require more than 256 attributes, which is 1059 the limit of the 8-bit [RFC2865] Vendor-Specific space. Those SDOs 1060 SHOULD use Vendor types of 16 bits. However, SDOs SHOULD NOT use 1061 Vendor types of 16 bits unless there are immediate requirements. 1062 Future-proofing a specification is insufficient grounds for using 1063 16-bit Vendor types. 1065 In general, Vendor-Specific attributes SHOULD follow the [RFC2865] 1066 suggested format, or the [EXTEN] format if more functionality, or a 1067 larger attribute space is necessary. 1069 A.4. New functionality in RADIUS. 1071 Does the specification extend RADIUS by adding new functionality, as 1072 outlined in the list below? If so, it SHOULD NOT use RADIUS. 1073 Another method of achieving the design objectives SHOULD be used. 1075 * Defining new commands in RADIUS using attributes. 1076 This restriction includes new commands created by overloading 1077 the Service-Type attribute to define new values that modify 1078 the functionality of Access-Request packets. 1079 * Using RADIUS as a transport protocol for non-AAA data. 1080 This restriction is partially a subset of the previous one. 1081 Note that using RADIUS to transport authentication methods 1082 (e.g., EAP) is explicitly permitted, even if those methods 1083 require the transport of relatively large amounts of data. 1084 * Extending the RADIUS packet length limitation past 4096 octets. 1085 A multi-packet sequence of Access-Request / Access-Challenge 1086 SHOULD be used instead. If that is not possible, then a method 1087 other than RADIUS SHOULD be used to transport the data. 1089 A.5. Allocation of attributes 1091 Does the attribute have a limited scope of applicability, as outlined 1092 below? If so, then the attributes SHOULD be allocated from the 1093 Vendor-Specific space. 1095 * attributes intended for a vendor to support their own systems, 1096 and not suitable for general usage 1097 * attributes relying on data types not defined within RADIUS 1098 * attributes intended primarily for use within an SDO 1099 * attributes intended primarily for use within a group of SDOs. 1101 Note that the points listed above do not relax the recommendations 1102 discussed in this document. Instead, they recognize that the RADIUS 1103 data model has limitations. In certain situations where 1104 interoperability can be strongly constrained, a data model extended 1105 by the SDO or vendor MAY be used. We recommend, however, that the 1106 RADIUS data model SHOULD be used, even if it is marginally less 1107 efficient than alternatives. 1109 Appendix B - Complex Attributes 1111 This section summarizes RADIUS attributes with complex data types 1112 that are defined in existing RFCs. 1114 B.1. CHAP-Password 1116 [RFC2865] Section 5.3 defines the CHAP-Password Attribute which is 1117 sent from the RADIUS client to the RADIUS server in an Access- 1118 Request. The the data type of the CHAP Identifier is not given, only 1119 the one octet length: 1121 0 1 2 1122 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 1123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1124 | Type | Length | CHAP Ident | String ... 1125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1127 Since this is an authentication attribute, code changes are required 1128 on the RADIUS client and server to support it, regardless of the 1129 attribute format. Therefore, this complex data type is acceptable in 1130 this situation. 1132 B.2. CHAP-Challenge 1134 [RFC2865] Section 5.40 defines the CHAP-Challenge Attribute which is 1135 sent from the RADIUS client to the RADIUS server in an Access- 1136 Request. While the data type of the CHAP Identifier is given, the 1137 text also says 1139 If the CHAP challenge value is 16 octets long it MAY be placed in 1140 the Request Authenticator field instead of using this attribute. 1142 Defining attributes to contain values taken from the RADIUS packet 1143 header is NOT RECOMMENDED. Attributes should have values that are 1144 packed into a RADIUS AVP. 1146 B.3. Tunnel-Password 1148 [RFC2868] Section 3.5 defines the Tunnel-Password Attribute, which is 1149 sent from the RADIUS server to the client in an Access-Accept. This 1150 attribute includes Tag and Salt fields, as well as a string field 1151 which consists of three logical sub-fields: the Data-Length (one 1152 octet) and Password sub-fields (both of which are required), and the 1153 optional Padding sub-field. The attribute appears as follows: 1155 0 1 2 3 1156 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 1158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1159 | Type | Length | Tag | Salt 1160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1161 Salt (cont) | String ... 1162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1164 Since this is a security attribute and is encrypted, code changes are 1165 required on the RADIUS client and server to support it, regardless of 1166 the attribute format. Therefore, this complex data type is 1167 acceptable in this situation. 1169 B.4. ARAP-Password 1171 [RFC2869] Section 5.4 defines the ARAP-Password attribute, which is 1172 sent from the RADIUS client to the server in an Access-Request. It 1173 contains four 4 octet values, instead of having a single Value field: 1175 0 1 2 3 1176 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 1177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1178 | Type | Length | Value1 1179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1180 | Value2 1181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1182 | Value3 1183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1184 | Value4 1185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1186 | 1187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1189 As with the CHAP-Password attribute, this is an authentication 1190 attribute which would have required code changes on the RADIUS client 1191 and server regardless of format. 1193 B.5. ARAP-Features 1195 [RFC2869] Section 5.5 defines the ARAP-Features Attribute, which is 1196 sent from the RADIUS server to the client in an Access-Accept or 1197 Access-Challenge. It contains a compound string of two single octet 1198 values, plus three 4-octet values, which the RADIUS client 1199 encapsulates in a feature flags packet in the ARAP protocol: 1201 0 1 2 3 1202 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 1203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1204 | Type | Length | Value1 | Value2 | 1205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1206 | Value3 | 1207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1208 | Value4 | 1209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1210 | Value5 | 1211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1213 Unlike the previous attributes, this attribute contains no encrypted 1214 component, nor is it directly involved in authentication. The 1215 individual sub-fields therefore could have been encapsulated in 1216 separate attributes. 1218 B.6. Connect-Info 1220 [RFC2869] Section 5.11 defines the Connect-Info attribute, which is 1221 used to indicate the nature of the connection. 1223 0 1 2 1224 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1226 | Type | Length | Text... 1227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1229 Even though the type is Text, the rest of the description indicates 1230 that it is a complex attribute: 1232 The Text field consists of UTF-8 encoded 10646 [8] characters. 1233 The connection speed SHOULD be included at the beginning of the 1234 first Connect-Info attribute in the packet. If the transmit and 1235 receive connection speeds differ, they may both be included in the 1236 first attribute with the transmit speed first (the speed the NAS 1237 modem transmits at), a slash (/), the receive speed, then 1238 optionally other information. 1239 For example, "28800 V42BIS/LAPM" or "52000/31200 V90" 1241 More than one Connect-Info attribute may be present in an 1242 Accounting-Request packet to accommodate expected efforts by ITU 1243 to have modems report more connection information in a standard 1244 format that might exceed 252 octets. 1246 This attribute contains no encrypted component, and is it not 1247 directly involved in authentication. The individual sub-fields could 1248 therefore have been encapsulated in separate attributes. 1250 B.7. Framed-IPv6-Prefix 1252 [RFC3162] Section 2.3 defines the Framed-IPv6-Prefix Attribute and 1253 [RFC4818] Section 3 reuses this format for the Delegated-IPv6-Prefix 1254 Attribute; these attributes are sent from the RADIUS server to the 1255 client in an Access-Accept. 1257 0 1 2 3 1258 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 1259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1260 | Type | Length | Reserved | Prefix-Length | 1261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1262 Prefix 1263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1264 Prefix 1265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1266 Prefix 1267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1268 Prefix | 1269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1271 The sub-fields encoded in these attributes are strongly related, and 1272 there was no previous definition of this data structure that could be 1273 referenced. Support for this attribute requires code changes on both 1274 the client and server, due to a new data type being defined. In this 1275 case it appears to be acceptable to encode them in one attribute. 1277 B.8. Egress-VLANID 1279 [RFC4675] Section 2.1 defines the Egress-VLANID Attribute which can 1280 be sent by a RADIUS client or server. 1282 0 1 2 3 1283 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 1284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1285 | Type | Length | Value 1286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1287 Value (cont) | 1288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1290 While it appears superficially to be of type Integer, the Value field 1291 is actually a packed structure, as follows: 1293 0 1 2 3 1294 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 1295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1296 | Tag Indic. | Pad | VLANID | 1297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1299 The length of the VLANID field is defined by the [IEEE-802.1Q] 1300 specification. The Tag indicator field is either 0x31 or 0x32, for 1301 compatibility with the Egress-VLAN-Name, as discussed below. The 1302 complex structure of Egress-VLANID overlaps with that of the base 1303 Integer data type, meaning that no code changes are required for a 1304 RADIUS server to support this attribute. Code changes are required 1305 on the NAS, if only to implement the VLAN ID enforcement. 1307 Given the IEEE VLAN requirements and the limited data model of 1308 RADIUS, the chosen method is likely the best of the possible 1309 alternatives. Future specifications that attempt to obtain similar 1310 functionality SHOULD use the extended types from [EXTEN]. 1312 B.9. Egress-VLAN-Name 1314 [RFC4675] Section 2.3 defines the Egress-VLAN-Name Attribute which 1315 can be sent by a RADIUS client or server. 1317 0 1 2 3 1318 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 1319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1320 | Type | Length | Tag Indic. | String... 1321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1323 The Tag Indicator is either the character '1' or '2', which in ASCII 1324 map to the identical values for Tag Indicator in Egress-VLANID, 1325 above. The complex structure of this attribute is acceptable for 1326 reasons identical to those given for Egress-VLANID. Future 1327 specifications that attempt to obtain similar functionality SHOULD 1328 use the extended types from [EXTEN]. 1330 Acknowledgments 1332 We would like to acknowledge David Nelson, Bernard Aboba, Emile van 1333 Bergen, Barney Wolff and Glen Zorn for contributions to this 1334 document. 1336 Authors' Addresses 1338 Greg Weber 1339 Knoxville, TN 37932 1340 USA 1342 Email: gdweber@gmail.com 1344 Alan DeKok 1345 The FreeRADIUS Server Project 1346 http://freeradius.org/ 1348 Email: aland@freeradius.org 1350 Full Copyright Statement 1352 Copyright (C) The IETF Trust (2008). 1354 This document is subject to the rights, licenses and restrictions 1355 contained in BCP 78, and except as set forth therein, the authors 1356 retain all their rights. 1358 This document and the information contained herein are provided on an 1359 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1360 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1361 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1362 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1363 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1364 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1366 Intellectual Property 1368 The IETF takes no position regarding the validity or scope of any 1369 Intellectual Property Rights or other rights that might be claimed to 1370 pertain to the implementation or use of the technology described in 1371 this document or the extent to which any license under such rights 1372 might or might not be available; nor does it represent that it has 1373 made any independent effort to identify any such rights. 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Please address the information to the IETF at ietf- 1388 ipr@ietf.org. 1390 Acknowledgment 1392 Funding for the RFC Editor function is provided by the IETF 1393 Administrative Support Activity (IASA). 1395 Open issues 1397 Open issues relating to this document are tracked on the following 1398 web site: 1400 http://www.drizzle.com/~aboba/RADEXT/