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Is this intentional? Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Alan DeKok (ed.) 3 INTERNET-DRAFT FreeRADIUS 4 Category: Best Current Practice G. Weber 5 Individual Contributor 6 Expires: April 12, 2010 7 12 October 2009 9 RADIUS Design Guidelines 10 draft-ietf-radext-design-09 12 This Internet-Draft is submitted to IETF in full conformance with the 13 provisions of BCP 78 and BCP 79. This document may contain material 14 from IETF Documents or IETF Contributions published or made publicly 15 available before November 10, 2008. The person(s) controlling the 16 copyright in some of this material may not have granted the IETF 17 Trust the right to allow modifications of such material outside the 18 IETF Standards Process. Without obtaining an adequate license from 19 the person(s) controlling the copyright in such materials, this 20 document may not be modified outside the IETF Standards Process, and 21 derivative works of it may not be created outside the IETF Standards 22 Process, except to format it for publication as an RFC or to 23 translate it into languages other than English. 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 April 12, 2010. 43 Copyright Notice 45 Copyright (c) 2009 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 in effect on the date of 50 publication of this document (http://trustee.ietf.org/license-info). 51 Please review these documents carefully, as they describe your rights 52 and restrictions with respect to this document. 54 Abstract 56 This document provides guidelines for the design of attributes used 57 by the Remote Authentication Dial In User Service (RADIUS) protocol. 58 It is expected that these guidelines will prove useful to authors and 59 reviewers of future RADIUS attribute specifications, both within the 60 IETF as well as other Standards Development Organizations (SDOs). 62 Table of Contents 64 1. Introduction ............................................. 4 65 1.1. Terminology ......................................... 4 66 1.2. Requirements Language ............................... 4 67 1.3. Applicability ....................................... 5 68 2. RADIUS Data Model ........................................ 6 69 2.1. Standard Space ...................................... 6 70 2.1.1. Basic Data Types ............................... 6 71 2.1.2. Tagging Mechanism .............................. 8 72 2.1.3. Complex Attribute Usage ........................ 8 73 2.1.4. Complex Attributes and Security ................ 11 74 2.1.5. Service definitions and RADIUS ................. 11 75 2.2. Vendor Space ........................................ 12 76 3. Data Model Issues ........................................ 14 77 3.1. Vendor Space ........................................ 14 78 3.1.1. Interoperability Considerations ................ 16 79 3.1.2. Vendor Allocations ............................. 17 80 3.1.3. SDO Allocations ................................ 17 81 3.1.4. Publication of specifications .................. 18 82 3.2. Polymorphic Attributes .............................. 18 83 3.3. RADIUS Operational Model ............................ 19 84 4. IANA Considerations ...................................... 22 85 5. Security Considerations .................................. 22 86 6. References ............................................... 23 87 6.1. Normative References ................................ 23 88 6.2. Informative References .............................. 23 89 Appendix A - Design Guidelines ............................... 26 90 A.1. Types matching the RADIUS data model ................. 26 91 A.1.1. Transport of simple data ........................ 26 92 A.1.2. Transport of Authentication and Security Data ... 27 93 A.1.3. Opaque data types ............................... 27 94 A.2. Improper Data Types .................................. 27 95 A.2.1. Simple Data Types ............................... 28 96 A.2.2. Complex Data Types .............................. 29 97 A.3. Vendor-Specific formats .............................. 29 98 A.4. Changes to the RADIUS Operational Model .............. 29 99 A.5. Allocation of attributes ............................. 31 100 Appendix B - Complex Attributes .............................. 32 101 B.1. CHAP-Password ........................................ 32 102 B.2. CHAP-Challenge ....................................... 32 103 B.3. Tunnel-Password ...................................... 32 104 B.4. ARAP-Password ........................................ 33 105 B.5. ARAP-Features ........................................ 33 106 B.6. Connect-Info ......................................... 34 107 B.7. Framed-IPv6-Prefix ................................... 35 108 B.8. Egress-VLANID ........................................ 35 109 B.9. Egress-VLAN-Name ..................................... 36 111 1. Introduction 113 This document provides guidelines for the design of RADIUS attributes 114 both within the IETF as well as within other SDOs. By articulating 115 RADIUS design guidelines, it is hoped that this document will 116 encourage the development and publication of high quality RADIUS 117 attribute specifications. 119 However, the advice in this document will not be helpful unless it is 120 put to use. As with "Guidelines for Authors and Reviewers of MIB 121 Documents" [RFC4181], it is expected that this document will be used 122 by authors to check their document against the guidelines prior to 123 requesting review (such as an "Expert Review" described in 124 [RFC3575]). Similarly, it is expected that this document will used 125 by reviewers (such as WG participants or the AAA Doctors [DOCTORS]), 126 resulting in an improvement in the consistency of reviews. 128 In order to meet these objectives, this document needs to cover not 129 only the science of attribute design, but also the art. As a result, 130 in addition to covering the most frequently encountered issues, this 131 document attempts to provide some of the considerations motivating 132 the guidelines. 134 In order to characterize current attribute usage, both the basic and 135 complex data types defined in the existing RADIUS RFCs are reviewed. 137 1.1. Terminology 139 This document uses the following terms: 141 Network Access Server (NAS) 142 A device that provides an access service for a user to a network. 144 RADIUS server 145 A RADIUS authentication, authorization, and/or accounting (AAA) 146 server is an entity that provides one or more AAA services to a 147 NAS. 149 RADIUS proxy 150 A RADIUS proxy acts as a RADIUS server to the NAS, and a RADIUS 151 client to the RADIUS server. 153 1.2. Requirements Language 155 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 156 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 157 document are to be interpreted as described in [RFC2119]. 159 1.3. Applicability 161 As RADIUS has become more widely accepted as a management protocol, 162 its usage has become more prevalent, both within the IETF as well as 163 within other SDOs. Given the expanded utilization of RADIUS, it has 164 become apparent that requiring SDOs to accomplish all their RADIUS 165 work within the IETF is inherently inefficient and unscalable. By 166 articulating guidelines for RADIUS attribute design, this document 167 enables SDOs out of the IETF to design their own RADIUS attributes 168 within the Vendor-Specific Attribute (VSA) space. 170 It is RECOMMENDED that SDOs follow the guidelines articulated in this 171 document. Doing so will ensure the widest possible applicability and 172 interoperability of the specifications, while requiring minimal 173 changes to existing systems. Specifications that do not follow the 174 guidelines articulated herein are NOT RECOMMENDED. However, we 175 recognize that there are some situations where SDOs or vendors 176 require the creation of specifications not following these 177 guidelines. We do not forbid these specifications, but it is 178 RECOMMENDED that they are created only if they have a limited scope 179 of applicability, and all attributes defined in those specifications 180 are VSAs, as discussed Appendix A.5, below. 182 It is RECOMMENDED that SDOs and vendors seek review of RADIUS 183 attribute specifications from the IETF. However, when specifications 184 are SDO specific, re-use existing data types, and follow these 185 guidelines, they do not require IETF review. 187 In order to enable IETF review of such specifications, the authors 188 recommend that: 190 * SDOs make their RADIUS attribute specifications publicly 191 available; 193 * SDOs request review of RADIUS attribute specifications by 194 sending email to the AAA Doctors [DOCTORS] or equivalent mailing 195 list; 197 * IETF and SDO RADIUS attribute specifications are reviewed 198 according to the guidelines proposed in this document; 200 * Reviews of specifications are posted to the RADEXT WG mailing 201 list, the AAA Doctors mailing list [DOCTORS] or another IETF 202 mailing list suggested by the Operations & Management Area 203 Directors of the IETF. 205 These reviews can assist with creation of specifications that meet 206 the SDO requirements, and which are also compatible with the 207 traditional data model and uses of RADIUS. While these reviews 208 require access to public specifications, the review process does not 209 require publication of an IETF RFC. 211 The advice in this document applies to attributes used to encode 212 service-provisioning or authentication data. RADIUS protocol 213 changes, or specification of attributes (such as Service-Type) that 214 can be used to, in effect, provide new RADIUS commands require 215 greater expertise and deeper review, as do changes to the RADIUS 216 operational model as discussed below in Section 3.3. Such changes 217 MUST NOT be undertaken outside the IETF and when handled within the 218 IETF require "IETF Consensus" for adoption, as noted in [RFC3575] 219 Section 2.1. 221 2. RADIUS Data Model 223 The Remote Authentication Dial In User Service (RADIUS) defined in 224 [RFC2865] and [RFC2866] uses elements known as attributes in order to 225 represent authentication, authorization and accounting data. 227 Unlike SNMP, first defined in [RFC1157] and [RFC1155], RADIUS does 228 not define a formal data definition language. A handful of basic 229 data types are in common use, and a data type is associated with an 230 attribute when the attribute is defined. 232 Two distinct attribute spaces are defined: the standard space, and a 233 Vendor-Specific space. Attributes in the standard space generally 234 are composed of a type, length, value (TLV) triplet, although complex 235 attributes have also been defined. The Vendor-Specific space is 236 encapsulated within a single attribute type (Vendor-Specific 237 Attribute). The format of this space is defined by individual 238 vendors, but the same TLV encoding used by the standard space is 239 recommended in [RFC2865] Section 5.26. The similarity between 240 attribute formats has enabled implementations to leverage common 241 parsing functionality, although in some cases the attributes in the 242 Vendor-Specific space have begun to diverge from the common format. 244 2.1. Standard Space 246 The following subsections describe common data types and formats 247 within the RADIUS standard attribute space. Common exceptions are 248 identified. 250 2.1.1. Basic Data Types 252 The data type of RADIUS attributes is not transported on the wire. 253 Rather, the data type of a RADIUS attribute is fixed when that 254 attribute is defined. Based on the RADIUS attribute type code, 255 RADIUS clients and servers can determine the data type based on pre- 256 configured entries within a data dictionary. 258 [RFC2865] defines the following data types: 260 text 1-253 octets containing UTF-8 encoded 10646 [RFC3629] 261 characters. Text of length zero (0) MUST NOT be sent; 262 omit the entire attribute instead. 263 string 1-253 octets containing binary data (values 0 through 264 255 decimal, inclusive). Strings of length zero (0) 265 MUST NOT be sent; omit the entire attribute instead. 266 IPv4 address 32 bit value, in network byte order. 267 integer 32 bit unsigned value, in network byte order. 268 time 32 bit unsigned value, in network byte order. 269 -- seconds since 00:00:00 UTC, January 1, 1970. 271 In addition to these data types, follow-on RADIUS specifications 272 define attributes using the following additional types: 274 IPv6 address 128 bit value, in network byte order. 275 IPv6 prefix 8 bits of reserved, 8 bits of prefix length, up to 276 128 bits of value, in network byte order. 277 integer64 64 bit unsigned value, in network byte order 278 This type has also been used to represent an IPv6 279 interface identifier. 281 Examples of the IPv6 address type include NAS-IPv6-Address defined in 282 [RFC3162] Section 2.1 and Login-IPv6-Host defined in [RFC3162] 283 Section 2.4. The IPv6 prefix type is used in [RFC3162] Section 2.3, 284 and in [RFC4818] Section 3. The integer64 type is used for the ARAP- 285 Challenge-Response Attribute defined in [RFC2869] Section 5.15, and 286 the Framed-Interface-Id Attribute defined in [RFC3162] Section 2.2. 287 [RFC4675] Section 2.4 defines User-Priority-Table as 64-bits in 288 length, but denotes it as type String. 290 Given that attributes of type IPv6 address, IPv6 prefix, and 291 integer64 are already in use, it is RECOMMENDED that RADIUS server 292 implementations include support for these additional basic types, in 293 addition to the types defined in [RFC2865]. 295 Where the intent is to represent a specific IPv6 address, the IPv6 296 address type SHOULD be used. Although it is possible to use the IPv6 297 IPv6 Prefix type with a prefix length of 128 to represent an IPv6 298 address, this usage is NOT RECOMMENDED. 300 It is worth noting that since RADIUS only supports unsigned integers 301 of 32 or 64 bits, attributes using signed integer data types or 302 unsigned integer types of other sizes will require code changes, and 303 SHOULD be avoided. 305 For [RFC2865] RADIUS VSAs, the length limitation of the String and 306 Text types is 247 octets instead of 253 octets, due to the additional 307 overhead of the Vendor-Specific Attribute. 309 2.1.2. Tagging Mechanism 311 [RFC2868] defines an attribute grouping mechanism based on the use of 312 a one octet tag value. Tunnel attributes that refer to the same 313 tunnel are grouped together by virtue of using the same tag value. 315 This tagging mechanism has some drawbacks. There are a limited 316 number of unique tags (31). The tags are not well suited for use 317 with arbitrary binary data values, because it is not always possible 318 to tell if the first byte after the Length is the tag or the first 319 byte of the untagged value (assuming the tag is optional). 321 Other limitations of the tagging mechanism are that when integer 322 values are tagged, the value portion is reduced to three bytes 323 meaning only 24-bit numbers can be represented. The tagging 324 mechanism does not offer an ability to create nested groups of 325 attributes. Some RADIUS implementations treat tagged attributes as 326 having additional data types tagged-string and tagged-integer. These 327 types increase the complexity of implementing and managing RADIUS 328 systems. 330 For these reasons, the tagging scheme described in RFC 2868 is NOT 331 RECOMMENDED for use as a generic grouping mechanism. 333 2.1.3. Complex Attribute Usage 335 The RADIUS attribute encoding is summarized in [RFC2865]: 337 0 1 2 338 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 340 | Type | Length | Value ... 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 343 However, some standard attributes do not follow this format. 344 Attributes that use sub-fields instead of using a basic data type are 345 known as "complex attributes". As described below, the definition of 346 complex attributes can lead to interoperability and deployment 347 issues, so they need to be introduced with care. 349 In general, complex attributes sent from the RADIUS server to the 350 client can be supported by concatenating the values into a String 351 data type field. However, separating these values into different 352 attributes, each with its own type and length, would have the 353 following benefits: 355 * it is easier for the user to enter the data as well-known 356 types, rather than complex structures; 358 * it enables additional error checking by leveraging the 359 parsing and validation routines for well-known types; 361 * it simplifies implementations by eliminating special-case 362 attribute-specific parsing. 364 One of the fundamental goals of the RADIUS protocol design was to 365 allow RADIUS servers to be configured to support new attributes 366 without requiring server code changes. RADIUS server implementations 367 typically provide support for basic data types, and define attributes 368 in a data dictionary. This architecture enables a new attribute to 369 be supported by the addition of a dictionary entry, without requiring 370 RADIUS server code changes. 372 On the RADIUS client, code changes are typically required in order to 373 implement a new attribute. The RADIUS client typically has to 374 compose the attribute dynamically when sending. When receiving, a 375 RADIUS client needs to be able to parse the attribute and carry out 376 the requested service. As a result, a detailed understanding of the 377 new attribute is required on clients, and data dictionaries are less 378 useful on clients than on servers. 380 Given these considerations, the introduction of a new basic or 381 complex attribute will typically require code changes on the RADIUS 382 client. The magnitude of changes for the complex attribute could be 383 greater, due to the potential need for custom parsing logic. 385 The RADIUS server can be configured to send a new static attribute by 386 entering its type and data format in the RADIUS server dictionary, 387 and then filling in the value within a policy based on the attribute 388 name, data type and type-specific value. For complex attribute types 389 not supported by RADIUS server dictionaries, changes to the 390 dictionary code can be required in order to allow the new attribute 391 to be supported by and configured on the RADIUS server. 393 Code changes can also be required in policy management and in the 394 RADIUS server's receive path. These changes are due to limitations 395 in RADIUS server policy languages, which typically only provide for 396 limited operations (such as comparisons or arithmetic operations) on 397 the basic data types. Many existing RADIUS policy languages 398 typically are not capable of parsing sub-elements, or providing 399 sophisticated matching functionality. 401 Given these limitations, the introduction of complex attributes can 402 require code changes on the RADIUS server which would be unnecessary 403 if basic data types had been used instead. In addition, attribute- 404 specific parsing means more complex software to develop and maintain. 405 More complexity can lead to more error prone implementations, 406 interoperability problems, and even security vulnerabilities. These 407 issues can increase costs to network administrators as well as 408 reducing reliability and introducing deployment barriers. As a 409 result, the introduction of new complex data types within RADIUS 410 attribute specifications SHOULD be avoided, except in the case of 411 complex attributes involving authentication or security 412 functionality. 414 As can be seen in Appendix B, most of the existing complex attributes 415 involve authentication or security functionality. Supporting this 416 functionality requires code changes on both the RADIUS client and 417 server, regardless of the attribute format. As a result, in most 418 cases, the use of complex attributes to represent these methods is 419 acceptable, and does not create additional interoperability or 420 deployment issues. 422 The only other exception to the recommendation against complex types 423 is for types that can be treated as opaque data by the RADIUS server. 424 For example, the EAP-Message attribute, defined in [RFC3579] Section 425 3.1 contains a complex data type that is an EAP packet. Since these 426 complex types do not need to be parsed by the RADIUS server, the 427 issues arising from policy language limitations do not arise. 428 Similarly, since attributes of these complex types can be configured 429 on the server using a data type of String, dictionary limitations are 430 also not encountered. Appendix A.1 below includes a series of 431 checklists that may be used to analyze a design for RECOMMENDED and 432 NOT RECOMMENDED behavior in relation to complex types. 434 If the RADIUS Server simply passes the contents of an attribute to 435 some non-RADIUS portion of the network, then the data is opaque, and 436 SHOULD be defined to be of type String. A concrete way of judging 437 this requirement is whether or not the attribute definition in the 438 RADIUS document contains delineated fields for sub-parts of the data. 439 If those fields need to be delineated in RADIUS, then the data is not 440 opaque, and it SHOULD be separated into individual RADIUS attributes. 442 An examination of existing RADIUS RFCs discloses a number of complex 443 attributes that have already been defined. Appendix B includes a 444 listing of complex attributes used within [RFC2865], [RFC2868], 445 [RFC2869], [RFC3162], [RFC4818], and [RFC4675]. The discussion of 446 these attributes includes reasons why a complex type is acceptable, 447 or suggestions for how the attribute could have been defined to 448 follow the RADIUS data model. 450 In other cases, the data in the complex type are described textually. 451 This is possible because the data types are not sent within the 452 attributes, but are a matter for endpoint interpretation. An 453 implementation can define additional data types, and use these data 454 types today by matching them to the attribute's textual description. 456 2.1.4. Complex Attributes and Security 458 The introduction of complex data types brings the potential for the 459 introduction of new security vulnerabilities. Experience shows that 460 the common data types have few security vulnerabilities, or else that 461 all known issues have been found and fixed. New data types require 462 new code, which may introduce new bugs, and therefore new attack 463 vectors. 465 RADIUS servers are highly valued targets, as they control network 466 access and interact with databases that store usernames and 467 passwords. An extreme outcome of a vulnerability due to a new, 468 complex type would be that an attacker is capable of taking complete 469 control over the RADIUS server. 471 The use of attributes representing opaque data does not reduce this 472 threat. The threat merely moves from the RADIUS server to the 473 application that consumes that opaque data. 475 The threat is particularly severe when the opaque data originates 476 from the user, and is not validated by the NAS. In those cases, the 477 RADIUS server is potentially exposed to attack by malware residing on 478 an unauthenticated host. Applications consuming opaque data that 479 reside on the RADIUS server SHOULD be properly isolated from the 480 RADIUS server, and SHOULD run with minimal privileges. Any potential 481 vulnerabilities in that application will then have minimal impact on 482 the security of the system as a whole. 484 2.1.5. Service definitions and RADIUS 486 RADIUS specifications define how an existing service or protocol can 487 be provisioned using RADIUS. Therefore, it is expected that a RADIUS 488 attribute specification will reference documents defining the 489 protocol or service to be provisioned. Within the IETF, a RADIUS 490 attribute specification SHOULD NOT be used to define the protocol or 491 service being provisioned. New services using RADIUS for 492 provisioning SHOULD be defined elsewhere and referenced in the RADIUS 493 specification. 495 New attributes, or new values of existing attributes, SHOULD NOT be 496 used to define new RADIUS commands. RADIUS attributes are intended 497 to: 499 * authenticate users 501 * authorize users (i.e., service provisioning or changes to 502 provisioning) 504 * account for user activity (i.e., logging of session activity) 506 New commands (i.e., the Code field in the packet header) are 507 allocated only through "IETF Consensus" as noted in [RFC3575] Section 508 2.1. Specifications also SHOULD NOT use new attributes to modify the 509 interpretation of existing RADIUS commands. 511 2.2. Vendor Space 513 As noted in [RFC2865] Section 5.26, the VSA format is defined as 514 follows: 516 0 1 2 3 517 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 1 518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 519 | Type | Length | Vendor-Id 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 Vendor-Id (cont) | String... 522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 524 The high-order octet of the Vendor-Id field is 0 and the low-order 3 525 octets are the Structure of Management Information (SMI) Network 526 Management Private Enterprise Code (PEC) of the Vendor in network 527 byte order. 529 While the format of the String field is defined by the vendor, 530 [RFC2865] Section 5.26 notes: 532 It SHOULD be encoded as a sequence of vendor type / vendor length 533 / value fields, as follows. The Attribute-Specific field is 534 dependent on the vendor's definition of that attribute. An 535 example encoding of the Vendor-Specific attribute using this 536 method follows: 538 0 1 2 3 539 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 1 540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 541 | Type | Length | Vendor-Id 542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 543 Vendor-Id (cont) | Vendor type | Vendor length | 544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 | Attribute-Specific... 546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 548 Multiple sub-attributes MAY be encoded within a single Vendor- 549 Specific attribute, although they do not have to be. 551 Note that the Vendor type field in the recommended VSA format is only 552 a single octet, like the RADIUS type field. While this limitation 553 results in an efficient encoding, there are situations in which a 554 vendor or SDO will eventually wish to define more than 255 555 attributes. Also, an SDO can be comprised of multiple subgroups, each 556 of whom can desire autonomy over the definition of attributes within 557 their group. The most interoperable way to address these issues is 558 for the vendor or SDO to request allocation of multiple Vendor 559 identifiers. 561 However, instead of doing this, vendors have defined the following 562 non-standard VSA formats: 564 * Vendor types of 16 bits, followed by an 8 bit length and 565 then attribute-specific data. 567 * Vendor types of 32 bits, followed by no length field, and 568 then attribute-specific data. 570 * Vendor types of the RFC format, but where some VSAs are 571 defined as "grouped" or TLV attributes. These attributes 572 are then used to carry sub-attributes. 574 * "Bare" ASCII strings that immediately follow the Vendor-Id, 575 without using a Vendor type or Vendor length. 577 All VSA schemes that do not follow the [RFC2865] recommendations are 578 NOT RECOMMENDED. These non-standard formats will typically not be 579 implementable without RADIUS server code changes. This includes all 580 the above formats, as well as Vendor types of more than 8 bits, 581 vendor lengths of less than 8 bits, vendor lengths of more than 8 582 bits and Vendor-Specific contents that are not in Type-Length-Value 583 format. 585 Although [RFC2865] does not mandate it, implementations commonly 586 assume that the Vendor Id can be used as a key to determine the on- 587 the-wire format of a VSA. Vendors therefore SHOULD NOT use multiple 588 formats for VSAs that are associated with a particular Vendor Id. A 589 vendor wishing to use multiple VSA formats SHOULD request one Vendor 590 Id for each VSA format that they will use. 592 3. Data Model Issues 594 Since the closure of the RADIUS Working Group, the popularity and 595 prevalence of RADIUS has continued to grow. In addition to 596 increasing demand for allocation of attributes within the RADIUS 597 standard attribute space, the number of vendors and SDOs creating new 598 attributes within the Vendor-Specific attribute space has grown, and 599 this has lead to some divergence in approaches to RADIUS attribute 600 design. 602 In general, standard RADIUS attributes have a more constrained data 603 model than attributes within the vendor space. For example, vendors 604 and SDOs have evolved the data model to support new functions such as 605 attribute grouping and attribute fragmentation, with different groups 606 taking different approaches. 608 Given these enhancements, it has become difficult for vendors or SDOs 609 to translate attributes from the vendor space to the more stringent 610 standards space. For example, a Vendor-Specific attribute using sub- 611 elements could require allocation of several standard space 612 attributes using basic data types. In this case not only would 613 translation require substantial additional work, it would further 614 deplete the RADIUS standard attribute space. Given these 615 limitations, translation of vendor attributes to the standards space 616 is not necessarily desirable, particularly if the VSA specification 617 is publicly available and can be implemented within existing RADIUS 618 clients and servers. In such situations, the costs may substantially 619 outweigh the benefits. It is possible that some of the enhancements 620 made within the vendor space may eventually become available within 621 the standard attribute space. However, the divergence of the 622 standard and vendor attribute spaces is most likely a permanent 623 feature, and should be recognized as such. 625 3.1. Vendor Space 627 The usage model for RADIUS VSAs is described in [RFC2865] Section 628 6.2: 630 Note that RADIUS defines a mechanism for Vendor-Specific 631 extensions (Attribute 26) and the use of that should be encouraged 632 instead of allocation of global attribute types, for functions 633 specific only to one vendor's implementation of RADIUS, where no 634 interoperability is deemed useful. 636 Nevertheless, many new attributes have been defined in the vendor 637 specific space in situations where interoperability is not only 638 useful, but is required. For example, SDOs outside the IETF (such as 639 the IEEE 802 and the 3rd Generation Partnership Project (3GPP)) have 640 been assigned Vendor-Ids, enabling them to define their own VSA 641 format and assign Vendor types within their own space. 643 The use of VSAs by SDOs outside the IETF has gained in popularity for 644 several reasons: 646 Efficiency 647 As with SNMP, which defines an "Enterprise" Object Identifier (OID) 648 space suitable for use by vendors as well as other SDOs, the 649 definition of Vendor-Specific RADIUS attributes has become a common 650 occurrence as part of standards activity outside the IETF. For 651 reasons of efficiency, it is easiest if the RADIUS attributes 652 required to manage a standard are developed within the same SDO 653 that develops the standard itself. As noted in "Transferring MIB 654 Work from IETF Bridge MIB WG to IEEE 802.1 WG" [RFC4663], today few 655 vendors are willing to simultaneously fund individuals to 656 participate within an SDO to complete a standard, as well as to 657 participate in the IETF in order to complete the associated RADIUS 658 attributes specification. 660 Attribute scarcity 661 The standard RADIUS attribute space is limited to 255 unique 662 attributes. Of these, only about half remain available for 663 allocation. In the Vendor-Specific space, the number of attributes 664 available is a function of the format of the attribute (the size of 665 the Vendor type field). 667 Along with these advantages, some limitations of VSA usage are noted 668 in [RFC2865] Section 5.26: 670 This Attribute is available to allow vendors to support their own 671 extended Attributes not suitable for general usage. It MUST NOT 672 affect the operation of the RADIUS protocol. 674 Servers not equipped to interpret the vendor-specific information 675 sent by a client MUST ignore it (although it may be reported). 676 Clients which do not receive desired vendor-specific information 677 SHOULD make an attempt to operate without it, although they may do 678 so (and report they are doing so) in a degraded mode. 680 The limitation on changes to the RADIUS protocol effectively 681 prohibits VSAs from changing fundamental aspects of RADIUS operation, 682 such as modifying RADIUS packet sequences, or adding new commands. 683 However, the requirement for clients and servers to be able to 684 operate in the absence of VSAs has proven to be less of a constraint, 685 since it is still possible for a RADIUS client and server to mutually 686 indicate support for VSAs, after which behavior expectations can be 687 reset. 689 Therefore, RFC 2865 provides considerable latitude for development of 690 new attributes within the vendor space, while prohibiting development 691 of protocol variants. This flexibility implies that RADIUS 692 attributes can often be developed within the vendor space without 693 loss (and possibly even with gain) in functionality. 695 As a result, translation of RADIUS attributes developed within the 696 vendor space into the standard space may provide only modest 697 benefits, while accelerating the exhaustion of the standard attribute 698 space. We do not expect that all RADIUS attribute specifications 699 requiring interoperability will be developed within the IETF, and 700 allocated from the standards space. A more scalable approach is to 701 recognize the flexibility of the vendor space, while working toward 702 improvements in the quality and availability of RADIUS attribute 703 specifications, regardless of where they are developed. 705 3.1.1. Interoperability Considerations 707 Vendors and SDOs are reminded that the standard RADIUS attribute 708 space, and the enumerated value space for enumerated attributes, are 709 reserved for allocation through work published via the IETF, as noted 710 in [RFC3575] Section 2.1. Some vendors and SDOs have in the past 711 performed self-allocation by assigning vendor-specific meaning to 712 "unused" values from the standard RADIUS attribute ID or enumerated 713 value space. This self-allocation results in interoperability 714 issues, and is counter-productive. Similarly, the Vendor-Specific 715 enumeration practice discussed in [RFC2882] Section 2.2.1 is NOT 716 RECOMMENDED. 718 If it is not possible to follow the IETF process, vendors and SDOs 719 SHOULD self-allocate an attribute from their Vendor-Specific space, 720 and define an appropriate value for it. 722 As a side note, [RFC2865] Section 5.26 uses the term "Vendor-Specific 723 Attribute" to refer to an encoding format which can be used by 724 individual vendors to define attributes not suitable for general 725 usage. However, since then VSAs have also become widely used by SDOs 726 defining attributes intended for multi-vendor interoperability. As 727 such, these attributes are not specific to any single vendor, and the 728 term "Vendor-Specific" may be misleading. An alternate term which 729 better describes this use case is SDO-Specific Attribute (SSA). 731 The design and specification of VSAs for multi-vendor usage SHOULD be 732 undertaken with the same level of care as standard RADIUS attributes. 733 Specifically, the provisions of this document that apply to standard 734 RADIUS attributes also apply to SSAs or VSAs for multi-vendor usage. 736 3.1.2. Vendor Allocations 738 Vendor RADIUS Attribute specifications SHOULD allocate attributes 739 from the vendor space, rather than requesting an allocation from the 740 RADIUS standard attribute space. 742 As discussed in [RFC2865] Section 5.26, the vendor space is intended 743 for vendors to support their own Attributes not suitable for general 744 use. However, it is RECOMMENDED that vendors follow the guidelines 745 outlined here, which are intended to enable maximum interoperability 746 with minimal changes to existing systems. 748 Following these guidelines means that RADIUS servers can be updated 749 to support the vendor's equipment by editing a RADIUS dictionary. If 750 these guidelines are not followed, then the vendor's equipment can 751 only be supported via code changes in RADIUS server implementations. 752 Such code changes add complexity and delay to implementations. 754 3.1.3. SDO Allocations 756 SDO RADIUS Attribute specifications SHOULD allocate attributes from 757 the vendor space, rather than requesting an allocation from the 758 RADIUS standard attribute space, for attributes matching any of the 759 following criteria: 761 * attributes relying on data types not defined within RADIUS 763 * attributes intended primarily for use within an SDO 765 * attributes intended primarily for use within a group of SDOs. 767 Any new RADIUS attributes or values intended for interoperable use 768 across a broad spectrum of the Internet Community SHOULD follow the 769 normal IETF process, and SHOULD result in allocations from the RADIUS 770 standard space. 772 The recommendation for SDOs to allocate attributes from a vendor 773 space rather than via the IETF process is a recognition that SDOs may 774 desire to assert change control over their own RADIUS specifications. 775 This change control can be obtained by requesting a PEC from the 776 Internet Assigned Number Authority (IANA), for use as a Vendor-Id 777 within a Vendor-Specific attribute. Further allocation of attributes 778 inside of the VSA space defined by that Vendor-Id is subject solely 779 to the discretion of the SDO. Similarly, the use of data types 780 (complex or not) within that VSA space is solely under the discretion 781 of the SDO. It is RECOMMENDED that SDOs follow the guidelines 782 outlined here, which are intended to enable maximum interoperability 783 with minimal changes to existing systems. 785 It should be understood that SDOs do not have to rehost VSAs into the 786 standards space solely for the purpose of obtaining IETF review. 787 Rehosting puts pressure on the standards space, and may be harmful to 788 interoperability, since it can create two ways to provision the same 789 service. Rehosting may also require changes to the RADIUS data model 790 which will affect implementations that do not intend to support the 791 SDO specifications. 793 3.1.4. Publication of specifications 795 SDOs are encouraged to seek early review of SSA specifications by the 796 IETF. This review may be initiated by sending mail to the AAA 797 Doctors list [DOCTORS], with the understanding that this review is a 798 voluntary-based service offered on best-effort basis. Since the IETF 799 is not a membership organization, in order to enable the RADIUS SSA 800 specification to be reviewed, it is RECOMMENDED that it be made 801 publicly available; this also encourages interoperability. Where the 802 RADIUS SSA specification is embedded within a larger document which 803 cannot be made public, the RADIUS attribute and value definitions 804 SHOULD be published instead as an Informational RFC, as with 805 [RFC4679]. This process SHOULD be followed instead of requesting 806 IANA allocations from within the standard RADIUS attribute space. 808 Similarly, vendors are encouraged to make their specifications 809 publicly available, for maximum interoperability. However, it is not 810 necessary for them to request publication of their VSA specifications 811 as Informational RFCs by the IETF. 813 All other specifications, including new authentication, 814 authorization, and/or security mechanisms SHOULD be allocated via the 815 standard RADIUS space, as noted in [RFC3575] Section 2.1. 817 3.2. Polymorphic Attributes 819 A polymorphic attribute is one whose format or meaning is dynamic. 820 For example, rather than using a fixed data format, an attribute's 821 format might change based on the contents of another attribute. Or, 822 the meaning of an attribute may depend on earlier packets in a 823 sequence. 825 RADIUS server dictionary entries are typically static, enabling the 826 user to enter the contents of an attribute without support for 827 changing the format based on dynamic conditions. However, this 828 limitation on static types does not prevent implementations from 829 implementing policies that return different attributes based on the 830 contents of received attributes; this is a common feature of existing 831 RADIUS implementations. 833 In general, polymorphism is NOT RECOMMENDED. Polymorphism rarely 834 enables capabilities that would not be available through use of 835 multiple attributes. Polymorphism requires code changes in the 836 RADIUS server in situations where attributes with fixed formats would 837 not require such changes. Thus, polymorphism increases complexity 838 while decreasing generality, without delivering any corresponding 839 benefits. 841 Note that changing an attribute's format dynamically is not the same 842 thing as using a fixed format and computing the attribute itself 843 dynamically. RADIUS authentication attributes such as User-Password, 844 EAP-Message, etc. while being computed dynamically, use a fixed 845 format. 847 3.3. RADIUS Operational Model 849 The RADIUS operational model includes several assumptions: 851 * The RADIUS protocol is stateless; 853 * Provisioning of services is not possible within an 854 Access-Reject; 856 * There is a distinction between authorization checks and user 857 authentication; 859 * The protocol provices for authentication and integrity 860 protection of packets; 862 * The RADIUS protocol is a Request/Response protocol; 864 * The protocol defines packet length restrictions. 866 While RADIUS server implementations may keep state, the RADIUS 867 protocol is stateless, although information may be passed from one 868 protocol transaction to another via the State Attribute. As a 869 result, documents which require stateful protocol behavior without 870 use of the State Attribute are inherently incompatible with RADIUS as 871 defined in [RFC2865], and need to be redesigned. See [RFC5080] 872 Section 2.1.1 for a more in-depth discussion of the use of the State 873 Attribute. 875 As noted in [RFC5080] Section 2.6, the intent of an Access-Reject is 876 to deny access to the requested service. As a result, RADIUS does 877 not allow the provisioning of services within an Access-Reject. 878 Documents which include provisioning of services within an Access- 879 Reject are inherently incompatible with RADIUS, and need to be 880 redesigned. 882 As noted in [RFC5080] Section 2.1.1, a RADIUS Access-Request may not 883 contain user authentication attributes or a State Attribute linking 884 the Access-Request to an earlier user authentication. Such an 885 Access-Request, known as an authorization check, provides no 886 assurance that it corresponds to a live user. RADIUS specifications 887 defining attributes containing confidential information (such as 888 Tunnel-Password) should be careful to prohibit such attributes from 889 being returned in response to an authorization check. Also, 890 [RFC5080] Section 2.1.1 notes that authentication mechanisms need to 891 tie a sequence of Access-Request/Access-Challenge packets together 892 into one authentication session. The State Attribute is RECOMMENDED 893 for this purpose. 895 While [RFC2865] did not require authentication and integrity 896 protection of RADIUS Access-Request packets, subsequent 897 authentication mechanism specifications such as RADIUS/EAP [RFC3579] 898 and Digest Authentication [RFC5090] have mandated authentication and 899 integrity protection for certain RADIUS packets. [RFC5080] Section 900 2.1.1 makes this behavior RECOMMENDED for all Access-Request packets, 901 including Access-Request packets performing authorization checks. It 902 is expected that specifications for new RADIUS authentication 903 mechanisms will continue this practice. 905 The RADIUS protocol as defined in [RFC2865] is a request-response 906 protocol spoken between RADIUS clients and servers. A single RADIUS 907 Access-Request packet will solicit in response at most a single 908 Access-Accept, Access-Reject or Access-Challenge packet, sent to the 909 IP address and port of the RADIUS Client that originated the Access- 910 Request. Similarly, a single Change-of-Authorization (CoA)-Request 911 packet [RFC5176] will solicit in response at most a single CoA-ACK or 912 CoA-NAK packet, sent to the IP address and port of the Dynamic 913 Authorization Client (DAC) that originated the CoA-Request. A single 914 Disconnect-Request packet will solicit in response at most a single 915 Disconnect-ACK or Disconnect-NAK packet, sent to the IP address and 916 port of the Dynamic Authorization Client (DAC) that originated the 917 Disconnect-Request. Changes to this model are likely to require 918 major revisions to existing implementations and so this practice is 919 NOT RECOMMENDED. 921 The Length field in the RADIUS packet header is defined in [RFC2865] 922 Section 3. It is noted there that the maximum length of a RADIUS 923 packet is 4096 octets. As a result, attribute designers SHOULD NOT 924 assume that a RADIUS implementation can successfully process RADIUS 925 packets larger than 4096 octets. 927 Even when packets are less than 4096 octets, they may be larger than 928 the Path Maximum Transmission Unit (PMTU). Any packet larger than 929 the PMTU will be fragmented, making communications more brittle as 930 firewalls and filtering devices often discard fragments. Transport 931 of fragmented UDP packets appears to be a poorly tested code path on 932 network devices. Some devices appear to be incapable of transporting 933 fragmented UDP packets, making it difficult to deploy RADIUS in a 934 network where those devices are deployed. We RECOMMEND that RADIUS 935 messages be kept as small possible. 937 If a situation is envisaged where it may be necessary to carry 938 authentication, authorization or accounting data in a packet larger 939 than 4096 octets, then one of the following approaches is 940 RECOMMENDED: 942 1. Utilization of a sequence of packets. 943 For RADIUS authentication, a sequence of Access-Request/ Access- 944 Challenge packets would be used. For this to be feasible, 945 attribute designers need to enable inclusion of attributes that 946 can consume considerable space within Access-Challenge packets. 947 To maintain compatibility with existing NASes, either the use of 948 Access-Challenge packets needs to be permissible (as with 949 RADIUS/EAP, defined in [RFC3579]), or support for receipt of an 950 Access-Challenge needs to be indicated by the NAS (as in RADIUS 951 Location [RFC5580]). Also, the specification needs to clearly 952 describe how attribute splitting is to be signalled and how 953 attributes included within the sequence are to be interpreted, 954 without requiring stateful operation. Unfortunately, previous 955 specifications have not always exhibited the required foresight. 956 For example, even though very large filter rules are 957 conceivable, the NAS-Filter-Rule Attribute defined in [RFC4849] 958 is not permitted in an Access-Challenge packet, nor is a 959 mechanism specified to allow a set of NAS-Filter-Rule attributes 960 to be split across an Access-Request/Access-Challenge sequence. 962 In the case of RADIUS accounting, transporting large amounts of 963 data would require a sequence of Accounting-Request packets. 964 This is a non-trivial change to RADIUS, since RADIUS accounting 965 clients would need to be modified to split the attribute stream 966 across multiple Accounting-Requests, and billing servers would 967 need to be modified to re-assemble and interpret the attribute 968 stream. 970 2. Utilization of names rather than values. 971 Where an attribute relates to a policy that could conceivably be 972 pre-provisioned on the NAS, then the name of the pre-provisioned 973 policy can be transmitted in an attribute, rather than the 974 policy itself, which could be quite large. An example of this 975 is the Filter-Id Attribute defined in [RFC2865] Section 5.11, 976 which enables a set of pre-provisioned filter rules to be 977 referenced by name. 979 3. Utilization of Packetization Layer Path MTU Discovery 980 techniques, as specified in [RFC4821]. As a last resort, where 981 the above techniques cannot be made to work, it may be possible 982 to apply the techniques described in [RFC4821] to discover the 983 maximum supported RADIUS packet size on the path between a 984 RADIUS client and a home server. While such an approach can 985 avoid the complexity of utilization of a sequence of packets, 986 dynamic discovery is likely to be time consuming and cannot be 987 guaranteed to work with existing RADIUS implementations. As a 988 result, this technique is not generally applicable. 990 4. IANA Considerations 992 This document does not require that the IANA update any existing 993 registry or create any new registry, but includes information that 994 affects the IANA, which: 996 * includes specific guidelines for Expert Reviewers appointed 997 under the IANA considerations of [RFC3575] 999 * includes guidelines that recommend against self allocation from 1000 the RADIUS standard attribute space in other SDO RADIUS 1001 Attribute specifications. 1003 * recommends that SDOs request a Private Enterprise Code (PEC) 1004 from the IANA, for use as a Vendor-Id within a Vendor-Specific 1005 attribute. 1007 5. Security Considerations 1009 This specification provides guidelines for the design of RADIUS 1010 attributes used in authentication, authorization and accounting. 1011 Threats and security issues for this application are described in 1012 [RFC3579] and [RFC3580]; security issues encountered in roaming are 1013 described in [RFC2607]. 1015 Obfuscation of RADIUS attributes on a per-attribute basis is 1016 necessary in some cases. The current standard mechanism for this is 1017 described in [RFC2865] Section 5.2 (for obscuring User-Password 1018 values) and is based on the MD5 algorithm specified in [RFC1321]. 1019 The MD5 and SHA-1 algorithms have recently become a focus of scrutiny 1020 and concern in security circles, and as a result, the use of these 1021 algorithms in new attributes is NOT RECOMMENDED. In addition, 1022 previous documents referred to this method as generating "encrypted" 1023 data. This terminology is no longer accepted within the 1024 cryptographic community. 1026 Where new RADIUS attributes use cryptographic algorithms, algorithm 1027 negotiation SHOULD be supported. Specification of a mandatory-to- 1028 implement algorithm is REQUIRED, and it is RECOMMENDED that the 1029 mandatory-to-implement algorithm be certifiable under FIPS 140 1030 [FIPS]. 1032 Where new RADIUS attributes encapsulate complex data types, or 1033 transport opaque data, the security considerations discussed in 1034 Section 2.1.4 SHOULD be addressed. 1036 Message authentication in RADIUS is provided largely via the Message- 1037 Authenticator attribute. See [RFC3579] Section 3.2, and also 1038 [RFC5080] 2.2.2, which says that client implementations SHOULD 1039 include a Message-Authenticator attribute in every Access-Request. 1041 In general, the security of the RADIUS protocol is poor. Robust 1042 deployments SHOULD support a secure communications protocol such as 1043 IPSec. See [RFC3579] Section 4, and [RFC3580] Section 5 for a more 1044 in-depth explanation of these issues. 1046 Implementations not following the suggestions outlined in this 1047 document may be subject to a problems such as ambiguous protocol 1048 decoding, packet loss leading to loss of billing information, and 1049 denial of service attacks. 1051 6. References 1053 6.1. Normative References 1055 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1056 Requirement Levels", BCP 14, RFC 2119, March 1997. 1058 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote 1059 Authentication Dial In User Service (RADIUS)", RFC 2865, June 1060 2000. 1062 [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote 1063 Authentication Dial In User Service)", RFC 3575, July 2003. 1065 6.2. Informative References 1067 [RFC1155] Rose, M. and K. McCloghrie, "Structure and identification of 1068 management information for TCP/IP-based internets", STD 16, 1069 RFC 1155, May 1990. 1071 [RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple 1072 Network Management Protocol (SNMP)", STD 15, RFC 1157, May 1073 1990. 1075 [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, 1076 April 1992. 1078 [RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy 1079 Implementation in Roaming", RFC 2607, June 1999. 1081 [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. 1083 [RFC2868] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M., 1084 and I. Goyret, "RADIUS Attributes for Tunnel Protocol 1085 Support", RFC 2868, June 2000. 1087 [RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RADIUS Extensions", 1088 RFC 2869, June 2000. 1090 [RFC2882] Mitton, D, "Network Access Servers Requirements: Extended 1091 RADIUS Practices", RFC 2882, July 2000. 1093 [RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 1094 3162, August 2001. 1096 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial 1097 In User Service) Support For Extensible Authentication 1098 Protocol (EAP)", RFC 3579, September 2003. 1100 [RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G., Roese, J., "IEEE 1101 802.1X Remote Authentication Dial In User Service (RADIUS) 1102 Usage Guidelines", RFC3580, September 2003. 1104 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 1105 RFC 3629, November 2003. 1107 [RFC4181] Heard, C., "Guidelines for Authors and Reviewers of MIB 1108 Documents", RFC 4181, September 2005. 1110 [RFC4663] Harrington, D., "Transferring MIB Work from IETF Bridge MIB WG 1111 to IEEE 802.1 WG", RFC 4663, September 2006. 1113 [RFC4675] Congdon, P., Sanchez, M. and B. Aboba, "RADIUS Attributes for 1114 Virtual LAN and Priority Support", RFC 4675, September 2006. 1116 [RFC4679] Mammoliti, V., et al., "DSL Forum Vendor-Specific RADIUS 1117 Attributes", RFC 4679, September 2006. 1119 [RFC4818] Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix 1120 Attribute", RFC 4818, April 2007. 1122 [RFC4821] Mathis, M. and Heffner, J, "Packetization Layer Path MTU 1123 Discovery", RFC 4821, March 2007. 1125 [RFC4849] Congdon, P. et al, "RADIUS Filter-Rule Attribute", RFC 4849, 1126 April 2007. 1128 [RFC5080] Nelson, D. and DeKok, A, "Common Remote Authentication Dial In 1129 User Service (RADIUS) Implementation Issues and Suggested 1130 Fixes", RFC 5080, December 2007. 1132 [RFC5090] Sterman, B. et al., "RADIUS Extension for Digest 1133 Authentication", RFC 5090, February 2008. 1135 [RFC5176] Chiba, M. et al., "Dynamic Authorization Extensions to Remote 1136 Authentication Dial In User Service (RADIUS)", RFC 5176, 1137 January 2008. 1139 [DOCTORS] AAA Doctors Mailing list 1141 [FIPS] FIPS 140-3 (DRAFT), "Security Requirements for Cryptographic 1142 Modules", http://csrc.nist.gov/publications/fips/fips140-3/ 1144 [IEEE-802.1Q] 1145 IEEE Standards for Local and Metropolitan Area Networks: Draft 1146 Standard for Virtual Bridged Local Area Networks, 1147 P802.1Q-2003, January 2003. 1149 [RFC5580] Tschofenig, H. (Ed.), "Carrying Location Objects in RADIUS and 1150 Diameter", RFC 5580, August 2009. 1152 Appendix A - Design Guidelines 1154 The following text provides guidelines for the design of attributes 1155 used by the RADIUS protocol. Specifications that follow these 1156 guidelines are expected to achieve maximum interoperability with 1157 minimal changes to existing systems. 1159 A.1. Types matching the RADIUS data model 1161 A.1.1. Transport of simple data 1163 Does the data fit within the existing RADIUS data model, as outlined 1164 below? If so, it SHOULD be encapsulated in a [RFC2865] format RADIUS 1165 attribute, or in a [RFC2865] format RADIUS VSA that uses one of the 1166 existing RADIUS data types. 1168 * 32-bit unsigned integer, in network byte order. 1170 * Enumerated data types, represented as a 32-bit unsigned integer 1171 with a list of name to value mappings. (e.g., Service-Type) 1173 * 64-bit unsigned integer, in network byte order. 1175 * IPv4 address in network byte order. 1177 * IPv6 address in network byte order. 1179 * IPv6 prefix. 1181 * time as 32 bit unsigned value, in network byte order, and in 1182 seconds since 00:00:00 UTC, January 1, 1970. 1184 * string (i.e., binary data), totalling 253 octets or less in 1185 length. This includes the opaque encapsulation of data 1186 structures defined outside of RADIUS. See also Appendix A.1.3, 1187 below. 1189 * UTF-8 text, totalling 253 octets or less in length. 1191 Note that the length limitations for VSAs of type String and Text are 1192 less than 253 octets, due to the additional overhead of the Vendor- 1193 Specific format. 1195 The following data also qualifies as "simple data types": 1197 * Attributes grouped into a logical container, using the 1198 [RFC2868] tagging mechanism. This approach is NOT 1199 RECOMMENDED (see Section 2.1.2), but is permissible where 1200 the alternatives are worse. 1202 * Attributes requiring the transport of more than 247 octets of 1203 Text or String data. This includes the opaque encapsulation 1204 of data structures defined outside of RADIUS. See also Section 1205 A.1.3, below. 1207 Nested groups or attributes do not qualify as "simple data types", 1208 and SHOULD NOT be used. 1210 A.1.2. Transport of Authentication and Security Data 1212 Does the data provide authentication and/or security capabilities, as 1213 outlined below? If so, it SHOULD be encapsulated in a [RFC2865] 1214 format RADIUS attribute. It SHOULD NOT be encapsulated in a 1215 [RFC2865] format RADIUS VSA. 1217 * Complex data types that carry authentication methods which 1218 RADIUS servers are expected to parse and verify as part of 1219 an authentication process. 1221 * Complex data types that carry security information intended 1222 to increase the security of the RADIUS protocol itself. 1224 Any data type carrying authentication and/or security data that is 1225 not meant to be parsed by a RADIUS server is an "opaque data type", 1226 as defined below. 1228 A.1.3. Opaque data types 1230 Does the attribute encapsulate an existing data structure defined 1231 outside of the RADIUS specifications? Can the attribute be treated 1232 as opaque data by RADIUS servers (including proxies?) If both 1233 questions can be answered affirmatively, a complex structure MAY be 1234 used in a RADIUS specification. 1236 The specification of the attribute SHOULD define the encapsulating 1237 attribute to be of type String. The specification SHOULD refer to an 1238 external document defining the structure. The specification SHOULD 1239 NOT define or describe the structure, as discussed above in Section 1240 2.1.3. 1242 A.2. Improper Data Types 1244 All data types other than the ones described above in Appendix A.1 1245 SHOULD NOT be used. This section describes in detail a number of 1246 data types that are NOT RECOMMENDED in new RADIUS specifications. 1247 Where possible, replacement data types are suggested. 1249 A.2.1. Simple Data Types 1251 Does the attribute use any of the following data types? If so, the 1252 data type SHOULD be replaced with the suggested alternatives, or it 1253 SHOULD NOT be used at all. 1255 * Signed integers of any size. 1256 SHOULD NOT be used. SHOULD be replaced with one or more 1257 unsigned integer attributes. The definition of the attribute 1258 can contain information that would otherwise go into the sign 1259 value of the integer. 1261 * 8 bit unsigned integers. 1262 SHOULD be replaced with 32-bit unsigned integer. There is 1263 insufficient justification to save three bytes. 1265 * 16 bit unsigned integers. 1266 SHOULD be replaced with 32-bit unsigned integer. There is 1267 insufficient justification to save two bytes. 1269 * Unsigned integers of size other than 32 or 64. 1270 SHOULD be replaced by an unsigned integer of 32 or 64 bits. 1271 There is insufficient justification to define a new size of 1272 integer. 1274 * Integers of any size in non-network byte order 1275 SHOULD be replaced by unsigned integer of 32 or 64 bits, 1276 in network byte order. There is no reason to transport integers 1277 in any format other than network byte order. 1279 * Tagged data types as described in [RFC2868]. 1280 These data types SHOULD NOT be used in new specifications. 1282 * Complex data structures defined only within RADIUS. 1283 SHOULD NOT be used. This recommendation does not apply to new 1284 attributes for authentication or security, as described below 1285 in Section A.2.2. 1287 * Multi-field text strings. 1288 Each field SHOULD be encapsulated in a separate attribute. 1290 * Polymorphic attributes. 1291 Multiple attributes, each with a static data type SHOULD be 1292 defined instead. 1294 * Nested AVPs. 1295 Attributes should be defined in a flat typespace, possibly using 1296 a 16-bit Vendor type field (see Section 2.3). 1298 A.2.2. Complex Data Types 1300 Does the attribute: 1302 * define a complex data type 1304 * That a RADIUS server and/or client is expected to parse? 1305 i.e. A type that cannot be treated as opaque data (Section A.1.3) 1307 * for purposes other than authentication or security? 1309 If so, this data type SHOULD be replaced with simpler types, as 1310 discussed above in Appendix A.2.1. Also see Section 2.1.3 for a 1311 discussion of why complex types are problematic. 1313 A.3. Vendor-Specific formats 1315 Does the specification contain Vendor-Specific attributes that match 1316 any of the following criteria? If so, the data type should be 1317 replaced with the suggested alternatives, or should not be used at 1318 all. 1320 * Vendor types of more than 8 bits. 1321 SHOULD NOT be used. Vendor types of 8 bits SHOULD be used 1322 instead. 1324 * Vendor lengths of less than 8 bits. (i.e., zero bits) 1325 SHOULD NOT be used. Vendor lengths of 8 bits SHOULD be used 1326 instead. 1328 * Vendor lengths of more than 8 bits. 1329 SHOULD NOT be used. Vendor lengths of 8 bits SHOULD be used 1330 instead. 1332 * Vendor-Specific contents that are not in Type-Length-Value 1333 format. 1334 SHOULD NOT be used. Vendor-Specific attributes SHOULD be in 1335 Type-Length-Value format. 1337 In general, Vendor-Specific attributes SHOULD follow the [RFC2865] 1338 suggested format. Vendor extensions to non-standard formats are NOT 1339 RECOMMENDED as they can negatively affect interoperability. 1341 A.4. Changes to the RADIUS Operational Model 1343 Does the specification change the RADIUS operation model, as outlined 1344 in the list below? If so, then another method of achieving the 1345 design objectives SHOULD be used. Potential problem areas include: 1347 * Defining new commands in RADIUS using attributes. 1348 The addition of new commands to RADIUS MUST be handled via 1349 allocation of a new Code, and not by the use of an attribute. 1350 This restriction includes new commands created by overloading 1351 the Service-Type attribute to define new values that modify 1352 the functionality of Access-Request packets. 1354 * Using RADIUS as a transport protocol for data unrelated to 1355 authentication, authorization, or accounting. Using RADIUS to 1356 transport authentication methods such as EAP is explicitly 1357 permitted, even if those methods require the transport of 1358 relatively large amounts of data. Transport of opaque data 1359 relating to AAA is also permitted, as discussed above in 1360 Section 2.1.3. However, if the specification does not relate 1361 to AAA, then RADIUS SHOULD NOT be used. 1363 * Assuming support for packet lengths greater than 4096 octets. 1364 Attribute designers cannot assume that RADIUS implementations 1365 can successfully handle packets larger than 4096 octets. 1366 If a specification could lead to a RADIUS packet larger than 1367 4096 octets, then the alternatives described in Section 3.3 1368 SHOULD be considered. 1370 * Stateless operation. The RADIUS protocol is stateless, and 1371 documents which require stateful protocol behavior without the 1372 use of the State Attribute need to be redesigned. 1374 * Provisioning of service in an Access-Reject. Such provisioning 1375 is not permitted, and MUST NOT be used. If limited access needs 1376 to be provided, then an Access-Accept with appropriate 1377 authorizations can be used instead. 1379 * Lack of user authentication or authorization restrictions. 1380 In an authorization check, where there is no demonstration of a 1381 live user, confidential data cannot be returned. Where there 1382 is a link to a previous user authentication, the State attribute 1383 needs to be present. 1385 * Lack of per-packet integrity and authentication. 1386 It is expected that documents will support per-packet 1387 integrity and authentication. 1389 * Modification of RADIUS packet sequences. 1390 In RADIUS, each request is encapsulated in it's own packet, and 1391 elicits a single response that is sent to the requester. Since 1392 changes to this paradigm are likely to require major 1393 modifications to RADIUS client and server implementations, they 1394 SHOULD be avoided if possible. 1396 For further details, see Section 3.3. 1398 A.5. Allocation of attributes 1400 Does the attribute have a limited scope of applicability, as outlined 1401 below? If so, then the attributes SHOULD be allocated from the 1402 Vendor-Specific space. 1404 * attributes intended for a vendor to support their own systems, 1405 and not suitable for general usage 1407 * attributes relying on data types not defined within RADIUS 1409 * attributes intended primarily for use within an SDO 1411 * attributes intended primarily for use within a group of SDOs. 1413 Note that the points listed above do not relax the recommendations 1414 discussed in this document. Instead, they recognize that the RADIUS 1415 data model has limitations. In certain situations where 1416 interoperability can be strongly constrained by the SDO or vendor, an 1417 expanded data model MAY be used. We recommend, however, that the 1418 RADIUS data model SHOULD be used, even if it is marginally less 1419 efficient than alternatives. 1421 When attributes are used primarily within a group of SDOs, and are 1422 not applicable to the wider Internet community, we expect that one 1423 SDO will be responsible for allocation from their own private space. 1425 Appendix B - Complex Attributes 1427 This section summarizes RADIUS attributes with complex data types 1428 that are defined in existing RFCs. 1430 This appendix is published for informational purposes only, and 1431 reflects the usage of attributes with complex data types at the time 1432 of the publication of this document. 1434 B.1. CHAP-Password 1436 [RFC2865] Section 5.3 defines the CHAP-Password Attribute which is 1437 sent from the RADIUS client to the RADIUS server in an Access- 1438 Request. The data type of the CHAP Identifier is not given, only the 1439 one octet length: 1441 0 1 2 1442 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 1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1444 | Type | Length | CHAP Ident | String ... 1445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1447 Since this is an authentication attribute, code changes are required 1448 on the RADIUS client and server to support it, regardless of the 1449 attribute format. Therefore, this complex data type is acceptable in 1450 this situation. 1452 B.2. CHAP-Challenge 1454 [RFC2865] Section 5.40 defines the CHAP-Challenge Attribute which is 1455 sent from the RADIUS client to the RADIUS server in an Access- 1456 Request. While the data type of the CHAP Identifier is given, the 1457 text also says: 1459 If the CHAP challenge value is 16 octets long it MAY be placed in 1460 the Request Authenticator field instead of using this attribute. 1462 Defining attributes to contain values taken from the RADIUS packet 1463 header is NOT RECOMMENDED. Attributes should have values that are 1464 packed into a RADIUS AVP. 1466 B.3. Tunnel-Password 1468 [RFC2868] Section 3.5 defines the Tunnel-Password Attribute, which is 1469 sent from the RADIUS server to the client in an Access-Accept. This 1470 attribute includes Tag and Salt fields, as well as a string field 1471 which consists of three logical sub-fields: the Data-Length (one 1472 octet) and Password sub-fields (both of which are required), and the 1473 optional Padding sub-field. The attribute appears as follows: 1475 0 1 2 3 1476 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 1477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1478 | Type | Length | Tag | Salt 1479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1480 Salt (cont) | String ... 1481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1483 Since this is a security attribute and is encrypted, code changes are 1484 required on the RADIUS client and server to support it, regardless of 1485 the attribute format. Therefore, this complex data type is 1486 acceptable in this situation. 1488 B.4. ARAP-Password 1490 [RFC2869] Section 5.4 defines the ARAP-Password attribute, which is 1491 sent from the RADIUS client to the server in an Access-Request. It 1492 contains four 4 octet values, instead of having a single Value field: 1494 0 1 2 3 1495 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 1496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1497 | Type | Length | Value1 1498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1499 | Value2 1500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1501 | Value3 1502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1503 | Value4 1504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1505 | 1506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1508 As with the CHAP-Password attribute, this is an authentication 1509 attribute which would have required code changes on the RADIUS client 1510 and server regardless of format. 1512 B.5. ARAP-Features 1514 [RFC2869] Section 5.5 defines the ARAP-Features Attribute, which is 1515 sent from the RADIUS server to the client in an Access-Accept or 1516 Access-Challenge. It contains a compound string of two single octet 1517 values, plus three 4-octet values, which the RADIUS client 1518 encapsulates in a feature flags packet in the ARAP protocol: 1520 0 1 2 3 1521 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 1522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1523 | Type | Length | Value1 | Value2 | 1524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1525 | Value3 | 1526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1527 | Value4 | 1528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1529 | Value5 | 1530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1532 Unlike the previous attributes, this attribute contains no encrypted 1533 component, nor is it directly involved in authentication. The 1534 individual sub-fields therefore could have been encapsulated in 1535 separate attributes. 1537 While the contents of this attribute is intended to be placed in an 1538 ARAP packet, the fields need to be set by the RADIUS server. Using 1539 standard RADIUS data types would have simplified RADIUS server 1540 implementations, and subsequent management. The current form of the 1541 attribute requires either the RADIUS server implementation, or the 1542 RADIUS server administrator, to understand the internals of the ARAP 1543 protocol. 1545 B.6. Connect-Info 1547 [RFC2869] Section 5.11 defines the Connect-Info attribute, which is 1548 used to indicate the nature of the connection. 1550 0 1 2 1551 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1553 | Type | Length | Text... 1554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1556 Even though the type is Text, the rest of the description indicates 1557 that it is a complex attribute: 1559 The Text field consists of UTF-8 encoded 10646 _8_ characters. 1560 The connection speed SHOULD be included at the beginning of the 1561 first Connect-Info attribute in the packet. If the transmit and 1562 receive connection speeds differ, they may both be included in the 1563 first attribute with the transmit speed first (the speed the NAS 1564 modem transmits at), a slash (/), the receive speed, then 1565 optionally other information. 1566 For example, "28800 V42BIS/LAPM" or "52000/31200 V90" 1568 More than one Connect-Info attribute may be present in an 1569 Accounting-Request packet to accommodate expected efforts by ITU 1570 to have modems report more connection information in a standard 1571 format that might exceed 252 octets. 1573 This attribute contains no encrypted component, and is it not 1574 directly involved in authentication. The individual sub-fields could 1575 therefore have been encapsulated in separate attributes. 1577 Since the form of the text string is well defined, there is no 1578 benefit in using a text string. Instead, an integer attribute should 1579 have been assigned for each of the transmit speed and the receive 1580 speed. A separate enumerated integer should have been assigned for 1581 the additional information, as is done for the NAS-Port-Type 1582 attribute. 1584 B.7. Framed-IPv6-Prefix 1586 [RFC3162] Section 2.3 defines the Framed-IPv6-Prefix Attribute and 1587 [RFC4818] Section 3 reuses this format for the Delegated-IPv6-Prefix 1588 Attribute; these attributes are sent from the RADIUS server to the 1589 client in an Access-Accept. 1591 0 1 2 3 1592 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 1593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1594 | Type | Length | Reserved | Prefix-Length | 1595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1596 Prefix 1597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1598 Prefix 1599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1600 Prefix 1601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1602 Prefix | 1603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1605 The sub-fields encoded in these attributes are strongly related, and 1606 there was no previous definition of this data structure that could be 1607 referenced. Support for this attribute requires code changes on both 1608 the client and server, due to a new data type being defined. In this 1609 case it appears to be acceptable to encode them in one attribute. 1611 B.8. Egress-VLANID 1613 [RFC4675] Section 2.1 defines the Egress-VLANID Attribute which can 1614 be sent by a RADIUS client or server. 1616 0 1 2 3 1617 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 1618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1619 | Type | Length | Value 1620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1621 Value (cont) | 1622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1624 While it appears superficially to be of type Integer, the Value field 1625 is actually a packed structure, as follows: 1627 0 1 2 3 1628 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 1629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1630 | Tag Indic. | Pad | VLANID | 1631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1633 The length of the VLANID field is defined by the [IEEE-802.1Q] 1634 specification. The Tag indicator field is either 0x31 or 0x32, for 1635 compatibility with the Egress-VLAN-Name, as discussed below. The 1636 complex structure of Egress-VLANID overlaps with that of the base 1637 Integer data type, meaning that no code changes are required for a 1638 RADIUS server to support this attribute. Code changes are required 1639 on the NAS, if only to implement the VLAN ID enforcement. 1641 Given the IEEE VLAN requirements and the limited data model of 1642 RADIUS, the chosen method is likely the best of the possible 1643 alternatives. 1645 B.9. Egress-VLAN-Name 1647 [RFC4675] Section 2.3 defines the Egress-VLAN-Name Attribute which 1648 can be sent by a RADIUS client or server. 1650 0 1 2 3 1651 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 1652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1653 | Type | Length | Tag Indic. | String... 1654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1656 The Tag Indicator is either the character '1' or '2', which in ASCII 1657 map to the identical values for Tag Indicator in Egress-VLANID, 1658 above. The complex structure of this attribute is acceptable for 1659 reasons identical to those given for Egress-VLANID. 1661 Acknowledgments 1663 We would like to acknowledge David Nelson, Bernard Aboba, Emile van 1664 Bergen, Barney Wolff and Glen Zorn for contributions to this 1665 document. 1667 Authors' Addresses 1669 Greg Weber 1670 Knoxville, TN 37932 1671 USA 1673 Email: gdweber@gmail.com 1675 Alan DeKok 1676 The FreeRADIUS Server Project 1677 http://freeradius.org/ 1679 Email: aland@freeradius.org