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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (June 28, 2012) is 4318 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RADIUS Extensions Working Group S. Winter 3 Internet-Draft RESTENA 4 Intended status: Experimental M. McCauley 5 Expires: December 30, 2012 OSC 6 June 28, 2012 8 NAI-based Dynamic Peer Discovery for RADIUS/TLS and RADIUS/DTLS 9 draft-ietf-radext-dynamic-discovery-04 11 Abstract 13 This document specifies a means to find authoritative RADIUS servers 14 for a given realm. It can be used in conjunction with RADIUS/TLS and 15 RADIUS/DTLS. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on December 30, 2012. 34 Copyright Notice 36 Copyright (c) 2012 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 53 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. DNS-based NAPTR/SRV Peer Discovery . . . . . . . . . . . . . . 3 55 2.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 3 56 2.2. DNS RR definition . . . . . . . . . . . . . . . . . . . . 3 57 2.3. Realm to AAA server resolution algorithm . . . . . . . . . 5 58 2.3.1. Input . . . . . . . . . . . . . . . . . . . . . . . . 5 59 2.3.2. Output . . . . . . . . . . . . . . . . . . . . . . . . 6 60 2.3.3. Algorithm . . . . . . . . . . . . . . . . . . . . . . 6 61 2.3.4. Validity of results . . . . . . . . . . . . . . . . . 7 62 2.3.5. Delay considerations . . . . . . . . . . . . . . . . . 8 63 2.3.6. Example . . . . . . . . . . . . . . . . . . . . . . . 8 64 3. Security Considerations . . . . . . . . . . . . . . . . . . . 10 65 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 66 5. Normative References . . . . . . . . . . . . . . . . . . . . . 10 68 1. Introduction 70 1.1. Requirements Language 72 In this document, several words are used to signify the requirements 73 of the specification. The key words "MUST", "MUST NOT", "REQUIRED", 74 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 75 and "OPTIONAL" in this document are to be interpreted as described in 76 RFC 2119. [RFC2119] 78 1.2. Terminology 80 RADIUS/TLS Client: a RADIUS/TLS [RFC6614] instance which initiates a 81 new connection. 83 RADIUS/TLS Server: a RADIUS/TLS [RFC6614] instance which listens on a 84 RADIUS/TLS port and accepts new connections 86 RADIUS/TLS node: a RADIUS/TLS client or server 88 2. DNS-based NAPTR/SRV Peer Discovery 90 2.1. Applicability 92 Dynamic server discovery as defined in this document is only 93 applicable for AAA transactions where a RADIUS server receives a 94 request with a realm for which no home RADIUS server is known. I.e. 95 where static server configuration does not contain a known home 96 authentication server, or where the server configuration explicitly 97 states that the realm destination is to be looked up dynamically. 98 Furthermore, it is only applicable for new user sessions, i.e. for 99 the initial Access-Request. Subsequent messages concerning this 100 session, for example Access-Challenges and Access-Accepts use the 101 previously-established communication channel between client and 102 server. 104 2.2. DNS RR definition 106 DNS definitions of RADIUS/TLS servers can be either S-NAPTR records 107 (see [RFC3958]) or SRV records. When both are defined, the 108 resolution algorithm prefers S-NAPTR results (see section Section 2.3 109 below). 111 This specification defines three S-NAPTR service tags: "aaa+auth", 112 "aaa+acct" and "aaa+dynauth". This specification defines two S-NAPTR 113 protocol tags: "radius.tls" for RADIUS/TLS [RFC6614] and 114 "radius.dtls" for RADIUS/DTLS [I-D.dekok-radext-dtls]. 116 Note well: 118 The S-NAPTR service and protocols are unrelated to the IANA 119 Service Name and Transport Protocol Number registry 121 The delimiter '.' in the protocol tags is only a separator for 122 human reading convenience - not for structure or namespacing; it 123 MUST NOT be parsed in any way by the querying application or 124 resolver. 126 The use of the separator '.' is common also in other protocols' 127 protocol tags. This is coincidence and does not imply a shared 128 semantics with such protocols. 130 This specification defines the SRV prefix "_radiustls._tcp" for 131 RADIUS over TLS [RFC6614] and "_radiustls._udp" for RADIUS over DTLS 132 [I-D.dekok-radext-dtls]. It is expected that in most cases, the 133 label used for the records is the DNS representation (punycode) of 134 the literal realm name for which the server is the AAA server. 136 However, arbitrary other labels may be used if, for example, a 137 roaming consortium uses realm names which are not associated to DNS 138 names or special-purpose consortia where a globally valid discovery 139 is not a use case. Such other labels require a consortium-wide 140 agreement about the transformation from realm name to lookup label. 142 Examples: 144 a. A general-purpose AAA server for realm example.com might have DNS 145 entries as follows: 147 example.com. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" "" 148 _radiustls._tcp.foobar.example.com. 150 _radiustls._tcp.foobar.example.com. IN SRV 0 10 2083 151 radsec.example.com. 153 b. The consortium "foo" provides roaming services for its members 154 only. The realms used are of the form enterprise-name.example. 155 The consortium operates a special purpose DNS server for the 156 (private) TLD "example" which all AAA servers use to resolve 157 realm names. "Bad, Inc." is part of the consortium. On the 158 consortium's DNS server, realm bad.example might have the 159 following DNS entries: 161 bad.example IN NAPTR 50 50 "a" "aaa+auth:radius.dtls" "" 162 "very.bad.example" 164 c. The eduroam consortium uses realms based on DNS, but provides its 165 services to a closed community only. However, a AAA domain 166 participating in eduroam may also want to expose AAA services to 167 other, general-purpose, applications (on the same or other AAA 168 servers). Due to that, the eduroam consortium uses the service 169 tag "x-eduroam" for authentication purposes and eduroam AAA 170 servers use this tag to look up other eduroam servers. An 171 eduroam participant example.org which also provides general- 172 purpose AAA on a different server uses the general "aaa+auth" 173 tag: 175 example.org. IN NAPTR 50 50 "s" "x-eduroam:radius.tls" "" 176 _radiustls._tcp.eduroam.example.org. 178 example.org. IN NAPTR 50 50 "s" "aaa+auth:radius.tls" "" 179 _radiustls._tcp.aaa.example.org 181 _radiustls._tcp.eduroam.example.org. IN SRV 0 10 2083 aaa- 182 eduroam.example.org. 184 _radiustls._tcp.aaa.example.org. IN SRV 0 10 2083 aaa- 185 default.example.org. 187 2.3. Realm to AAA server resolution algorithm 189 This algorithm can be used to discover RADIUS servers (for RADIUS 190 Authentication and RADIUS Accounting) or to discover RADIUS DynAuth 191 servers. 193 2.3.1. Input 195 For RADIUS Authentication and RADIUS Accounting server discovery, 196 input I to the algorithm is the RADIUS User-Name attribute with 197 content of the form "user@realm"; the literal @ sign being the 198 separator between a local user identifier within a realm and its 199 realm. The use of multiple literal @ signs in a User-Name is 200 strongly discouraged; but if present, the last @ sign is to be 201 considered the separator. All previous instances of the @ sign are 202 to be considered part of the local user identifier. 204 For RADIUS DynAuth Server discovery, input I to the algorithm is the 205 domain name of the operator of a RADIUS realm as was communicated 206 during user authentication using the Operator-Name attribute 207 ([RFC5580], section 4.1). Only Operator-Name values with the 208 namespace "1" are supported by this algorithm - the input to the 209 algorithm is the actual domain name, preceeded with an "@" (but 210 without the "1" namespace identifier byte of that attribute). 212 Note well: The attribute User-Name is defined to contain UTF-8 text. 213 In practice, the content may or may not be UTF-8. Even if UTF-8, it 214 may or may not map to a domain name in the realm part. Implementors 215 MUST take possible conversion error paths into consideration when 216 parsing incoming User-Name attributes. This document describes 217 server discovery only for well-formed realms mapping to DNS domain 218 names in UTF-8 encoding. The result of all other possible contents 219 of User-Name is unspecified; this includes, but is not limited to: 221 Usage of separators other than @ 223 Usage of multiple @ separators 225 Encoding of User-Name in local encodings 227 UTF-8 realms which fail the conversion rules as per [RFC5891] 229 UTF-8 realms which end with a . ("dot") character. 231 For the last bullet point, "trailing dot", special precautions should 232 be taken to avoid problems when resolving servers with the algorithm 233 below: they may resolve to a AAA server even if the peer RADIUS 234 server only is configured to handle the realm without the trailing 235 dot. If that RADIUS server again uses NAI discovery to determine the 236 authoritative server, the server will forward the request to 237 localhost, resulting in a tight endless loop. 239 2.3.2. Output 241 Output O of the algorithm is a set of the tuple {hostname; port; 242 order/preference; TTL} - the set can be empty. 244 2.3.3. Algorithm 246 The algorithm to determine the RADIUS server to contact is as 247 follows: 249 1. Determine P = (position of last "@" character) in I. 251 2. generate R = (substring from P+1 to end of I) 253 3. Optional: modify R according to agreed consortium procedures 255 4. Using the host's name resolution library, perform a NAPTR query 256 for R (see "Delay considerations" below). The name resolution 257 library may need to convert R to a different respresentation, 258 depending on the resolution backend used. If no result, 259 continue at step 9. If name resolution returns with error, O = 260 { } and terminate. 262 5. Extract NAPTR records with service tag "aaa+auth", "aaa+acct", 263 "aaa+dynauth" as appropriate. Keep note of the remaining TTL of 264 each of the discovered NAPTR records. 266 6. If no result, continue at step 9. 268 7. Evaluate NAPTR result(s) for desired protocol tag, perform 269 subsequent lookup steps until lookup yields one or more 270 hostnames. O = (set of {hostname; port; order/preference; 271 min{all TTLs that led to this result} } for all lookup results). 272 Keep note of the remaining TTL of each of the discovered records 273 (e.g. SRV and AAAA). 275 8. Terminate. 277 9. Generate R' = (prefix R with "_radiustls._tcp." or 278 "_radiustls._udp") 280 10. Using the host's name resolution library, perform SRV lookup 281 with R' as label (see "Delay considerations" below). Keep note 282 of the TTL of each of the discovered SRV records. 284 11. If name resolution returns with error, O = { } and terminate. 286 12. If no result, O = {} and terminate. 288 13. Perform subsequent lookup steps until lookup yields one or more 289 hostnames (see "Delay considerations" below). Keep note of the 290 TTL of each of the discovered records. 292 14. O = (set of {hostname; port; order/preference; min{all TTLs that 293 led to this result} } for all hostnames). Terminate. 295 2.3.4. Validity of results 297 After executing the above algorithm, the RADIUS server establishes a 298 connection to a home server from the result set. This connection can 299 potentially remain open for an indefinite amount of time. This 300 conflicts with the possibility of changing device and network 301 configurations on the receiving end. Typically, TTL values for 302 records in the name resolution system are used to indicate how long 303 it is safe to rely on the results of the name resolution. To allow 304 for a change of configuration, a RADIUS server SHOULD re-execute the 305 algorithm above after the lowest of the TTL values that are 306 associated with this connection have expired. The server MAY keep 307 the session open during this re-assessment to avoid closure and 308 immediate re-opening of the connection should the result not have 309 changed. 311 Should the algorithm above terminate with an empty set (but no 312 error), the RADIUS server SHOULD NOT attempt another execution of 313 this algorithm for the same target realm before the negative TTL has 314 expired. 316 Should the algorithm above terminate due to an error with no TTL 317 value known (e.g. DNS SERVFAIL), the RADIUS server SHOULD NOT 318 attempt another execution of this algorithm for the same target realm 319 before a configurable timeout interval has passed. 321 2.3.5. Delay considerations 323 The host's name resolution library may need to contact outside 324 entities to perform the name resolution (e.g. authoritative name 325 servers for a domain), and since the NAI discovery algorithm is based 326 on uncontrollable user input, the destination of the lookups is out 327 of control of the server that performs NAI discovery. If such 328 outside entities are misconfigured or unreachable, the algorithm 329 above may need an unacceptably long time to terminate. Many RADIUS 330 implementations time out after five seconds of delay between Request 331 and Response. It is not useful to wait until the host name 332 resolution library signals a time-out of its name resolution 333 algorithms; instead, implementations of NAI discovery SHOULD 334 terminate the algorithm after the fixed upper bound of time of three 335 seconds. If no final output of the algorithm is available after this 336 timeout, the RADIUS server MUST assume the empty set as a result and 337 treat the pending request according to its static configuration 338 (e.g., fallback to a default route to a home server). Execution of 339 the NAI discovery algorithm SHOULD be non-blocking (i.e. allow other 340 requests to be processed in parallel to the execution of the 341 algorithm). 343 2.3.6. Example 345 Example: Assume a user from the Technical University of Munich, 346 Germany, has a RADIUS User-Name of 347 "foobar@tu-m[U+00FC]nchen.example". The name resolution library on 348 the RADIUS client uses DNS for name resolution. If DNS contains the 349 following records: 351 xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "aaa+ 352 auth:radius.tls" "" _radiustls._tcp.xn--tu-mnchen-t9a.example. 354 xn--tu-mnchen-t9a.example. IN NAPTR 50 50 "s" "fooservice: 355 bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example. 357 _radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 10 2083 358 radsec.xn--tu-mnchen-t9a.example. 360 _radiustls._tcp.xn--tu-mnchen-t9a.example. IN SRV 0 20 2083 361 backup.xn--tu-mnchen-t9a.example. 363 radsec.xn--tu-mnchen-t9a.example. IN AAAA 2001:0DB8::202:44ff: 364 fe0a:f704 366 radsec.xn--tu-mnchen-t9a.example. IN A 192.0.2.3 368 backup.xn--tu-mnchen-t9a.example. IN A 192.0.2.7 370 Then the algorithm executes as follows, with I = 371 "foobar@tu-m[U+00FC]nchen.example", and no consortium name mangling 372 in use: 374 1. P = 7 376 2. R = "tu-m[U+00FC]nchen.example" 378 3. NOOP 380 4. [name resolution library converts R to xn--tu-mnchen- 381 t9a.example] Query result: ( 50 50 "s" "aaa+auth:radius.tls" "" 382 _radiustls._tcp.xn--tu-mnchen-t9a.example. ; 50 50 "s" 383 "fooservice:bar.dccp" "" _abc._def.xn--tu-mnchen-t9a.example. ) 385 5. Result: 50 50 "s" "aaa+auth:radius.tls" "" _radiustls._tcp.xn-- 386 tu-mnchen-t9a.example. 388 6. NOOP 390 7. O = {(radsec.xn--tu-mnchen-t9a.example.; 2083; 10; TTL 391 A),(backup.xn--tu-mnchen-t9a. example.;2083; 20; TTL B)} 393 8. Terminate. 395 9. (not executed) 397 10. (not executed) 399 11. (not executed) 401 12. (not executed) 403 13. (not executed) 404 14. (not executed) 406 The implementation will then attempt to connect to two servers, with 407 preference to radsec.xn--tu-mnchen-t9a.example.:2083, using either 408 the AAAA or A addresses depending on the host configuration and its 409 IP stack's capabilities. 411 3. Security Considerations 413 When using DNS without DNSSEC security extensions, the replies to 414 NAPTR, SRV and A/AAAA requests as described in section Section 2 can 415 not be trusted. RADIUS transports have an out-of-DNS-band means to 416 verify that the discovery attempt led to the intended target: 417 certificate verification or TLS-PSK keys. 419 4. IANA Considerations 421 This document requests IANA registration of the following S-NAPTR 422 parameter: 424 o Application Service Tags 426 * aaa+auth 428 * aaa+acct 430 * aaa+dynauth 432 o Application Protocol Tags 434 * radius.tls 436 * radius.dtls 438 5. Normative References 440 [RFC2119] Bradner, S., "Key words for use in RFCs to 441 Indicate Requirement Levels", BCP 14, 442 RFC 2119, March 1997. 444 [RFC3958] Daigle, L. and A. Newton, "Domain-Based 445 Application Service Location Using SRV RRs 446 and the Dynamic Delegation Discovery Service 447 (DDDS)", RFC 3958, January 2005. 449 [RFC5580] Tschofenig, H., Adrangi, F., Jones, M., 450 Lior, A., and B. Aboba, "Carrying Location 451 Objects in RADIUS and Diameter", RFC 5580, 452 August 2009. 454 [RFC5891] Klensin, J., "Internationalized Domain Names 455 in Applications (IDNA): Protocol", RFC 5891, 456 August 2010. 458 [I-D.dekok-radext-dtls] DeKok, A., "DTLS as a Transport Layer for 459 RADIUS", draft-dekok-radext-dtls-03 (work in 460 progress), July 2010. 462 [RFC6614] Winter, S., McCauley, M., Venaas, S., and K. 463 Wierenga, "Transport Layer Security (TLS) 464 Encryption for RADIUS", RFC 6614, May 2012. 466 Authors' Addresses 468 Stefan Winter 469 Fondation RESTENA 470 6, rue Richard Coudenhove-Kalergi 471 Luxembourg 1359 472 LUXEMBOURG 474 Phone: +352 424409 1 475 Fax: +352 422473 476 EMail: stefan.winter@restena.lu 477 URI: http://www.restena.lu. 479 Mike McCauley 480 Open Systems Consultants 481 9 Bulbul Place 482 Currumbin Waters QLD 4223 483 AUSTRALIA 485 Phone: +61 7 5598 7474 486 Fax: +61 7 5598 7070 487 EMail: mikem@open.com.au 488 URI: http://www.open.com.au.