idnits 2.17.1 draft-ietf-radext-radius-fragmentation-05.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == The 'Updates: ' line in the draft header should list only the _numbers_ of the RFCs which will be updated by this document (if approved); it should not include the word 'RFC' in the list. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 7, 2014) is 3695 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Missing Reference: 'M' is mentioned on line 1141, but not defined == Missing Reference: 'MT' is mentioned on line 1142, but not defined ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RADIUS EXTensions Working Group A. Perez-Mendez 3 Internet-Draft R. Marin-Lopez 4 Updates: RFC6929 (if approved) F. Pereniguez-Garcia 5 Intended status: Experimental G. Lopez-Millan 6 Expires: September 8, 2014 University of Murcia 7 D. Lopez 8 Telefonica I+D 9 A. DeKok 10 Network RADIUS 11 March 7, 2014 13 Support of fragmentation of RADIUS packets 14 draft-ietf-radext-radius-fragmentation-05 16 Abstract 18 The Remote Authentication Dial-In User Service (RADIUS) protocol is 19 limited to a total packet size of 4096 octets. Provisions exist for 20 fragmenting large amounts of authentication data across multiple 21 packets, via Access-Challenge. No similar provisions exist for 22 fragmenting large amounts of authorization data. This document 23 specifies how existing RADIUS mechanisms can be leveraged to provide 24 that functionality. These mechanisms are largely compatible with 25 existing implementations, and are designed to be invisible to 26 proxies, and "fail-safe" to legacy clients and servers. 28 Status of this Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on September 8, 2014. 45 Copyright Notice 47 Copyright (c) 2014 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 64 2. Scope of this document . . . . . . . . . . . . . . . . . . . . 4 65 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 4. Fragmentation of packets . . . . . . . . . . . . . . . . . . . 8 67 4.1. Pre-authorization . . . . . . . . . . . . . . . . . . . . 9 68 4.2. Post-authorization . . . . . . . . . . . . . . . . . . . . 13 69 5. Chunk size . . . . . . . . . . . . . . . . . . . . . . . . . . 16 70 6. Allowed large packet size . . . . . . . . . . . . . . . . . . 17 71 7. Handling special attributes . . . . . . . . . . . . . . . . . 18 72 7.1. Proxy-State attribute . . . . . . . . . . . . . . . . . . 18 73 7.2. State attribute . . . . . . . . . . . . . . . . . . . . . 19 74 7.3. Service-Type attribute . . . . . . . . . . . . . . . . . . 20 75 7.4. Rebuilding the original large packet . . . . . . . . . . . 20 76 8. New flag T field for the Long Extended Type attribute 77 definition . . . . . . . . . . . . . . . . . . . . . . . . . . 20 78 9. New attribute definition . . . . . . . . . . . . . . . . . . . 21 79 9.1. Frag-Status attribute . . . . . . . . . . . . . . . . . . 21 80 9.2. Proxy-State-Len attribute . . . . . . . . . . . . . . . . 22 81 9.3. Table of attributes . . . . . . . . . . . . . . . . . . . 23 82 10. Operation with proxies . . . . . . . . . . . . . . . . . . . . 23 83 10.1. Legacy proxies . . . . . . . . . . . . . . . . . . . . . . 23 84 10.2. Updated proxies . . . . . . . . . . . . . . . . . . . . . 24 85 11. Security Considerations . . . . . . . . . . . . . . . . . . . 25 86 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 87 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 88 13.1. Normative References . . . . . . . . . . . . . . . . . . . 26 89 13.2. Informative References . . . . . . . . . . . . . . . . . . 27 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 92 1. Introduction 94 The RADIUS [RFC2865] protocol carries authentication, authorization, 95 and accounting information between a Network Access Server (NAS) and 96 an Authentication Server (AS). Information is exchanged between the 97 NAS and the AS through RADIUS packets. Each RADIUS packet is 98 composed of a header, and zero or more attributes, up to a maximum 99 packet size of 4096 octets. The protocol is a request/response 100 protocol, as described in the operational model ( [RFC6158], Section 101 3.1). 103 The above packet size limitation mean that peers desiring to send 104 large amounts of data must fragment it across multiple packets. For 105 example, RADIUS-EAP [RFC3579] defines how an EAP exchange occurs 106 across multiple Access-Request / Access-Challenge sequences. No such 107 exchange is possible for accounting or authorization data. [RFC6158] 108 Section 3.1 suggests that exchanging large amounts authorization data 109 is unnecessary in RADIUS. Instead, the data should be referenced by 110 name. This requirement allows large policies to be pre-provisioned, 111 and then referenced in an Access-Accept. In some cases, however, the 112 authorization data sent by the server is large and highly dynamic. 113 In other cases, the NAS needs to send large amounts of authorization 114 data to the server. Both of these cases are un-met by the 115 requirements in [RFC6158]. As noted in that document, the practical 116 limit on RADIUS packet sizes is governed by the Path MTU (PMTU), 117 which may be significantly smaller than 4096 octets. The combination 118 of the two limitations means that there is a pressing need for a 119 method to send large amounts of authorization data between NAS and 120 AS, with no accompanying solution. 122 [RFC6158] recommends three approaches for the transmission of large 123 amount of data within RADIUS. However, they are not applicable to 124 the problem statement of this document for the following reasons: 126 o The first approach does not talk about large amounts of data sent 127 from the NAS to a server. Leveraging EAP (request/challenge) to 128 send the data is not feasible, as EAP already fills packet to 129 PMTU, and not all authentications use EAP. Moreover, as noted for 130 NAS-Filter-Rule ([RFC4849]), this approach does entirely solve the 131 problem of sending large amounts of data from a server to a NAS. 133 o The second approach is not usable either, as using names rather 134 than values is difficult when the nature of the data to be sent is 135 highly dynamic (e.g. SAML sentences or NAS-Filter-Rule 136 attributes). URLs could be used as a pointer to the location of 137 the actual data, but their use would require them to be (a) 138 dynamically created and modified, (b) securely accessed and (c) 139 accessible from remote systems. Satisfying these constraints 140 would require the modification of several networking systems (e.g. 141 firewalls and web servers). Furthermore, the set up of an 142 additional trust infrastructure (e.g. PKI) would be required to 143 allow secure retrieving of the information from the web server. 145 o PMTU discovery does not solve the problem, as it does not allow to 146 send data larger than the minimum of (PMTU or 4096) octets. 148 This document provides a mechanism to allow RADIUS peers to exchange 149 large amounts of authorization data exceeding the 4096 octet limit, 150 by fragmenting it across several client/server exchanges. The 151 proposed solution does not impose any additional requirements to the 152 RADIUS system administrators (e.g. need to modify firewall rules, set 153 up web servers, configure routers, or modify any application server). 154 It maintains compatibility with intra-packet fragmentation mechanisms 155 (like those defined in [RFC3579] or in [RFC6929]). It is also 156 transparent to existing RADIUS proxies, which do not implement this 157 specification. The only systems needing to implement the draft are 158 the ones which either generate, or consume the fragmented data being 159 transmitted. Intermediate proxies just pass the packets without 160 changes. Nevertheless, if a proxy supports this specification, it 161 may re-assemble the data in order to either examine and/or modify it. 163 1.1. Requirements Language 165 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 166 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 167 document are to be interpreted as described in RFC 2119 [RFC2119]. 168 When these words appear in lower case, they have their natural 169 language meaning. 171 2. Scope of this document 173 This specification describes how a RADIUS client and a RADIUS server 174 can exchange data exceeding the 4096 octet limit imposed by one 175 packet. However, the mechanism described in this specification MUST 176 NOT be used to exchange more than 100K of data. It has not been 177 designed to substitute for stream-oriented transport protocols, such 178 as TCP or SCTP. Experience shows that attempts to transport bulk 179 data across the Internet with UDP will inevitably fail, unless they 180 re-implement all of the behavior of TCP. The underlying design of 181 RADIUS lacks the proper retransmission policies or congestion control 182 mechanisms which would make it a competitor to TCP. 184 Therefore, RADIUS/UDP transport is by design unable to transport bulk 185 data. It is both undesired and impossible to change the protocol at 186 this point in time. This specification is intended to allow the 187 transport of slightly more than 4096 octets of data through existing 188 RADIUS/UDP proxies. Other solutions such as RADIUS/TCP MUST be used 189 when a "green field" deployment requires the transport of bulk data. 191 Section 6, below, describes with further details the reasoning for 192 this limitation, and recommends administrators to adjust it according 193 to the specific capabilities of their existing systems in terms of 194 memory and processing power. 196 Moreover, its scope is limited to the exchange of authorization data, 197 as other exchanges do not require of such a mechanism. In 198 particular, authentication exchanges have already been defined to 199 overcome this limitation (e.g. RADIUS-EAP). Moreover, as they 200 represent the most critical part of a RADIUS conversation, its 201 preferable to not introduce any modification to their operation that 202 may affect existing equipment. 204 There is no need to fragment accounting packets either. While the 205 accounting process can send large amounts of data, that data is 206 typically composed of many small updates. That is, there is no 207 demonstrated need to send indivisible blocks of more than 4K of data. 208 The need to send large amounts of data per user session often 209 originates from the need for flow-based accounting. In this use- 210 case, the client may send accounting data for many thousands of 211 flows, where all those flows are tied to one user session. The 212 existing Acct-Multi-Session-Id attribute defined in [RFC2866] Section 213 5.11 has been proven to work here. 215 Similarly, there is no need to fragment CoA packets. Instead, the 216 CoA client MUST send a CoA-Request packet containing session 217 identification attributes, along with Service-Type = Additional- 218 Authorization, and a State attribute. Implementations not supporting 219 fragmentation will respond with a CoA-NAK, and an Error-Cause of 220 Unsupported-Service. 222 The above requirement does not assume that the CoA client and the 223 RADIUS server are co-located. They may, in fact be run on separate 224 parts of the infrastructure, or even by separate administrators. 225 There is, however, a requirement that the two communicate. We can 226 see that the CoA client needs to send session identification 227 attributes in order to send CoA packets. These attributes cannot be 228 known a priori by the CoA client, and can only come from the RADIUS 229 server. Therefore, even when the two systems are not co-located, 230 they must be able to communicate in order to operate in unison. The 231 alternative is for the two systems to have differing views of the 232 users authorization parameters, which is a security disaster. 234 This specification does not allow for fragmentation of CoA packets. 236 Allowing for fragmented CoA packets would involve changing multiple 237 parts of the RADIUS protocol, with the corresponding possibility for 238 implementation issues, mistakes, etc. 240 Where CoA clients need to send large amounts of authorization data to 241 a NAS, they need only send a minimal CoA-Request packet, containing 242 Service-Type of Authorize-Only, as per RFC 5176. They SHOULD also 243 have a co-located RADIUS server, for the sole purpose of implementing 244 this specification. 246 The NAS will then perform fragmentation as per this draft to the 247 RADIUS server it is configured to use. That RADIUS server SHOULD 248 then act as a proxy, and forward the Access-Request to the RADIUS 249 server on the CoA client. That RADIUS server can then send the large 250 amounts of authorization to the proxy, which then sends them to the 251 NAS. 253 That is, the NAS sends packets to a server which proxies them to the 254 system which is co-located with the CoA client.This process is more 255 complicated than allowing for fragmented CoA packets. However, the 256 CoA client and the RADIUS server must communicate even when not using 257 this specification. We believe that standardizing that 258 communication, and using one method for exchange of large data is 259 preferred to unspecified communication methods and multiple ways of 260 achieving the same result. 262 The above requirement solves a number of issues. It clearly 263 separates session identification from authorization. Without this 264 separation, it is difficult to both identify a session, and change 265 its authorization using the same attribute. It also ensures that the 266 authorization process is the same for initial authentication, and for 267 CoA. 269 When a sessions authorization is changed, the CoA server MUST 270 continue the existing service until the new authorization parameters 271 are applied. The change of service SHOULD be done atomically. If 272 the CoA server is unable to apply the new authorization, it MUST 273 terminate the user session. 275 3. Overview 277 Authorization exchanges can occur either before or after end user 278 authentication has been completed. An authorization exchange before 279 authentication allows a RADIUS client to provide the RADIUS server 280 with information that MAY modify how the authentication process will 281 be performed (e.g. it may affect the selection of the EAP method). 282 An authorization exchange after authentication allows the RADIUS 283 server to provide the RADIUS client with information about the end 284 user, the results of the authentication process and/or obligations to 285 be enforced. In this specification we refer to the "pre- 286 authorization" as the exchange of authorization information before 287 the end user authentication has started, while the term "post- 288 authorization" is used to refer to an authorization exchange 289 happening after this authentication process. 291 In this specification we refer to the "size limit" as the practical 292 limit on RADIUS packet sizes. This limit is the minimum of 4096 293 octets, and the current PMTU. We define below a method which uses 294 Access-Request and Access-Accept in order to exchange fragmented 295 data. The NAS and server exchange a series of Access-Request / 296 Access-Accept packets, until such time as all of the fragmented data 297 has been transported. Each packet contains a Frag-Status attribute 298 which lets the other party know if fragmentation is desired, ongoing, 299 or finished. Each packet may also contain the fragmented data, or 300 instead be an "ACK" to a previous fragment from the other party. 301 Each Access-Request contains a User-Name attribute, allowing the 302 packet to be proxied if necessary (see Section 10.1). Each Access- 303 Request may also contain a State attribute, which serves to tie it to 304 a previous Access-Accept. Each Access-Accept contains a State 305 attribute, for use by the NAS in a later Access-Request. Each 306 Access-Accept contains a Service-Type indicating that the service 307 being provided is fragmentation, and that the Access-Accept should 308 not be interpreted as providing network access to the end user. 310 When a RADIUS client or server need to send data that exceeds the 311 size limit, the mechanism proposed in this document is used. Instead 312 of encoding one large RADIUS packet, a series of smaller RADIUS 313 packets of the same type are encoded. Each smaller packet is called 314 a "chunk" in this specification, in order to distinguish it from 315 traditional RADIUS packets. The encoding process is a simple linear 316 walk over the attributes to be encoded. This walk preserves the 317 order of the attributes of the same type, as required by [RFC2865]. 318 The number of attributes encoded in a particular chunk depends on the 319 size limit, the size of each attribute, the number of proxies between 320 client and server, and the overhead for fragmentation signalling 321 attributes. Specific details are given in Section 5. A a new 322 attribute called Frag-Status (Section 9.1) signals the fragmentation 323 status. 325 After the first chunk is encoded, it is sent to the other party. The 326 packet is identified as a chunk via the Frag-Status attribute. The 327 other party then requests additional chunks, again using the Frag- 328 Status attribute. This process is repeated until all the attributes 329 have been sent from one party to the other. When all the chunks have 330 been received, the original list of attributes is reconstructed and 331 processed as if it had been received in one packet. 333 When multiple chunks are sent, a special situation may occur for 334 Extended Type attributes as defined in [RFC6929]. The fragmentation 335 process may split a fragmented attribute across two or more chunks, 336 which is not permitted by that specification. We address this issue 337 by using the newly defined flag "T" in the Reserved field of the 338 "Long Extended Type" attribute format (see Section 8 for further 339 details on this flag). 341 This last situation is expected to be the most common occurrence in 342 chunks. Typically, packet fragmentation will occur as a consequence 343 of a desire to send one or more large (and therefore fragmented) 344 attributes. The large attribute will likely be split into two or 345 more pieces. Where chunking does not split a fragmented attribute, 346 no special treatment is necessary. 348 The setting of the "T" flag is the only case where the chunking 349 process affects the content of an attribute. Even then, the "Value" 350 fields of all attributes remain unchanged. Any per-packet security 351 attributes such as Message-Authenticator are calculated for each 352 chunk independently. There are neither integrity nor security checks 353 performed on the "original" packet. 355 Each RADIUS packet sent or received as part of the chunking process 356 MUST be a valid packet, subject to all format and security 357 requirements. This requirement ensures that a "transparent" proxy 358 not implementing this specification can receive and send compliant 359 packets. That is, a proxy which simply forwards packets without 360 detailed examination or any modification will be able to proxy 361 "chunks". 363 4. Fragmentation of packets 365 When the NAS or the AS desires to send a packet that exceeds the size 366 limit, it is split into chunks and sent via multiple client/server 367 exchanges. The exchange is indicated via the Frag-Status attribute, 368 which has value More-Data-Pending for all but the last chunk of the 369 series. The chunks are tied together via the State attribute. 371 The following sections describe how to perform fragmentation for 372 packets from the NAS to the server, followed by packets from the 373 server to the NAS. We give the packet type, along with a RADIUS 374 Identifier, to indicate that requests and responses are connected. 375 We then give a list of attributes. We do not give values for most 376 attributes, as we wish to concentrate on the fragmentation behaviour, 377 rather than packet contents. Attribute values are given for 378 attributes relevant to the fragmentation process. Where "long 379 extended" attributes are used, we indicate the M (More) and T 380 (Truncation) flags as optional square brackets after the attribute 381 name. As no "long extended" attributes have yet been defined, we use 382 example attributes, named as "Example-Long-1", etc. The maximum 383 chunk size is established in term of number of attributes (11), for 384 sake of simplicity. 386 4.1. Pre-authorization 388 When the client needs to send a large amount of data to the server, 389 the data to be sent is split into chunks and sent to the server via 390 multiple Access-Request / Access-Accept exchanges. The example below 391 shows this exchange. 393 The following is an Access-Request which the NAS intends to send to a 394 server. However, due to a combination of issues (PMTU, large 395 attributes, etc.), the content does not fit into one Access-Request 396 packet. 398 Access-Request 399 User-Name 400 NAS-Identifier 401 Calling-Station-Id 402 Example-Long-1 [M] 403 Example-Long-1 [M] 404 Example-Long-1 [M] 405 Example-Long-1 [M] 406 Example-Long-1 [M] 407 Example-Long-1 [M] 408 Example-Long-1 [M] 409 Example-Long-1 [M] 410 Example-Long-1 411 Example-Long-2 [M] 412 Example-Long-2 [M] 413 Example-Long-2 415 Figure 1: Desired Access-Request 417 The NAS therefore must send the attributes listed above in a series 418 of chunks. The first chunk contains eight (8) attributes from the 419 original Access-Request, and a Frag-Status attribute. Since last 420 attribute is "Example-Long-1" with the "M" flag set, the chunking 421 process also sets the "T" flag in that attribute. The Access-Request 422 is sent with a RADIUS Identifier field having value 23. The Frag- 423 Status attribute has value More-Data-Pending, to indicate that the 424 NAS wishes to send more data in a subsequent Access-Request. The NAS 425 also adds a Service-Type attribute, which indicates that it is part 426 of the chunking process. The packet is signed with the Message- 427 Authenticator attribute, completing the maximum number of attributes 428 (11). 430 Access-Request (ID = 23) 431 User-Name 432 NAS-Identifier 433 Calling-Station-Id 434 Example-Long-1 [M] 435 Example-Long-1 [M] 436 Example-Long-1 [M] 437 Example-Long-1 [M] 438 Example-Long-1 [MT] 439 Frag-Status = More-Data-Pending 440 Service-Type = Additional-Authorization 441 Message-Authenticator 443 Figure 2: Access-Request (chunk 1) 445 Compliant servers (i.e. servers implementing fragmentation) receiving 446 this packet will see the Frag-Status attribute, and postpone all 447 authorization and authentication handling until all of the chunks 448 have been received. This postponement also affects to the 449 verification that the Access-Request packet contains some kind of 450 authentication attribute (e.g. User-Password, CHAP-Password, State 451 or other future attribute), as required by [RFC2865]. This checking 452 will therefore be delayed until the original large packet has been 453 rebuilt, as some of the chunks may not contain any of them. The 454 authors acknowledge this is formally violating [RFC2865], but there 455 are no known operational issues with it. Once this document goes 456 beyond being considered as experimental, it will state it updates 457 [RFC2865]. 459 Non-compliant servers (i.e. servers not implementing fragmentation) 460 should also see the Service-Type requesting provisioning for an 461 unknown service, and return Access-Reject. Other non-compliant 462 servers may return an Access-Reject, Access-Challenge, or an Access- 463 Accept with a particular Service-Type other then Additional- 464 Authorization. Compliant NAS implementations MUST treat these 465 responses as if they had received Access-Reject instead. 467 Compliant servers who wish to receive all of the chunks will respond 468 with the following packet. The value of the State here is arbitrary, 469 and serves only as a unique token for example purposes. We only note 470 that it MUST be temporally unique to the server. 472 Access-Accept (ID = 23) 473 Frag-Status = More-Data-Request 474 Service-Type = Additional-Authorization 475 State = 0xabc00001 476 Message-Authenticator 478 Figure 3: Access-Accept (chunk 1) 480 The NAS will see this response, and use the RADIUS Identifier field 481 to associate it with an ongoing chunking session. Compliant NASes 482 will then continue the chunking process. Non-compliant NASes will 483 never see a response such as this, as they will never send a Frag- 484 Status attribute. The Service-Type attribute is included in the 485 Access-Accept in order to signal that the response is part of the 486 chunking process. This packet therefore does not provision any 487 network service for the end user. 489 The NAS continues the process by sending the next chunk, which 490 includes an additional six (6) attributes from the original packet. 491 It again includes the User-Name attribute, so that non-compliant 492 proxies can process the packet (see Section 10.1). It sets the Frag- 493 Status attribute to More-Data-Pending, as more data is pending. It 494 includes a Service-Type for reasons described above. It includes the 495 State attribute from the previous Access-accept. It signs the packet 496 with Message-Authenticator, as there are no authentication attributes 497 in the packet. It uses a new RADIUS Identifier field. 499 Access-Request (ID = 181) 500 User-Name 501 Example-Long-1 [M] 502 Example-Long-1 [M] 503 Example-Long-1 [M] 504 Example-Long-1 505 Example-Long-2 [M] 506 Example-Long-2 [MT] 507 Frag-Status = More-Data-Pending 508 Service-Type = Additional-Authorization 509 State = 0xabc000001 510 Message-Authenticator 512 Figure 4: Access-Request (chunk 2) 514 Compliant servers receiving this packet will see the Frag-Status 515 attribute, and look for a State attribute. Since one exists and it 516 matches a State sent in an Access-Accept, this packet is part of a 517 chunking process. The server will associate the attributes with the 518 previous chunk. Since the Frag-Status attribute has value More-Data- 519 Request, the server will respond with an Access-Accept as before. It 520 MUST include a State attribute, with a value different from the 521 previous Access-Accept. This State MUST again be globally and 522 temporally unique. 524 Access-Accept (ID = 181) 525 Frag-Status = More-Data-Request 526 Service-Type = Additional-Authorization 527 State = 0xdef00002 528 Message-Authenticator 530 Figure 5: Access-Accept (chunk 2) 532 The NAS will see this response, and use the RADIUS Identifier field 533 to associate it with an ongoing chunking session. The NAS continues 534 the chunking process by sending the next chunk, with the final 535 attribute(s) from the original packet, and again includes the 536 original User-Name attribute. The Frag-Status attribute is not 537 included in the next Access-Request, as no more chunks are available 538 for sending. The NAS includes the State attribute from the previous 539 Access-accept. It signs the packet with Message-Authenticator, as 540 there are no authentication attributes in the packet. It again uses 541 a new RADIUS Identifier field. 543 Access-Request (ID = 241) 544 User-Name 545 Example-Long-2 546 State = 0xdef00002 547 Message-Authenticator 549 Figure 6: Access-Request (chunk 3) 551 On reception of this last chunk, the server matches it with an 552 ongoing session via the State attribute, and sees that there is no 553 Frag-Status attribute present. It then process the received 554 attributes as if they had been sent in one RADIUS packet. See 555 Section 7.4 for further details of this process. It generates the 556 appropriate response, which can be either Access-Accept or Access- 557 Reject. In this example, we show an Access-Accept. The server MUST 558 send a State attribute, which permits link the received data with the 559 authentication process. 561 Access-Accept (ID = 241) 562 State = 0x98700003 563 Message-Authenticator 565 Figure 7: Access-Accept (chunk 3) 567 The above example shows in practice how the chunking process works. 569 We re-iterate the implementation and security requirements here. 571 Each chunk is a valid RADIUS packet, and all RADIUS format and 572 security requirements MUST be followed before any chunking process is 573 applied. 575 Every chunk except for the last one from a NAS MUST include a Frag- 576 Status attribute, with value More-Data-Pending. The last chunk MUST 577 NOT contain a Frag-Status attribute. Each chunk except for the last 578 from a NAS MUST include a Service-Type attribute, with value 579 Additional-Authorization. Each chunk MUST include a User-Name 580 attribute, which MUST be identical in all chunks. Each chunk except 581 for the first one from a NAS MUST include a State attribute, which 582 MUST be copied from a previous Access-Accept. 584 Each Access-Accept MUST include a State attribute. The value for 585 this attribute MUST change in every new Access-Accept, and MUST be 586 globally and temporally unique. 588 4.2. Post-authorization 590 When the AS wants to send a large amount of authorization data to the 591 NAS after authentication, the operation is very similar to the pre- 592 authorization one. The presence of Service-Type = Additional- 593 Authorization attribute ensures that a NAS not supporting this 594 specification will treat that unrecognized Service-Type as though an 595 Access-Reject had been received instead ([RFC2865] Section 5.6). If 596 the original large Access-Accept packet contained a Service-Type 597 attribute, it will be included with its original value in the last 598 transmitted chunk, to avoid confusion with the one used for 599 fragmentation signalling. It is strongly RECOMMENDED that servers 600 include a State attribute on their original Access-Accept packets, 601 even if fragmentation is not taking place, to allow the client to 602 send additional authorization data in subsequent exchanges. This 603 State attribute would be included in the last transmitted chunk, to 604 avoid confusion with the ones used for fragmentation signalling. 606 Client supporting this specification MUST include a Frag-Status = 607 Fragmentation-Supported attribute in the first Access-Request sent to 608 the server, in order to indicate they would accept fragmented data 609 from the sever. This is not required if pre-authorization process 610 was carried out, as it is implicit. 612 The following is an Access-Accept which the AS intends to send to a 613 client. However, due to a combination of issues (PMTU, large 614 attributes, etc.), the content does not fit into one Access-Accept 615 packet. 617 Access-Accept 618 User-Name 619 EAP-Message 620 Service-Type(Login) 621 Example-Long-1 [M] 622 Example-Long-1 [M] 623 Example-Long-1 [M] 624 Example-Long-1 [M] 625 Example-Long-1 [M] 626 Example-Long-1 [M] 627 Example-Long-1 [M] 628 Example-Long-1 [M] 629 Example-Long-1 630 Example-Long-2 [M] 631 Example-Long-2 [M] 632 Example-Long-2 633 State = 0xcba00003 635 Figure 8: Desired Access-Accept 637 The AS therefore must send the attributes listed above in a series of 638 chunks. The first chunk contains seven (7) attributes from the 639 original Access-Accept, and a Frag-Status attribute. Since last 640 attribute is "Example-Long-1" with the "M" flag set, the chunking 641 process also sets the "T" flag in that attribute. The Access-Accept 642 is sent with a RADIUS Identifier field having value 30 corresponding 643 to a previous Access-Request not depicted. The Frag-Status attribute 644 has value More-Data-Pending, to indicate that the AS wishes to send 645 more data in a subsequent Access-Accept. The AS also adds a Service- 646 Type attribute with value Additional-Authorization, which indicates 647 that it is part of the chunking process. Note that the original 648 Service-Type is not included in this chunk. Finally, a State 649 attribute is included to allow matching subsequent requests with this 650 conversation, and the packet is signed with the Message-Authenticator 651 attribute, completing the maximum number of attributes of 11. 653 Access-Accept (ID = 30) 654 User-Name 655 EAP-Message 656 Example-Long-1 [M] 657 Example-Long-1 [M] 658 Example-Long-1 [M] 659 Example-Long-1 [M] 660 Example-Long-1 [MT] 661 Frag-Status = More-Data-Pending 662 Service-Type = Additional-Authorization 663 State = 0xcba00004 664 Message-Authenticator 666 Figure 9: Access-Accept (chunk 1) 668 Compliant clients receiving this packet will see the Frag-Status 669 attribute, wand suspend all authorization and authentication handling 670 until all of the chunks have been received. Non-compliant clients 671 should also see the Service-Type indicating the provisioning for an 672 unknown service, and will treat it as an Access-Reject. 674 Clients who wish to receive all of the chunks will respond with the 675 following packet, where the value of the State attribute is taken 676 from the received Access-Accept. They also include the User-Name 677 attribute so that non-compliant proxies can process the packet 678 (Section 10.1). 680 Access-Request (ID = 131) 681 User-Name 682 Frag-Status = More-Data-Request 683 Service-Type = Additional-Authorization 684 State = 0xcba00004 685 Message-Authenticator 687 Figure 10: Access-Request (chunk 1) 689 The AS receives this request, and uses the State attribute to 690 associate it with an ongoing chunking session. Compliant ASes will 691 then continue the chunking process. Non-compliant ASes will never 692 see a response such as this, as they will never send a Frag-Status 693 attribute. 695 The AS continues the chunking process by sending the next chunk, with 696 the final attribute(s) from the original packet. The value of the 697 Identifier field is taken from the received Access-Request. A Frag- 698 Status attribute is not included in the next Access-Accept, as no 699 more chunks are available for sending. The AS includes the original 700 State attribute to allow the client to send additional authorization 701 data. The original Service-Type attribute is included as well. 703 Access-Accept (ID = 131) 704 Example-Long-1 [M] 705 Example-Long-1 [M] 706 Example-Long-1 [M] 707 Example-Long-1 708 Example-Long-2 [M] 709 Example-Long-2 [M] 710 Example-Long-2 711 Service-Type = Login 712 State = 0xfda000003 713 Message-Authenticator 715 Figure 11: Access-Accept (chunk 2) 717 On reception of this last chunk, the client matches it with an 718 ongoing session via the Identifier field, and sees that there is no 719 Frag-Status attribute present. It then processes the received 720 attributes as if they had been sent in one RADIUS packet. See 721 Section 7.4 for further details of this process. 723 5. Chunk size 725 In an ideal scenario, each intermediate chunk would be exactly the 726 size limit in length. In this way, the number of round trips 727 required to send a large packet would be optimal. However, this is 728 not possible for several reasons. 730 1. RADIUS attributes have a variable length, and must be included 731 completely in a chunk. Thus, it is possible that, even if there 732 is some free space in the chunk, it is not enough to include the 733 next attribute. This can generate up to 254 octets of spare 734 space on every chunk. 736 2. RADIUS fragmentation requires the introduction of some extra 737 attributes for signalling. Specifically, a Frag-Status attribute 738 (7 octets) is included on every chunk of a packet, except the 739 last one. A RADIUS State attribute (from 3 to 255 octets) is 740 also included in most chunks, to allow the server to bind an 741 Access-Request with a previous Access-Challenge. User-Name 742 attributes (from 3 to 255 octets) are introduced on every chunk 743 the client sends as they are required by the proxies to route the 744 packet to its destination. Together, these attributes can 745 generate from up to 13 to 517 octets of signalling data, reducing 746 the amount of payload information that can be sent on each chunk. 748 3. RADIUS packets SHOULD be adjusted to avoid exceeding the network 749 MTU. Otherwise, IP fragmentation may occur, having undesirable 750 consequences. Hence, maximum chunk size would be decreased from 751 4096 to the actual MTU of the network. 753 4. The inclusion of Proxy-State attributes by intermediary proxies 754 can decrease the availability of usable space into the chunk. 755 This is described with further detail in Section 7.1. 757 6. Allowed large packet size 759 There are no provisions for signalling how much data is to be sent 760 via the fragmentation process as a whole. It is difficult to define 761 what is meant by the "length" of any fragmented data. That data can 762 be multiple attributes, which includes RADIUS attribute header 763 fields. Or it can be one or more "large" attributes (more than 256 764 octets in length). Proxies can also filter these attributes, to 765 modify, add, or delete them and their contents. These proxies act on 766 a "packet by packet" basis, and cannot know what kind of filtering 767 actions they take on future packets. As a result, it is impossible 768 to signal any meaningful value for the total amount of additional 769 data. 771 Unauthenticated clients are permitted to trigger the exchange of 772 large amounts of fragmented data between the NAS and the AS, having 773 the potential to allow Denial of Service (DoS) attacks. An attacker 774 could initiate a large number of connections, each of which requests 775 the server to store a large amount of data. This data could cause 776 memory exhaustion on the server, and result in authentic users being 777 denied access. It is worth noting that authentication mechanisms are 778 already designed to avoid exceeding the size limit. 780 Hence, implementations of this specification MUST limit the total 781 amount of data they send and/or receive via this specification to 782 100K. Any more than this may turn RADIUS into a generic transport 783 protocol, which is undesired. It is RECOMMENDED that this limit be 784 exposed to administrators, so that it can be changed if necessary. 786 Implementations of this specification MUST limit the total number of 787 round trips used during the fragmentation process to 25. Any more 788 than this may indicate an implementation error, misconfiguration, or 789 a denial of service (DoS) attack. It is RECOMMENDED that this limit 790 be exposed to administrators, so that it can be changed if necessary. 792 For instance, let's imagine the RADIUS server wants to transport an 793 SAML assertion which is 15000 octets long, to the RADIUS client. In 794 this hypothetical scenario, we assume there are 3 intermediate 795 proxies, each one inserting a Proxy-State attribute of 20 octets. 796 Also we assume the State attributes generated by the RADIUS server 797 have a size of 6 octets. Therefore, the amount of free space in a 798 chunk for the transport of the SAML assertion attributes is: Total 799 (4096) - RADIUS header (20) - Frag-Status (7 octets) - Service-Type 800 (6 octets) - State (6 octets) - Proxy-State (20 octets) - Proxy-State 801 (20) - Proxy-State (20) - Message-Authenticator (18 octets), 802 resulting in a total of 3979 octets, that is, 15 attributes of 255 803 bytes. 805 According to [RFC6929], a Long-Extended-Type provides a payload of 806 251 octets. Therefore, the SAML assertion described above would 807 result into 60 attributes, requiring of 4 round-trips to be 808 completely transmitted. 810 7. Handling special attributes 812 7.1. Proxy-State attribute 814 RADIUS proxies may introduce Proxy-State attributes into any Access- 815 Request packet they forward. Should they cannot add this information 816 to the packet, they may silently discard forwarding it to its 817 destination, leading to DoS situations. Moreover, any Proxy-State 818 attribute received by a RADIUS server in an Access-Request packet 819 MUST be copied into the reply packet to it. For these reasons, 820 Proxy-State attributes require a special treatment within the packet 821 fragmentation mechanism. 823 When the RADIUS server replies to an Access-Request packet as part of 824 a conversation involving a fragmentation (either a chunk or a request 825 for chunks), it MUST include every Proxy-State attribute received 826 into the reply packet. This means that the server MUST take into 827 account the size of these Proxy-State attributes in order to 828 calculate the size of the next chunk to be sent. 830 However, while a RADIUS server will always know how much space MUST 831 be left on each reply packet for Proxy-State attributes (as they are 832 directly included by the RADIUS server), a RADIUS client cannot know 833 this information, as Proxy-State attributes are removed from the 834 reply packet by their respective proxies before forwarding them back. 835 Hence, clients need a mechanism to discover the amount of space 836 required by proxies to introduce their Proxy-State attributes. In 837 the following we describe a new mechanism to perform such a 838 discovery: 840 1. When a RADIUS client does not know how much space will be 841 required by intermediate proxies for including their Proxy-State 842 attributes, it SHOULD start using a conservative value (e.g. 1024 843 octets) as the chunk size. 845 2. When the RADIUS server receives a chunk from the client, it can 846 calculate the total size of the Proxy-State attributes that have 847 been introduced by intermediary proxies along the path. This 848 information MUST be returned to the client in the next reply 849 packet, encoded into a new attribute called Proxy-State-Len. The 850 server MAY artificially increase this quantity in order to handle 851 with situations where proxies behave inconsistently (e.g. they 852 generate Proxy-State attributes with a different size for each 853 packet), or for situations where intermediary proxies remove 854 Proxy-State attributes generated by other proxies. Increasing 855 this value would make the client to leave some free space for 856 these situations. 858 3. The RADIUS client SHOULD react upon the reception of this 859 attribute by adjusting the maximum size for the next chunk 860 accordingly. However, as the Proxy-State-Len offers just an 861 estimation of the space required by the proxies, the client MAY 862 select a smaller amount in environments known to be problematic. 864 7.2. State attribute 866 This RADIUS fragmentation mechanism makes use of the State attribute 867 to link all the chunks belonging to the same fragmented packet. 868 However, some considerations are required when the RADIUS server is 869 fragmenting a packet that already contains a State attribute for 870 other purposes not related with the fragmentation. If the procedure 871 described in Section 4 is followed, two different State attributes 872 could be included into a single chunk, incurring into two problems. 873 First, [RFC2865] explicitly forbids that more than one State 874 attribute appears into a single packet. 876 A straightforward solution consists on making the RADIUS server to 877 send the original State attribute into the last chunk of the sequence 878 (attributes can be re-ordered as specified in [RFC2865]). As the 879 last chunk (when generated by the RADIUS server) does not contain any 880 State attribute due to the fragmentation mechanism, both situations 881 described above are avoided. 883 Something similar happens when the RADIUS client has to send a 884 fragmented packet that contains a State attribute on it. The client 885 MUST assure that this original State is included into the first chunk 886 sent to the server (as this one never contains any State attribute 887 due to fragmentation). 889 7.3. Service-Type attribute 891 This RADIUS fragmentation mechanism makes use of the Service-Type 892 attribute to indicate an Access-Accept packet is not granting access 893 to the service yet, since additional authorization exchange needs to 894 be performed. Similarly to the State attribute, the RADIUS server 895 has to send the original Service-Type attribute into the last Access- 896 Accept of the RADIUS conversation to avoid ambiguity. 898 7.4. Rebuilding the original large packet 900 The RADIUS client stores the RADIUS attributes received on each chunk 901 in order to be able to rebuild the original large packet after 902 receiving the last chunk. However, some of these received attributes 903 MUST NOT be stored in this list, as they have been introduced as part 904 of the fragmentation signalling and hence, they are not part of the 905 original packet. 907 o State (except the one in the last chunk, if present) 909 o Service-Type = Additional-Authorization 911 o Frag-Status 913 o Proxy-State-Len 915 Similarly, the RADIUS server MUST NOT store the following attributes 916 as part of the original large packet: 918 o State (except the one in the first chunk, if present) 920 o Service-Type = Additional-Authorization 922 o Frag-Status 924 o Proxy-State (except the ones in the last chunk) 926 o User-Name (except the one in the first chunk) 928 8. New flag T field for the Long Extended Type attribute definition 930 This document defines a new field in the "Long Extended Type" 931 attribute format. This field is one bit in size, and is called "T" 932 for Truncation. It indicates that the attribute is intentionally 933 truncated in this chunk, and is to be continued in the next chunk of 934 the sequence. The combination of the flags "M" and "T" indicates 935 that the attribute is fragmented (flag M), but that all the fragments 936 are not available in this chunk (flag T). Proxies implementing 937 [RFC6929] will see these attributes as invalid (they will not be able 938 to reconstruct them), but they will still forward them as [RFC6929] 939 section 5.2 indicates they SHOULD forward unknown attributes anyway. 941 As a consequence of this addition, the Reserved field is now 6 bits 942 long. The following figure represents the new attribute format. 944 0 1 2 3 945 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 1 946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 947 | Type | Length | Extended-Type |M|T| Reserved | 948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 949 | Value ... 950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 952 Figure 12: Updated Long Extended Type attribute format 954 9. New attribute definition 956 This document proposes the definition of two new extended type 957 attributes, called Frag-Status and Proxy-State-Len. The format of 958 these attributes follows the indications for an Extended Type 959 attribute defined in [RFC6929]. 961 9.1. Frag-Status attribute 963 This attribute is used for fragmentation signalling, and its meaning 964 depends on the code value transported within it. The following 965 figure represents the format of the Frag-Status attribute. 967 1 2 3 968 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 1 969 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 970 | Type | Length | Extended-Type | Code 971 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 972 Code (cont) | 973 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 975 Figure 13: Frag-Status format 977 Type 979 To be assigned (TBA) 981 Length 982 7 984 Extended-Type 986 To be assigned (TBA). 988 Code 990 4 byte. Integer indicating the code. The values defined in this 991 specifications are: 993 0 - Reserved 995 1 - Fragmentation-Supported 997 2 - More-Data-Pending 999 3 - More-Data-Request 1001 This attribute MAY be present in Access-Request, Access-Challenge and 1002 Access-Accept packets. It MUST NOT be included in Access-Reject 1003 packets. Clients supporting this specification MUST include a Frag- 1004 Status = Fragmentation-Supported attribute in the first Access- 1005 Request sent to the server, in order to indicate they would accept 1006 fragmented data from the sever. 1008 9.2. Proxy-State-Len attribute 1010 This attribute indicates to the RADIUS client the length of the 1011 Proxy-State attributes received by the RADIUS server. This 1012 information is useful to adjust the length of the chunks sent by the 1013 RADIUS client. The format of this Proxy-State-Len attribute is the 1014 following: 1016 1 2 3 1017 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 1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1019 | Type | Length | Extended-Type | Value 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1021 Value (cont) | 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1024 Figure 14: Proxy-State-Len format 1026 Type 1028 To be assigned (TBA) 1030 Length 1032 7 1034 Extended-Type 1036 To be assigned (TBA). 1038 Value 1040 4 octets. Total length (in octets) of received Proxy-State 1041 attributes (including headers). 1043 This attribute MAY be present in Access-Challenge and Access-Accept 1044 packets. It MUST NOT be included in Access-Request or Access-Reject 1045 packets. 1047 9.3. Table of attributes 1049 The following table shows the different attributes defined in this 1050 document related with the kind of RADIUS packets where they can be 1051 present. 1053 | Kind of packet | 1054 +-----+-----+-----+-----+ 1055 Attribute Name | Req | Acc | Rej | Cha | 1056 ----------------------+-----+-----+-----+-----+ 1057 Frag-Status | 0-1 | 0-1 | 0 | 0-1 | 1058 ----------------------+-----+-----+-----+-----+ 1059 Proxy-State-Len | 0 | 0-1 | 0 | 0-1 | 1060 ----------------------+-----+-----+-----+-----+ 1062 Figure 15 1064 10. Operation with proxies 1066 The fragmentation mechanism defined above is designed to be 1067 transparent to legacy proxies, as long as they do not want to modify 1068 any fragmented attribute. Nevertheless, updated proxies supporting 1069 this specification can even modify fragmented attributes. 1071 10.1. Legacy proxies 1073 As every chunk is indeed a RADIUS packet, legacy proxies treat them 1074 as the rest of packets, routing them to their destination. Proxies 1075 can introduce Proxy-State attributes to Access-Request packets, even 1076 if they are indeed chunks. This will not affect how fragmentation is 1077 managed. The server will include all the received Proxy-State 1078 attributes into the generated response, as described in [RFC2865]. 1079 Hence, proxies do not distinguish between a regular RADIUS packet and 1080 a chunk. 1082 This proposal assumes legacy proxies to base their routing decisions 1083 on the value of the User-Name attribute. For this reason, every 1084 packet sent from the client to the server (either chunks or requests 1085 for more chunks) MUST contain a User-Name attribute. 1087 10.2. Updated proxies 1089 Updated proxies can interact with clients and servers in order to 1090 obtain the complete large packet before starting forwarding it. In 1091 this way, proxies can manipulate (modify and/or remove) any attribute 1092 of the packet, or introduce new attributes, without worrying about 1093 crossing the boundaries of the chunk size. Once the manipulated 1094 packet is ready, it is sent to the original destination using the 1095 fragmentation mechanism (if required). The following example shows 1096 how an updated proxy interacts with the NAS to obtain a large Access- 1097 Request packet, modify an attribute resulting into a even more large 1098 packet, and interacts with the AS to complete the transmission of the 1099 modified packet. 1101 +-+-+-+-+ +-+-+-+-+ 1102 | NAS | | Proxy | 1103 +-+-+-+-+ +-+-+-+-+ 1104 | | 1105 | Access-Request(1){User-Name,Calling-Station-Id, | 1106 | Example-Long-1[M],Example-Long-1[M], | 1107 | Example-Long-1[M],Example-Long-1[M], | 1108 | Example-Long-1[MT],Frag-Status(MDP)} | 1109 |--------------------------------------------------->| 1110 | | 1111 | Access-Challenge(1){User-Name, | 1112 | Frag-Status(MDR),State1} | 1113 |<---------------------------------------------------| 1114 | | 1115 | Access-Request(2)(User-Name,State1, | 1116 | Example-Long-1[M],Example-Long-1[M], | 1117 | Example-Long-1[M],Example-Long-1} | 1118 |--------------------------------------------------->| 1120 PROXY MODIFIES ATTRIBUTE Data INCREASING ITS 1121 SIZE FROM 9 FRAGMENTS TO 11 FRAGMENTS 1123 Figure 16: Updated proxy interacts with NAS 1125 +-+-+-+-+ +-+-+-+-+ 1126 | Proxy | | AS | 1127 +-+-+-+-+ +-+-+-+-+ 1128 | | 1129 | Access-Request(3){User-Name,Calling-Station-Id, | 1130 | Example-Long-1[M],Example-Long-1[M], | 1131 | Example-Long-1[M],Example-Long-1[M], | 1132 | Example-Long-1[MT],Frag-Status(MDP)} | 1133 |--------------------------------------------------->| 1134 | | 1135 | Access-Challenge(1){User-Name, | 1136 | Frag-Status(MDR),State2} | 1137 |<---------------------------------------------------| 1138 | | 1139 | Access-Request(4){User-Name,State2, | 1140 | Example-Long-1[M],Example-Long-1[M], | 1141 | Example-Long-1[M],Example-Long-1[M], | 1142 | Example-Long-1[MT],Frag-Status(MDP)} | 1143 |--------------------------------------------------->| 1144 | | 1145 | Access-Challenge(1){User-Name, | 1146 | Frag-Status(MDR),State3} | 1147 |<---------------------------------------------------| 1148 | | 1149 | Access-Request(5){User-Name,State3,Example-Long-1} | 1150 |--------------------------------------------------->| 1152 Figure 17: Updated proxy interacts with AS 1154 11. Security Considerations 1156 As noted in many earlier specifications ([RFC5080], [RFC6158], etc.) 1157 RADIUS security is problematic. This specification changes nothing 1158 related to the security of the RADIUS protocol. It requires that all 1159 Access-Request packets associated with fragmentation are 1160 authenticated using the existing Message-Authenticator attribute. 1161 This signature prevents forging and replay, to the limits of the 1162 existing security. 1164 The ability to send bulk data from one party to another creates new 1165 security considerations. Clients and servers may have to store large 1166 amounts of data per session. The amount of this data can be 1167 significant, leading to the potential for resource exhaustion. We 1168 therefore suggest that implementations limit the amount of bulk data 1169 stored per session. The exact method for this limitation is 1170 implementation-specific. Section 6 gives some indications on what 1171 could be reasonable limits. 1173 The bulk data can often be pushed off to storage methods other than 1174 the memory of the RADIUS implementation. For example, it can be 1175 stored in an external database, or in files. This approach mitigates 1176 the resource exhaustion issue, as servers today already store large 1177 amounts of accounting data. 1179 12. IANA Considerations 1181 The authors request that Attribute Types and Attribute Values defined 1182 in this document be registered by the Internet Assigned Numbers 1183 Authority (IANA) from the RADIUS namespaces as described in the "IANA 1184 Considerations" section of [RFC3575], in accordance with BCP 26 1185 [RFC5226]. For RADIUS packets, attributes and registries created by 1186 this document IANA is requested to place them at 1187 http://www.iana.org/assignments/radius-types. 1189 This document defines the following RADIUS messages: 1191 o Frag-Status 1193 o Proxy-State-Len 1195 Additionally, allocation of a new Service-Type value for "Additional- 1196 Authorization" is requested. 1198 13. References 1200 13.1. Normative References 1202 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1203 Requirement Levels", BCP 14, RFC 2119, March 1997. 1205 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 1206 "Remote Authentication Dial In User Service (RADIUS)", 1207 RFC 2865, June 2000. 1209 [RFC3575] Aboba, B., "IANA Considerations for RADIUS (Remote 1210 Authentication Dial In User Service)", RFC 3575, 1211 July 2003. 1213 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1214 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1215 May 2008. 1217 [RFC6158] DeKok, A. and G. Weber, "RADIUS Design Guidelines", 1218 BCP 158, RFC 6158, March 2011. 1220 [RFC6929] DeKok, A. and A. Lior, "Remote Authentication Dial In User 1221 Service (RADIUS) Protocol Extensions", RFC 6929, 1222 April 2013. 1224 13.2. Informative References 1226 [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. 1228 [RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication 1229 Dial In User Service) Support For Extensible 1230 Authentication Protocol (EAP)", RFC 3579, September 2003. 1232 [RFC4849] Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Filter 1233 Rule Attribute", RFC 4849, April 2007. 1235 [RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication 1236 Dial In User Service (RADIUS) Implementation Issues and 1237 Suggested Fixes", RFC 5080, December 2007. 1239 Authors' Addresses 1241 Alejandro Perez-Mendez (Ed.) 1242 University of Murcia 1243 Campus de Espinardo S/N, Faculty of Computer Science 1244 Murcia, 30100 1245 Spain 1247 Phone: +34 868 88 46 44 1248 Email: alex@um.es 1250 Rafa Marin-Lopez 1251 University of Murcia 1252 Campus de Espinardo S/N, Faculty of Computer Science 1253 Murcia, 30100 1254 Spain 1256 Phone: +34 868 88 85 01 1257 Email: rafa@um.es 1258 Fernando Pereniguez-Garcia 1259 University of Murcia 1260 Campus de Espinardo S/N, Faculty of Computer Science 1261 Murcia, 30100 1262 Spain 1264 Phone: +34 868 88 78 82 1265 Email: pereniguez@um.es 1267 Gabriel Lopez-Millan 1268 University of Murcia 1269 Campus de Espinardo S/N, Faculty of Computer Science 1270 Murcia, 30100 1271 Spain 1273 Phone: +34 868 88 85 04 1274 Email: gabilm@um.es 1276 Diego R. Lopez 1277 Telefonica I+D 1278 Don Ramon de la Cruz, 84 1279 Madrid, 28006 1280 Spain 1282 Phone: +34 913 129 041 1283 Email: diego@tid.es 1285 Alan DeKok 1286 Network RADIUS 1287 15 av du Granier 1288 Meylan, 38240 1289 France 1291 Phone: +34 913 129 041 1292 Email: aland@networkradius.com 1293 URI: http://networkradius.com