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'5' -- Unexpected draft version: The latest known version of draft-ietf-mobileip-mn-nai is -06, but you're referring to -07. ** Obsolete normative reference: RFC 2409 (ref. '7') (Obsoleted by RFC 4306) ** Obsolete normative reference: RFC 1510 (ref. '9') (Obsoleted by RFC 4120, RFC 6649) ** Downref: Normative reference to an Informational RFC: RFC 2356 (ref. '11') ** Obsolete normative reference: RFC 2002 (ref. '13') (Obsoleted by RFC 3220) == Outdated reference: A later version (-11) exists of draft-ietf-mobileip-optim-08 -- Possible downref: Normative reference to a draft: ref. '15' ** Obsolete normative reference: RFC 2138 (ref. '16') (Obsoleted by RFC 2865) Summary: 16 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Mobile IP Working Group S. Glass 2 INTERNET DRAFT Sun Microsystems 3 11 January 2000 T. Hiller 4 Lucent Technologies 5 S. Jacobs 6 GTE Laboratories 7 C. Perkins 8 Nokia Research Center 10 Mobile IP Authentication, Authorization, and Accounting Requirements 11 draft-ietf-mobileip-aaa-reqs-01.txt 13 Status of This Memo 15 This document is a submission by the mobile-ip Working Group of the 16 Internet Engineering Task Force (IETF). Comments should be submitted 17 to the MOBILE-IP@STANDARDS.NORTELNETWORKS.COM mailing list. 19 Distribution of this memo is unlimited. 21 This document is an Internet-Draft and is in full conformance with 22 all provisions of Section 10 of RFC2026. Internet-Drafts are working 23 documents of the Internet Engineering Task Force (IETF), its areas, 24 and its working groups. Note that other groups may also distribute 25 working documents as Internet-Drafts. 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 29 any time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at: 33 http://www.ietf.org/ietf/1id-abstracts.txt 34 The list of Internet-Draft Shadow Directories can be accessed at: 35 http://www.ietf.org/shadow.html. 37 Abstract 39 The Mobile IP and AAA working groups are currently looking at 40 defining the requirements for Authentication, Authorization, and 41 Accounting. This document contains the requirements which would 42 have to be supported by a AAA service to aid in providing Mobile IP 43 services. 45 1. Introduction 47 Clients obtain Internet services by negotiating a point of attachment 48 to a "home domain", generally from an ISP, or other organization from 49 which service requests are made, and fulfilled. With the increasing 50 popularity of mobile devices, a need has been generated to allow 51 users to attach to any domain convenient to their current location. 52 In this way, a client needs access to resources being provided by 53 an administrative domain different than their home domain (called 54 a "foreign domain"). The need for service from a foreign domain 55 requires, in many models, Authorization, which leads directly to 56 Authentication, and of course Accounting (whence, "AAA"). There 57 is some argument which of these leads to, or is derived from the 58 others, but there is common agreement that the three AAA functions 59 are closely interdependent. 61 An agent in a foreign domain, being called on to provide access to a 62 resource by a mobile user, is likely to request or require the client 63 to provide credentials which can be authenticated before access to 64 resources are permitted. The resource may be as simple as a conduit 65 to the Internet, or may be as complex as access to specific private 66 resources within the foreign domain. Credentials can be exchanged 67 in many different ways, all of which are beyond the scope of this 68 document. Once authenticated, the mobile user may be authorized to 69 access services within the foreign domain. An accounting of the 70 actual resources may then be assembled. 72 Mobile IP is a technology that allows a network node ("mobile 73 node") to migrate from its "home" network to other networks, either 74 within the same administrative domain, or to other administrative 75 domains. The possibility of movement between domains which require 76 AAA services has created an immediate demand to design and specify 77 AAA protocols. Once available, the AAA protocols and infrastructure 78 will provide the economic incentive for a wide-ranging deployment of 79 Mobile IP. This document will identify, describe, and discuss the 80 functional and performance requirements that Mobile IP places on AAA 81 protocols. 83 The formal description of Mobile IP can be found in [13, 12, 14, 17]. 85 In this document, we have attempted to exhibit requirements in a 86 progressive fashion. After showing the basic AAA model for Mobile 87 IP, we derive requirements as follows: 89 - requirements based on the general model 90 - requirements based on providing IP service for mobile nodes 91 - requirements derived from specific Mobile IP protocol needs 93 Then, we exhibit some related AAA models and describe requirements 94 derived from the related models. 96 2. Terminology 98 This document frequently uses the following terms in addition to 99 those defined in RFC 2002 [13]: 101 Accounting The act of collecting information on resource usage 102 for the purpose of trend analysis, auditing, billing, 103 or cost allocation. 105 Administrative Domain 106 An intranet, or a collection of networks, 107 computers, and databases under a common 108 administration. Computer entities operating in 109 a common administration may be assumed to share 110 administratively created security associations. 112 Attendant A node designed to provide the service interface 113 between a client and the local domain. 115 Authentication 116 The act of verifying a claimed identity, in the 117 form of a pre-existing label from a mutually known 118 name space, as the originator of a message (message 119 authentication) or as the end-point of a channel 120 (entity authentication). 122 Authorization 123 The act of determining if a particular right, such 124 as access to some resource, can be granted to the 125 presenter of a particular credential. 127 Billing The act of preparing an invoice. 129 Broker An intermediary agent, trusted by two other AAA 130 servers, able to obtain and provide security services 131 from those AAA servers. For instance, a broker may 132 obtain and provide authorizations, or assurances that 133 credentials are valid. 135 Client A node wishing to obtain service from an attendant 136 within an administrative domain. 138 Foreign Domain 139 An administrative domain, visited by a Mobile IP 140 client, and containing the AAA infrastructure needed 141 to carry out the necessary operations enabling 142 Mobile IP registrations. From the point of view of 143 the foreign agent, the foreign domain is the local 144 domain. 146 Inter-domain Accounting 147 Inter-domain accounting is the collection of 148 information on resource usage of an entity with 149 an administrative domain, for use within another 150 administrative domain. In inter-domain accounting, 151 accounting packets and session records will typically 152 cross administrative boundaries. 154 Intra-domain Accounting 155 Intra-domain accounting is the collection of 156 information on resource within an administrative 157 domain, for use within that domain. In intra-domain 158 accounting, accounting packets and session records 159 typically do not cross administrative boundaries. 161 Local Domain 162 An administrative domain containing the AAA 163 infrastructure of immediate interest to a Mobile IP 164 client when it is away from home. 166 Real-time Accounting 167 Real-time accounting involves the processing of 168 information on resource usage within a defined time 169 window. Time constraints are typically imposed in 170 order to limit financial risk. 172 Session record 173 A session record represents a summary of the resource 174 consumption of a user over the entire session. 175 Accounting gateways creating the session record may 176 do so by processing interim accounting events. 178 In this document, the key words "MAY", "MUST, "MUST NOT", "optional", 179 "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as 180 described in [4]. 182 3. Basic Model 184 In this section, we attempt to capture the main features of a basic 185 model for operation of AAA servers that seems to have good support 186 within the Mobile IP working group. Within the Internet, a client 187 belonging to one administrative domain (called the home domain) often 188 needs to use resources provided by another administrative domain 189 (called the foreign domain). An agent in the foreign domain that 190 attends to the client's request (call the agent the "attendant") is 191 likely to require that the client provide some credentials that can 192 be authenticated before access to the resources is permitted. 194 Local Domain Home Domain 195 +--------------+ +----------------------+ 196 | +------+ | | +------+ | 197 | | | | | | | | 198 | | AAAL | | | | AAAH | | 199 | | +-------------------+ | | 200 | +---+--+ | | +------+ | 201 | | | | | 202 | | | +----------------------+ 203 +------+ | +---+--+ | 204 | | | | | | C = client 205 | C |- -|- -| A | | A = attendant 206 | | | | | | AAAL = local authority 207 +------+ | +------+ | AAAH = home authority 208 | | 209 +--------------+ 211 Figure 1: AAA Servers in Home and Local Domains 213 The attendant often does not have direct access to the data needed 214 to complete the transaction. Instead, the attendant is expected 215 to consult an authority (typically in the same foreign domain) in 216 order to request proof that the client has acceptable credentials. 217 Since the attendant and the local authority are part of the 218 same administrative domain, they are expected to have security 219 relationships that enable them to securely transact information 220 locally. 222 The local authority (AAAL) itself may not have enough information 223 stored locally to carry out the verification for the credentials 224 of the client. In contrast to the attendant, however, the AAAL 225 is expected to be configured with enough information to negotiate 226 the verification of client credentials with external authorities. 227 The local and the external authorities should be configured with 228 sufficient security relationships and access controls so that they, 229 possibly without the need for any other AAA agents, can negotiate 230 the authorization that may enable the client to have access to the 231 requested resources. In many typical cases, the authorization 232 depends only upon secure authentication of the client's credentials. 234 Once the authorization has been obtained by the local authority, 235 and the authority has notified the attendant about the successful 236 negotiation, the attendant can provide the requested resources to the 237 client. 239 In the picture, there might be many attendants for each AAAL, and 240 there might be many clients from many different Home Domains. Each 241 Home Domain provides a AAAH that can check credentials originating 242 from clients administered by that Home Domain. 244 There is a security model implicit in the above figure, and it is 245 crucial to identify the specific security associations assumed in the 246 security model. 248 First, it is natural to assume that the client has a security 249 association with the AAAH, since that is roughly what it means for 250 the client to belong to the home domain. 252 Second, from the model illustrated in figure 1 it is clear that AAAL 253 and AAAH have to share a security association, because otherwise 254 they could not rely on the authentication results, authorizations, 255 nor even the accounting data which might be transacted between them. 256 Requiring such bilateral security relationships is, however, in the 257 end not scalable; the AAA framework MUST provide for more scalable 258 mechanisms, as suggested below in section 6. 260 Finally, in the figure, it is clear that the attendant can naturally 261 share a security association with the AAAL. This is necessary in 262 order for the model to work because the attendant has to be know that 263 it is permissible to allocate the local resources to the client. 265 As an example in today's Internet, we can cite the deployment of 266 RADIUS [16] to allow mobile computer clients to have access to the 267 Internet by way of a local ISP. The ISP wants to make sure that 268 the mobile client can pay for the connection. Once the client 269 has provided credentials (e.g., identification, unique data, and 270 an unforgeable signature), the ISP checks with the client's home 271 authority to verify the signature, and to obtain assurance that the 272 client will pay for the connection. Here, the attendant function can 273 be carried out by the NAS, and the local and home authorities can use 274 RADIUS servers. Credentials allowing authorization at one attendant 275 SHOULD be unusable in any future negotiations at the same or any 276 other attendant. 278 From the description and example above, we can identify several 279 requirements. 281 - Each local attendant has to have a security relationship with the 282 local AAA server (AAAL) 283 - The local authority has to share, or dynamically establish, 284 security relationships with external authorities that are able to 285 check client credentials 286 - The attendant has to keep state for pending client requests while 287 the local authority contacts the appropriate external authority 288 - Since the mobile node may not necessarily initiate network 289 connectivity from within its home domain, it MUST be able to 290 provide complete, yet unforgeable credentials without ever having 291 been in touch with its home domain. 292 - Since the mobile node's credentials have to remain unforgeable, 293 intervening nodes (e.g., neither the attendant or the local 294 authority (AAAL) or any other intermediate nodes) MUST NOT be 295 able to learn any (secret) information which may enable them to 296 reconstruct and reuse the credentials. 298 From this last requirement, we can see the reasons for the natural 299 requirement that the client has to share, or dynamically establish, 300 a security relationship with the external authority in the Home 301 Domain. Otherwise, it is technically infeasible (given the implied 302 network topology) for the client to produce unforgeable signatures 303 that can be checked by the AAAH. Figure 2 illustrates the natural 304 security associations we understand from our proposed model. Note 305 that, according to the discussion in section 6, there may, by mutual 306 agreement between AAAL and AAAH, be a third party inserted between 307 AAAL and AAAH to help them arbitrate secure transactions in a more 308 scalable fashion. 310 +------+ +------+ 311 | | | | 312 | AAAL +--------------+ AAAH | 313 | | | | 314 +---+--+ +--+---+ 315 | | 316 | | 317 +---+--+ +--+---+ 318 C = client | | | | 319 A = attendant | A | | C | 320 AAAL = local authority | | | | 321 AAAH = home authority +------+ +------+ 323 Figure 2: Security Associations 325 In addition to the requirements listed above, we specify the 326 following requirements which derive from operational experience with 327 today's roaming protocols. 329 - There are scenarios in which an attendant will have to manage 330 requests for many clients at the same time. 331 - The attendant MUST protect against replay attacks. 332 - The attendant equipment should be as inexpensive as possible, 333 since it will be replicated as many times as possible to handle 334 as many clients as possible in the foreign domain. 335 - Attendants SHOULD be configured to obtain authorization, 336 from a trusted local AAA server (AAAL) for Quality of Service 337 requirements placed by the client. 339 Nodes in two separate administrative domains (for instance, AAAH 340 and AAAL) often must take additional steps to verify the identity 341 of their communication partners, or alternatively to guarantee 342 the privacy of the data making up the communication. While these 343 considerations lead to important security requirements, as mentioned 344 above in the context of security between servers, we consider the 345 exact choice of security associations between the AAA servers to be 346 beyond the scope of this document. The choices are unlikely even to 347 depend upon any specific features of the general model illustrated 348 in figure 1. On the other hand, the security associations needed 349 between Mobile IP entities will be of central importance in the 350 design of a suitable AAA infrastructure for Mobile IP. The general 351 model shown above is generally compatible with the needs of Mobile 352 IP. However, some basic changes are needed in the security model of 353 Mobile IP, as detailed in section 5. 355 Lastly, recent discussion in the mobile-ip working group has 356 indicated that the attendant MUST be able to terminate service to the 357 client based on policy determination by either AAAH or AAAL server. 359 3.1. AAA Protocol Roaming Requirements 361 In this section we will detail additional requirements based on 362 issues discovered through operational experience of existing roaming 363 RADIUS networks. The AAA protocol MUST satisfy these requirements in 364 order for providers to offer a robust service. These requirements 365 have been identified by TR45.6 as part of their involvement with the 366 Mobile IP working group. 368 - Support a reliable AAA transport mechanism. 369 * There must be an effective hop-by-hop retransmission and 370 failover mechanism so that reliability does not solely depend 371 on end-to-end retransmission 372 * This transport mechanism will be able indicate to an AAA 373 application that a message was delivered to the next peer AAA 374 application or that a time out occurred. 375 * Retransmission is controlled by the reliable AAA transport 376 mechanism, and not by lower layer protocols such as TCP. 377 * Even if the AAA message is to be forwarded, or the message's 378 options or semantics do not conform with the AAA protocol, 379 the transport mechanism will acknowledge that the peer 380 received the AAA message. 381 * Acknowledgements SHOULD be allowed to be piggybacked in AAA 382 messages 383 * AAA responses have to be delivered in a timely fashion so 384 that Mobile IP does not timeout and retransmit 385 - Transport a digital certificate in an AAA message, in order 386 to minimize the number of round trips associated with AAA 387 transactions. Note: This requirement applies to AAA 388 applications and not mobile stations. The certificates could be 389 used by foreign and home agents to establish an IPSec security 390 association to secure the mobile node's tunneled data. In this 391 case, the AAA infrastructure could assist by obtaining the 392 revocation status of such a certificate (either by performing 393 online checks or otherwise validating the certificate) so that 394 home and foreign agents could avoid a costly online certificate 395 status check. 396 - Provide message integrity and identity authentication on a per 397 hop (AAA node) basis. 398 - Support replay protection and optional non-repudiation 399 capabilities for all authorization and accounting messages. The 400 AAA protocol must provide the capability for accounting messages 401 to be matched with prior authorization messages. 402 - Support accounting via both bilateral arrangements and via broker 403 AAA servers providing accounting clearinghouse and reconciliation 404 between serving and home networks. There is an explicit 405 agreement that if the private network or home ISP authenticates 406 the mobile station requesting service, then the private network 407 or home ISP network also agrees to reconcile charges with the 408 home service provider or broker. Real time accounting must be 409 supported. 411 4. Requirements related to basic IP connectivity 413 The requirements listed in the previous section pertain to the 414 relationships between the functional units, and don't depend on the 415 underlying network addressing. On the other hand, many nodes (mobile 416 or merely portable) are programmed to receive some IP-specific 417 resources during the initialization phase of their attempt to connect 418 to the Internet. 420 We place the following additional requirements on the AAA services in 421 order to satisfy such clients. 423 - Either AAA server MUST be able to obtain, or to coordinate the 424 allocation of, a suitable IP address for the customer, upon 425 request by the customer. 426 - AAA servers MUST be able to identify the client by some means 427 other than its IP address. 429 Policy in the home domain may dictate that the home agent instead 430 of the AAAH manages the allocation of an IP address for the mobile 431 node. AAA servers MUST be able to coordinate the allocation of an IP 432 address for the mobile node at least in this way. 434 AAA servers today identify clients by using the Network Access 435 Identifier (NAI) [1]. A mobile node can identify itself by including 436 the NAI along with the Mobile IP Registration Request [6]. The 437 NAI is of the form "user@realm"; it is unique and well suited for 438 use in the AAA model illustrated in figure 1. Using a NAI (e.g., 439 "user@realm") allows AAAL to easily determine the home domain (e.g., 440 "realm") for the client. Both the AAAL and the AAAH can use the NAI 441 to keep records indexed by the client's specific identity. 443 5. AAA for Mobile IP 445 Clients using Mobile IP require specific features from the AAA 446 services, in addition to the requirements already mentioned in 447 connection with the basic AAA functionality and what is needed for 448 IP connectivity. To understand the application of the general model 449 for Mobile IP, we consider the mobile node (MN) to be the client 450 in figure 1, and the attendant to be the foreign agent (FA). If a 451 situation arises that there is no foreign agent present, e.g. in the 452 case of an IPv4 mobile node with a co-located care of address or an 453 IPv6 mobile node, the equivalent attendant functionality is to be 454 provided by the address allocation entity, e.g. a DHCP server. Such 455 an attendant functionality is outside the scope of this document. 456 The home agent, while important to Mobile IP, is allowed to play 457 a role during the initial registration that is subordinate to the 458 role played by the AAAH. For application to Mobile IP, we modify 459 the general model (as illustrated in figure 3). After the initial 460 registration, the mobile node is authorized to continue using Mobile 461 IP at the foreign domain without requiring further involvement by 462 the AAA servers. Thus, the initial registration will probably take 463 longer than subsequent Mobile IP registrations. 465 In order to reduce this extra time overhead as much as possible, it 466 is important to reduce the time taken for communications between 467 the AAA servers. A major component of this communications latency 468 is the time taken to traverse the wide-area Internet that is likely 469 to separate the AAAL and the AAAH. This leads to a further strong 470 motivation for integration of the AAA functions themselves, as 471 well as integration of AAA functions with the initial Mobile IP 472 registration. In order to reduce the number of messages that 473 traverse the network for initial registration of a Mobile Node, the 474 AAA functions in the visited network (AAAL) and the home network 475 (AAAH) need to interface with the foreign agent and the home agent 476 to handle the registration message. Latency would be reduced as a 477 result of initial registration being handled in conjunction with 478 AAA and the mobile IP mobility agents. Subsequent registrations, 479 however, would be handled according to RFC 2002 [13]. 481 The AAA home domain and the HA home domain of the mobile node need 482 not be part of the same administrative domain. Such an situation 483 can occur if the home address of the mobile node is provided by one 484 domain, e.g. an ISP that the mobile user uses while at home, and the 485 authorization and accounting by another (specialized) domain, e.g. a 486 credit card company. The foreign agent sends only the authentication 487 information of the mobile node to the AAAL, which interfaces to 488 the AAAH. After a successful authorization of the mobile node, the 489 foreign agent is able to continue with the mobile IP registration 490 procedure. Such a scheme introduces more delay if the access to 491 the AAA functionality and the mobile IP protocol is sequentialized. 492 Subsequent registrations would be handled according to RFC2002 [13] 493 without further interaction with the AAA. Whether to combine or 494 separate the Mobile IP protocol data with/from the AAA messages is 495 ultimately a policy decision. A separation of the Mobile IP protocol 496 data and the AAA messages can be successfully accomplished only if 497 the IP address of the mobile node's home agent is provided to the 498 foreign agent performing the attendant function. 500 All needed AAA and Mobile IP functions SHOULD be processed during 501 a single Internet traversal. This MUST be done without requiring 502 AAA servers to process protocol messages sent to Mobile IP agents. 503 The AAA servers MUST identify the Mobile IP agents and security 504 associations necessary to process the Mobile IP registration, pass 505 the necessary registration data to those Mobile IP agents, and 506 remain uninvolved in the routing and authentication processing steps 507 particular to Mobile IP registration. 509 For Mobile IP, the AAAL and the AAAH servers have the following 510 additional general tasks: 512 - enable authentication for Mobile IP registration 513 - authorize the mobile node (once its identity has been 514 established) to use at least the set of resources for minimal 515 Mobile IP functionality, plus potentially other services 516 requested by the mobile node 517 - initiate accounting for service utilization 518 - use AAA protocol extensions specifically for including Mobile 519 IP registration messages as part of the initial registration 520 sequence to be handled by the AAA servers. 522 These tasks, and the resulting more specific tasks to be listed later 523 in this section, are beneficially handled and expedited by the AAA 524 servers shown in figure 1 because the tasks often happen together, 525 and task processing needs access to the same data at the same time. 527 Local Domain Home Domain 528 +--------------+ +----------------------+ 529 | +------+ | | +------+ | 530 | | | | | | | | 531 | | AAAL | | | | AAAH | | 532 | | +-------------------+ | | 533 | +---+--+ | | +--+---+ | 534 | | | | | | 535 | | | | | | 536 +------+ | +---+--+ | | +--+---+ | 537 | | | | | | | | | | 538 | MN +- -|- -+ FA + -- -- -- -- - + HA | | 539 | | | | | | | | | | 540 +------+ | +------+ | | +------+ | 541 | | | | 542 +--------------+ +----------------------+ 544 Figure 3: AAA Servers with Mobile IP agents 546 In the model in figure 1, the initial AAA transactions are handled 547 without needing the home agent, but Mobile IP requires every 548 registration to be handled between the home agent (HA) and the 549 foreign agent (FA), as shown by the sparse dashed (lower) line in 550 figure 3. This means that during the initial registration, something 551 has to happen that enables the home agent and foreign agent to 552 perform subsequent Mobile IP registrations. After the initial 553 registration, the AAAH and AAAL in figure 3 would not be needed, 554 and subsequent Mobile IP registrations would only follow the lower 555 control path between the foreign agent and the home agent. 557 Any Mobile IP data that is sent by FA through the AAAL to AAAH MUST 558 be considered opaque to the AAA servers. Authorization data needed 559 by the AAA servers then MUST be delivered to them by the foreign 560 agent from the data supplied by the mobile node. The foreign agent 561 becomes a translation agent between the Mobile IP registration 562 protocol and AAA. 564 As mentioned in section 3, nodes in two separate administrative 565 domains often must take additional steps to guarantee their security 566 and privacy. In today's Internet, such security measures may be 567 provided by using several different algorithms. Some algorithms rely 568 on the existence of a public-key infrastructure [8]; others rely on 569 distribution of symmetric keys to the communicating nodes [9]. AAA 570 servers SHOULD be able to verify credentials using either style in 571 their interactions with Mobile IP entities. 573 In order to enable subsequent registrations, the AAA servers MUST 574 be able to perform some key distribution during the initial Mobile 575 IP registration process from any particular administrative domain. 577 This key distribution MUST be able to provide the following security 578 functions: 580 - identify or create a security association between MN and 581 home agent (HA); this is required for the MN to produce the 582 authentication data for the MN--HA authentication extension, 583 which is mandatory on Mobile IP registrations. 584 - identify or create a security association between mobile node and 585 foreign agent, for use with subsequent registrations at the same 586 foreign agent, so that the foreign agent can continue to obtain 587 assurance that the same mobile node has requested the continued 588 authorization for Mobile IP services. 589 - identify or create a security association between home agent 590 and foreign agent, for use with subsequent registrations at 591 the same foreign agent, so that the foreign agent can continue 592 to obtain assurance that the same home agent has continued the 593 authorization for Mobile IP services for the mobile node. 594 - participate in the distribution of the security association (and 595 Security Parameter Index, or SPI) to the Mobile IP entities 596 - The AAA server MUST also be able to validate certificates 597 provided by the mobile node and provide reliable indication to 598 the foreign agent. 599 - The AAAL SHOULD accept an indication from the foreign agent about 600 the acceptable lifetime for its security associations with the 601 mobile node and/or the mobile node's home agent. This lifetime 602 for those security associations SHOULD be an integer multiple of 603 registration lifetime offered by the foreign agent to the mobile 604 node. 605 - The AAA servers SHOULD be able to condition their acceptance of 606 a Mobile IP registration authorization depending upon whether 607 the registration requires broadcast or multicast service to the 608 mobile node tunneled through the foreign agent. 609 - In addition, reverse tunneling may also be a necessary 610 requirement for mobile node connectivity. Therefore, AAA 611 servers SHOULD also be able to condition their acceptance of 612 Mobile IP registration authorization depending upon whether the 613 registration requires reverse tunnelling support to the home 614 domain through the foreign agent. 616 The lifetime of any security associations distributed by the AAA 617 server for use with Mobile IP SHOULD be great enough to avoid 618 too-frequent initiation of the AAA key distribution, since each 619 invocation of this process is likely to cause lengthy delays between 620 registrations [5]. Registration delays in Mobile IP cause dropped 621 packets and noticeable disruptions in service. Note that any key 622 distributed by AAAH to the foreign agent and home agent MAY be used 623 to initiate Internet Key Exchange (IKE) [7]. 625 Note further that the mobile node and home agent may well have a 626 security association established that does not depend upon any action 627 by the AAAH. 629 5.1. Mobile IP with Dynamic IP Addresses 631 According to section 4, many people would like their mobile nodes to 632 be identified by their NAI, and to obtain a dynamically allocated 633 home address for use in the foreign domain. These people may often 634 be unconcerned with details about how their computers implement 635 Mobile IP, and indeed may not have any knowledge of their home agent 636 or any security association except that between themselves and the 637 AAAH (see figure 2. In this case the Mobile IP registration data has 638 to be carried along with the AAA messages. The AAA home domain and 639 the HA home domain have to be part of the same administrative domain. 641 Mobile IP requires the home address assigned to the mobile node 642 belong to the same subnet as the Home Agent providing service to the 643 mobile node. For effective use of IP home addresses, the home AAA 644 (AAAH) SHOULD be able to select a home agent for use with the newly 645 allocated home address. In many cases, the mobile node will already 646 know the address of its home agent, even if the mobile node does 647 not already have an existing home address. Therefore, the home AAA 648 (AAAH) MUST be able to coordinate the allocation of a home address 649 with a home agent that might be designated by the mobile node. 651 Allocating a home address and a home agent for the mobile would 652 provide a further simplification in the configuration needs for the 653 client's mobile node. Currently, in the Proposed Standard Mobile IP 654 specification [13] a mobile node has to be configured with a home 655 address and the address of a home agent, as well as with a security 656 association with that home agent. In contrast, the proposed AAA 657 features would only require the mobile node to be configured with 658 its NAI and a secure shared secret for use by the AAAH. The mobile 659 node's home address, the address of its home agent, the security 660 association between the mobile node and the home agent, and even the 661 identity (DNS name or IP address) of the AAAH can all be dynamically 662 determined as part of Mobile IP initial registration with the 663 mobility agent in the foreign domain (i.e., a foreign agent with AAA 664 interface features). Nevertheless, the mobile node may choose to 665 include the MN-HA security extension as well as AAA credentials, and 666 the proposed Mobile IP and AAA server model MUST work when both are 667 present. 669 The reason for all this simplification is that the NAI encodes the 670 client's identity as well as the name of the client's home domain; 671 this follows existing industry practice for the way NAIs are used 672 today (see section 4). The home domain name is then available for 673 use by the local AAA (AAAL) to locate the home AAA serving the 674 client's home domain. In the general model, the AAAL would also have 675 to identify the appropriate security association for use with that 676 AAAH. Section 6 discusses a way to reduce the number of security 677 associations that have to be maintained between pairs of AAA servers 678 such as the AAAL and AAAH just described. 680 5.2. Firewalls and AAA 682 Mobile IP has encountered some deployment difficulties related to 683 firewall traversal; see for instance [11]. Since the firewall and 684 AAA server can be part of the same administrative domain, we propose 685 that the AAA server SHOULD be able to issue control messages and keys 686 to the firewall at the boundary of its administrative domain that 687 will configure the firewall to be permeable to Mobile IP registration 688 and data traffic from the mobile node. 690 5.3. Mobile IP with Local Home Agents 692 +-------------------------+ +--------------+ 693 | +------+ +------+ | | +------+ | 694 | | | | | | | | | | 695 | | HA +----+ AAAL | | | | AAAH | | 696 | | | | +-------------------+ | | 697 | +-+----+ +---+--+ | | +------+ | 698 | | | | | Home Domain | 699 | | +- - - - - + | +--------------+ 700 +------+ | +-+--+-+ | 701 | | | | | | 702 | MN +------+ FA | | 703 | | | | | Local Domain | 704 +------+ | +------+ | 705 +-------------------------+ 707 Figure 4: Home Agent Allocated by AAAL 709 In some Mobile IP models, mobile nodes boot on subnets which are 710 technically foreign subnets, but the services they need are local, 711 and hence communication with the home subnet as if they were residing 712 on the home is not necessary. As long as the mobile node can get an 713 address routable from within the current domain (be it publicly, or 714 privately addressed) it can use mobile IP to roam around that domain, 715 calling the subnet on which it booted its temporary home. This 716 address is likely to be dynamically allocated upon request by the 717 mobile node. 719 In such situations, when the client is willing to use a dynamically 720 allocated IP address and does not have any preference for the 721 location of the home network (either geographical or topological), 722 the local AAA server (AAAL) may be able to offer this additional 723 allocation service to the client. Then, the home agent will be 724 located in the local domain, which is likely to be offer smaller 725 delays for new Mobile IP registrations. 727 In figure 4, AAAL has received a request from the mobile node to 728 allocate a home agent in the local domain. The new home agent 729 receives keys from AAAL to enable future Mobile IP registrations. 730 From the picture, it is evident that such a configuration avoids 731 problems with firewall protection at the domain boundaries, such 732 as were described briefly in section 5.2. On the other hand, this 733 configuration makes it difficult for the mobile node to receive 734 data from any communications partners in the mobile node's home 735 administrative domain. Note that, in this model, the mobile node's 736 home address is affiliated with the foreign domain for routing 737 purposes. Thus, any dynamic update to DNS, to associate the mobile 738 node's home FQDN (Fully Qualified Domain Name [10]) with its new IP 739 address, will require insertion of a foreign IP address into the home 740 DNS server database. 742 5.4. Mobile IP with Local Payments 744 +-------------------------+ 745 | +------+ +------+ | 746 | | | | | | 747 | | HA +----+ AAAL | | 748 | | | | | | 749 | +--+---+ +----+-+ | 750 | | | | 751 | +- - - - - + | | 752 +------+ | +-+--+-+ | 753 | | | | | | 754 | MN +- -|- - - - - - - + FA | | 755 | | | Local Domain | | | 756 +------+ | +------+ | 757 +-------------------------+ 759 Figure 5: Local Payment for Local Mobile IP services 761 Since the AAAL is expected to be enabled to allocate a local home 762 agent upon demand, we can make a further simplification. In cases 763 where the AAAL can manage any necessary authorization function 764 locally (e.g., if the client pays with cash or a credit card), then 765 there is no need for an AAA protocol or infrastructure to interact 766 with the AAAH. The resulting simple configuration is illustrated in 767 figure 5. 769 In this simplified model, we may consider that the role of the AAAH 770 is taken over either by a national government (in the case of a 771 cash payment), or by a card authorization service if payment is by 772 credit card, or some such authority acceptable to all parties. Then, 773 the AAAL expects those external authorities to guarantee the value 774 represented by the client's payment credentials (cash or credit). 775 There are likely to be other cases where clients are granted access 776 to local resources, or access to the Internet, without any charges at 777 all. Such configurations may be found in airports and other common 778 areas where business clients are likely to spend time. The service 779 provider may find sufficient reward in the goodwill of the clients, 780 or from advertisements displayed on Internet portals that are to 781 be used by the clients. In such situations, the AAAL SHOULD still 782 allocate a home agent, appropriate keys, and the mobile node's home 783 address. 785 5.5. Fast Handover 787 Since the movement from coverage area to coverage area may be 788 frequent in Mobile IP networks, it is imperative that the latency 789 involved in the handoff process be minimized. See, for instance, the 790 Route Optimization draft [15] for one way to do this using Binding 791 Updates. When the mobile node enters a new visited subnet, it would 792 be desirable for it to provide the previous foreign agent's NAI. 793 The new FA can use this information to either contact the previous 794 FA to retrieve the KDC session key information, or it can attempt 795 to retrieve the keys from the AAAL. If the AAAL cannot provide the 796 necessary keying information, the request will have to be sent to the 797 mobile node's AAAH to retrieve new keying information. After initial 798 authorization, further authorizations SHOULD be done locally within 799 the Local Domain. 801 6. Broker Model 803 The picture in Figure 1 shows a configuration in which the local and 804 the home authority have to share trust. Depending on the security 805 model used, this configuration can cause a quadratic growth in the 806 number of trust relationships, as the number of AAA authorities 807 (AAAL and AAAH) increases. This has been identified as a problem 808 by the roamops working group [3], and any AAA proposal MUST solve 809 this problem. Using brokers solves many of the scalability problems 810 associated with requiring direct business/roaming relationships 811 between every two administrative domains. In order to provide 812 scalable networks in highly diverse service provider networks in 813 which there are many domains (e.g. many service providers and large 814 numbers of private networks), multiple layers of brokers MUST be 815 supported for both of the broker models described. 817 Integrity or privacy of information between the home and serving 818 domains may be achieved by either hop-by-hop security associations 819 or end-to-end security associations established with the help of the 820 broker infrastructure. A broker may play the role of a proxy between 821 two administrative domains which have security associations with the 822 broker, and relay AAA messages back and forth securely. 824 Alternatively, a broker may also enable the two domains with which 825 it has associations, but the domains themselves do not have a 826 direct association, in establishing a security association, thereby 827 bypassing the broker for carrying the messages between the domains. 828 This may be established by virtue of having the broker relay a shared 829 secret key to both the domains that are trying to establish secure 830 communication and then have the domains use the keys supplied by the 831 broker in setting up a security association. 833 Assuming that AAAB accepts responsibility for payment to the serving 834 domain on behalf of the home domain, the serving domain is assured of 835 receiving payments for services offered. However, the redirection 836 broker will usually require a copy of authorization messages from the 837 home domain and accounting messages from the serving domain, in order 838 for the broker to determine if it is willing to accept responsibility 839 for the services being authorized and utilized. If the broker does 840 not accept such responsibility for any reason, then it must be able 841 to terminate service to a mobile node in the serving network. In 842 the event that multiple brokers are involved, in most situations all 843 brokers must be so copied. This may represent an additional burden 844 on foreign agents and AAALs. 846 Though this mechanism may reduce latency in the transit of messages 847 between the domains after the broker has completed its involvement, 848 there may be many more messages involved as a result of additional 849 copies of authorization and accounting messages to the brokers 850 involved. There may also be additional latency for initial access to 851 the network, especially when a new security association needs to be 852 created between AAAL and AAAH (for example, from the use of ISAKMP). 853 These delays may become important factors for latency- critical 854 applications. 856 Local Domain Home Domain 857 +--------------+ +----------------------+ 858 | +------+ | +------+ | +------+ | 859 | | | | | | | | | | 860 | | AAAL +-------+ AAAB +--------+ AAAH | | 861 | | | | | | | | | | 862 | +------+ | +------+ | +------+ | 863 | | | | | 864 | | | +----------------------+ 865 +------+ | +---+--+ | 866 | | | | | | C = client 867 | C +- -|- -+ A | | A = attendant 868 | | | | | | AAAL = local authority 869 +------+ | +------+ | AAAH = home authority 870 | | AAAB = broker authority 871 +--------------+ 873 Figure 6: AAA Servers Using a Broker 875 The AAAB in figure 6 is the broker's authority server. The broker 876 acts as a settlement agent, providing security and a central point of 877 contact for many service providers and enterprises. 879 The AAAB enables the local and home domains to cooperate without 880 requiring each of the networks to have a direct business or security 881 relationship with all the other networks. Thus, brokers offer the 882 needed scalability for managing trust relationships between otherwise 883 independent network domains. Use of the broker does not preclude 884 managing separate trust relationships between domains, but it does 885 offer an alternative to doing so. Just as with the AAAH and AAAL 886 (see section 5), data specific to Mobile IP control messages MUST 887 NOT be processed by the AAAB. Any credentials or accounting data to 888 be processed by the AAAB must be present in AAA message units, not 889 extracted from Mobile IP protocol extensions. 891 The following requirements come mostly from [2], which discusses 892 use of brokers in the particular case of authorization for roaming 893 dial-up users. 895 - allowing management of trust with external domains by way of 896 brokered AAA. 897 - accounting reliability. Accounting data that traverses 898 the Internet may suffer substantial packet loss. Since 899 accounting packets may traverse one or more intermediate 900 authorization points (e.g., brokers), retransmission is needed 901 from intermediate points to avoid long end-to-end delays. 903 - End to End security. The Local Domain and Home Domain must be 904 able to verify signatures within the message, even though the 905 message is passed through an intermediate authority server. 906 - Since the AAAH in the home domain MAY be sending sensitive 907 information, such as registration keys, the broker MUST be able 908 to pass encrypted data between the AAA servers. 910 The need for End-to-End security results from the following attacks 911 which were identified when brokered operation uses RADIUS [16] 912 (see [2] for more information on the individual attacks): 914 + Message editing 915 + Attribute editing 916 + Theft of shared secrets 917 + Theft and modification of accounting data 918 + Replay attacks 919 + Connection hijacking 920 + Fraudulent accounting 922 These are serious problems which cannot be allowed to persist in any 923 acceptable AAA protocol and infrastructure. 925 7. Security Considerations 927 This is a requirements draft for AAA based on Mobile IP. Because AAA 928 is security driven, most of this document addresses the security 929 considerations AAA MUST make on behalf of Mobile IP. As with any 930 security proposal, adding more entities that interact using security 931 protocols creates new administrative requirements for maintaining 932 the appropriate security associations between the entities. In the 933 case of the AAA services proposed however, these administrative 934 requirements are natural, and already well understood in today's 935 Internet because of experience with dial up network access. 937 8. Acknowledgements 939 Thanks to Gopal Dommety, and Basavaraj Patil for participating in 940 the Mobile IP subcommittee of the aaa-wg which was charged with 941 formulating the requirements detailed in this document. Thanks to N. 942 Asokan for perceptive comments to the mobile-ip mailing list. Some 943 of the text of this document was taken from a draft co-authored by 944 Pat Calhoun. Patrik Flykt suggested text about allowing AAA home 945 domain functions to be separated from the domain managing the home 946 address of the mobile computer. 948 The requirements in section 5.5 and section 3.1 were taken from 949 a draft submitted by members of the TIA's TR45.6 Working Group. 951 We would like to acknowledge the work done by the authors of that 952 draft: Tom Hiller, Pat Walsh, Xing Chen, Mark Munson, Gopal Dommety, 953 Sanjeevan Sivalingham, Byng-Keun Lim, Pete McCann, Brent Hirschman, 954 Serge Manning, Ray Hsu, Hang Koo, Mark Lipford, Pat Calhoun, Eric 955 Jaques, Ed Campbell, and Yingchun Xu. 957 References 959 [1] B. Aboba and M. Beadles. The Network Access Identifier. 960 Request for Comments (Proposed Standard) 2486, Internet 961 Engineering Task Force, January 1999. 963 [2] B. Aboba and J. Vollbrecht. Proxy Chaining and Policy 964 Implementation in Roaming. Internet Draft, Internet Engineering 965 Task Force. 966 draft-ietf-roamops-auth-10.txt, February 1999. Work in 967 progress. 969 [3] B. Aboba and G. Zorn. Criteria for Evaluating Roaming 970 Protocols. Request for Comments (Informational) 2477, Internet 971 Engineering Task Force, December 1998. 973 [4] S. Bradner. Key words for use in RFCs to Indicate Requirement 974 Levels. Request for Comments (Best Current Practice) 2119, 975 Internet Engineering Task Force, March 1997. 977 [5] Ramon Caceres and Liviu Iftode. Improving the Performance 978 of Reliable Transport Protocols in Mobile Computing 979 Environments. IEEE Journal on Selected Areas in Communications, 980 13(5):850--857, June 1995. 982 [6] Pat R. Calhoun and Charles E. Perkins. Mobile IP Network 983 Address Identifier Extension. 984 draft-ietf-mobileip-mn-nai-07.txt, January 2000. (work in 985 progress). 987 [7] D. Harkins and D. Carrel. The Internet Key Exchange (IKE). 988 Request for Comments (Proposed Standard) 2409, Internet 989 Engineering Task Force, November 1998. 991 [8] R. Housley, W. Ford, T. Polk, and D. Solo. Internet X.509 992 Public Key Infrastructure Certificate and CRL Profile. Internet 993 Draft, Internet Engineering Task Force. 994 draft-ietf-pkix-ipki-part1-11.txt, September 1998. Work in 995 progress. 997 [9] J. Kohl and C. Neuman. The Kerberos Network Authentication 998 Service (V5). Request for Comments (Proposed Standard) 1510, 999 Internet Engineering Task Force, September 1993. 1001 [10] P. V. Mockapetris. Domain names - implementation and 1002 specification. Request for Comments (Standard) 1035, Internet 1003 Engineering Task Force, November 1987. 1005 [11] G. Montenegro and V. Gupta. Sun's SKIP Firewall Traversal for 1006 Mobile IP. Request for Comments (Informational) 2356, Internet 1007 Engineering Task Force, June 1998. 1009 [12] C. Perkins. IP Encapsulation within IP. Request for Comments 1010 (Proposed Standard) 2003, Internet Engineering Task Force, 1011 October 1996. 1013 [13] C. Perkins. IP Mobility Support. Request for Comments 1014 (Proposed Standard) 2002, Internet Engineering Task Force, 1015 October 1996. 1017 [14] C. Perkins. Minimal Encapsulation within IP. Request for 1018 Comments (Proposed Standard) 2004, Internet Engineering Task 1019 Force, October 1996. 1021 [15] C. Perkins and D. Johnson. Route Optimization in Mobile IP. 1022 Internet Draft, Internet Engineering Task Force. 1023 draft-ietf-mobileip-optim-08.txt, February 1999. Work in 1024 progress. 1026 [16] C. Rigney, A. Rubens, W. Simpson, and S. Willens. Remote 1027 Authentication Dial In User Service (RADIUS). Request for 1028 Comments (Proposed Standard) 2138, Internet Engineering Task 1029 Force, April 1997. 1031 [17] J. Solomon and S. Glass. Mobile-IPv4 Configuration Option 1032 for PPP IPCP. Request for Comments (Proposed Standard) 2290, 1033 Internet Engineering Task Force, February 1998. 1035 Addresses 1037 The working group can be contacted via the current chairs: 1039 Basavaraj Patil Phil Roberts 1040 Nortel Networks Inc. Motorola 1041 2201 Lakeside Blvd. 1501 West Shure Drive 1042 Richardson, TX. 75082-4399 Arlington Heights, IL 60004 1043 USA USA 1045 Phone: +1 972-684-1489 Phone: +1 847-632-3148 1046 EMail: bpatil@nortelnetworks.com EMail: QA3445@email.mot.com 1048 Questions about this memo can be directed to: 1050 Pat R. Calhoun Gopal Dommety 1051 Network and Security Center IOS Network Protocols 1052 Sun Microsystems Laboratories Cisco Systems, Inc. 1053 15 Network Circle 170 West Tasman Drive 1054 Menlo Park, California 94025 San Jose, CA 95134-1706 1055 USA USA 1056 Phone: +1 650-786-7733 Phone: +1-408-525-1404 1057 pcalhoun@eng.sun.co EMail: gdommety@cisco.com 1058 Fax: +1 650-786-6445 Fax: +1 408-526-4952 1060 Steven M. Glass Stuart Jacobs 1061 Sun Microsystems Secure Systems Department 1062 1 Network Drive GTE Laboratories 1063 Burlington, MA 40 Sylvan Road 1064 01803 Waltham, MA 02451-1128 1065 USA USA 1066 Phone: +1-781-442-0504 Phone: +1 781-466-3076 1067 EMail: steven.glass@sun.com EMail: sjacobs@gte.com 1068 Fax: +1 781-466-2838 1070 Tom Hiller Peter J. McCann 1071 Lucent Technologies Lucent Technologies 1072 Rm 2F-218 Rm 2Z-305 1073 263 Shuman Blvd 263 Shuman Blvd 1074 Naperville, IL 60566 Naperville, IL 60566 1075 USA USA 1076 email: tomhiller@lucent.com email: mccap@lucent.com 1077 phone: +1 630 979 7673 phone: +1 630 713 9359 1078 fax: +1 630 713 3663 fax: +1 630 713 4982 1080 Basavaraj Patil Charles E. Perkins 1081 Wireless Technology Labs Communications Systems Lab 1082 Nortel Networks Nokia Research Center 1083 2221 Lakeside Blvd. 313 Fairchild Drive 1084 Richardson, TX 75082-4399 Mountain View, California 94043 1085 USA USA 1086 Phone: +1 972-684-1489 Phone: +1-650 625-2986 1087 EMail: bpatil@nortelnetworks.com EMail: charliep@iprg.nokia.com 1088 Fax: +1 972-685-3207 Fax: +1 650 625-2502