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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group S. Kiesel, Ed. 3 Internet-Draft University of Stuttgart 4 Intended status: Informational S. Previdi 5 Expires: July 28, 2011 Cisco Systems, Inc. 6 M. Stiemerling 7 NEC Europe Ltd. 8 R. Woundy 9 Comcast Corporation 10 Y R. Yang 11 Yale University 12 January 24, 2011 14 Application-Layer Traffic Optimization (ALTO) Requirements 15 draft-ietf-alto-reqs-07.txt 17 Abstract 19 Many Internet applications are used to access resources, such as 20 pieces of information or server processes, which are available in 21 several equivalent replicas on different hosts. This includes, but 22 is not limited to, peer-to-peer file sharing applications. The goal 23 of Application-Layer Traffic Optimization (ALTO) is to provide 24 guidance to applications, which have to select one or several hosts 25 from a set of candidates, that are able to provide a desired 26 resource. This guidance shall be based on parameters that affect 27 performance and efficiency of the data transmission between the 28 hosts, e.g., the topological distance. The ultimate goal is to 29 improve performance (or Quality of Experience) in the application 30 while reducing resource consumption in the underlying network 31 infrastructure. 33 This document enumerates requirements for ALTO, which should be 34 considered when specifying, assessing, or comparing protocols and 35 implementations. 37 Status of this Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at http://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on July 28, 2011. 54 Copyright Notice 56 Copyright (c) 2011 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (http://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 2. Terminology and Architectural Framework . . . . . . . . . . . 5 73 2.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5 74 2.2. ALTO Terminology . . . . . . . . . . . . . . . . . . . . . 5 75 2.3. Architectural Framework for ALTO . . . . . . . . . . . . . 6 76 3. ALTO Requirements . . . . . . . . . . . . . . . . . . . . . . 7 77 3.1. ALTO Client Protocol . . . . . . . . . . . . . . . . . . . 7 78 3.1.1. General Requirements . . . . . . . . . . . . . . . . . 7 79 3.1.2. Host Group Descriptor Support . . . . . . . . . . . . 7 80 3.1.3. Rating Criteria Support . . . . . . . . . . . . . . . 8 81 3.1.4. Placement of Entities and Timing of Transactions . . . 10 82 3.1.5. Protocol Extensibility . . . . . . . . . . . . . . . . 12 83 3.1.6. Error Handling and Overload Protection . . . . . . . . 12 84 3.2. ALTO Server Discovery . . . . . . . . . . . . . . . . . . 12 85 3.3. Security and Privacy . . . . . . . . . . . . . . . . . . . 13 86 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 87 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 88 5.1. High-level security considerations . . . . . . . . . . . . 16 89 5.2. Information Disclosure Scenarios . . . . . . . . . . . . . 16 90 5.2.1. Classification of Information Disclosure Scenarios . . 16 91 5.2.2. Discussion of Information Disclosure Scenarios . . . . 17 92 5.3. Security Requirements . . . . . . . . . . . . . . . . . . 18 93 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 94 6.1. Normative References . . . . . . . . . . . . . . . . . . . 19 95 6.2. Informative References . . . . . . . . . . . . . . . . . . 19 96 Appendix A. Contributors List and Acknowledgments . . . . . . . . 20 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 99 1. Introduction 101 The motivation for Application-Layer Traffic Optimization (ALTO) is 102 described in the ALTO problem statement [RFC5693]. 104 The goal of ALTO is to provide information which can help peer-to- 105 peer (P2P) applications to make better decisions with respect to peer 106 selection. However, ALTO may be useful for non-P2P applications as 107 well. For example, clients of client-server applications may use 108 information provided by ALTO to select one of several servers or 109 information replicas. As another example, ALTO information could be 110 used to select a media relay needed for NAT traversal. The goal of 111 these informed decisions is to improve performance (or Quality of 112 Experience) in the application while reducing resource consumption in 113 the underlying network infrastructure. 115 Usually, it would be difficult or even impossible for application 116 entities to acquire this information by other mechanisms (e.g., using 117 measurements between the peers of a P2P overlay), because of 118 complexity or because it is based on network topology information, 119 network operational costs, or network policies, which the respective 120 network provider does not want to disclose in detail. 122 The logical entities that provide the ALTO service do not take part 123 in the actual user data transport, i.e., they do not implement 124 functions for relaying user data. They may be placed on various 125 kinds of physical nodes, e.g., on dedicated servers, as auxiliary 126 processes in routers, on "trackers" or "super peers" of a P2P 127 application, etc. 129 2. Terminology and Architectural Framework 131 2.1. Requirements Notation 133 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 134 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 135 document are to be interpreted as described in [RFC2119]. 137 2.2. ALTO Terminology 139 This document uses the following ALTO-related terms, which are 140 defined in [RFC5693]: 142 Application, Peer, P2P, Resource, Resource Identifier, Resource 143 Provider, Resource Consumer, Transport Address, Overlay Network, 144 Resource Directory, ALTO Service, ALTO Server, ALTO Client, ALTO 145 Query, ALTO Response, ALTO Transaction, Local Traffic, Peering 146 Traffic, Transit Traffic, Application protocol, ALTO Client Protocol, 147 Provisioning protocol. 149 Furthermore, the following additional terms will be used: 151 o Host Group Descriptor: Information used to describe the resource 152 consumer which seeks ALTO guidance, or one or several candidate 153 resource providers. This can be, for example, a single IP 154 address, an address prefix or address range that contains the 155 host(s), or an autonomous system (AS) number. Different options 156 may provide different levels of detail. Depending on the system 157 architecture, this may have implications on the quality of the 158 guidance ALTO is able to provide, on whether recommendations can 159 be aggregated, and on how much privacy-sensitive information about 160 users might be disclosed to additional parties. 162 o Host Characteristics Attribute: Properties of a host (other than 163 the host group descriptor), in particular related to its 164 attachment to the network. This information may be stored in the 165 ALTO server and transmitted in the ALTO protocol. It may be 166 evaluated according to the rating criteria. 168 o Rating Criterion: The condition or relation that defines the 169 "better" in "better-than-random peer selection", which is the 170 ultimate goal of ALTO. Examples may include "host's Internet 171 access is not subject to volume based charging (flat rate)" or 172 "low topological distance". Some rating criteria, such as "low 173 topological distance", need to include a reference point, i. e., 174 "low topological distance from a given resource consumer", which 175 can be described by means of a host group descriptor. 177 2.3. Architectural Framework for ALTO 179 There are various architectural options for how ALTO could be 180 implemented, and specifying or mandating one specific architecture is 181 out of the scope of this document. 183 The ALTO Working Group Charter [ALTO-charter] itemizes several key 184 components, which shall be elaborated and specified by the ALTO 185 Working Group. The ALTO problem statement [RFC5693] defines a 186 terminology (see Section 2.2) and presents a figure that gives a 187 high-level overview of protocol interaction between ALTO elements. 189 This document itemizes requirements for the following components and 190 information elements that are part of the above-mentioned 191 architecture: 193 o The ALTO client protocol, which is used for sending ALTO queries 194 and ALTO responses between ALTO client and ALTO server. 196 o The discovery mechanism, which will be used by ALTO clients in 197 order to find out where to send ALTO requests. 199 o The overall architecture, especially with respect to security and 200 privacy issues. 202 o Host group descriptors, which are used to describe the location of 203 a host in the network topology. 205 o Rating criteria, i. e., conditions or relations that shall be 206 evaluated in order to generate the ALTO guidance. 208 3. ALTO Requirements 210 3.1. ALTO Client Protocol 212 3.1.1. General Requirements 214 REQ. ARv07-1: The ALTO service is provided by one or more ALTO 215 servers. ALTO servers MUST implement the ALTO client protocol, for 216 receiving ALTO queries from ALTO clients and for sending the 217 corresponding ALTO responses. 219 REQ. ARv07-2: ALTO clients MUST implement the ALTO client protocol, 220 for sending ALTO queries to ALTO servers and for receiving the 221 corresponding ALTO responses. 223 REQ. ARv07-3: The format of the ALTO query message MUST allow the 224 ALTO client to solicit guidance for selecting appropriate resource 225 providers. 227 REQ. ARv07-4: The format of the ALTO response message MUST allow the 228 ALTO server to express its guidance for selecting appropriate 229 resource providers. 231 REQ. ARv07-5: The detailed specification of a protocol is out of the 232 scope of this document. However, any protocol specification that 233 claims to implement the ALTO client protocol MUST be compliant to the 234 requirements itemized in this document. 236 3.1.2. Host Group Descriptor Support 238 The ALTO guidance is based on the evaluation of several resource 239 providers or groups of resource providers, which are characterized by 240 means of host group descriptors, considering one or more rating 241 criteria. 243 REQ. ARv07-6: The ALTO client protocol MUST support the usage of 244 several different host group descriptor types. 246 REQ. ARv07-7: The ALTO client protocol specification MUST define a 247 basic set of host group descriptor types, which MUST be supported by 248 all implementations of the ALTO client protocol. 250 REQ. ARv07-8: The ALTO client protocol MUST support the host group 251 descriptor types "IPv4 address prefix" and "IPv6 address prefix." 252 They can be used to specify the IP address of one host, or an IP 253 address range (in CIDR notation), which contains all hosts in 254 question. It is also possible to specify a broader address range 255 (i.e., a shorter prefix length) than the intended group of hosts 256 actually uses, in order to conceal their exact identity. 258 REQ. ARv07-9: The ALTO client protocol specification MUST define an 259 appropriate procedure for adding new host group descriptor types, 260 e.g., by establishing an IANA registry. 262 REQ. ARv07-10: ALTO clients and ALTO servers MUST clearly identify 263 the type of each host group descriptor sent in ALTO queries or 264 responses. 266 REQ. ARv07-11: For host group descriptor types other than "IPv4 267 address prefix" and "IPv6 address prefix", the host group descriptor 268 type identification MUST be supplemented by a reference to a 269 facility, which can be used to translate host group descriptors of 270 that type to IPv4/IPv6 address prefixes, e.g., by means of a mapping 271 table or an algorithm. 273 REQ. ARv07-12: Protocol functions for mapping other host group 274 descriptor types to IPv4/IPv6 address prefixes SHOULD be designed and 275 specified as part of the ALTO client protocol, and the corresponding 276 address mapping information SHOULD be made available by the same 277 entity that wants to use these host group descriptors within the ALTO 278 client protocol. However, an ALTO server or an ALTO client MAY also 279 send a reference to an external mapping facility, e.g., a translation 280 table to be downloaded as file via HTTP. 282 REQ. ARv07-13: The ALTO client protocol specification MUST define 283 mechanisms, which can be used by the ALTO client and the ALTO server 284 to indicate that a host group descriptor used by the other party is 285 of an unsupported type, or that the indicated mapping mechanism could 286 not be used. 288 3.1.3. Rating Criteria Support 290 REQ. ARv07-14: The ALTO client protocol MUST support the usage of 291 several different rating criteria types. 293 REQ. ARv07-15: The ALTO client protocol specification MUST define a 294 basic set of rating criteria types, which MUST be supported by all 295 implementations of the ALTO client protocol. 297 REQ. ARv07-16: The ALTO client protocol specification MUST support 298 the rating criteria type "relative operator's preference." This is a 299 relative measure, i.e., it is not associated with any unit of 300 measurement. A higher rating according to this criterion indicates 301 that the application should prefer the respective candidate resource 302 provider over others with lower ratings (unless information from non- 303 ALTO sources suggests a different choice, such as transmission 304 attempts suggesting that the path is currently congested). The 305 operator of the ALTO server does not have to disclose how and based 306 on which data the ratings are actually computed. Examples could be: 307 cost for peering or transit traffic, traffic engineering inside the 308 network, and other policies. 310 REQ. ARv07-17: The ALTO client protocol specification MUST define an 311 appropriate procedure for adding new rating criteria types, e.g., by 312 establishing an IANA registry. 314 One design assumption for ALTO is that it is acceptable that the host 315 characteristics attributes, which are stored and processed in the 316 ALTO servers for giving the guidance, are updated rather 317 infrequently. Typical update intervals may be several orders of 318 magnitude longer than the typical network-layer packet round-trip 319 time (RTT). Therefore, ALTO cannot be a replacement for TCP-like 320 congestion control mechanisms. The definition of alternate 321 approaches for congestion control is explicitly a non-goal for the 322 ALTO working group [ALTO-charter]. 324 REQ. ARv07-18: ALTO client protocol specifications MUST NOT define 325 rating criteria closely related to the instantaneous network 326 congestion state, whose primary aim is to serve an alternative to 327 established congestion control strategies, such as using TCP-based 328 transport. 330 REQ. ARv07-19: Applications using ALTO guidance MUST NOT rely on the 331 ALTO guidance to avoid network congestion. Instead, applications 332 MUST use other appropriate means, such as TCP based transport, to 333 avoid causing excessive congestion. 335 REQ. ARv07-20: The ALTO query message SHOULD allow the ALTO client 336 to express which rating criteria should be considered, as well as 337 their relative relevance for the specific application that will 338 eventually make use of the guidance. 340 REQ. ARv07-21: The ALTO response message SHOULD allow the ALTO 341 server to express which rating criteria have been considered when 342 generating the response. 344 REQ. ARv07-22: The ALTO client protocol specification MUST define 345 mechanisms, which can be used by the ALTO client and the ALTO server 346 to indicate that a rating criteria used by the other party is of an 347 unsupported type. 349 3.1.4. Placement of Entities and Timing of Transactions 351 With respect to the placement of ALTO clients, several modes of 352 operation exist: 354 o One mode of ALTO operation is that an ALTO client may be embedded 355 directly in the resource consumer, i.e., the application protocol 356 entity that will eventually initiate data transmission to/from the 357 selected resource provider(s) in order to access the desired 358 resource. For example, an ALTO client could be integrated into 359 the peer of a P2P application that uses a distributed algorithm 360 such as "query flooding" for resource discovery. 362 o Another mode of operation is to integrate the ALTO client into a 363 third party such as a resource directory, which may issue ALTO 364 queries to solicit preference on potential resource providers, 365 considering the respective resource consumer. For example, an 366 ALTO client could be integrated into the tracker of a tracker- 367 based P2P application, in order to request ALTO guidance on behalf 368 of the peers contacting the tracker. 370 REQ. ARv07-23: The ALTO client protocol MUST support the mode of 371 operation, in which the ALTO client is directly embedded in the 372 resource consumer. 374 REQ. ARv07-24: The ALTO client protocol MUST support the mode of 375 operation, in which the ALTO client is embedded in a third party, 376 which performs queries on behalf of resource consumers. 378 REQ. ARv07-25: The ALTO client protocol MUST be designed in a way 379 that the ALTO service can be provided by an entity which is not the 380 operator of the IP access network. 382 REQ. ARv07-26: The ALTO client protocol MUST be designed in a way 383 that different instances of the ALTO service operated by different 384 providers can coexist. 386 With respect to the timing of ALTO queries, several modes of 387 operation exist: 389 o In target-aware query mode, an ALTO client performs the ALTO query 390 when the desired resource and a set of candidate resource 391 providers are already known, i. e., after DHT lookups, queries to 392 the resource directory, etc. 394 o In target-independent query mode, ALTO queries are performed in 395 advance or periodically, in order to receive comprehensive, 396 "target-independent" guidance, which will be cached locally and 397 evaluated later, when a resource is to be accessed. 399 REQ. ARv07-27: The ALTO client protocol MUST support at least one of 400 these two modes, either the target-aware or the target-independent 401 query mode. 403 REQ. ARv07-28: The ALTO client protocol SHOULD support both the 404 target-aware and the target-independent query mode. 406 REQ. ARv07-29: The ALTO client protocol SHOULD support lifetime 407 attributes, to enable caching of recommendations at ALTO clients. 409 REQ. ARv07-30: The ALTO client protocol SHOULD specify an aging 410 mechanism, which allows to give newer recommendations precedence over 411 older ones. 413 REQ. ARv07-31: The ALTO client protocol SHOULD allow the ALTO server 414 to add information about appropriate modes of re-use to its ALTO 415 responses. Re-use may include redistributing an ALTO response to 416 other parties, as well as using the same ALTO information in a 417 resource directory to improve the responses to different resource 418 consumers, within the specified lifetime of the ALTO response. The 419 ALTO server SHOULD be able to express that 421 o no re-use should occur 423 o re-use is appropriate for a specific "target audience", i.e., a 424 set of resource consumers explicitly defined by a list of host 425 group descriptors. The ALTO server MAY specify a "target 426 audience" in the ALTO response, which is only a subset of the 427 known actual "target audience", e.g., if required by operator 428 policies 430 o re-use is appropriate for any resource consumer that would send 431 (or cause a third party sending on behalf of it) the same ALTO 432 query (i.e., with the same query parameters, except for the 433 resource consumer ID, if applicable) to this ALTO server 435 o re-use is appropriate for any resource consumer that would send 436 (or cause a third party sending on behalf of it) the same ALTO 437 query (i.e., with the same query parameters, except for the 438 resource consumer ID, if applicable) to any ALTO server 440 REQ. ARv07-32: The ALTO client protocol MUST support scenarios with 441 the ALTO client located in the private address realm behind a network 442 address translator (NAT). There are different types of NAT, see 443 [RFC4787] and [RFC5382]. 445 3.1.5. Protocol Extensibility 447 REQ. ARv07-33: The ALTO client protocol MUST include support for 448 adding protocol extensions in a non-disruptive, backward-compatible 449 way. 451 REQ. ARv07-34: The ALTO client protocol MUST include protocol 452 versioning support, in order to clearly distinguish between 453 incompatible versions of the protocol. 455 3.1.6. Error Handling and Overload Protection 457 REQ. ARv07-35: Any application designed to use ALTO MUST also work 458 if no ALTO servers can be found or if no responses to ALTO queries 459 are received, e.g., due to connectivity problems or overload 460 situation. 462 REQ. ARv07-36: The ALTO client protocol MUST use TCP based 463 transport. 465 REQ. ARv07-37: An ALTO server, which is operating close to its 466 capacity limit, MUST be able to inform clients about its impending 467 overload situation, and require them to throttle their query rate. 469 REQ. ARv07-38: An ALTO server, which is operating close to its 470 capacity limit, MUST be able to inform clients about its impending 471 overload situation, and redirect them to another ALTO server. 473 REQ. ARv07-39: An ALTO server, which is operating close to its 474 capacity limit, MUST be able to inform clients about its impending 475 overload situation, and terminate the conversation with the ALTO 476 client. 478 REQ. ARv07-40: An ALTO server, which is operating close to its 479 capacity limit, MUST be able to inform clients about its impending 480 overload situation, and reject new conversation attempts. 482 3.2. ALTO Server Discovery 484 The ALTO client protocol is supported by one or several ALTO server 485 discovery mechanisms, which will be used by ALTO clients in order to 486 find out where to send ALTO requests. 488 REQ. ARv07-41: ALTO clients which are embedded in the resource 489 consumer MUST be able to use the ALTO server discovery mechanism, in 490 order to find one or several ALTO servers that can provide ALTO 491 guidance suitable for the resource consumer. This mode of operation 492 is called "resource consumer initiated ALTO server discovery". 494 REQ. ARv07-42: ALTO clients which are embedded in a resource 495 directory and perform third-party ALTO queries on behalf of a remote 496 resource consumer MUST be able to use the ALTO server discovery 497 mechanism, in order to find one or several ALTO servers that can 498 provide ALTO guidance suitable for the respective resource consumer. 499 This mode of operation is called "third-party ALTO server discovery". 501 REQ. ARv07-43: ALTO clients MUST be able to perform resource 502 consumer initiated ALTO server discovery, even if they are located 503 behind a network address translator (NAT). 505 REQ. ARv07-44: ALTO clients MUST be able to perform third-party ALTO 506 server discovery, even if they are located behind a network address 507 translator (NAT). 509 REQ. ARv07-45: ALTO clients MUST be able to perform third-party ALTO 510 server discovery, even if the resource consumer, on behalf of which 511 the ALTO query will be sent, is located behind a network address 512 translator (NAT). 514 REQ. ARv07-46: The ALTO server discovery mechanism SHOULD leverage 515 an existing protocol or mechanism, such as DNS, DHCP, or PPP based 516 automatic configuration, etc. A single mechanism with a broad 517 spectrum of applicability SHOULD be preferred over several different 518 mechanisms with narrower scopes. 520 REQ. ARv07-47: The ALTO server discovery mechanism SHOULD be able to 521 return the respective contact information for multiple ALTO servers. 523 REQ. ARv07-48: The ALTO server discovery mechanism SHOULD be able to 524 indicate preferences for each returned ALTO server contact 525 information. 527 3.3. Security and Privacy 529 REQ. ARv07-49: The ALTO client protocol MUST support mechanisms for 530 the authentication of ALTO servers. 532 REQ. ARv07-50: The ALTO client protocol MUST support mechanisms for 533 the authentication of ALTO clients. 535 REQ. ARv07-51: The ALTO client protocol MUST support mechanisms for 536 the encryption of messages. 538 REQ. ARv07-52: The ALTO client protocol MUST support different 539 levels of detail in queries and responses, in order for the operator 540 of an ALTO service to be able to control how much information (e.g., 541 about the network topology) is disclosed. 543 REQ. ARv07-53: The operator of an ALTO server MUST NOT assume that 544 an ALTO client will implement mechanisms or comply with rules that 545 limit the ALTO client's ability to redistribute information retrieved 546 from the ALTO server to third parties. 548 REQ. ARv07-54: The ALTO client protocol MUST support different 549 levels of detail in queries and responses, in order to protect the 550 privacy of users, to ensure that the operators of ALTO servers and 551 other users of the same application cannot derive sensitive 552 information. 554 REQ. ARv07-55: The ALTO client protocol SHOULD be defined in a way, 555 that the operator of one ALTO server cannot easily deduce the 556 resource identifier (e.g., file name in P2P file sharing) which the 557 resource consumer seeking ALTO guidance wants to access. 559 REQ. ARv07-56: The ALTO client protocol MUST support appropriate 560 mechanisms to protect the ALTO service against DoS attacks. 562 4. IANA Considerations 564 This requirements document does not mandate any immediate IANA 565 actions. However, such IANA considerations may arise from future 566 ALTO specification documents which try to meet the requirements given 567 here. 569 5. Security Considerations 571 5.1. High-level security considerations 573 High-level security considerations for the ALTO service can be found 574 in the "Security Considerations" section of the ALTO problem 575 statement document [RFC5693]. 577 5.2. Information Disclosure Scenarios 579 The unwanted disclosure of information is one key concern related to 580 ALTO. This section presents a classification and discussion of 581 information disclosure scenarios and potential countermeasures. 583 5.2.1. Classification of Information Disclosure Scenarios 585 o (1) Excess disclosure of ALTO server operator's data to an 586 authorized ALTO client. The operator of an ALTO server has to 587 feed information, such as tables mapping host group descriptors to 588 host characteristics attributes, into the server, thereby enabling 589 it to give guidance to ALTO clients. Some operators might 590 consider the full set of this information confidential (e.g., a 591 detailed map of the operator's network topology), and might want 592 to disclose only a subset of it or somehow obfuscated information 593 to an ALTO client. 595 o (2) Disclosure of the application behavior to the ALTO server. 596 The operator of an ALTO server could infer the application 597 behavior (e.g., content identifiers in P2P file sharing 598 applications, or lists of resource providers that are considered 599 for establishing a connection) from the ALTO queries sent by an 600 ALTO client. 602 o (3) Disclosure of ALTO server operator's data (e.g., network 603 topology information) to an unauthorized third party. There are a 604 couple of sub-cases here: 606 * (3a) An ALTO server sends the information directly to an 607 unauthorized ALTO client. 609 * (3b) An unauthorized party snoops on the data transmission from 610 the ALTO server to an authorized ALTO client. 612 * (3c) An authorized ALTO client knowingly forwards the 613 information it had received from the ALTO server to an 614 unauthorized party. 616 o (4) Disclosure of the application behavior to an unauthorized 617 third party. 619 o (5) Excess retrieval of ALTO server operator's data by 620 collaborating ALTO clients. Several authorized ALTO clients could 621 ask an ALTO server for guidance, and redistribute the responses 622 among each other (see also case 3c). By correlating the ALTO 623 responses they could find out more information than intended to be 624 disclosed by the ALTO server operator. 626 5.2.2. Discussion of Information Disclosure Scenarios 628 Scenario (1) may be addressed by the ALTO server operator choosing 629 the level of detail of the information to be populated into the ALTO 630 server. Furthermore, access control mechanisms for filtering ALTO 631 responses according to the authenticated ALTO client identity might 632 be installed in the ALTO server, although this might not be effective 633 given the lack of efficient mechanisms for addressing (3c) and (5), 634 see below. 636 (2) is addressed by allowing ALTO clients to use the target- 637 independent query mode. In this mode of operation, guiding 638 information (e.g., "maps") is retrieved from the ALTO server and used 639 entirely locally by the ALTO client, i.e., without sending host 640 location attributes of candidate resource providers to the ALTO 641 server. In the target-aware query mode, (2) can be addressed by ALTO 642 clients by obfuscating the identity of candidate resource consumers, 643 e.g., by zeroing-out or randomizing the last few bits of the IP 644 addresses. However, there is the potential side effect of yielding 645 inaccurate results. 647 (3a), (3b), and (4) may be addressed by authentication, access 648 control, and encryption schemes for the ALTO client protocol. 649 However, deployment of encryption schemes might not be effective 650 given the lack of efficient mechanisms for addressing (3c) and (5), 651 see below. 653 Straightforward authentication and encryption schemes will not help 654 solving (3c) and (5), and there is no other simple and efficient 655 mechanism known. The cost of complex approaches, e.g., based on 656 digital rights management (DRM), might easily outweigh the benefits 657 of the whole ALTO solution, and therefore they are not considered as 658 a viable solution. That is, ALTO server operators must be aware that 659 (3c) and (5) cannot be prevented from happening, and therefore they 660 should feed only such data into an ALTO server, which they do not 661 consider sensitive with respect to (3c) and (5). 663 These insights are reflected in the requirements in this document. 665 5.3. Security Requirements 667 For a set of specific security requirements please refer to 668 Section 3.3 of this document. 670 6. References 672 6.1. Normative References 674 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 675 Requirement Levels", BCP 14, RFC 2119, March 1997. 677 6.2. Informative References 679 [ALTO-charter] 680 Marocco, E. and V. Gurbani, "Application-Layer Traffic 681 Optimization (ALTO) Working Group Charter", February 2009. 683 [RFC4787] Audet, F. and C. Jennings, "Network Address Translation 684 (NAT) Behavioral Requirements for Unicast UDP", BCP 127, 685 RFC 4787, January 2007. 687 [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. 688 Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, 689 RFC 5382, October 2008. 691 [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic 692 Optimization (ALTO) Problem Statement", RFC 5693, 693 October 2009. 695 Appendix A. Contributors List and Acknowledgments 697 The initial version of this document was co-authored by Laird Popkin. 699 The authors would like to thank 701 o Vijay K. Gurbani 703 o Enrico Marocco 705 for fostering discussions that lead to the creation of this document, 706 and for giving valuable comments on it. 708 The authors were supported by the following people, who have 709 contributed to this document: 711 o Richard Alimi 713 o Zoran Despotovic 715 o Jason Livingood 717 o Saverio Niccolini 719 o Jan Seedorf 721 The authors would like to thank the members of the P2PI and ALTO 722 mailing lists for their feedback. 724 Laird Popkin and Y. Richard Yang are grateful to the many 725 contributions made by the members of the P4P working group and Yale 726 Laboratory of Networked Systems. The P4P working group is hosted by 727 DCIA. 729 Martin Stiemerling, Saverio Niccolini, and Jan Seedorf are partially 730 supported by the NAPA-WINE project (Network-Aware P2P-TV Application 731 over Wise Networks, http://www.napa-wine.org), a research project 732 supported by the European Commission under its 7th Framework Program 733 (contract no. 214412). The views and conclusions contained herein 734 are those of the authors and should not be interpreted as necessarily 735 representing the official policies or endorsements, either expressed 736 or implied, of the NAPA-WINE project or the European Commission. 738 Authors' Addresses 740 Sebastian Kiesel (editor) 741 University of Stuttgart Computing Center 742 Networks and Communication Systems Department 743 Allmandring 30 744 70550 Stuttgart 745 Germany 747 Email: ietf-alto@skiesel.de 748 URI: http://www.rus.uni-stuttgart.de/nks/ 750 Stefano Previdi 751 Cisco Systems, Inc. 753 Email: sprevidi@cisco.com 755 Martin Stiemerling 756 NEC Laboratories Europe/University of Goettingen 758 Email: martin.stiemerling@neclab.eu 759 URI: http://ietf.stiemerling.org 761 Richard Woundy 762 Comcast Corporation 764 Email: Richard_Woundy@cable.comcast.com 766 Yang Richard Yang 767 Yale University 769 Email: yry@cs.yale.edu