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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ALTO WG R. Alimi, Ed. 3 Internet-Draft Google 4 Intended status: Standards Track R. Penno, Ed. 5 Expires: August 20, 2014 Cisco Systems 6 Y. Yang, Ed. 7 Yale University 8 February 16, 2014 10 ALTO Protocol 11 draft-ietf-alto-protocol-26.txt 13 Abstract 15 Applications using the Internet already have access to some topology 16 information of Internet Service Provider (ISP) networks. For 17 example, views to Internet routing tables at looking glass servers 18 are available and can be practically downloaded to many network 19 application clients. What is missing is knowledge of the underlying 20 network topologies from the point of view of ISPs. In other words, 21 what an ISP prefers in terms of traffic optimization -- and a way to 22 distribute it. 24 The Application-Layer Traffic Optimization (ALTO) Service provides 25 network information (e.g., basic network location structure and 26 preferences of network paths) with the goal of modifying network 27 resource consumption patterns while maintaining or improving 28 application performance. The basic information of ALTO is based on 29 abstract maps of a network. These maps provide a simplified view, 30 yet enough information about a network for applications to 31 effectively utilize them. Additional services are built on top of 32 the maps. 34 This document describes a protocol implementing the ALTO Service. 35 Although the ALTO Service would primarily be provided by ISPs, other 36 entities such as content service providers could also operate an ALTO 37 Service. Applications that could use this service are those that 38 have a choice to which end points to connect. Examples of such 39 applications are peer-to-peer (P2P) and content delivery networks. 41 Requirements Language 43 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 44 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 45 document are to be interpreted as described in RFC 2119 [RFC2119]. 47 Status of this Memo 48 This Internet-Draft is submitted in full conformance with the 49 provisions of BCP 78 and BCP 79. 51 Internet-Drafts are working documents of the Internet Engineering 52 Task Force (IETF). Note that other groups may also distribute 53 working documents as Internet-Drafts. The list of current Internet- 54 Drafts is at http://datatracker.ietf.org/drafts/current/. 56 Internet-Drafts are draft documents valid for a maximum of six months 57 and may be updated, replaced, or obsoleted by other documents at any 58 time. It is inappropriate to use Internet-Drafts as reference 59 material or to cite them other than as "work in progress." 61 This Internet-Draft will expire on August 20, 2014. 63 Copyright Notice 65 Copyright (c) 2014 IETF Trust and the persons identified as the 66 document authors. All rights reserved. 68 This document is subject to BCP 78 and the IETF Trust's Legal 69 Provisions Relating to IETF Documents 70 (http://trustee.ietf.org/license-info) in effect on the date of 71 publication of this document. Please review these documents 72 carefully, as they describe your rights and restrictions with respect 73 to this document. Code Components extracted from this document must 74 include Simplified BSD License text as described in Section 4.e of 75 the Trust Legal Provisions and are provided without warranty as 76 described in the Simplified BSD License. 78 Table of Contents 80 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 7 81 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 7 82 1.2. Design Overview . . . . . . . . . . . . . . . . . . . . . 8 83 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 84 2.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . . . . 8 85 2.2. Endpoint Address . . . . . . . . . . . . . . . . . . . . . 8 86 2.3. Network Location . . . . . . . . . . . . . . . . . . . . . 9 87 2.4. ALTO Information . . . . . . . . . . . . . . . . . . . . . 9 88 2.5. ALTO Information Base . . . . . . . . . . . . . . . . . . 9 89 2.6. ALTO Service . . . . . . . . . . . . . . . . . . . . . . . 9 90 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 9 91 3.1. ALTO Service and Protocol Scope . . . . . . . . . . . . . 9 92 3.2. ALTO Information Reuse and Redistribution . . . . . . . . 11 93 4. ALTO Information Service Framework . . . . . . . . . . . . . . 11 94 4.1. ALTO Information Services . . . . . . . . . . . . . . . . 12 95 4.1.1. Map Service . . . . . . . . . . . . . . . . . . . . . 12 96 4.1.2. Map Filtering Service . . . . . . . . . . . . . . . . 13 97 4.1.3. Endpoint Property Service . . . . . . . . . . . . . . 13 98 4.1.4. Endpoint Cost Service . . . . . . . . . . . . . . . . 13 99 5. Network Map . . . . . . . . . . . . . . . . . . . . . . . . . 13 100 5.1. Provider-defined Identifier (PID) . . . . . . . . . . . . 13 101 5.2. Endpoint Addresses . . . . . . . . . . . . . . . . . . . . 14 102 5.3. Example Network Map . . . . . . . . . . . . . . . . . . . 14 103 6. Cost Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 104 6.1. Cost Types . . . . . . . . . . . . . . . . . . . . . . . . 16 105 6.1.1. Cost Metric . . . . . . . . . . . . . . . . . . . . . 16 106 6.1.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 17 107 6.2. Cost Map Structure . . . . . . . . . . . . . . . . . . . . 18 108 6.3. Network Map and Cost Map Dependency . . . . . . . . . . . 18 109 6.4. Cost Map Update . . . . . . . . . . . . . . . . . . . . . 18 110 7. Endpoint Properties . . . . . . . . . . . . . . . . . . . . . 19 111 7.1. Endpoint Property Type . . . . . . . . . . . . . . . . . . 19 112 7.1.1. Endpoint Property Type: pid . . . . . . . . . . . . . 19 113 8. Protocol Specification: General Processing . . . . . . . . . . 19 114 8.1. Overall Design . . . . . . . . . . . . . . . . . . . . . . 19 115 8.2. Notation . . . . . . . . . . . . . . . . . . . . . . . . . 20 116 8.3. Basic Operations . . . . . . . . . . . . . . . . . . . . . 20 117 8.3.1. Client Discovering Information Resources . . . . . . . 21 118 8.3.2. Client Requesting Information Resources . . . . . . . 21 119 8.3.3. Server Responding to IR Request . . . . . . . . . . . 22 120 8.3.4. Client Handling Server Response . . . . . . . . . . . 22 121 8.3.5. Authentication and Encryption . . . . . . . . . . . . 23 122 8.3.6. Information Refreshing . . . . . . . . . . . . . . . . 23 123 8.3.7. Parsing of Unknown Fields . . . . . . . . . . . . . . 23 124 8.4. Server Response Encoding . . . . . . . . . . . . . . . . . 24 125 8.4.1. Meta Information . . . . . . . . . . . . . . . . . . . 24 126 8.4.2. Data Information . . . . . . . . . . . . . . . . . . . 24 127 8.5. Protocol Errors . . . . . . . . . . . . . . . . . . . . . 24 128 8.5.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 25 129 8.5.2. Response Format and Error Codes . . . . . . . . . . . 25 130 8.5.3. Overload Conditions and Server Unavailability . . . . 27 131 9. Protocol Specification: Information Resource Directory . . . . 28 132 9.1. Information Resource Attributes . . . . . . . . . . . . . 28 133 9.1.1. Resource ID . . . . . . . . . . . . . . . . . . . . . 28 134 9.1.2. Media Type . . . . . . . . . . . . . . . . . . . . . . 28 135 9.1.3. Capabilities . . . . . . . . . . . . . . . . . . . . . 28 136 9.1.4. Accepts Input Parameters . . . . . . . . . . . . . . . 28 137 9.1.5. Dependent Resources . . . . . . . . . . . . . . . . . 29 138 9.2. Information Resource Directory (IRD) . . . . . . . . . . . 29 139 9.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 29 140 9.2.2. Encoding . . . . . . . . . . . . . . . . . . . . . . . 29 141 9.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 31 142 9.2.4. Delegation using IRD . . . . . . . . . . . . . . . . . 34 143 9.2.5. Considerations of Using IRD . . . . . . . . . . . . . 36 144 10. Protocol Specification: Basic Data Types . . . . . . . . . . . 36 145 10.1. PID Name . . . . . . . . . . . . . . . . . . . . . . . . . 37 146 10.2. Resource ID . . . . . . . . . . . . . . . . . . . . . . . 37 147 10.3. Version Tag . . . . . . . . . . . . . . . . . . . . . . . 37 148 10.4. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 38 149 10.4.1. Typed Endpoint Addresses . . . . . . . . . . . . . . . 38 150 10.4.2. Address Type . . . . . . . . . . . . . . . . . . . . . 38 151 10.4.3. Endpoint Address . . . . . . . . . . . . . . . . . . . 38 152 10.4.4. Endpoint Prefixes . . . . . . . . . . . . . . . . . . 39 153 10.4.5. Endpoint Address Group . . . . . . . . . . . . . . . . 39 154 10.5. Cost Mode . . . . . . . . . . . . . . . . . . . . . . . . 40 155 10.6. Cost Metric . . . . . . . . . . . . . . . . . . . . . . . 40 156 10.7. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . 40 157 10.8. Endpoint Property . . . . . . . . . . . . . . . . . . . . 41 158 10.8.1. Resource Specific Endpoint Properties . . . . . . . . 41 159 10.8.2. Global Endpoint Properties . . . . . . . . . . . . . . 41 160 11. Protocol Specification: Service Information Resources . . . . 42 161 11.1. Meta Information . . . . . . . . . . . . . . . . . . . . . 42 162 11.2. Map Service . . . . . . . . . . . . . . . . . . . . . . . 42 163 11.2.1. Network Map . . . . . . . . . . . . . . . . . . . . . 42 164 11.2.2. Mapping IP Addresses to PIDs for 'ipv4'/'ipv6' 165 Network Maps . . . . . . . . . . . . . . . . . . . . . 45 166 11.2.3. Cost Map . . . . . . . . . . . . . . . . . . . . . . . 46 167 11.3. Map Filtering Service . . . . . . . . . . . . . . . . . . 49 168 11.3.1. Filtered Network Map . . . . . . . . . . . . . . . . . 49 169 11.3.2. Filtered Cost Map . . . . . . . . . . . . . . . . . . 51 170 11.4. Endpoint Property Service . . . . . . . . . . . . . . . . 55 171 11.4.1. Endpoint Property . . . . . . . . . . . . . . . . . . 56 172 11.5. Endpoint Cost Service . . . . . . . . . . . . . . . . . . 59 173 11.5.1. Endpoint Cost . . . . . . . . . . . . . . . . . . . . 59 175 12. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 62 176 12.1. ALTO Client Embedded in P2P Tracker . . . . . . . . . . . 63 177 12.2. ALTO Client Embedded in P2P Client: Numerical Costs . . . 64 178 12.3. ALTO Client Embedded in P2P Client: Ranking . . . . . . . 65 179 13. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 66 180 13.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 66 181 13.2. Hosts with Multiple Endpoint Addresses . . . . . . . . . . 67 182 13.3. Network Address Translation Considerations . . . . . . . . 67 183 13.4. Endpoint and Path Properties . . . . . . . . . . . . . . . 68 184 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 68 185 14.1. application/alto-* Media Types . . . . . . . . . . . . . . 68 186 14.2. ALTO Cost Metric Registry . . . . . . . . . . . . . . . . 70 187 14.3. ALTO Endpoint Property Type Registry . . . . . . . . . . . 71 188 14.4. ALTO Address Type Registry . . . . . . . . . . . . . . . . 73 189 14.5. ALTO Error Code Registry . . . . . . . . . . . . . . . . . 74 190 15. Security Considerations . . . . . . . . . . . . . . . . . . . 74 191 15.1. Authenticity and Integrity of ALTO Information . . . . . . 75 192 15.1.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 75 193 15.1.2. Protection Strategies . . . . . . . . . . . . . . . . 75 194 15.1.3. Limitations . . . . . . . . . . . . . . . . . . . . . 75 195 15.2. Potential Undesirable Guidance from Authenticated ALTO 196 Information . . . . . . . . . . . . . . . . . . . . . . . 76 197 15.2.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 76 198 15.2.2. Protection Strategies . . . . . . . . . . . . . . . . 76 199 15.3. Confidentiality of ALTO Information . . . . . . . . . . . 77 200 15.3.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 77 201 15.3.2. Protection Strategies . . . . . . . . . . . . . . . . 77 202 15.3.3. Limitations . . . . . . . . . . . . . . . . . . . . . 78 203 15.4. Privacy for ALTO Users . . . . . . . . . . . . . . . . . . 78 204 15.4.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 78 205 15.4.2. Protection Strategies . . . . . . . . . . . . . . . . 78 206 15.5. Availability of ALTO Service . . . . . . . . . . . . . . . 79 207 15.5.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 79 208 15.5.2. Protection Strategies . . . . . . . . . . . . . . . . 79 209 16. Manageability Considerations . . . . . . . . . . . . . . . . . 79 210 16.1. Operations . . . . . . . . . . . . . . . . . . . . . . . . 80 211 16.1.1. Installation and Initial Setup . . . . . . . . . . . . 80 212 16.1.2. Migration Path . . . . . . . . . . . . . . . . . . . . 80 213 16.1.3. Dependencies on Other Protocols and Functional 214 Components . . . . . . . . . . . . . . . . . . . . . . 81 215 16.1.4. Impact and Observation on Network Operation . . . . . 81 216 16.2. Management . . . . . . . . . . . . . . . . . . . . . . . . 82 217 16.2.1. Management Interoperability . . . . . . . . . . . . . 82 218 16.2.2. Management Information . . . . . . . . . . . . . . . . 82 219 16.2.3. Fault Management . . . . . . . . . . . . . . . . . . . 82 220 16.2.4. Configuration Management . . . . . . . . . . . . . . . 82 221 16.2.5. Performance Management . . . . . . . . . . . . . . . . 83 222 16.2.6. Security Management . . . . . . . . . . . . . . . . . 83 224 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 83 225 17.1. Normative References . . . . . . . . . . . . . . . . . . . 83 226 17.2. Informative References . . . . . . . . . . . . . . . . . . 84 227 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 87 228 Appendix B. Design History and Merged Proposals . . . . . . . . . 88 229 Appendix C. Authors . . . . . . . . . . . . . . . . . . . . . . . 88 230 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 89 232 1. Introduction 234 1.1. Problem Statement 236 This document defines the ALTO Protocol, which provides a solution 237 for the problem stated in [RFC5693]. Specifically, in today's 238 networks, network information such as network topologies, link 239 availability, routing policies, and path costs are hidden from the 240 application layer, and many applications benefited from such hiding 241 of network complexity. However, new applications, such as 242 application-layer overlays, can benefit from information about the 243 underlying network infrastructure. In particular, these new network 244 applications can be adaptive, and hence become more network-efficient 245 (e.g., reduce network resource consumption) and achieve better 246 application performance (e.g., accelerated download rate), by 247 leveraging network-provided information. 249 At a high level, the ALTO Protocol specified in this document is a 250 unidirectional interface that allows a network to publish its network 251 information such as network locations, costs between them at 252 configurable granularities, and endhost properties to network 253 applications. The information published by the ALTO Protocol should 254 benefit both the network and the applications (i.e., the consumers of 255 the information). Either the operator of the network or a third- 256 party (e.g., an information aggregator) can retrieve or derive 257 related information of the network and publish it using the ALTO 258 Protocol. When a network provides information through the ALTO 259 Protocol, we say that the network provides the ALTO Service. 261 To better understand the goal of the ALTO Protocol, we provide a 262 short, non-normative overview of the benefits of ALTO to both 263 networks and applications: 265 o A network that provides an ALTO Service can achieve better 266 utilization of its networking infrastructure. For example, by 267 using ALTO as a tool to interact with applications, a network is 268 able to provide network information to applications so that the 269 applications can better manage traffic on more expensive or 270 difficult-to-provision links such as long distance, transit or 271 backup links. During the interaction, the network can choose to 272 protect its sensitive and confidential network state information, 273 by abstracting real metric values into non-real numerical scores 274 or ordinal ranking. 276 o An application that uses an ALTO Service can benefit from better 277 knowledge of the network to avoid network bottlenecks. For 278 example, an overlay application can use information provided by 279 the ALTO Service to avoid selecting peers connected via high-delay 280 links (e.g., some intercontinental links). Using ALTO to 281 initialize each node with promising ("better-than-random") peers, 282 an adaptive peer-to-peer overlay may achieve faster, better 283 convergence. 285 1.2. Design Overview 287 The ALTO Protocol specified in this document meets the ALTO 288 requirements specified in [RFC5693], and unifies multiple protocols 289 previously designed with similar intentions. See Appendix A for a 290 list of people and Appendix B for a list of proposals that have made 291 significant contributions to this effort. 293 The ALTO Protocol uses a REST-ful design [Fielding-Thesis], and 294 encodes its requests and responses using JSON [RFC4627]. These 295 designs are chosen because of their flexibility and extensibility. 296 In addition, these designs make it possible for ALTO to be deployed 297 at scale by leveraging existing HTTP [RFC2616] implementations, 298 infrastructures and deployment experience. 300 2. Terminology 302 We use the following terms defined in [RFC5693]: Application, Overlay 303 Network, Peer, Resource, Resource Identifier, Resource Provider, 304 Resource Consumer, Resource Directory, Transport Address, Host 305 Location Attribute, ALTO Service, ALTO Server, ALTO Client, ALTO 306 Query, ALTO Reply, ALTO Transaction, Local Traffic, Peering Traffic, 307 Transit Traffic. 309 We also use the following additional terms: Endpoint Address, Network 310 Location, ALTO Information, ALTO Information Base, and ALTO Service. 312 2.1. Endpoint 314 An Endpoint is an application or host that is capable of 315 communicating (sending and/or receiving messages) on a network. 317 An Endpoint is typically either a Resource Provider or a Resource 318 Consumer. 320 2.2. Endpoint Address 322 An Endpoint Address represents the communication address of an 323 endpoint. Common forms of Endpoint Addresses include IP address, MAC 324 address and overlay ID. An Endpoint Address can be network- 325 attachment based (e.g., IP address) or network-attachment agnostic 326 (e.g., MAC address). 328 Each Endpoint Address has an associated Address Type, which indicates 329 both its syntax and semantics. 331 2.3. Network Location 333 Network Location is a generic term denoting a single Endpoint or a 334 group of Endpoints. For instance, it can be a single IPv4 or IPv6 335 address, an IPv4 or IPv6 prefix, or a set of prefixes. 337 2.4. ALTO Information 339 ALTO Information is a generic term referring to the network 340 information sent by an ALTO Server. 342 2.5. ALTO Information Base 344 We use the term ALTO Information Base to refer to the internal 345 representation of ALTO Information maintained by an ALTO Server. 346 Note that the structure of this internal representation is not 347 defined by this document. 349 2.6. ALTO Service 351 A network that provides ALTO Information through the ALTO Protocol is 352 said to provide the ALTO Service. 354 3. Architecture 356 We now define the ALTO architecture and the ALTO Protocol's place in 357 the overall architecture. 359 3.1. ALTO Service and Protocol Scope 361 Each network region in the global Internet can provide its ALTO 362 Service, which conveys network information from the perspective of 363 that network region. A network region in this context can be an 364 Autonomous System (AS), an ISP, a region smaller than an AS or ISP, 365 or a set of ISPs. The specific network region that an ALTO Service 366 represents will depend on the ALTO deployment scenario and ALTO 367 service discovery mechanism. 369 The ALTO Service specified in this document defines network Endpoints 370 (and aggregations thereof) and generic costs amongst them from the 371 region's perspective. The network Endpoints may include all 372 Endpoints in the global Internet. Hence, we say that the network 373 information provided by the ALTO Service of a network region 374 represents the "my-Internet view" of the network region. 376 The "my-Internet view" defined in this document does not specify the 377 internal topology of a network, and hence, we say that it provides a 378 "single-node" abstract topology. Extensions to this document may 379 provide topology details in "my-Internet view". 381 To better understand the ALTO Service and the role of the ALTO 382 Protocol, we show in Figure 1 the overall ALTO system architecture. 383 In this architecture, an ALTO Server prepares ALTO Information; an 384 ALTO Client uses ALTO Service Discovery to identify an appropriate 385 ALTO Server; and the ALTO Client requests available ALTO Information 386 from the ALTO Server using the ALTO Protocol. 388 The ALTO Information provided by the ALTO Server can be updated 389 dynamically based on network conditions, or can be seen as a policy 390 which is updated at a larger time-scale. 392 +-------------------------------------------------------------------+ 393 | Network Region | 394 | | 395 | +-----------+ | 396 | | Routing | | 397 | +--------------+ | Protocols | | 398 | | Provisioning | +-----------+ | 399 | | Policy | | | 400 | +--------------+\ | | 401 | \ | | 402 | \ | | 403 | +-----------+ \+---------+ +--------+ | 404 | |Dynamic | | ALTO | ALTO Protocol | ALTO | | 405 | |Network |.......| Server | ==================== | Client | | 406 | |Information| +---------+ +--------+ | 407 | +-----------+ / / | 408 | / ALTO SD Query/Response / | 409 | / / | 410 | +----------+ +----------------+ | 411 | | External | | ALTO Service | | 412 | | Interface| | Discovery (SD) | | 413 | +----------+ +----------------+ | 414 | | | 415 +-------------------------------------------------------------------+ 416 | 417 +------------------+ 418 | Third Parties | 419 | | 420 | Content Providers| 421 +------------------+ 423 Figure 1: Basic ALTO Architecture. 425 Figure 1 illustrates that the ALTO Information provided by an ALTO 426 Server may be influenced (at the service provider's discretion) by 427 other systems. In particular, the ALTO Server can aggregate 428 information from multiple systems to provide an abstract and unified 429 view that can be more useful to applications. Examples of other 430 systems include (but are not limited to) static network configuration 431 databases, dynamic network information, routing protocols, 432 provisioning policies, and interfaces to outside parties. These 433 components are shown in the figure for completeness but are outside 434 the scope of this specification. Recall that while the ALTO Protocol 435 may convey dynamic network information, it is not intended to replace 436 near-real-time congestion control protocols. 438 It may also be possible for an ALTO Server to exchange network 439 information with other ALTO Servers (either within the same 440 administrative domain or another administrative domain with the 441 consent of both parties) in order to adjust exported ALTO 442 Information. Such a protocol is also outside the scope of this 443 specification. 445 3.2. ALTO Information Reuse and Redistribution 447 ALTO Information may be useful to a large number of applications and 448 users. At the same time, distributing ALTO Information must be 449 efficient and not become a bottleneck. 451 The design of the ALTO Protocol allows integration with the existing 452 HTTP caching infrastructure to redistribute ALTO Information. If 453 caching or redistribution is used, the response message to an ALTO 454 Client may be returned from a third-party. 456 Application-dependent mechanisms, such as P2P DHTs or P2P file- 457 sharing, may be used to cache and redistribute ALTO Information. 458 This document does not define particular mechanisms for such 459 redistribution. 461 Additional protocol mechanisms (e.g., expiration times and digital 462 signatures for returned ALTO information) are left for future 463 investigation. 465 4. ALTO Information Service Framework 467 The ALTO Protocol conveys network information through services, where 468 each service defines a set of related functionalities. An ALTO 469 Client can request each service individually. All of the services 470 defined in ALTO are said to form the ALTO service framework and are 471 provided through a common transport protocol, messaging structure and 472 encoding, and transaction model. Functionalities offered in 473 different services can overlap. 475 The goals of the services defined in this document are to convey (1) 476 Network Locations, which denote the locations of Endpoints at a 477 network, (2) provider-defined costs for paths between pairs of 478 Network Locations, and (3) network related properties of endhosts. 479 The aforementioned goals are achieved by defining the Map Service, 480 which provides the core ALTO information to clients, and three 481 additional services: the Map Filtering Service, Endpoint Property 482 Service, and Endpoint Cost Service. Additional services can be 483 defined in companion documents. Below we give an overview of the 484 services. Details of the services will be presented in the following 485 sections. 487 .-----------------------------------------. 488 | ALTO Information Services | 489 | .-----------. .----------. .----------. | 490 | | Map | | Endpoint | | Endpoint | | 491 | | Filtering | | Property | | Cost | | 492 | | Service | | Service | | Service | | 493 | `-----------' `----------' `----------' | 494 | .-------------------------------------. | 495 | | Map Service | | 496 | | .-------------. .--------------. | | 497 | | | Network Map | | Cost Map | | | 498 | | `-------------' `--------------' | | 499 | `-------------------------------------' | 500 `-----------------------------------------' 502 Figure 2: ALTO Service Framework. 504 4.1. ALTO Information Services 506 4.1.1. Map Service 508 The Map Service provides batch information to ALTO Clients in the 509 form of Network Map and Cost Map. A Network Map (See Section 5) 510 provides a full set of Network Location groupings defined by the ALTO 511 Server and the Endpoints contained within each grouping. A Cost Map 512 (see Section 6) provides costs between a defined grouping. 514 These two maps can be thought of (and implemented as) as simple files 515 with appropriate encoding provided by the ALTO Server. 517 4.1.2. Map Filtering Service 519 Resource constrained ALTO Clients may benefit from filtering of query 520 results at the ALTO Server. This avoids that an ALTO Client first 521 spends network bandwidth and CPU cycles to collect results and then 522 performs client-side filtering. The Map Filtering Service allows 523 ALTO Clients to query an ALTO Server on Network Map and Cost Map 524 based on additional parameters. 526 4.1.3. Endpoint Property Service 528 This service allows ALTO Clients to look up properties for individual 529 Endpoints. An example property of an Endpoint is its Network 530 Location (i.e., its grouping defined by the ALTO Server). Another 531 example property is its connectivity type such as ADSL (Asymmetric 532 Digital Subscriber Line), Cable, or FTTH (Fiber To The Home). 534 4.1.4. Endpoint Cost Service 536 Some ALTO Clients may also benefit from querying for costs and 537 rankings based on Endpoints. The Endpoint Cost Service allows an 538 ALTO Server to return either numerical costs or ordinal costs 539 (rankings) directly amongst Endpoints. 541 5. Network Map 543 An ALTO Network Map defines a grouping of network endpoints. In this 544 document, we use Network Map to refer to the syntax and semantics of 545 how an ALTO Server distributes the grouping. This document does not 546 discuss the internal representation of this data structure within the 547 ALTO Server. 549 The definition of Network Map is based on the observation that in 550 reality, many endpoints are close by to one another in terms of 551 network connectivity. By treating a group of close-by endpoints 552 together as a single entity, an ALTO Server indicates aggregation of 553 these endpoints due to their proximity. This aggregation can also 554 lead to greater scalability without losing critical information when 555 conveying other network information (e.g., when defining Cost Map). 557 5.1. Provider-defined Identifier (PID) 559 One issue is that proximity varies depending on the granularity of 560 the ALTO information configured by the provider. In one deployment, 561 endpoints on the same subnet may be considered close; while in 562 another deployment, endpoints connected to the same Point of Presence 563 (PoP) may be considered close. 565 ALTO introduces provider-defined Network Location identifiers called 566 Provider-defined Identifiers (PIDs) to provide an indirect and 567 network-agnostic way to specify an aggregation of network endpoints 568 that may be treated similarly, based on network topology, type, or 569 other properties. Specifically, a PID is a string of type PIDName 570 (see Section 10.1) and its associated set of Endpoint Addresses. As 571 we discussed above, there can be many different ways of grouping the 572 endpoints and assigning PIDs. For example, a PID may denote a 573 subnet, a set of subnets, a metropolitan area, a PoP, an autonomous 574 system, or a set of autonomous systems. Interpreting the PIDs 575 defined in a Network Map using the "single-node" abstraction, one can 576 consider that each PID represents an abstract port (PoP) that 577 connects a set of endpoints. 579 A key use case of PIDs is to specify network preferences (costs) 580 between PIDs instead of individual endpoints. This allows cost 581 information to be more compactly represented and updated at a faster 582 time scale than the network aggregations themselves. For example, an 583 ISP may prefer that endpoints associated with the same PoP (Point-of- 584 Presence) in a P2P application communicate locally instead of 585 communicating with endpoints in other PoPs. The ISP may aggregate 586 endhosts within a PoP into a single PID in the Network Map. The cost 587 may be encoded to indicate that Network Locations within the same PID 588 are preferred; for example, cost(PID_i, PID_i) == c and cost(PID_i, 589 PID_j) > c for i != j. Section 6 provides further details on using 590 PIDs to represent costs in an ALTO Cost Map. 592 5.2. Endpoint Addresses 594 The endpoints aggregated into a PID are denoted by endpoint 595 addresses. There are many types of addresses, such as IP addresses, 596 MAC addresses, or overlay IDs. This document specifies in Section 597 10.4 how to specify IPv4/IPv6 addresses or prefixes. Extension 598 documents may define further address types; Section 14.4 of this 599 document provides an IANA registry for endpoint address types. 601 5.3. Example Network Map 603 We use the Network Map shown in Figure 3 in most examples of this 604 document. 606 .------------------------------------------------------------. 607 | An ALTO Network Map | 608 | | 609 | .-----------------------------------. .----------------. | 610 | | NetLoc: PID-1 | | NetLoc: PID-3 | | 611 | | .------------------------------. | | | | 612 | | | 192.0.2.0/24 | | | .-----------. | | 613 | | | .--------------------------. | | | | 0.0.0.0/0 | | | 614 | | | | Endpoint: 192.0.2.34 | | | | `-----------` | | 615 | | | `--------------------------` | | | | | 616 | | `------------------------------` | | | | 617 | | .------------------------------. | | | | 618 | | | 198.51.100.0/25 | | | | | 619 | | | .--------------------------. | | | | | 620 | | | | Endpoint: 198.51.100.100 | | | | | | 621 | | | `--------------------------` | | | | | 622 | | `------------------------------` | | | | 623 | `-----------------------------------` | | | 624 | | | | 625 | .-----------------------------------. | | | 626 | | NetLoc: PID-2 | | | | 627 | | .------------------------------. | | | | 628 | | | 198.51.100.128/25 | | | | | 629 | | `------------------------------` | | | | 630 | `-----------------------------------` `----------------` | 631 `------------------------------------------------------------` 633 Figure 3: Example Network Map. 635 6. Cost Map 637 An ALTO Server indicates preferences amongst network locations in the 638 form of Path Costs. Path Costs are generic costs and can be 639 internally computed by a network provider according to its own 640 policy. 642 For a given Network Map, an ALTO Cost Map defines Path Costs pairwise 643 amongst sets of source and destination Network Locations defined by 644 PIDs defined in the Network Map. Each Path Cost is the end-to-end 645 cost when a unit of traffic goes from the source to the destination. 647 Since cost is directional from the source to the destination, an 648 application, when using ALTO Information, may independently determine 649 how the Resource Consumer and Resource Provider are designated as the 650 source or destination in an ALTO query, and hence how to utilize the 651 Path Cost provided by ALTO Information. For example, if the cost is 652 expected to be correlated with throughput, a typical application 653 concerned with bulk data retrieval may use the Resource Provider as 654 the source, and Resource Consumer as the destination. 656 One advantage of separating ALTO information into a Network Map and a 657 Cost Map is that the two components can be updated at different time 658 scales. For example, Network Maps may be stable for a longer time 659 while Cost Maps may be updated to reflect dynamic network conditions. 661 As used in this document, a Cost Map refers to the syntax and 662 semantics of the information distributed by the ALTO Server. This 663 document does not discuss the internal representation of this data 664 structure within the ALTO Server. 666 6.1. Cost Types 668 Path Costs have attributes: 670 o Metric: identifies what the costs represent; 672 o Mode: identifies how the costs should be interpreted. 674 The combination of a metric and a mode defines a Cost Type. Certain 675 queries for Cost Maps allow the ALTO Client to indicate the desired 676 Cost Type. For a given ALTO Server, the combination of Cost Type and 677 Network Map defines a key. In other words, an ALTO Server MUST NOT 678 define two Cost Maps with the same Cost Type, Network Map pair. 680 6.1.1. Cost Metric 682 The Metric attribute indicates what the cost represents. For 683 example, an ALTO Server could define costs representing air-miles, 684 hop-counts, or generic routing costs. 686 Cost metrics are indicated in protocol messages as strings. 688 6.1.1.1. Cost Metric: routingcost 690 An ALTO Server MUST offer the 'routingcost' Cost Metric. 692 This Cost Metric conveys a generic measure for the cost of routing 693 traffic from a source to a destination. A lower value indicates a 694 higher preference for traffic to be sent from a source to a 695 destination. 697 Note that an ISP may internally compute routing cost using any method 698 that it chooses (e.g., air-miles or hop-count) as long as it conforms 699 to these semantics. 701 6.1.2. Cost Mode 703 The Mode attribute indicates how costs should be interpreted. 704 Specifically, the Mode attribute indicates whether returned costs 705 should be interpreted as numerical values or ordinal rankings. 707 It is important to communicate such information to ALTO Clients, as 708 certain operations may not be valid on certain costs returned by an 709 ALTO Server. For example, it is possible for an ALTO Server to 710 return a set of IP addresses with costs indicating a ranking of the 711 IP addresses. Arithmetic operations that would make sense for 712 numerical values, do not make sense for ordinal rankings. ALTO 713 Clients may handle such costs differently. 715 Cost Modes are indicated in protocol messages as strings. 717 An ALTO Server MUST support at least one of 'numerical' and 'ordinal' 718 modes. An ALTO Client SHOULD be cognizant of operations when a 719 desired Cost Mode is not supported. For example, an ALTO Client 720 desiring numerical costs may adjust its behaviors if only the ordinal 721 Cost Mode is available. Alternatively, an ALTO Client desiring 722 ordinal costs may construct ordinal costs from retrieved numerical 723 values, if only the numerical Cost Mode is available. 725 6.1.2.1. Cost Mode: numerical 727 This Cost Mode is indicated by the string 'numerical'. This mode 728 indicates that it is safe to perform numerical operations (e.g. 729 normalization or computing ratios for weighted load-balancing) on the 730 returned costs. The values are floating-point numbers. 732 6.1.2.2. Cost Mode: ordinal 734 This Cost Mode is indicated by the string 'ordinal'. This mode 735 indicates that the costs values in a Cost Map are a ranking (relative 736 to all other values in a Cost Map), with a lower value indicating a 737 higher preference. The values are non-negative integers. Ordinal 738 cost values in a Cost Map need not be unique nor contiguous. In 739 particular, it is possible that two entries in a map have an 740 identical rank (ordinal cost value). This document does not specify 741 any behavior by an ALTO Client in this case; an ALTO Client may 742 decide to break ties by random selection, other application 743 knowledge, or some other means. 745 It is important to note that the values in the Cost Map provided with 746 the ordinal Cost Mode are not necessarily the actual costs known to 747 the ALTO Server. 749 6.2. Cost Map Structure 751 A request for a Cost Map either explicitly or implicitly includes a 752 list of Source Network Locations and a list of Destination Network 753 Locations. (Recall that a Network Location can be an endpoint 754 address or a PID.) 756 Specifically, assume that a request specifies a list of multiple 757 Source Network Locations, say [Src_1, Src_2, ..., Src_m], and a list 758 of multiple Destination Network Locations, say [Dst_1, Dst_2, ..., 759 Dst_n]. 761 The ALTO Server will return the Path Cost for each of the m*n 762 communicating pairs (i.e., Src_1 -> Dst_1, ..., Src_1 -> Dst_n, ..., 763 Src_m -> Dst_1, ..., Src_m -> Dst_n). If the ALTO Server does not 764 define a Path Cost for a particular pair, it may be omitted. We 765 refer to this structure as a Cost Map. 767 If the Cost Mode is 'ordinal', the Path Cost of each communicating 768 pair is relative to the m*n entries. 770 6.3. Network Map and Cost Map Dependency 772 A Cost Map gives Path Costs between the PIDs defined in a Network 773 Map. An ALTO Server may modify a Network Map at any time, say by 774 adding or deleting PIDs, or even redefining them. Hence to 775 effectively use an instance of a Cost Map, an ALTO Client must know 776 which version of the Network Map defined the PIDs in that Cost Map. 777 Version Tags allow ALTO Clients to correlate Cost Map instances with 778 the corresponding versions of the Network Map. 780 A Version Tag is a tuple of (1) an ID for the resource (e.g., a 781 Network Map), and (2) a tag (an opaque string) associated with the 782 version of that resource. A Network Map distributed by an ALTO 783 Server includes its Version Tag. A Cost Map referring to PIDs also 784 includes Version Tag for the Network Map on which it is based. 786 Two Network Maps are the same if they have the same Version Tag. 787 Whenever the content of the Network Map maintained by an ALTO Server 788 changes, tag MUST also be changed. Possibilities of setting the tag 789 component include the last-modified timestamp for the Network Map, or 790 a hash of its contents, where the collision probability is considered 791 zero in practical deployment scenarios. 793 6.4. Cost Map Update 795 An ALTO Server can update a Cost Map at any time. Hence, the same 796 Cost Map retrieved from the same ALTO Server but from different 797 requests can be inconsistent. 799 7. Endpoint Properties 801 An endpoint property defines a network-aware property of an endpoint. 803 7.1. Endpoint Property Type 805 For each endpoint and an endpoint property type, there can be a value 806 for the property. The type of an Endpoint property is indicated in 807 protocol messages as a string. The value depends on the specific 808 property. For example, for a property such as whether an endpoint is 809 metered, the value is a true or false value. 811 7.1.1. Endpoint Property Type: pid 813 An ALTO Server MUST define the 'pid' Endpoint Property Type for each 814 Network Map that it provides. Specifically, each Network Map defines 815 multiple PIDs. For an 'ipv4'/'ipv6' Network Map, given an endpoint's 816 IP address, the ALTO Server uses the algorithm specified in 817 Section 11.2.2 to lookup the PID of the endpoint. This PID is the 818 'pid' property of the endpoint for the Network Map. See 819 Section 11.4.1.7 for an example. 821 8. Protocol Specification: General Processing 823 This section first specifies general client and server processing. 824 The details of specific services will be covered in the following 825 sections. 827 8.1. Overall Design 829 The ALTO Protocol uses a REST-ful design. There are two primary 830 components to this design: 832 o Information Resources: An ALTO Server provides a set of network 833 information resources. Each information resource has a media type 834 [RFC2046]. An ALTO Client may construct an HTTP request for a 835 particular information resource (including any parameters, if 836 necessary), and the ALTO Server returns the requested information 837 resource in an HTTP response. 839 o Information Resource Directory (IRD): An ALTO Server provides to 840 ALTO Clients a list of available information resources and the URI 841 at which each is provided. This document refers to this list as 842 the Information Resource Directory. ALTO Clients consult the 843 directory to determine the services provided by an ALTO Server. 845 8.2. Notation 847 This document uses 'JSONString', 'JSONNumber', 'JSONBool' to indicate 848 the JSON string, number, and boolean types, respectively. The type 849 'JSONValue' indicates a JSON value, as specified in Section 2.1 of 850 [RFC4627]. 852 We use an adaptation of the C-style struct notation to define the 853 fields (names/values) of JSON objects. An optional field is enclosed 854 by [ ], and an array is indicated by two numbers in angle brackets, 855 , where m indicates the minimal number of values, and n is the 856 maximum. When we write * for n, it means no upper bound. In the 857 definitions, the JSON names of the fields are case sensitive. 859 For example, the definition below defines a new type Type4, with 860 three field members (or fields for short) named "name1", "name2", and 861 "name3" respectively. The field named "name3" is optional, and the 862 field named "name2" is an array of at least one value. 863 object { Type1 name1; Type2 name2<1..*>; [Type3 name3;] 864 } Type4; 866 We also define dictionary maps (or maps for short) from strings to 867 JSON values. For example, the definition below defines a Type3 868 object as a map. Type1 must be defined as string, and Type2 can be 869 defined as any type. 870 object-map { Type1 -> Type2; } Type3; 872 We use subtyping to denote that one type is derived from another 873 type. The example below denotes that TypeDerived is derived from 874 TypeBase. TypeDerived includes all fields defined in TypeBase. If 875 TypeBase does not have a field named "name1", TypeDerived will have a 876 new field named "name1". If TypeBase already has a field named 877 "name1" but with a different type, TypeDerived will have a field 878 named "name1" with the type defined in TypeDerived (i.e., Type1 in 879 the example). 880 object { Type1 name1; } TypeDerived : TypeBase; 882 Note that despite the notation, no standard, machine-readable 883 interface definition or schema is provided in this document. 884 Extension documents may document these as necessary. 886 8.3. Basic Operations 888 The ALTO Protocol employs standard HTTP [RFC2616]. It is used for 889 discovering available Information Resources at an ALTO Server and 890 retrieving Information Resources. ALTO Clients and ALTO Servers use 891 HTTP requests and responses carrying ALTO-specific content with 892 encoding as specified in this document, and MUST be compliant with 893 [RFC2616]. 895 Instead of specifying the generic application/json Media Type for all 896 ALTO request parameters (if any) and responses, ALTO Clients and 897 Servers use multiple, specific JSON-based Media Types (e.g., 898 application/alto-networkmap+json, application/alto-costmap+json) to 899 indicate content types; see Table 2 for a list of Media Types defined 900 in this document. This allows easy extensibility while maintaining 901 clear semantics and versioning. For example, a new version of a 902 component of the ALTO Protocol (e.g., a new version of the Network 903 Map) can be defined by simply introducing a new Media Type (e.g., 904 application/alto-networkmap-v2+json). 906 8.3.1. Client Discovering Information Resources 908 To discover available Information Resources, an ALTO Client requests 909 Information Resource Directories. Informally, an Information 910 Resource Directory enumerates URIs at which an ALTO Server offers 911 Information Resources. 913 Specifically, using the ALTO Discovery protocol, an ALTO Client 914 obtains a URI through which it can request an Information Resource 915 Directory (IRD). We refer to this IRD as the Root IRD of the ALTO 916 Client. Each entry in an IRD indicates a URI at which an ALTO Server 917 accepts requests, and returns either an Information Resource or an 918 Information Resource Directory that references additional Information 919 Resources. Beginning with its Root IRD and following links to IRDs 920 recursively, an ALTO Client can discover all Information Resources 921 available to it. We refer to this set of Information Resources as 922 the Information Resource Closure of the ALTO Client. By inspecting 923 its Information Resource Closure, an ALTO Client can determine 924 whether an ALTO Server supports the desired Information Resource, and 925 if it is supported, the URI at which it is available. 927 See Section 9.2 for a detailed specification on IRDs. 929 8.3.2. Client Requesting Information Resources 931 Where possible, the ALTO Protocol uses the HTTP GET method to request 932 resources. However, some ALTO services provide Information Resources 933 that are the function of one or more input parameters. Input 934 parameters are encoded in the HTTP request's entity body, and the 935 ALTO Client MUST use the HTTP POST method to send the parameters. 937 When requesting an ALTO Information Resource that requires input 938 parameters specified in a HTTP POST request, an ALTO Client MUST set 939 the Content-Type HTTP header to the media type corresponding to the 940 format of the supplied input parameters. 942 8.3.3. Server Responding to IR Request 944 Upon receiving a request for an Information Resource that the ALTO 945 Server can provide, the ALTO Server normally returns the requested 946 Information Resource. In other cases, to be more informative 947 ([I-D.ietf-httpbis-p2-semantics]), the ALTO Server MAY provide the 948 ALTO Client with an Information Resource Directory indicating how to 949 reach the desired information resource, or return an ALTO error 950 object; see Section 8.5 for more details on ALTO error handling. 952 It is possible for an ALTO Server to leverage caching HTTP 953 intermediaries to respond to both GET and POST requests by including 954 explicit freshness information (see Section 14 of [RFC2616]). 955 Caching of POST requests is not widely implemented by HTTP 956 intermediaries, however an alternative approach is for an ALTO 957 Server, in response to POST requests, to return an HTTP 303 status 958 code ("See Other") indicating to the ALTO Client that the resulting 959 Information Resource is available via a GET request to an alternate 960 URL. HTTP intermediaries that do not support caching of POST 961 requests could then cache the response to the GET request from the 962 ALTO Client following the alternate URL in the 303 response if the 963 response to the subsequent GET request contains explicit freshness 964 information. 966 The ALTO Server MUST indicate the type of its response using a media 967 type (i.e., the Content-Type HTTP header of the response). 969 8.3.4. Client Handling Server Response 971 8.3.4.1. Using Information Resources 973 This specification does not indicate any required actions taken by 974 ALTO Clients upon successfully receiving an Information Resource from 975 an ALTO Server. Although ALTO Clients are suggested to interpret the 976 received ALTO Information and adapt application behavior, ALTO 977 Clients are not required to do so. 979 8.3.4.2. Handling Server Response and IRD 981 After receiving an Information Resource Directory, the Client can 982 consult it to determine if any of the offered URIs contain the 983 desired Information Resource. However, an ALTO Client MUST NOT 984 assume that the media type returned by the ALTO Server for a request 985 to a URI is the media type advertised in the IRD or specified in its 986 request (i.e., the client must still check the Content-Type header). 988 The expectation is that the media type returned should normally be 989 the media type advertised and requested, but in some cases it may 990 legitimately not be so. 992 In particular, it is possible for an ALTO Client to receive an 993 Information Resource Directory from an ALTO Server as a response to 994 its request for a specific Information Resource. In this case, the 995 ALTO Client may ignore the response or still parse the response. To 996 indicate that an ALTO Client will always check if a response is an 997 Information Resource Directory, the ALTO Client can indicate in the 998 "Accept" header of a HTTP request that it can accept Information 999 Resource Directory; see Section 9.2 for the media type. 1001 8.3.4.3. Handling Error Conditions 1003 If an ALTO Client does not successfully receive a desired Information 1004 Resource from a particular ALTO Server (i.e., server response 1005 indicates error or there is no response), the Client can either 1006 choose another server (if one is available) or fall back to a default 1007 behavior (e.g., perform peer selection without the use of ALTO 1008 information, when used in a peer-to-peer system). 1010 8.3.5. Authentication and Encryption 1012 ALTO server implementations as well as ALTO client implementations 1013 MUST support the "https" URI scheme [RFC2818] and TLS [RFC5246]. See 1014 Section 15.1.2 for security considerations and Section 16 for 1015 manageability considerations regarding the usage of HTTPS/TLS. 1017 For deployment scenarios where client authentication is desired, HTTP 1018 Digest Authentication MUST be supported. TLS Client Authentication 1019 is the preferred mechanism if it is available. 1021 8.3.6. Information Refreshing 1023 An ALTO Client MAY determine the frequency at which ALTO Information 1024 is refreshed based on information made available via HTTP. 1026 8.3.7. Parsing of Unknown Fields 1028 This document only details object fields used by this specification. 1029 Extensions may include additional fields within JSON objects defined 1030 in this document. ALTO implementations MUST ignore unknown fields 1031 when processing ALTO messages. 1033 8.4. Server Response Encoding 1035 Though each type of ALTO Server response (i.e., an Information 1036 Resource Directory, an individual Information Resource, or an error 1037 message) has its distinct syntax and hence its unique Media Type, 1038 they are designed to have a similar structure: a meta field providing 1039 meta definitions, and another field containing the data, if needed. 1041 Specifically, we define the base type of each ALTO Server response as 1042 ResponseEntityBase: 1043 object { ResponseMeta meta; } ResponseEntityBase; 1045 with field: 1047 meta meta information pertaining to the response. 1049 8.4.1. Meta Information 1051 Meta information is encoded as a map object for flexibility. 1052 Specifically, ResponseMeta is defined as: 1053 object-map { JSONString -> JSONValue } ResponseMeta; 1055 8.4.2. Data Information 1057 The data component of the response encodes the response-specific 1058 data. In this document, we derive five types from ResponseEntityBase 1059 to add different types of data component: InfoResourceDirectory 1060 (Section 9.2.2), InfoResourceNetworkMap (Section 11.2.1.6), 1061 InfoResourceCostMap (Section 11.2.3.6), 1062 InfoResourceEndpointProperties (Section 11.4.1.6), and 1063 InfoResourceEndpointCostMap (Section 11.5.1.6). 1065 8.5. Protocol Errors 1067 If there is an error processing a request, an ALTO Server SHOULD 1068 return additional ALTO-layer information, if it is available, in the 1069 form of an ALTO Error Resource encoded in the HTTP response' entity 1070 body. If no ALTO-layer information is available, an ALTO Server may 1071 omit an ALTO Error resource from the response. 1073 With or without additional ALTO-layer error information, an ALTO 1074 Server MUST set an appropriate HTTP status code. It is important to 1075 note that the HTTP Status Code and ALTO Error Resource have distinct 1076 roles. An ALTO Error Resource provides detailed information about 1077 why a particular request for an ALTO Resource was not successful. 1078 The HTTP status code indicates to HTTP processing elements (e.g., 1079 intermediaries and clients) how the response should be treated. 1081 8.5.1. Media Type 1083 The media type for an ALTO Error Response is "application/ 1084 alto-error+json". 1086 8.5.2. Response Format and Error Codes 1088 An ALTO Error Response MUST include the "code" key in the "meta" 1089 field of the response. The value of "code" MUST be an ALTO Error 1090 Code, encoded in string, defined in Table 1. Note that the ALTO 1091 Error Codes defined in Table 1 are limited to support the error 1092 conditions needed for purposes of this document. Additional status 1093 codes may be defined in companion or extension documents. 1095 +-----------------------+-------------------------------------------+ 1096 | ALTO Error Code | Description | 1097 +-----------------------+-------------------------------------------+ 1098 | E_SYNTAX | Parsing error in request (including | 1099 | | identifiers) | 1100 | E_MISSING_FIELD | A required JSON field is missing | 1101 | E_INVALID_FIELD_TYPE | The type of the value of a JSON field is | 1102 | | invalid | 1103 | E_INVALID_FIELD_VALUE | The value of a JSON field is invalid | 1104 +-----------------------+-------------------------------------------+ 1106 Table 1: Defined ALTO Error Codes. 1108 After an ALTO Server receives a request, it needs to verify the 1109 syntactic and semantic validity of the request. The following 1110 paragraphs in this section are intended to illustrate the usage of 1111 the error codes defined above during the verification. An individual 1112 implementation may define its message processing in a different 1113 order. 1115 In the first step after an ALTO Server receives a request, it checks 1116 the syntax of the request body (i.e., whether the JSON structure can 1117 be parsed), and indicates a syntax error using the error code 1118 E_SYNTAX. For an E_SYNTAX error, the ALTO Server MAY provide an 1119 optional key "syntax-error" in the "meta" field of the error 1120 response. The objective of providing "syntax-error" is to provide 1121 technical debugging information to developers, not end users. Hence, 1122 it should be a human-readable, free-form text describing the syntax 1123 error. If possible, the text should include position information 1124 such as line number and offset within line about the syntax error. 1125 If nothing else, "syntax-error" could have just the position. If a 1126 syntax error occurs in a production environment, the ALTO Client 1127 could inform the end user that there was an error communicating with 1128 the ALTO Server, and suggest that the user submit the error 1129 information, which includes "syntax-error", to the developers. 1131 A request without syntax errors may still be invalid. An error case 1132 is that the request misses a required field. The server indicates 1133 such an error using the error code E_MISSING_FIELD. This document 1134 defines required fields for Network Map Filtering (Section 11.3.1.3), 1135 Cost Map Filtering (Section 11.3.2.3), Endpoint Properties 1136 (Section 11.4.1.3), and Endpoint Cost (Section 11.5.1.3). For an 1137 E_MISSING_FIELD error, the server may include an optional "field" key 1138 in the "meta" field of the error response, to indicate the missing 1139 field. "field" should be a JSONString indicating the full path of the 1140 missing field. For example, assume that a Filtered CostMap request 1141 (see Section 11.3.2.3) misses the "cost-metric" field in the request. 1142 The error response from the ALTO Server may specify the "field" key 1143 as "cost-type/cost-mode". 1145 A request with the correct fields might use a wrong type for the 1146 value of a field. For example, the value of a field could be a 1147 JSONString when a JSONNumber is expected. The server indicates such 1148 an error using the error code E_INVALID_FIELD_TYPE. The server may 1149 include an optional "field" key in the "meta" field of the response, 1150 to indicate the field that contains the wrong type. 1152 A request with the correct fields and types of values for the fields 1153 may specify a wrong value for a field. For example, a cost map 1154 filtering request may specify a wrong value of CostMode in the "cost- 1155 type" field (Section 11.3.2.3). The server indicates such an error 1156 with the error code E_INVALID_FIELD_VALUE. For an 1157 E_INVALID_FIELD_VALUE error, the server may include an optional 1158 "field" key in the "meta" field of the response, to indicate the 1159 field that contains the wrong value. The server may also include an 1160 optional "value" key in the "meta" field of the response to indicate 1161 the wrong value that triggered the error. 1163 A request with the correct fields and types of values for the fields 1164 may specify a wrong value for a field. For example, a filtered cost 1165 map request may specify a wrong value for CostMode in the "cost-type" 1166 field (Section 11.3.2.3). The server indicates such an error with 1167 the error code E_INVALID_FIELD_VALUE. For an E_INVALID_FIELD_VALUE 1168 error, the server may include an optional "field" key in the "meta" 1169 field of the response, to indicate the field that contains the wrong 1170 value. The server may also include an optional "value" key in the 1171 "meta" field of the response to indicate the wrong value that 1172 triggered the error. If the "value" key is specified, the "field" 1173 key MUST be specified. The "value" key MUST have a JSONString value. 1174 If the invalid value is not a string, the ALTO Server MUST convert it 1175 to a string. Below are the rules to specify the "value" key: 1177 o If the invalid value is a string, "value" is that string; 1179 o If the invalid value is a number, "value" must be the invalid 1180 number as a string; 1182 o If the invalid value is a subfield, the server must set the 1183 "field" key to the full path of the field name and "value" to the 1184 invalid subfield value, converting it to a string if needed. For 1185 example, if the "cost-mode" subfield of the "cost-type" field is 1186 an invalid mode "foo", the server should set "value" to "foo", and 1187 "field" to "cost-mode/cost-type"; 1189 o If an element of a JSON array has an invalid value, the server 1190 sets "value" to the value of the invalid element, as a string, and 1191 "field" to the name of the array. An array element of the wrong 1192 type (e.g., a number in what is supposed to be an array of 1193 strings) is an invalid value error, not an invalid type error. 1194 The server sets "value" to the string version of the incorrect 1195 element, and "field" to the name of the array. 1197 If multiple errors are present in a single request (e.g., a request 1198 uses a JSONString when a JSONNumber is expected and a required field 1199 is missing), then the ALTO Server MUST return exactly one of the 1200 detected errors. However, the reported error is implementation 1201 defined, since specifying a particular order for message processing 1202 encroaches needlessly on implementation techniques. 1204 8.5.3. Overload Conditions and Server Unavailability 1206 If an ALTO Server detects that it cannot handle a request from an 1207 ALTO Client due to excessive load, technical problems, or system 1208 maintenance, it SHOULD do one of the following: 1210 o Return an HTTP 503 ("Service Unavailable") status code to the ALTO 1211 Client. As indicated by [RFC2616], the Retry-After HTTP header 1212 may be used to indicate when the ALTO Client should retry the 1213 request. 1215 o Return an HTTP 307 ("Temporary Redirect") status code indicating 1216 an alternate ALTO Server that may be able to satisfy the request. 1217 Using Temporary Redirect may generate infinite redirection loops. 1218 Although [RFC2616] Section 10.3 requires that an HTTP client 1219 SHOULD detect infinite redirection loops, it is more desirable 1220 that multiple ALTO Servers are configured to not form redirection 1221 loops. 1223 The ALTO Server MAY also terminate the connection with the ALTO 1224 Client. 1226 The particular policy applied by an ALTO Server to determine that it 1227 cannot service a request is outside of the scope of this document. 1229 9. Protocol Specification: Information Resource Directory 1231 As we discussed, an ALTO Client starts by retrieving an Information 1232 Resource Directory, which specifies the attributes of individual 1233 Information Resources that an ALTO Server provides. 1235 9.1. Information Resource Attributes 1237 In this document, each Information Resource has five attributes 1238 associated with it, including its assigned ID, its response format, 1239 its capabilities, its accepted input parameters, and other resources 1240 that it may depend on. The function of an Information Resource 1241 Directory is to publishes these attributes. 1243 9.1.1. Resource ID 1245 Each Information Resource that an ALTO Client can request MUST be 1246 assigned an ID that is unique amongst all Information Resources in 1247 the Information Resource Closure of the client. The ID SHOULD remain 1248 stable even when the data provided by that resource changes. For 1249 example, even though the number of PIDs in a Network Map may be 1250 adjusted, its Resource ID should remain the same. Similarly, if the 1251 entries in a Cost Map are updated, its Resource ID should remain the 1252 same. IDs SHOULD NOT be re-used for different resources over time. 1254 9.1.2. Media Type 1256 ALTO uses Media Type [RFC2046] to uniquely indicate the data format 1257 used to encode the content to be transmitted between an ALTO Server 1258 and an ALTO Client in the HTTP entity body. 1260 9.1.3. Capabilities 1262 The Capabilities attribute of an Information Resource indicates 1263 specific capabilities that the server can provide. For example, if 1264 an ALTO Server allows an ALTO Client to specify cost constraints when 1265 the Client requests a Cost Map Information Resource, then the Server 1266 advertises the cost-constraints capability of the Cost Map 1267 Information Resource. 1269 9.1.4. Accepts Input Parameters 1271 An ALTO Server may allow an ALTO Client to supply input parameters 1272 when requesting certain Information Resources. The associated 1273 accepts attribute of an Information Resource is a Media Type, which 1274 indicates how the Client specifies the input parameters as contained 1275 in the entity body of the HTTP POST request. 1277 9.1.5. Dependent Resources 1279 The information provided in an Information Resource may use 1280 information provided in some other resources (e.g., a Cost Map uses 1281 the PIDs defined in a Network Map). The uses attribute conveys such 1282 information. 1284 9.2. Information Resource Directory (IRD) 1286 An ALTO Server uses Information Resource Directory to publish 1287 available Information Resources and their aforementioned attributes. 1288 Since resource selection happens after consumption of the Information 1289 Resource Directory, the format of the Information Resource Directory 1290 is designed to be simple with the intention of future ALTO Protocol 1291 versions maintaining backwards compatibility. Future extensions or 1292 versions of the ALTO Protocol SHOULD be accomplished by extending 1293 existing media types or adding new media types, but retaining the 1294 same format for the Information Resource Directory. 1296 An ALTO Server MUST make an Information Resource Directory available 1297 via the HTTP GET method to a URI discoverable by an ALTO Client. 1298 Discovery of this URI is out of scope of this document, but could be 1299 accomplished by manual configuration or by returning the URI of an 1300 Information Resource Directory from the ALTO Discovery Protocol 1301 [I-D.ietf-alto-server-discovery]. For recommendations on how the URI 1302 may look like, see [I-D.ietf-alto-server-discovery]. 1304 9.2.1. Media Type 1306 The media type to indicate an information directory is "application/ 1307 alto-directory+json". 1309 9.2.2. Encoding 1311 An Information Resource Directory response may include in "meta" the 1312 "cost-types" key, whose value is of type IRDMetaCostTypes defined 1313 below, where CostType is defined in Section 10.7: 1315 object-map { 1316 JSONString -> CostType; 1317 } IRDMetaCostTypes; 1318 The function of "cost-types" is to assign names to a set of CostTypes 1319 that can be used in one or more "resources" entries in the IRD to 1320 simplify specification. The names defined in "cost-types" in an IRD 1321 are local to the IRD. 1323 For a Root IRD, "meta" MUST include the "default-alto-network-map" 1324 key, which specifies the Resource ID of a Network Map. When there are 1325 multiple Network Maps defined in an IRD (e.g., with different levels 1326 of granularity), the "default-alto-network-map" key provides a 1327 guideline to simple clients that use only one Network Map. 1329 The data component of an Information Resource Directory response is 1330 named "resources", which is a JSON object of type IRDResourceEntries: 1332 object { 1333 IRDResourceEntries resources; 1334 } InfoResourceDirectory : ResponseEntityBase; 1336 object-map { 1337 ResourceID -> IRDResourceEntry; 1338 } IRDResourceEntries; 1340 object { 1341 JSONString uri; 1342 JSONString media-type; 1343 [JSONString accepts;] 1344 [Capabilities capabilities;] 1345 [ResourceID uses<0..*>;] 1346 } IRDResourceEntry; 1348 object { 1349 ... 1350 } Capabilities; 1352 An IRDResourceEntries object is a dictionary map keyed by 1353 ResourceIDs, where ResourceID is defined in Section 10.2. The value 1354 of each entry specifies: 1356 uri A URI at which the ALTO Server provides one or more Information 1357 Resources, or an Information Resource Directory indicating 1358 additional Information Resources. URIs can be relative to the URI 1359 of the IRD and MUST be resolved according to Section 5 of 1360 [RFC3986]. 1362 media-type The media type of Information Resource (see 1363 Section 9.1.2) available via GET or POST requests to the 1364 corresponding URI or "application/alto-directory+json", which 1365 indicates that the response for a request to the URI will be an 1366 Information Resource Directory for URIs discoverable via the URI. 1368 accepts The media type of input parameters (see Section 9.1.4) 1369 accepted by POST requests to the corresponding URI. If this field 1370 is not present, it MUST be assumed to be empty. 1372 capabilities A JSON Object enumerating capabilities of an ALTO 1373 Server in providing the Information Resource at the corresponding 1374 URI and Information Resources discoverable via the URI. If this 1375 field is not present, it MUST be assumed to be an empty object. 1376 If a capability for one of the offered Information Resources is 1377 not explicitly listed here, an ALTO Client may either issue an 1378 OPTIONS HTTP request to the corresponding URI to determine if the 1379 capability is supported, or assume its default value documented in 1380 this specification or an extension document describing the 1381 capability. 1383 uses A list of Resource IDs, defined in the same IRD, that define 1384 the resources on which this resource directly depends. An ALTO 1385 Server SHOULD include in this list any resources that the ALTO 1386 Client would need to retrieve in order to interpret the contents 1387 of this resource. For example, a Cost Map resource should include 1388 in this list the Network Map on which it depends. ALTO Clients 1389 may wish to consult this list in order to pre-fetch necessary 1390 resources. 1392 If an entry has an empty list for "accepts", then the corresponding 1393 URI MUST support GET requests. If an entry has a non-empty 1394 "accepts", then the corresponding URI MUST support POST requests. If 1395 an ALTO Server wishes to support both GET and POST on a single URI, 1396 it MUST specify two entries in the Information Resource Directory. 1398 9.2.3. Example 1400 The following is an example Information Resource Directory returned 1401 by an ALTO Server to an ALTO Client. Assume it is the Root IRD of 1402 the Client. 1404 GET /directory HTTP/1.1 1405 Host: alto.example.com 1406 Accept: application/alto-directory+json,application/alto-error+json 1407 HTTP/1.1 200 OK 1408 Content-Length: 2333 1409 Content-Type: application/alto-directory+json 1411 { 1412 "meta" : { 1413 "cost-types": { 1414 "num-routing": { 1415 "cost-mode" : "numerical", 1416 "cost-metric": "routingcost", 1417 "description": "My default" 1418 }, 1419 "num-hop": { 1420 "cost-mode" : "numerical", 1421 "cost-metric": "hopcount" 1422 }, 1423 "ord-routing": { 1424 "cost-mode" : "ordinal", 1425 "cost-metric": "routingcost" 1426 }, 1427 "ord-hop": { 1428 "cost-mode" : "ordinal", 1429 "cost-metric": "hopcount" 1430 } 1431 }, 1432 "default-alto-network-map" : "my-default-network-map" 1433 }, 1434 "resources" : { 1435 "my-default-network-map" : { 1436 "uri" : "http://alto.example.com/networkmap", 1437 "media-type" : "application/alto-networkmap+json" 1438 }, 1439 "numerical-routing-cost-map" : { 1440 "uri" : "http://alto.example.com/costmap/num/routingcost", 1441 "media-type" : "application/alto-costmap+json", 1442 "capabilities" : { 1443 "cost-type-names" : [ "num-routing" ] 1444 }, 1445 "uses": [ "my-default-network-map" ] 1446 }, 1447 "numerical-hopcount-cost-map" : { 1448 "uri" : "http://alto.example.com/costmap/num/hopcount", 1449 "media-type" : "application/alto-costmap+json", 1450 "capabilities" : { 1451 "cost-type-names" : [ "num-hop" ] 1452 }, 1453 "uses": [ "my-default-network-map" ] 1454 }, 1455 "custom-maps-resources" : { 1456 "uri" : "http://custom.alto.example.com/maps", 1457 "media-type" : "application/alto-directory+json" 1458 }, 1459 "endpoint-property" : { 1460 "uri" : "http://alto.example.com/endpointprop/lookup", 1461 "media-type" : "application/alto-endpointprop+json", 1462 "accepts" : "application/alto-endpointpropparams+json", 1463 "capabilities" : { 1464 "prop-types" : [ "my-default-network-map.pid", 1465 "priv:ietf-example-prop" ] 1466 }, 1467 }, 1468 "endpoint-cost" : { 1469 "uri" : "http://alto.example.com/endpointcost/lookup", 1470 "media-type" : "application/alto-endpointcost+json", 1471 "accepts" : "application/alto-endpointcostparams+json", 1472 "capabilities" : { 1473 "cost-constraints" : true, 1474 "cost-type-names" : [ "num-routing", "num-hop", 1475 "ord-routing", "ord-hop"] 1476 } 1477 } 1478 } 1479 } 1481 Specifically, the "cost-types" key of "meta" of the example IRD 1482 defines names for four cost types in this IRD. For example, "num- 1483 routing" in the example is the name that refers to a Cost Type with 1484 Cost Mode being "numerical" and Cost Metric being "routingcost". 1485 This name is used in the second entry of "resources", which defines a 1486 Cost Map. In particular, the "cost-type-names" of its "capabilities" 1487 specifies that this resource supports a Cost Type named as "num- 1488 routing". The ALTO Client looks up the name "num-routing" in "cost- 1489 types" of the IRD to obtain the Cost Type named as "num-routing". 1490 The last entry of "resources" uses all four names defined in "cost- 1491 types". 1493 Another key defined in "meta" of the example IRD is "default-alto- 1494 network-map", which has value "my-default-network-map", which is the 1495 Resource ID of a Network Map that will be defined in "resources". 1497 The "resources" field of the example IRD defines six Information 1498 Resources. For example, the second entry, which is assigned a 1499 Resource ID "numerical-routing-cost-map", provides a Cost Map, as 1500 indicated by the media-type "application/alto-costmap+json". The 1501 Cost Map is based on the Network Map defined with Resource ID "my- 1502 default-network-map". As another example, the last entry, which is 1503 assigned Resource ID "endpoint-cost", provides the Endpoint Cost 1504 Service, which is indicated by the media-type "application/ 1505 alto-endpointcost+json". An ALTO Client should use uri 1506 "http://alto.example.com/endpointcost/lookup" to access the service. 1507 The ALTO Client should format its request body to be the 1508 "application/alto-endpointcostparams+json" media type, as specified 1509 by the "accepts" attribute of the Information Resource. The "cost- 1510 type-names" field of the "capabilities" attribute of the Information 1511 Resource includes four defined cost types specified in the "cost- 1512 types" key of "meta" of the IRD. Hence, one can verify that the 1513 Endpoint Cost Information Resource supports both Cost Metrics 1514 'routingcost' and 'hopcount', each available for both 'numerical' and 1515 'ordinal'. When requesting the Information Resource, an ALTO Client 1516 can specify cost constraints, as indicated by the "cost-constraints" 1517 field of the "capabilities" attribute. 1519 9.2.4. Delegation using IRD 1521 ALTO Information Resource Directory provides flexibility to provide 1522 ALTO Service (e.g., delegation to another domain). Consider the 1523 preceding example. Assume that the ALTO Server running at 1524 alto.example.com wants to delegate some Information Resources to a 1525 separate subdomain: "custom.alto.example.com". In particular, assume 1526 that the maps available via this subdomain are filtered Network Maps, 1527 filtered Cost Maps, and some pre-generated maps for the "hopcount" 1528 and "routingcost" Cost Metrics in the "ordinal" Cost Mode. The 1529 fourth entry of "resources" in the preceding example IRD implements 1530 the delegation. The entry has a media-type of "application/ 1531 alto-directory+json", and an ALTO Client can discover the Information 1532 Resources available at "custom.alto.example.com" if its request to 1533 "http://custom.alto.example.com/maps" is successful: 1535 GET /maps HTTP/1.1 1536 Host: custom.alto.example.com 1537 Accept: application/alto-directory+json,application/alto-error+json 1539 HTTP/1.1 200 OK 1540 Content-Length: 1900 1541 Content-Type: application/alto-directory+json 1543 { 1544 "meta" : { 1545 "cost-types": { 1546 "num-routing": { 1547 "cost-mode" : "numerical", 1548 "cost-metric": "routingcost", 1549 "description": "My default" 1550 }, 1551 "num-hop": { 1552 "cost-mode" : "numerical", 1553 "cost-metric": "hopcount" 1554 }, 1555 "ord-routing": { 1556 "cost-mode" : "ordinal", 1557 "cost-metric": "routingcost" 1558 }, 1559 "ord-hop": { 1560 "cost-mode" : "ordinal", 1561 "cost-metric": "hopcount" 1562 } 1563 } 1564 }, 1565 "resources" : { 1566 "filtered-network-map" : { 1567 "uri" : "http://custom.alto.example.com/networkmap/filtered", 1568 "media-type" : "application/alto-networkmap+json", 1569 "accepts" : "application/alto-networkmapfilter+json", 1570 "uses": [ "my-default-network-map" ] 1571 }, 1572 "filtered-cost-map" : { 1573 "uri" : "http://custom.alto.example.com/costmap/filtered", 1574 "media-type" : "application/alto-costmap+json", 1575 "accepts" : "application/alto-costmapfilter+json", 1576 "capabilities" : { 1577 "cost-constraints" : true, 1578 "cost-type-names" : [ "num-routing", "num-hop", 1579 "ord-routing", "ord-hop" ] 1580 }, 1581 "uses": [ "my-default-network-map" ] 1582 }, 1583 "ordinal-routing-cost-map" : { 1584 "uri" : "http://custom.alto.example.com/ord/routingcost", 1585 "media-type" : "application/alto-costmap+json", 1586 "capabilities" : { 1587 "cost-type-names" : [ "ord-routing" ] 1588 }, 1589 "uses": [ "my-default-network-map" ] 1590 }, 1591 "ordinal-hopcount-cost-map" : { 1592 "uri" : "http://custom.alto.example.com/ord/hopcount", 1593 "media-type" : "application/alto-costmap+json", 1594 "capabilities" : { 1595 "cost-type-names" : [ "ord-hop" ], 1596 }, 1597 "uses": [ "my-default-network-map" ] 1598 } 1599 } 1600 } 1602 Note that the subdomain does not define Network Map, and uses the 1603 Network Map with Resource ID "my-default-network-map" defined in the 1604 Root IRD. 1606 9.2.5. Considerations of Using IRD 1608 9.2.5.1. ALTO Client 1610 This document specifies no requirements or constraints on ALTO 1611 Clients with regards to how they process an Information Resource 1612 Directory to identify the URI corresponding to a desired Information 1613 Resource. However, some advice is provided for implementors. 1615 It is possible that multiple entries in the directory match a desired 1616 Information Resource. For instance, in the example in Section 9.2.3, 1617 a full Cost Map with "numerical" Cost Mode and "routingcost" Cost 1618 Metric could be retrieved via a GET request to 1619 "http://alto.example.com/costmap/num/routingcost", or via a POST 1620 request to "http://custom.alto.example.com/costmap/filtered". 1622 In general, it is preferred for ALTO Clients to use GET requests 1623 where appropriate, since it is more likely for responses to be 1624 cachable. However, an ALTO Client may need to use POST, for example, 1625 to get ALTO costs or properties that are for a restricted set of PIDs 1626 or Endpoints, or to update cached information previously acquired via 1627 GET requests." 1629 9.2.5.2. ALTO Server 1631 This document indicates that an ALTO Server may or may not provide 1632 the Information Resources specified in the Map Filtering Service. If 1633 these resources are not provided, it is indicated to an ALTO Client 1634 by the absence of a Network Map or Cost Map with any media types 1635 listed under "accepts". 1637 10. Protocol Specification: Basic Data Types 1639 This section details the format of basic data types. 1641 10.1. PID Name 1643 A PID Name is encoded as a JSON string. The string MUST be no more 1644 than 64 characters, and MUST NOT contain characters other than 1645 alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and U+0061- 1646 U+007A), the hyphen ('-', U+002D), the colon (':', U+003A), the at 1647 ('@', code point U+0040), the low line ('_', U+005F), or the '.' 1648 separator (U+002E). The '.' separator is reserved for future use and 1649 MUST NOT be used unless specifically indicated in this document, or 1650 an extension document. 1652 The type 'PIDName' is used in this document to indicate a string of 1653 this format. 1655 10.2. Resource ID 1657 A Resource ID uniquely identifies an particular resource (e.g., a 1658 Network Map) within an ALTO Server (see Section 9.2). 1660 A Resource ID is encoded as a JSON string with the same format as 1661 that of PIDName. 1663 The type 'ResourceID' is used in this document to indicate a string 1664 of this format. 1666 10.3. Version Tag 1668 A Version Tag is defined as: 1670 object { 1671 ResourceID resource-id; 1672 JSONString tag; 1673 } VersionTag; 1675 The 'resource-id' attribute is the Resource ID of a resource (e.g., a 1676 Network Map) defined in the Information Resource Directory, and 'tag' 1677 is a case-sensitive string. The 'tag' string MUST be no more than 64 1678 characters, and MUST NOT contain any character below U+0021 or above 1679 U+007E. It is RECOMMENDED that the tag have a low collision 1680 probability with other tags. One suggested mechanism is to compute 1681 it using a hash of the data contents of the resource. 1683 Two values of the VersionTag are equal if and only if both the the 1684 'resource-id' attributes are byte-for-byte equal and the 'tag' 1685 attributes are byte-for-byte equal. 1687 10.4. Endpoints 1689 This section defines formats used to encode addresses for Endpoints. 1690 In a case that multiple textual representations encode the same 1691 Endpoint address or prefix (within the guidelines outlined in this 1692 document), the ALTO Protocol does not require ALTO Clients or ALTO 1693 Servers to use a particular textual representation, nor does it 1694 require that ALTO Servers reply to requests using the same textual 1695 representation used by requesting ALTO Clients. ALTO Clients must be 1696 cognizant of this. 1698 10.4.1. Typed Endpoint Addresses 1700 When an Endpoint Address is used, an ALTO implementation must be able 1701 to determine its type. For this purpose, the ALTO Protocol allows 1702 endpoint addresses to also explicitly indicate their types. We refer 1703 to such addresses as Typed Endpoint Addresses. 1705 Typed Endpoint Addresses are encoded as strings of the format 1706 'AddressType:EndpointAddr', with the ':' character as a separator. 1707 The type 'TypedEndpointAddr' is used to indicate a string of this 1708 format. 1710 10.4.2. Address Type 1712 The AddressType component of TypedEndPointAddr is defined as a string 1713 consisting of only alphanumeric characters (U+0030-U+0039, U+0041- 1714 U+005A, and U+0061-U+007A). The type 'AddressType' is used in this 1715 document to indicate a string of this format. 1717 This document defines two values for AddressType: 'ipv4' to refer to 1718 IPv4 addresses, and 'ipv6' to refer to IPv6 addresses. All 1719 AddressType identifiers appearing in an HTTP request or response with 1720 an 'application/alto-*' media type MUST be registered in the ALTO 1721 Address Type registry (see Section 14.4). 1723 10.4.3. Endpoint Address 1725 The EndpointAddr component of TypedEndPointAddr is also encoded as a 1726 string. The exact characters and format depend on AddressType. This 1727 document defines EndpointAddr when AddressType is 'ipv4' or 'ipv6'. 1729 10.4.3.1. IPv4 1731 IPv4 Endpoint Addresses are encoded as specified by the 'IPv4address' 1732 rule in Section 3.2.2 of [RFC3986]. 1734 10.4.3.2. IPv6 1736 IPv6 Endpoint Addresses are encoded as specified in Section 4 of 1737 [RFC5952]. 1739 10.4.4. Endpoint Prefixes 1741 For efficiency, it is useful to denote a set of Endpoint Addresses 1742 using a special notation (if one exists). This specification makes 1743 use of the prefix notations for both IPv4 and IPv6 for this purpose. 1745 Endpoint Prefixes are encoded as strings. The exact characters and 1746 format depend on the type of endpoint address. 1748 The type 'EndpointPrefix' is used in this document to indicate a 1749 string of this format. 1751 10.4.4.1. IPv4 1753 IPv4 Endpoint Prefixes are encoded as specified in Section 3.1 of 1754 [RFC4632]. 1756 10.4.4.2. IPv6 1758 IPv6 Endpoint Prefixes are encoded as specified in Section 7 of 1759 [RFC5952]. 1761 10.4.5. Endpoint Address Group 1763 The ALTO Protocol includes messages that specify potentially large 1764 sets of endpoint addresses. Endpoint Address Groups provide a more 1765 efficient way to encode such sets, even when the set contains 1766 endpoint addresses of different types. 1768 An Endpoint Address Group is defined as: 1770 object-map { 1771 AddressType -> EndpointPrefix<0..*>; 1772 } EndpointAddrGroup; 1774 In particular, an Endpoint Address Group is a JSON object 1775 representing a map, where each key is the string corresponding to an 1776 address type, and the corresponding value is an array listing 1777 prefixes of addresses of that type. 1779 The following is an example with both IPv4 and IPv6 endpoint 1780 addresses: 1782 { 1783 "ipv4": [ 1784 "192.0.2.0/24", 1785 "198.51.100.0/25" 1786 ], 1787 "ipv6": [ 1788 "2001:db8:0:1::/64", 1789 "2001:db8:0:2::/64" 1790 ] 1791 } 1793 10.5. Cost Mode 1795 A Cost Mode is encoded as a string. The string MUST either have the 1796 value 'numerical' or 'ordinal'. 1798 The type 'CostMode' is used in this document to indicate a string of 1799 this format. 1801 10.6. Cost Metric 1803 A Cost Metric is encoded as a string. The string MUST be no more 1804 than 32 characters, and MUST NOT contain characters other than 1805 alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and U+0061- 1806 U+007A), the hyphen ('-', U+002D), the colon (':', U+003A), the low 1807 line ('_', U+005F), or the '.' separator (U+002E). The '.' separator 1808 is reserved for future use and MUST NOT be used unless specifically 1809 indicated by a companion or extension document. 1811 Identifiers prefixed with 'priv:' are reserved for Private Use 1812 [RFC5226]. For an identifier with the 'priv:' prefix, an additional 1813 string (e.g., company identifier or random string) MUST follow to 1814 reduce potential collisions. All other identifiers that appear in an 1815 HTTP request or response with an 'application/alto-*' media type and 1816 indicate Cost Metrics MUST be registered in the ALTO Cost Metrics 1817 registry Section 14.2. 1819 The type 'CostMetric' is used in this document to indicate a string 1820 of this format. 1822 10.7. Cost Type 1824 The combination of a CostMetric and a CostMode defines a CostType: 1826 object { 1827 CostMetric cost-metric; 1828 CostMode cost-mode; 1829 [JSONString description;] 1830 } CostType; 1832 'description', if present, MUST contain a string with a human- 1833 readable description of the cost-metric and cost-mode. An ALTO 1834 Client MAY present this string to a developer, as part of a discovery 1835 process. But the field is not intended to be interpreted by an ALTO 1836 Client. 1838 10.8. Endpoint Property 1840 We distinguish two types of Endpoint Properties: Resource Specific 1841 Endpoint Properties and Global Endpoint Properties. The type 1842 'EndpointPropertyType' is used in this document to indicate a string 1843 denoting either a Resource Specific Endpoint Property or a Global 1844 Endpoint Property. 1846 10.8.1. Resource Specific Endpoint Properties 1848 We define only one Resource Specific Endpoint Property in this 1849 document: pid. It has the following format: a Resource ID, followed 1850 by the '.' separator (U+002E), followed by "pid". An example is "my- 1851 default-networkmap.pid". 1853 10.8.2. Global Endpoint Properties 1855 An Global Endpoint Property is encoded as a string. The string MUST 1856 be no more than 32 characters, and MUST NOT contain characters other 1857 than alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and 1858 U+0061-U+007A), the hyphen ('-', U+002D), the colon (':', U+003A), or 1859 the low line ('_', U+005F). Note that the '.' separator is not 1860 allowed so that there is no ambiguity on whether an endpoint property 1861 is global or resource specific. 1863 Identifiers prefixed with 'priv:' are reserved for Private Use 1864 [RFC5226]. For an identifier with the 'priv:' prefix, an additional 1865 string (e.g., company identifier or random string) MUST follow to 1866 reduce potential collisions. All other identifiers for Endpoint 1867 Properties appearing in an HTTP request or response with an 1868 'application/alto-*' media type MUST be registered in the ALTO 1869 Endpoint Property registry Section 14.3. 1871 11. Protocol Specification: Service Information Resources 1873 This section documents the individual Information Resources defined 1874 to provide the services defined in this document. 1876 11.1. Meta Information 1878 For the "meta" field of the response to an individual Information 1879 Resource, we define two generic keys: "vtag", which is the Version 1880 Tag (see Section 10.3) of the current Information Resource; and 1881 "dependent-vtags", which is an array of Version Tags, to indicate the 1882 Version Tags of the resources that this resource depends on. 1884 11.2. Map Service 1886 The Map Service provides batch information to ALTO Clients in the 1887 form of two types of maps: a Network Map and Cost Map. 1889 11.2.1. Network Map 1891 A Network Map Information Resource defines a set of PIDs, and for 1892 each PID, lists the network locations (endpoints) within the PID. An 1893 ALTO Server MUST provide at least one Network Map. 1895 11.2.1.1. Media Type 1897 The media type of Network Map is "application/alto-networkmap+json". 1899 11.2.1.2. HTTP Method 1901 A Network Map resource is requested using the HTTP GET method. 1903 11.2.1.3. Accept Input Parameters 1905 None. 1907 11.2.1.4. Capabilities 1909 None. 1911 11.2.1.5. Uses 1913 None. 1915 11.2.1.6. Response 1917 The "meta" field of a Network Map response MUST include "vtag", which 1918 is the Version Tag of the retrieved Network Map. 1920 The data component of a Network Map response is named "network-map", 1921 which is a JSON object of type NetworkMapData: 1923 object { 1924 NetworkMapData network-map; 1925 } InfoResourceNetworkMap : ResponseEntityBase; 1927 object-map { 1928 PIDName -> EndpointAddrGroup; 1929 } NetworkMapData; 1931 Specifically, a NetworkMapData object is a dictionary map keyed by 1932 PIDs, and each value representing the associated set of endpoint 1933 addresses of a PID. 1935 The returned Network Map MUST include all PIDs known to the ALTO 1936 Server. 1938 11.2.1.7. Example 1940 GET /networkmap HTTP/1.1 1941 Host: alto.example.com 1942 Accept: application/alto-networkmap+json,application/alto-error+json 1943 HTTP/1.1 200 OK 1944 Content-Length: 449 1945 Content-Type: application/alto-networkmap+json 1947 { 1948 "meta" : { 1949 "vtag": { 1950 "resource-id": "my-default-network-map", 1951 "tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785" 1952 } 1953 }, 1954 "network-map" : { 1955 "PID1" : { 1956 "ipv4" : [ 1957 "192.0.2.0/24", 1958 "198.51.100.0/25" 1959 ] 1960 }, 1961 "PID2" : { 1962 "ipv4" : [ 1963 "198.51.100.128/25" 1964 ] 1965 }, 1966 "PID3" : { 1967 "ipv4" : [ 1968 "0.0.0.0/0" 1969 ], 1970 "ipv6" : [ 1971 "::/0" 1972 ] 1973 } 1974 } 1975 } 1977 When parsing a Network Map, an ALTO Client MUST ignore any 1978 EndpointAddressGroup whose address type it does not recognize. If as 1979 a result a PID does not have any address types known to the client, 1980 the client still MUST recognize that PID name as valid, even though 1981 the PID then contains no endpoints. 1983 Note that the encoding of a Network Map response was chosen for 1984 readability and compactness. If lookup efficiency at runtime is 1985 crucial, then the returned Network Map can be transformed into data 1986 structures offering more efficient lookup. For example, one may 1987 store the Network Map as a trie-based data structure, which may allow 1988 efficient longest-prefix matching of IP addresses. 1990 11.2.2. Mapping IP Addresses to PIDs for 'ipv4'/'ipv6' Network Maps 1992 A key usage of a Network Map is to map Endpoint Addresses to PIDs. 1993 For Network Maps containing the 'ipv4' and 'ipv6' address types 1994 defined in this document, when either an ALTO Client or an ALTO 1995 Server needs to compute the mapping from IP addresses to PIDs, the 1996 longest-prefix matching algorithm [RFC1812] MUST be used. 1998 To ensure that the longest-prefix matching algorithm yields one and 1999 only one PID, Network Maps containing the 'ipv4/'ipv6' address types 2000 MUST satisfy the following two requirements. 2002 First, such a Network Map MUST define a PID for each possible address 2003 in the IP address space for all of the address types contained in the 2004 map. We refer to this as the completeness property of such a Network 2005 Map. A RECOMMENDED way to satisfy this property is to define a PID 2006 with the shortest enclosing prefix of the addresses provided in the 2007 map. For a map with full IPv4 reachability, this would mean 2008 including the 0.0.0.0/0 prefix in a PID; for full IPv6 reachability, 2009 this would be the ::/0 prefix. 2011 Second, such a Network Map MUST NOT define two or more PIDs that 2012 contain an identical IP prefix, in order to ensure that the longest- 2013 prefix matching algorithm maps each IP addresses into exactly one 2014 PID. We refer to this as the non-overlapping property of such a 2015 Network Map. Specifically, to map an IP address to its PID in a non- 2016 overlapping Network Map, one considers the set S which consists of 2017 all prefixes defined in the Network Map, applies the longest-prefix 2018 mapping algorithm to S to identify the longest prefix containing the 2019 IP address, and assigns that the IP address belongs to the PID 2020 containing the identified longest prefix. 2022 The following example shows a complete and non-overlapping Network 2023 Map: 2025 "network-map" : { 2026 "PID0" : { "ipv6" : [ "::/0" ] }, 2027 "PID1" : { "ipv4" : [ "0.0.0.0/0" ] }, 2028 "PID2" : { "ipv4" : [ "192.0.2.0/24", "198.51.100.0/24" ] }, 2029 "PID3" : { "ipv4" : [ "192.0.2.0/25", "192.0.2.128/25" ] } 2030 } 2032 The IP address 192.0.2.1 should be mapped to PID3. 2034 If, however, the two adjacent prefixes in PID3 were combined as a 2035 single prefix, then PID3 was changed to 2037 "PID3" : { "ipv4" : [ "192.0.2.0/24" ] } 2039 The new map is no longer non-overlapping, and 192.0.2.1 could no 2040 longer be mapped unambiguously to a PID by means of longest-prefix 2041 matching. 2043 Extension documents may define techniques to allow a single IP 2044 address being mapped to multiple PIDs, when a need is identified. 2046 11.2.3. Cost Map 2048 A Cost Map resource lists the Path Cost for each pair of source/ 2049 destination PID defined by the ALTO Server for a given Cost Metric 2050 and Cost Mode. This resource MUST be provided for at least the 2051 'routingcost' Cost Metric. 2053 11.2.3.1. Media Type 2055 The media type of Cost Map is "application/alto-costmap+json". 2057 11.2.3.2. HTTP Method 2059 A Cost Map resource is requested using the HTTP GET method. 2061 11.2.3.3. Accept Input Parameters 2063 None. 2065 11.2.3.4. Capabilities 2067 The capabilities of an ALTO Server URI providing an unfiltered cost 2068 map is a JSON Object of type CostMapCapabilities: 2070 object { 2071 JSONString cost-type-names<1..1>; 2072 } CostMapCapabilities; 2074 with field: 2076 cost-type-names Note that the array MUST include a single CostType 2077 name defined by key "cost-types" in "meta" of the IRD. This is 2078 because an unfiltered Cost Map (accept == "") is requested via an 2079 HTTP GET that accepts no input parameters. As a contrast, for 2080 filtered cost maps (see Section 11.3.2), the array can have 2081 multiple elements. 2083 11.2.3.5. Uses 2085 The Resource ID of the Network Map based on which the Cost Map will 2086 be defined. Recall (Section 6) that the combination of a Network Map 2087 and a CostType defines a key. In other words, an ALTO Server MUST 2088 NOT define two Cost Maps with the same Cost Type, Network Map pair. 2090 11.2.3.6. Response 2092 The "meta" field of a Cost Map response MUST include the "dependent- 2093 vtags" key, whose value is a single-element array to indicate the 2094 Version Tag of the Network Map used, where the Network Map is 2095 specified in "uses" of the IRD. The "meta" MUST also include "cost- 2096 type", to indicate the Cost Type (Section 10.7) of the Cost Map. 2098 The data component of a Cost Map response is named "cost-map", which 2099 is a JSON object of type CostMapData: 2101 object { 2102 CostMapData cost-map; 2103 } InfoResourceCostMap : ResponseEntityBase; 2105 object-map { 2106 PIDName -> DstCosts; 2107 } CostMapData; 2109 object-map { 2110 PIDName -> JSONValue; 2111 } DstCosts; 2113 Specifically, a CostMapData object is a dictionary map object, with 2114 each key being the PIDName string identifying the corresponding 2115 Source PID, and value being a type of DstCosts, which denotes the 2116 associated costs from the Source PID to a set of destination PIDs ( 2117 Section 6.2). An implementation of the protocol in this document 2118 SHOULD assume that the cost is a JSONNumber and fail to parse if it 2119 is not, unless the implementation is using an extension to this 2120 document that indicates when and how costs of other data types are 2121 signaled. 2123 The returned Cost Map MUST include the Path Cost for each (Source 2124 PID, Destination PID) pair for which a Path Cost is defined. An ALTO 2125 Server MAY omit entries for which a Path Cost is not defined (e.g., 2126 both the Source and Destination PIDs contain addresses outside of the 2127 Network Provider's administrative domain). 2129 Similar to Network Map, the encoding of Cost Map was chosen for 2130 readability and compactness. If lookup efficiency at runtime is 2131 crucial, then the returned Cost Map can be transformed into data 2132 structures offering more efficient lookup. For example, one may 2133 store a Cost Map as a matrix. 2135 11.2.3.7. Example 2137 GET /costmap/num/routingcost HTTP/1.1 2138 Host: alto.example.com 2139 Accept: application/alto-costmap+json,application/alto-error+json 2141 HTTP/1.1 200 OK 2142 Content-Length: 435 2143 Content-Type: application/alto-costmap+json 2145 { 2146 "meta" : { 2147 "dependent-vtags" : [ 2148 {"resource-id": "my-default-network-map", 2149 "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e" 2150 } 2151 ], 2152 "cost-type" : {"cost-mode" : "numerical", 2153 "cost-metric": "routingcost" 2154 } 2155 }, 2156 "cost-map" : { 2157 "PID1": { "PID1": 1, "PID2": 5, "PID3": 10 }, 2158 "PID2": { "PID1": 5, "PID2": 1, "PID3": 15 }, 2159 "PID3": { "PID1": 20, "PID2": 15 } 2160 } 2161 } 2163 Similar to the Network Map case, we considered array-based encoding 2164 for "map", but chose the current encoding for clarity. 2166 11.3. Map Filtering Service 2168 The Map Filtering Service allows ALTO Clients to specify filtering 2169 criteria to return a subset of the full maps available in the Map 2170 Service. 2172 11.3.1. Filtered Network Map 2174 A Filtered Network Map is a Network Map Information Resource 2175 (Section 11.2.1) for which an ALTO Client may supply a list of PIDs 2176 to be included. A Filtered Network Map MAY be provided by an ALTO 2177 Server. 2179 11.3.1.1. Media Type 2181 Since a Filtered Network Map is still a Network Map, it uses the 2182 media type defined for Network Map at Section 11.2.1.1. 2184 11.3.1.2. HTTP Method 2186 A Filtered Network Map is requested using the HTTP POST method. 2188 11.3.1.3. Accept Input Parameters 2190 An ALTO Client supplies filtering parameters by specifying media type 2191 "application/alto-networkmapfilter+json" with HTTP POST body 2192 containing a JSON Object of type ReqFilteredNetworkMap, where: 2194 object { 2195 PIDName pids<0..*>; 2196 [AddressType address-types<0..*>;] 2197 } ReqFilteredNetworkMap; 2199 with fields: 2201 pids Specifies list of PIDs to be included in the returned Filtered 2202 Network Map. If the list of PIDs is empty, the ALTO Server MUST 2203 interpret the list as if it contained a list of all currently- 2204 defined PIDs. The ALTO Server MUST interpret entries appearing 2205 multiple times as if they appeared only once. 2207 address-types Specifies list of address types to be included in the 2208 returned Filtered Network Map. If the "address-types" field is not 2209 specified, or the list of address types is empty, the ALTO Server 2210 MUST interpret the list as if it contained a list of all address 2211 types known to the ALTO Server. The ALTO Server MUST interpret 2212 entries appearing multiple times as if they appeared only once. 2214 11.3.1.4. Capabilities 2216 None. 2218 11.3.1.5. Uses 2220 The Resource ID of the Network Map based on which the filtering is 2221 performed. 2223 11.3.1.6. Response 2225 The format is the same as unfiltered Network Map. See 2226 Section 11.2.1.6 for the format. 2228 The ALTO Server MUST only include PIDs in the response that were 2229 specified (implicitly or explicitly) in the request. If the input 2230 parameters contain a PID name that is not currently defined by the 2231 ALTO Server, the ALTO Server MUST behave as if the PID did not appear 2232 in the input parameters. Similarly, the ALTO Server MUST only 2233 enumerate addresses within each PID that have types which were 2234 specified (implicitly or explicitly) in the request. If the input 2235 parameters contain an address type that is not currently known to the 2236 ALTO Server, the ALTO Server MUST behave as if the address type did 2237 not appear in the input parameters. 2239 The Version Tag included in the "vtag" of the response MUST 2240 correspond to the full (unfiltered) Network Map Information Resource 2241 from which the filtered information is provided. This ensures that a 2242 single, canonical Version Tag is used independent of any filtering 2243 that is requested by an ALTO Client. 2245 11.3.1.7. Example 2247 POST /networkmap/filtered HTTP/1.1 2248 Host: custom.alto.example.com 2249 Content-Length: 33 2250 Content-Type: application/alto-networkmapfilter+json 2251 Accept: application/alto-networkmap+json,application/alto-error+json 2253 { 2254 "pids": [ "PID1", "PID2" ] 2255 } 2257 HTTP/1.1 200 OK 2258 Content-Length: 342 2259 Content-Type: application/alto-networkmap+json 2261 { 2262 "meta" : { 2263 "vtag" : { 2264 "resource-id": "my-default-network-map", 2265 "tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d" 2266 } 2267 }, 2268 "network-map" : { 2269 "PID1" : { 2270 "ipv4" : [ 2271 "192.0.2.0/24", 2272 "198.51.100.0/24" 2273 ] 2274 }, 2275 "PID2" : { 2276 "ipv4": [ 2277 "198.51.100.128/24" 2278 ] 2279 } 2280 } 2281 } 2283 11.3.2. Filtered Cost Map 2285 A Filtered Cost Map is a Cost Map Information Resource 2286 (Section 11.2.3) for which an ALTO Client may supply additional 2287 parameters limiting the scope of the resulting Cost Map. A Filtered 2288 Cost Map MAY be provided by an ALTO Server. 2290 11.3.2.1. Media Type 2292 Since a Filtered Cost Map is still a Cost Map, it uses the media type 2293 defined for Cost Map at Section 11.2.3.1. 2295 11.3.2.2. HTTP Method 2297 A Filtered Cost Map is requested using the HTTP POST method. 2299 11.3.2.3. Accept Input Parameters 2301 The input parameters for a Filtered Map are supplied in the entity 2302 body of the POST request. This document specifies the input 2303 parameters with a data format indicated by the media type 2304 "application/alto-costmapfilter+json", which is a JSON Object of type 2305 ReqFilteredCostMap, where: 2307 object { 2308 CostType cost-type; 2309 [JSONString constraints<0..*>;] 2310 [PIDFilter pids;] 2311 } ReqFilteredCostMap; 2313 object { 2314 PIDName srcs<0..*>; 2315 PIDName dsts<0..*>; 2316 } PIDFilter; 2318 with fields: 2320 cost-type The CostType (Section 10.7) for the returned costs. The 2321 cost-metric and cost-mode fields MUST match one of the supported 2322 Cost Types indicated in this resource's capabilities 2323 (Section 11.3.2.4). The ALTO Client SHOULD omit the description 2324 field, and if present, the ALTO Server MUST ignore the description 2325 field. 2327 constraints Defines a list of additional constraints on which 2328 elements of the Cost Map are returned. This parameter MUST NOT be 2329 specified if this resource's capabilities ( Section 11.3.2.4) 2330 indicate that constraint support is not available. A constraint 2331 contains two entities separated by whitespace: (1) an operator, 2332 'gt' for greater than, 'lt' for less than, 'ge' for greater than 2333 or equal to, 'le' for less than or equal to, or 'eq' for equal to; 2334 (2) a target cost value. The cost value is a number that MUST be 2335 defined in the same units as the Cost Metric indicated by the 2336 cost-metric parameter. ALTO Servers SHOULD use at least IEEE 754 2337 double-precision floating point [IEEE.754.2008] to store the cost 2338 value, and SHOULD perform internal computations using double- 2339 precision floating-point arithmetic. If multiple 'constraint' 2340 parameters are specified, they are interpreted as being related to 2341 each other with a logical AND. 2343 pids A list of Source PIDs and a list of Destination PIDs for which 2344 Path Costs are to be returned. If a list is empty, the ALTO 2345 Server MUST interpret it as the full set of currently-defined 2346 PIDs. The ALTO Server MUST interpret entries appearing in a list 2347 multiple times as if they appeared only once. If the "pids" field 2348 is not present, both lists MUST be interpreted by the ALTO Server 2349 as containing the full set of currently-defined PIDs. 2351 11.3.2.4. Capabilities 2353 The URI providing this resource supports all capabilities documented 2354 in Section 11.2.3.4 (with identical semantics), plus additional 2355 capabilities. In particular, the capabilities are defined by a JSON 2356 object of type FilteredCostMapCapabilities: 2358 object { 2359 JSONString cost-type-names<1..*>; 2360 JSONBool cost-constraints; 2361 } FilteredCostMapCapabilities; 2363 with fields: 2365 cost-type-names See Section 11.2.3.4 and note that the array can 2366 have 1 to many cost types. 2368 cost-constraints If true, then the ALTO Server allows cost 2369 constraints to be included in requests to the corresponding URI. 2370 If not present, this field MUST be interpreted as if it specified 2371 false. ALTO Clients should be aware that constraints may not have 2372 the intended effect for cost maps with the 'ordinal' Cost Mode 2373 since ordinal costs are not restricted to being sequential 2374 integers. 2376 11.3.2.5. Uses 2378 The Resource ID of the Network Map based on which the Cost Map will 2379 be filtered. 2381 11.3.2.6. Response 2383 The format is the same as an unfiltered Cost Map. See 2384 Section 11.2.3.6 for the format. 2386 The "dependent-vtags" key in the "meta" field is an array consisting 2387 of a single element, which is the Version Tag of the Network Map used 2388 in filtering. ALTO Clients should verify that the Version Tag 2389 included in the response is equal to the Version Tag of the Network 2390 Map used to generate the request (if applicable). If it is not, the 2391 ALTO Client may wish to request an updated Network Map, identify 2392 changes, and consider requesting a new Filtered Cost Map. 2394 The returned Cost Map MUST contain only source/destination pairs that 2395 have been indicated (implicitly or explicitly) in the input 2396 parameters. If the input parameters contain a PID name that is not 2397 currently defined by the ALTO Server, the ALTO Server MUST behave as 2398 if the PID did not appear in the input parameters. 2400 If any constraints are specified, Source/Destination pairs for which 2401 the Path Costs do not meet the constraints MUST NOT be included in 2402 the returned Cost Map. If no constraints were specified, then all 2403 Path Costs are assumed to meet the constraints. 2405 11.3.2.7. Example 2407 POST /costmap/filtered HTTP/1.1 2408 Host: custom.alto.example.com 2409 Content-Type: application/alto-costmapfilter+json 2410 Content-Length: 181 2411 Accept: application/alto-costmap+json,application/alto-error+json 2413 { 2414 "cost-type" : {"cost-mode": "numerical", 2415 "cost-metric": "routingcost" 2416 }, 2417 "pids" : { 2418 "srcs" : [ "PID1" ], 2419 "dsts" : [ "PID1", "PID2", "PID3" ] 2420 } 2421 } 2423 HTTP/1.1 200 OK 2424 Content-Length: 341 2425 Content-Type: application/alto-costmap+json 2427 { 2428 "meta" : { 2429 "dependent-vtags" : [ 2430 {"resource-id": "my-default-network-map", 2431 "tag": "75ed013b3cb58f896e839582504f622838ce670f" 2432 } 2433 ], 2434 "cost-type": {"cost-mode" : "numerical", 2435 "cost-metric" : "routingcost" 2436 } 2437 }, 2438 "cost-map" : { 2439 "PID1": { "PID1": 0, "PID2": 1, "PID3": 2 } 2440 } 2441 } 2443 11.4. Endpoint Property Service 2445 The Endpoint Property Service provides information about Endpoint 2446 properties to ALTO Clients. 2448 11.4.1. Endpoint Property 2450 An Endpoint Property resource provides information about properties 2451 for individual endpoints. It MAY be provided by an ALTO Server. 2453 11.4.1.1. Media Type 2455 The media type of Endpoint Property is "application/ 2456 alto-endpointprop+json". 2458 11.4.1.2. HTTP Method 2460 The Endpoint Property resource is requested using the HTTP POST 2461 method. 2463 11.4.1.3. Accept Input Parameters 2465 An ALTO Client supplies the endpoint properties to be queried through 2466 a media type "application/alto-endpointpropparams+json", and 2467 specifies in the HTTP POST entity body a JSON Object of type 2468 ReqEndpointProp: 2470 object { 2471 EndpointPropertyType properties<1..*>; 2472 TypedEndpointAddr endpoints<1..*>; 2473 } ReqEndpointProp; 2475 with fields: 2477 properties List of endpoint properties to be returned for each 2478 endpoint. Each specified property MUST be included in the list of 2479 supported properties indicated by this resource's capabilities 2480 (Section 11.4.1.4). The ALTO Server MUST interpret entries 2481 appearing multiple times as if they appeared only once. 2483 endpoints List of endpoint addresses for which the specified 2484 properties are to be returned. The ALTO Server MUST interpret 2485 entries appearing multiple times as if they appeared only once. 2487 11.4.1.4. Capabilities 2489 This resource may be defined across multiple types of endpoint 2490 properties. The capabilities of an ALTO Server URI providing 2491 Endpoint Properties are defined by a JSON Object of type 2492 EndpointPropertyCapabilities: 2494 object { 2495 EndpointPropertyType prop-types<1..*>; 2496 } EndpointPropertyCapabilities; 2498 with field: 2500 prop-types The Endpoint Properties (see Section 10.8) supported by 2501 the corresponding URI. 2503 In particular, the Information Resource Closure MUST provide the look 2504 up of pid for every Network Map defined. 2506 11.4.1.5. Uses 2508 None. 2510 11.4.1.6. Response 2512 The "dependent-vtags" key in the "meta" field of the response MUST be 2513 an array that includes the Version Tags of all Network Maps whose 2514 'pid' is queried. 2516 The data component of an Endpoint Properties response is named 2517 "endpoint-properties", which is a JSON object of type 2518 EndpointPropertyMapData, where: 2520 object { 2521 EndpointPropertyMapData endpoint-properties; 2522 } InfoResourceEndpointProperties : ResponseEntityBase; 2524 object-map { 2525 TypedEndpointAddr -> EndpointProps; 2526 } EndpointPropertyMapData; 2528 object { 2529 EndpointPropertyType -> JSONValue; 2530 } EndpointProps; 2532 Specifically, an EndpointPropertyMapData object has one member for 2533 each endpoint indicated in the input parameters (with the name being 2534 the endpoint encoded as a TypedEndpointAddr). The requested 2535 properties for each endpoint are encoded in a corresponding 2536 EndpointProps object, which encodes one name/value pair for each 2537 requested property, where the property names are encoded as strings 2538 of type EndpointPropertyType. An implementation of the protocol in 2539 this document SHOULD assume that the property value is a JSONString 2540 and fail to parse if it is not, unless the implementation is using an 2541 extension to this document that indicates when and how property 2542 values of other data types are signaled. 2544 The ALTO Server returns the value for each of the requested endpoint 2545 properties for each of the endpoints listed in the input parameters. 2547 If the ALTO Server does not define a requested property's value for a 2548 particular endpoint, then it MUST omit that property from the 2549 response for only that endpoint. 2551 11.4.1.7. Example 2553 POST /endpointprop/lookup HTTP/1.1 2554 Host: alto.example.com 2555 Content-Length: 181 2556 Content-Type: application/alto-endpointpropparams+json 2557 Accept: application/alto-endpointprop+json,application/alto-error+json 2559 { 2560 "properties" : [ "my-default-networkmap.pid", 2561 "priv:ietf-example-prop" ], 2562 "endpoints" : [ "ipv4:192.0.2.34", 2563 "ipv4:203.0.113.129" ] 2564 } 2566 HTTP/1.1 200 OK 2567 Content-Length: 396 2568 Content-Type: application/alto-endpointprop+json 2570 { 2571 "meta" : { 2572 "dependent-vtags" : [ 2573 {"resource-id": "my-default-network-map", 2574 "tag": "7915dc0290c2705481c491a2b4ffbec482b3cf62" 2575 } 2576 ] 2577 }, 2578 "endpoint-properties": { 2579 "ipv4:192.0.2.34" : { "my-default-network-map.pid": "PID1", 2580 "priv:ietf-example-prop": "1" }, 2581 "ipv4:203.0.113.129" : { "my-default-network-map.pid": "PID3" } 2582 } 2583 } 2585 11.5. Endpoint Cost Service 2587 The Endpoint Cost Service provides information about costs between 2588 individual endpoints. 2590 In particular, this service allows lists of Endpoint prefixes (and 2591 addresses, as a special case) to be ranked (ordered) by an ALTO 2592 Server. 2594 11.5.1. Endpoint Cost 2596 An Endpoint Cost resource provides information about costs between 2597 individual endpoints. It MAY be provided by an ALTO Server. 2599 It is important to note that although this resource allows an ALTO 2600 Server to reveal costs between individual endpoints, an ALTO Server 2601 is not required to do so. A simple alternative would be to compute 2602 the cost between two endpoints as the cost between the PIDs 2603 corresponding to the endpoints. See Section 15.3 for additional 2604 details. 2606 11.5.1.1. Media Type 2608 The media type of Endpoint Cost is "application/ 2609 alto-endpointcost+json". 2611 11.5.1.2. HTTP Method 2613 The Endpoint Cost resource is requested using the HTTP POST method. 2615 11.5.1.3. Accept Input Parameters 2617 An ALTO Client supplies the endpoint cost parameters through a media 2618 type "application/alto-endpointcostparams+json", with an HTTP POST 2619 entity body of a JSON Object of type ReqEndpointCostMap: 2621 object { 2622 CostType cost-type; 2623 [JSONString constraints<0..*>;] 2624 EndpointFilter endpoints; 2625 } ReqEndpointCostMap; 2627 object { 2628 [TypedEndpointAddr srcs<0..*>;] 2629 [TypedEndpointAddr dsts<0..*>;] 2630 } EndpointFilter; 2631 with fields: 2633 cost-type The Cost Type (Section 10.7) to use for returned costs. 2634 The cost-metric and cost-mode fields MUST match one of the 2635 supported Cost Types indicated in this resource's capabilities ( 2636 Section 11.5.1.4). The ALTO Client SHOULD omit the description 2637 field, and if present, the ALTO Server MUST ignore the description 2638 field. 2640 constraints Defined equivalently to the "constraints" input 2641 parameter of a Filtered Cost Map (see Section 11.3.2). 2643 endpoints A list of Source Endpoints and Destination Endpoints for 2644 which Path Costs are to be returned. If the list of Source or 2645 Destination Endpoints is empty (or not included), the ALTO Server 2646 MUST interpret it as if it contained the Endpoint Address 2647 corresponding to the client IP address from the incoming 2648 connection (see Section 13.3 for discussion and considerations 2649 regarding this mode). The Source and Destination Endpoint lists 2650 MUST NOT be both empty. The ALTO Server MUST interpret entries 2651 appearing multiple times in a list as if they appeared only once. 2653 11.5.1.4. Capabilities 2655 In this document, we define EndpointCostCapabilities the same as 2656 FilteredCostMapCapabilities. See Section 11.3.2.4. 2658 11.5.1.5. Uses 2660 It is important to note that although this resource allows an ALTO 2661 Server to reveal costs between individual endpoints, an ALTO Server 2662 is not required to do so. A simple implementation of an ECS resource 2663 may compute the cost between two endpoints as the cost between the 2664 PIDs corresponding to the endpoints, using one of the exposed network 2665 and cost maps defined by the server. However, to preserve 2666 flexibility, the ECS resource MAY omit declaring in the "uses" 2667 attribute the network map and/or cost map on which it depends. 2669 11.5.1.6. Response 2671 The "meta" field of an Endpoint Cost response MUST include the "cost- 2672 type" key, to indicate the Cost Type used. 2674 The data component of an Endpoint Cost response is named "endpoint- 2675 cost-map", which is a JSON object of type EndpointCostMapData: 2677 object { 2678 EndpointCostMapData endpoint-cost-map; 2679 } InfoResourceEndpointCostMap : ResponseEntityBase; 2681 object-map { 2682 TypedEndpointAddr -> EndpointDstCosts; 2683 } EndpointCostMapData; 2685 object-map { 2686 TypedEndpointAddr -> JSONValue; 2687 } EndpointDstCosts; 2689 Specifically, an EndpointCostMapData object is a dictionary map with 2690 each key representing a TypedEndpointAddr string identifying the 2691 Source Endpoint specified in the input parameters. For each Source 2692 Endpoint, a EndpointDstCosts dictionary map object denotes the 2693 associated cost to each Destination Endpoint specified in input 2694 parameters. An implementation of the protocol in this document 2695 SHOULD assume that the cost value is a JSONNumber and fail to parse 2696 if it is not, unless the implementation is using an extension to this 2697 document that indicates when and how costs of other data types are 2698 signaled. If the ALTO Server does not define a cost value from a 2699 Source Endpoint to a particular Destination Endpoint, it MAY be 2700 omitted from the response. 2702 11.5.1.7. Example 2704 POST /endpointcost/lookup HTTP/1.1 2705 Host: alto.example.com 2706 Content-Length: 248 2707 Content-Type: application/alto-endpointcostparams+json 2708 Accept: application/alto-endpointcost+json,application/alto-error+json 2710 { 2711 "cost-type": {"cost-mode" : "ordinal", 2712 "cost-metric" : "routingcost"}, 2713 "endpoints" : { 2714 "srcs": [ "ipv4:192.0.2.2" ], 2715 "dsts": [ 2716 "ipv4:192.0.2.89", 2717 "ipv4:198.51.100.34", 2718 "ipv4:203.0.113.45" 2719 ] 2720 } 2721 } 2723 HTTP/1.1 200 OK 2724 Content-Length: 274 2725 Content-Type: application/alto-endpointcost+json 2727 { 2728 "meta" : { 2729 "cost-type": {"cost-mode" : "ordinal", 2730 "cost-metric" : "routingcost" 2731 } 2732 }, 2733 "endpoint-cost-map" : { 2734 "ipv4:192.0.2.2": { 2735 "ipv4:192.0.2.89" : 1, 2736 "ipv4:198.51.100.34" : 2, 2737 "ipv4:203.0.113.45" : 3 2738 } 2739 } 2740 } 2742 12. Use Cases 2744 The sections below depict typical use cases. While these use cases 2745 focus on peer-to-peer applications, ALTO can be applied to other 2746 environments such as CDNs [I-D.jenkins-alto-cdn-use-cases]. 2748 12.1. ALTO Client Embedded in P2P Tracker 2750 Many currently-deployed P2P systems use a Tracker to manage swarms 2751 and perform peer selection. Such a P2P Tracker can already use a 2752 variety of information to perform peer selection to meet application- 2753 specific goals. By acting as an ALTO Client, the P2P Tracker can use 2754 ALTO information as an additional information source to enable more 2755 network-efficient traffic patterns and improve application 2756 performance. 2758 A particular requirement of many P2P trackers is that they must 2759 handle a large number of P2P clients. A P2P tracker can obtain and 2760 locally store ALTO information (the Network Map and Cost Map) from 2761 the ISPs containing the P2P clients, and benefit from the same 2762 aggregation of network locations done by ALTO Servers. 2764 .---------. (1) Get Network Map .---------------. 2765 | | <----------------------> | | 2766 | ALTO | | P2P Tracker | 2767 | Server | (2) Get Cost Map | (ALTO Client) | 2768 | | <----------------------> | | 2769 `---------' `---------------' 2770 ^ | 2771 (3) Get Peers | | (4) Selected Peer 2772 | v List 2773 .---------. .-----------. 2774 | Peer 1 | <-------------- | P2P | 2775 `---------' | Client | 2776 . (5) Connect to `-----------' 2777 . Selected Peers / 2778 .---------. / 2779 | Peer 50 | <------------------ 2780 `---------' 2782 Figure 4: ALTO Client Embedded in P2P Tracker 2784 Figure 4 shows an example use case where a P2P tracker is an ALTO 2785 Client and applies ALTO information when selecting peers for its P2P 2786 clients. The example proceeds as follows: 2788 1. The P2P Tracker requests from the ALTO Server using the Network 2789 Map query the Network Map covering all PIDs. The Network Map 2790 includes the IP prefixes contained in each PID, allowing the P2P 2791 tracker to locally map P2P clients into PIDs. 2793 2. The P2P Tracker requests from the ALTO Server the Cost Map 2794 amongst all PIDs identified in the preceding step. 2796 3. A P2P Client joins the swarm, and requests a peer list from the 2797 P2P Tracker. 2799 4. The P2P Tracker returns a peer list to the P2P client. The 2800 returned peer list is computed based on the Network Map and Cost 2801 Map returned by the ALTO Server, and possibly other information 2802 sources. Note that it is possible that a tracker may use only 2803 the Network Map to implement hierarchical peer selection by 2804 preferring peers within the same PID and ISP. 2806 5. The P2P Client connects to the selected peers. 2808 Note that the P2P tracker may provide peer lists to P2P clients 2809 distributed across multiple ISPs. In such a case, the P2P tracker 2810 may communicate with multiple ALTO Servers. 2812 12.2. ALTO Client Embedded in P2P Client: Numerical Costs 2814 P2P clients may also utilize ALTO information themselves when 2815 selecting from available peers. It is important to note that not all 2816 P2P systems use a P2P tracker for peer discovery and selection. 2817 Furthermore, even when a P2P tracker is used, the P2P clients may 2818 rely on other sources, such as peer exchange and DHTs, to discover 2819 peers. 2821 When an P2P Client uses ALTO information, it typically queries only 2822 the ALTO Server servicing its own ISP. The my-Internet view provided 2823 by its ISP's ALTO Server can include preferences to all potential 2824 peers. 2826 .---------. (1) Get Network Map .---------------. 2827 | | <----------------------> | | 2828 | ALTO | | P2P Client | 2829 | Server | (2) Get Cost Map | (ALTO Client) | 2830 | | <----------------------> | | .---------. 2831 `---------' `---------------' <- | P2P | 2832 .---------. / | ^ ^ | Tracker | 2833 | Peer 1 | <-------------- | | \ `---------' 2834 `---------' | (3) Gather Peers 2835 . (4) Select Peers | | \ 2836 . and Connect / .--------. .--------. 2837 .---------. / | P2P | | DHT | 2838 | Peer 50 | <---------------- | Client | `--------' 2839 `---------' | (PEX) | 2840 `--------' 2842 Figure 5: ALTO Client Embedded in P2P Client 2844 Figure 5 shows an example use case where a P2P Client locally applies 2845 ALTO information to select peers. The use case proceeds as follows: 2847 1. The P2P Client requests the Network Map covering all PIDs from 2848 the ALTO Server servicing its own ISP. 2850 2. The P2P Client requests the Cost Map amongst all PIDs from the 2851 ALTO Server. The Cost Map by default specifies numerical costs. 2853 3. The P2P Client discovers peers from sources such as Peer Exchange 2854 (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and 2855 P2P Trackers. 2857 4. The P2P Client uses ALTO information as part of the algorithm for 2858 selecting new peers, and connects to the selected peers. 2860 12.3. ALTO Client Embedded in P2P Client: Ranking 2862 It is also possible for a P2P Client to offload the selection and 2863 ranking process to an ALTO Server. In this use case, the ALTO Client 2864 embedded in the P2P Client gathers a list of known peers in the 2865 swarm, and asks the ALTO Server to rank them. We limit the use case 2866 to when the P2P Client and the ALTO Server belong to the same trust 2867 domain, and hence the P2P Client uses the ranking provided by the 2868 ALTO Server directly. 2870 As in the use case using numerical costs, the P2P Client typically 2871 only queries the ALTO Server servicing its own ISP. 2873 .---------. .---------------. 2874 | | | | 2875 | ALTO | (2) Get Endpoint Ranking | P2P Client | 2876 | Server | <----------------------> | (ALTO Client) | 2877 | | | | .---------. 2878 `---------' `---------------' <- | P2P | 2879 .---------. / | ^ ^ | Tracker | 2880 | Peer 1 | <-------------- | | \ `---------' 2881 `---------' | (1) Gather Peers 2882 . (3) Connect to | | \ 2883 . Selected Peers / .--------. .--------. 2884 .---------. / | P2P | | DHT | 2885 | Peer 50 | <---------------- | Client | `--------' 2886 `---------' | (PEX) | 2887 `--------' 2889 Figure 6: ALTO Client Embedded in P2P Client: Ranking 2891 Figure 6 shows an example of this scenario. The use case proceeds as 2892 follows: 2894 1. The P2P Client discovers peers from sources such as Peer Exchange 2895 (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and 2896 P2P Trackers. 2898 2. The P2P Client queries the ALTO Server's Ranking Service, 2899 including discovered peers as the set of Destination Endpoints, 2900 and indicates the 'ordinal' Cost Mode. The response indicates 2901 the ranking of the candidate peers. 2903 3. The P2P Client connects to the peers in the order specified in 2904 the ranking. 2906 13. Discussions 2908 13.1. Discovery 2910 The discovery mechanism by which an ALTO Client locates an 2911 appropriate ALTO Server is out of scope for this document. This 2912 document assumes that an ALTO Client can discover an appropriate ALTO 2913 Server. Once it has done so, the ALTO Client may use the Information 2914 Resource Directory (see Section 9.2) to locate an Information 2915 Resource with the desired ALTO Information. 2917 13.2. Hosts with Multiple Endpoint Addresses 2919 In practical deployments, a particular host can be reachable using 2920 multiple addresses (e.g., a wireless IPv4 connection, a wireline IPv4 2921 connection, and a wireline IPv6 connection). In general, the 2922 particular network path followed when sending packets to the host 2923 will depend on the address that is used. Network providers may 2924 prefer one path over another. An additional consideration may be how 2925 to handle private address spaces (e.g., behind carrier-grade NATs). 2927 To support such behavior, this document allows multiple endpoint 2928 addresses and address types. With this support, the ALTO Protocol 2929 allows an ALTO Service Provider the flexibility to indicate 2930 preferences for paths from an endpoint address of one type to an 2931 endpoint address of a different type. 2933 13.3. Network Address Translation Considerations 2935 At this day and age of NAT v4<->v4, v4<->v6 [RFC6144], and possibly 2936 v6<->v6 [RFC6296], a protocol should strive to be NAT friendly and 2937 minimize carrying IP addresses in the payload, or provide a mode of 2938 operation where the source IP address provide the information 2939 necessary to the server. 2941 The protocol specified in this document provides a mode of operation 2942 where the source network location is computed by the ALTO Server 2943 (i.e., the the Endpoint Cost Service) from the source IP address 2944 found in the ALTO Client query packets. This is similar to how some 2945 P2P Trackers (e.g., BitTorrent Trackers - see "Tracker HTTP/HTTPS 2946 Protocol" in [BitTorrent]) operate. 2948 There may be cases where an ALTO Client needs to determine its own IP 2949 address, such as when specifying a source Endpoint Address in the 2950 Endpoint Cost Service. It is possible that an ALTO Client has 2951 multiple network interface addresses, and that some or all of them 2952 may require NAT for connectivity to the public Internet. 2954 If a public IP address is required for a network interface, the ALTO 2955 Client SHOULD use the Session Traversal Utilities for NAT (STUN) 2956 [RFC5389]. If using this method, the host MUST use the "Binding 2957 Request" message and the resulting "XOR-MAPPED-ADDRESS" parameter 2958 that is returned in the response. Using STUN requires cooperation 2959 from a publicly accessible STUN server. Thus, the ALTO Client also 2960 requires configuration information that identifies the STUN server, 2961 or a domain name that can be used for STUN server discovery. To be 2962 selected for this purpose, the STUN server needs to provide the 2963 public reflexive transport address of the host. 2965 ALTO Clients should be cognizant that the network path between 2966 Endpoints can depend on multiple factors, e.g., source address, and 2967 destination address used for communication. An ALTO Server provides 2968 information based on Endpoint Addresses (more generally, Network 2969 Locations), but the mechanisms used for determining existence of 2970 connectivity or usage of NAT between Endpoints are out of scope of 2971 this document. 2973 13.4. Endpoint and Path Properties 2975 An ALTO Server could make available many properties about Endpoints 2976 beyond their network location or grouping. For example, connection 2977 type, geographical location, and others may be useful to 2978 applications. This specification focuses on network location and 2979 grouping, but the protocol may be extended to handle other Endpoint 2980 properties. 2982 14. IANA Considerations 2984 This document defines registries for application/alto-* Media Types, 2985 ALTO Cost Metric, ALTO Endpoint Property Types, ALTO Address Types, 2986 and ALTO Error Codes. Initial values for the registries and the 2987 process of future assignments are given below. 2989 14.1. application/alto-* Media Types 2991 This document requests the registration of multiple media types, 2992 listed in Table 2. 2994 +-------------+------------------------------+----------------+ 2995 | Type | Subtype | Specification | 2996 +-------------+------------------------------+----------------+ 2997 | application | alto-directory+json | Section 9.2 | 2998 | application | alto-networkmap+json | Section 11.2.1 | 2999 | application | alto-networkmapfilter+json | Section 11.3.1 | 3000 | application | alto-costmap+json | Section 11.2.3 | 3001 | application | alto-costmapfilter+json | Section 11.3.2 | 3002 | application | alto-endpointprop+json | Section 11.4.1 | 3003 | application | alto-endpointpropparams+json | Section 11.4.1 | 3004 | application | alto-endpointcost+json | Section 11.5.1 | 3005 | application | alto-endpointcostparams+json | Section 11.5.1 | 3006 | application | alto-error+json | Section 8.5 | 3007 +-------------+------------------------------+----------------+ 3009 Table 2: ALTO Protocol Media Types. 3011 Type name: application 3013 Subtype name: This documents requests the registration of multiple 3014 subtypes, as listed in Table 2. 3016 Required parameters: n/a 3018 Optional parameters: n/a 3020 Encoding considerations: Encoding considerations are identical to 3021 those specified for the 'application/json' media type. See 3022 [RFC4627]. 3024 Security considerations: Security considerations relating to the 3025 generation and consumption of ALTO Protocol messages are discussed 3026 in Section 15. 3028 Interoperability considerations: This document specifies format of 3029 conforming messages and the interpretation thereof. 3031 Published specification: This document is the specification for 3032 these media types; see Table 2 for the section documenting each 3033 media type. 3035 Applications that use this media type: ALTO Servers and ALTO Clients 3036 either standalone or embedded within other applications. 3038 Additional information: 3040 Magic number(s): n/a 3042 File extension(s): This document uses the mime type to refer to 3043 protocol messages and thus does not require a file extension. 3045 Macintosh file type code(s): n/a 3047 Person & email address to contact for further information: See 3048 "Authors' Addresses" section. 3050 Intended usage: COMMON 3052 Restrictions on usage: n/a 3054 Author: See "Authors' Addresses" section. 3056 Change controller: Internet Engineering Task Force 3057 (mailto:iesg@ietf.org). 3059 14.2. ALTO Cost Metric Registry 3061 This document requests the creation of an ALTO Cost Metric registry, 3062 listed in Table 3, to be maintained by IANA. 3064 +-------------+---------------------+ 3065 | Identifier | Intended Semantics | 3066 +-------------+---------------------+ 3067 | routingcost | See Section 6.1.1.1 | 3068 | priv: | Private use | 3069 +-------------+---------------------+ 3071 Table 3: ALTO Cost Metrics. 3073 This registry serves two purposes. First, it ensures uniqueness of 3074 identifiers referring to ALTO Cost Metrics. Second, it provides 3075 references to particular semantics of allocated Cost Metrics to be 3076 applied by both ALTO Servers and applications utilizing ALTO Clients. 3078 New ALTO Cost Metrics are assigned after IETF Review [RFC5226] to 3079 ensure that proper documentation regarding ALTO Cost Metric semantics 3080 and security considerations has been provided. The RFCs documenting 3081 the new metrics should be detailed enough to provide guidance to both 3082 ALTO Service Providers and applications utilizing ALTO Clients as to 3083 how values of the registered ALTO Cost Metric should be interpreted. 3084 Updates and deletions of ALTO Cost Metrics follow the same procedure. 3086 Registered ALTO Cost Metric identifiers MUST conform to the 3087 syntactical requirements specified in Section 10.6. Identifiers are 3088 to be recorded and displayed as strings. 3090 Identifiers prefixed with 'priv:' are reserved for Private Use. 3092 Requests to add a new value to the registry MUST include the 3093 following information: 3095 o Identifier: The name of the desired ALTO Cost Metric. 3097 o Intended Semantics: ALTO Costs carry with them semantics to guide 3098 their usage by ALTO Clients. For example, if a value refers to a 3099 measurement, the measurement units must be documented. For proper 3100 implementation of the ordinal Cost Mode (e.g., by a third-party 3101 service), it should be documented whether higher or lower values 3102 of the cost are more preferred. 3104 o Security Considerations: ALTO Costs expose information to ALTO 3105 Clients. As such, proper usage of a particular Cost Metric may 3106 require certain information to be exposed by an ALTO Service 3107 Provider. Since network information is frequently regarded as 3108 proprietary or confidential, ALTO Service Providers should be made 3109 aware of the security ramifications related to usage of a Cost 3110 Metric. 3112 This specification requests registration of the identifier 3113 'routingcost'. Semantics for the this Cost Metric are documented in 3114 Section 6.1.1.1, and security considerations are documented in 3115 Section 15.3. 3117 14.3. ALTO Endpoint Property Type Registry 3119 This document requests the creation of an ALTO Endpoint Property 3120 Types registry, listed in Table 4, to be maintained by IANA. 3122 +------------+--------------------+ 3123 | Identifier | Intended Semantics | 3124 +------------+--------------------+ 3125 | pid | See Section 7.1.1 | 3126 | priv: | Private use | 3127 +------------+--------------------+ 3129 Table 4: ALTO Endpoint Property Types. 3131 The maintenance of this registry is similar to that of the preceding 3132 ALTO Cost Metrics. That is, the registry will be maintained by IANA. 3134 New Endpoint Property Types are assigned after IETF Review [RFC5226] 3135 to ensure that proper documentation regarding ALTO Endpoint Property 3136 Type semantics and security considerations has been provided. 3137 Updates and deletions of ALTO Endpoint Property Type follow the same 3138 procedure. 3140 Registered ALTO Endpoint Property Type identifiers MUST conform to 3141 the syntactical requirements specified in Section 10.8.1. 3142 Identifiers are to be recorded and displayed as strings. 3144 Identifiers prefixed with 'priv:' are reserved for Private Use. 3146 Requests to add a new value to the registry MUST include the 3147 following information: 3149 o Identifier: The name of the desired ALTO Endpoint Property Type. 3151 o Intended Semantics: ALTO Endpoint Properties carry with them 3152 semantics to guide their usage by ALTO Clients. Hence, a document 3153 defining a new type should provide guidance to both ALTO Service 3154 Providers and applications utilizing ALTO Clients as to how values 3155 of the registered ALTO Endpoint Property should be interpreted. 3156 For example, if a value refers to a measurement, the measurement 3157 units must be documented. 3159 o Security Considerations: ALTO Endpoint Properties expose 3160 information to ALTO Clients. ALTO Service Providers should be 3161 made aware of the security ramifications related to the exposure 3162 of an Endpoint Property. 3164 In particular, the request should discuss the sensitivity of the 3165 information, and why such sensitive information is required for ALTO- 3166 based operations. It may recommend that ISP provide mechanisms for 3167 users to grant or deny consent to such information sharing. 3168 Limitation to a trust domain being a type of consent bounding. 3170 A request defining new Endpoint Properties should focus on exposing 3171 attributes of endpoints that are related to the goals of ALTO -- 3172 optimization of application-layer traffic -- as opposed to more 3173 general properties of endpoints. Maintaining this focus on 3174 technical, network-layer data will also help extension developers 3175 avoid the privacy concerns associated with publishing information 3176 about endpoints. For example: 3178 o An extension to indicate the capacity of a server would likely be 3179 appropriate, since server capacities can be used by a client to 3180 choose between multiple equivalent servers. In addition, these 3181 properties are unlikely to be viewed as private information. 3183 o An extension to indicate the geolocation of endpoints might be 3184 appropriate. In some cases, a certain level of geolocation (e.g., 3185 to the country level) can be useful for selecting content sources. 3186 More precise geolocation, however, is not relevant to content 3187 delivery, and is typically considered private. 3189 o An extension indicating demographic attributes of the owner of an 3190 endpoint (e.g., age, sex, income) would not be appropriate, 3191 because these attributes are not related to delivery optimization, 3192 and because they are clearly private data. 3194 This specification requests registration of the identifier 'pid'. 3195 Semantics for this property is documented in Section 7.1.1, and 3196 security considerations are documented in Section 15.4. 3198 14.4. ALTO Address Type Registry 3200 This document requests the creation of an ALTO Address Type registry, 3201 listed in Table 5, to be maintained by IANA. 3203 +------------+-----------------+-----------------+------------------+ 3204 | Identifier | Address | Prefix Encoding | Mapping to/from | 3205 | | Encoding | | IPv4/v6 | 3206 +------------+-----------------+-----------------+------------------+ 3207 | ipv4 | See | See | Direct mapping | 3208 | | Section 10.4.3 | Section 10.4.4 | to IPv4 | 3209 | ipv6 | See | See | Direct mapping | 3210 | | Section 10.4.3 | Section 10.4.4 | to IPv6 | 3211 +------------+-----------------+-----------------+------------------+ 3213 Table 5: ALTO Address Types. 3215 This registry serves two purposes. First, it ensures uniqueness of 3216 identifiers referring to ALTO Address Types. Second, it states the 3217 requirements for allocated Address Type identifiers. 3219 New ALTO Address Types are assigned after IETF Review [RFC5226] to 3220 ensure that proper documentation regarding the new ALTO Address Types 3221 and their security considerations has been provided. RFCs defining 3222 new Address Types should indicate how an address of a registered type 3223 is encoded as an EndpointAddr and, if possible, a compact method 3224 (e.g., IPv4 and IPv6 prefixes) for encoding a set of addresses as an 3225 EndpointPrefix. Updates and deletions of ALTO Address Types follow 3226 the same procedure. 3228 Registered ALTO Address Type identifiers MUST conform to the 3229 syntactical requirements specified in Section 10.4.2. Identifiers 3230 are to be recorded and displayed as strings. 3232 Requests to add a new value to the registry MUST include the 3233 following information: 3235 o Identifier: The name of the desired ALTO Address Type. 3237 o Endpoint Address Encoding: The procedure for encoding an address 3238 of the registered type as an EndpointAddr (see Section 10.4.3). 3240 o Endpoint Prefix Encoding: The procedure for encoding a set of 3241 addresses of the registered type as an EndpointPrefix (see 3242 Section 10.4.4). If no such compact encoding is available, the 3243 same encoding used for a singular address may be used. In such a 3244 case, it must be documented that sets of addresses of this type 3245 always have exactly one element. 3247 o Mapping to/from IPv4/IPv6 Addresses: If possible, a mechanism to 3248 map addresses of the registered type to and from IPv4 or IPv6 3249 addresses should be specified. 3251 o Security Considerations: In some usage scenarios, Endpoint 3252 Addresses carried in ALTO Protocol messages may reveal information 3253 about an ALTO Client or an ALTO Service Provider. Applications 3254 and ALTO Service Providers using addresses of the registered type 3255 should be made aware of how (or if) the addressing scheme relates 3256 to private information and network proximity. 3258 This specification requests registration of the identifiers 'ipv4' 3259 and 'ipv6', as shown in Table 5. 3261 14.5. ALTO Error Code Registry 3263 This document requests the creation of an ALTO Error Code registry, 3264 to be maintained by IANA. Initial values are listed in Table 1, and 3265 recommended usage of the Error Codes is specified in Section 8.5.2. 3267 Although the Error Codes defined in Table 1 are already quite 3268 complete, future extensions may define new Error Codes. The ALTO 3269 Error Code registry ensures the uniqueness of Error Codes when new 3270 Error Codes are added. 3272 New ALTO Error Codes are assigned after IETF Review [RFC5226] to 3273 ensure that proper documentation regarding the new ALTO Error Codes 3274 and their usage has been provided. 3276 A request to add a new ALTO Error Code to the registry MUST include 3277 the following information: 3279 o Error Code: A string starting with E_ to indicate the error. 3281 o Intended Usage: ALTO Error Codes carry with them semantics to 3282 guide their usage by ALTO Servers and Clients. In particular, if 3283 a new Error Code indicates conditions that overlap with those of 3284 an existing ALTO Error Code, recommended usage of the new Error 3285 Code should be specified. 3287 15. Security Considerations 3289 Some environments and use cases of ALTO require consideration of 3290 security attacks on ALTO Servers and Clients. In order to support 3291 those environments interoperably, the ALTO requirements document 3292 [RFC6708] outlines minimum-to-implement authentication and other 3293 security requirements. Below we consider the threats and protection 3294 strategies. 3296 15.1. Authenticity and Integrity of ALTO Information 3298 15.1.1. Risk Scenarios 3300 An attacker may want to provide false or modified ALTO Information 3301 Resources or Information Resource Directory to ALTO Clients to 3302 achieve certain malicious goals. As an example, an attacker may 3303 provide false endpoint properties. For example, suppose that a 3304 network supports an endpoint property named "hasQuota" which reports 3305 whether an endpoint has usage quota. An attacker may want to 3306 generate a false reply to lead to unexpected charges to the endpoint. 3307 An attack may also want to provide false Cost Map. For example, by 3308 faking a Cost Map that highly prefers a small address range or a 3309 single address, the attacker may be able to turn a distributed 3310 application into a Distributed Denial of Service (DDoS) tool. 3312 Depending on the network scenario, an attacker can attack 3313 authenticity and integrity of ALTO Information Resources using 3314 various techniques, including, but not limited to, sending forged 3315 DHCP replies in an Ethernet, DNS poisoning, and installing a 3316 transparent HTTP proxy that does some modifications. 3318 15.1.2. Protection Strategies 3320 ALTO protects the authenticity and integrity of ALTO Information 3321 (both Information Directory and individual Information Resources) by 3322 leveraging the authenticity and integrity mechanisms in TLS (see 3323 Section 8.3.5). 3325 ALTO Providers who request server certificates and certification 3326 authorities who issue ALTO-specific certificates SHOULD consider the 3327 recommendations and guidelines defined in [RFC6125]. 3329 Software engineers developing and service providers deploying ALTO 3330 should make themselves familiar with possibly updated standards 3331 documents as well as up-to-date Best Current Practices on configuring 3332 HTTP over TLS. 3334 15.1.3. Limitations 3336 The protection of HTTP over TLS for ALTO depends on that the domain 3337 name in the URI for the Information Resources is not comprised. This 3338 will depend on the protection implemented by service discovery. 3340 A deployment scenario may require redistribution of ALTO information 3341 to improve scalability. When authenticity and integrity of ALTO 3342 information are still required, then ALTO Clients obtaining ALTO 3343 information through redistribution must be able to validate the 3344 received ALTO information. Support for this validation is not 3345 provided in this document, but may be provided by extension 3346 documents. 3348 15.2. Potential Undesirable Guidance from Authenticated ALTO 3349 Information 3351 15.2.1. Risk Scenarios 3353 The ALTO Service makes it possible for an ALTO Provider to influence 3354 the behavior of network applications. An ALTO Provider may be 3355 hostile to some applications and hence try to use ALTO Information 3356 Resources to achieve certain goals [RFC5693]: "redirecting 3357 applications to corrupted mediators providing malicious content, or 3358 applying policies in computing Cost Map based on criteria other than 3359 network efficiency." See [I-D.ietf-alto-deployments] for additional 3360 discussions on faked ALTO Guidance. 3362 A related scenario is that an ALTO Server could unintentionally give 3363 "bad" guidance. For example, if many ALTO Clients follow the Cost 3364 Map or Endpoint Cost guidance without doing additional sanity checks 3365 or adaptation, more preferable hosts and/or links could get 3366 overloaded while less preferable ones remain idle; see AR-14 of 3367 [RFC6708] for related application considerations. 3369 15.2.2. Protection Strategies 3371 To protect applications from undesirable ALTO Information Resources, 3372 it is important to note that there is no protocol mechanism to 3373 require conforming behaviors on how applications use ALTO Information 3374 Resources. An application using ALTO may consider including a 3375 mechanism to detect misleading or undesirable results from using ALTO 3376 Information Resources. For example, if throughput measurements do 3377 not show "better-than-random" results when using the Cost Map to 3378 select resource providers, the application may want to disable ALTO 3379 usage or switch to an external ALTO Server provided by an 3380 "independent organization" (see AR-20 and AR-21 in [RFC6708]). If 3381 the first ALTO Server is provided by the access network service 3382 provider and the access network service provider tries to redirect 3383 access to the external ALTO Server back to the provider's ALTO Server 3384 or try to tamper with the responses, the preceding authentication and 3385 integrity protection can detect such a behavior. 3387 15.3. Confidentiality of ALTO Information 3389 15.3.1. Risk Scenarios 3391 Although in many cases ALTO Information Resources may be regarded as 3392 non-confidential information, there are deployment cases where ALTO 3393 Information Resources can be sensitive information that can pose 3394 risks if exposed to unauthorized parties. We discuss the risks and 3395 protection strategies for such deployment scenarios. 3397 For example, an attacker may infer details regarding the topology, 3398 status, and operational policies of a network through the Network and 3399 Cost Maps. As a result, a sophisticated attacker may be able to 3400 infer more fine-grained topology information than an ISP hosting an 3401 ALTO Server intends to disclose. The attacker can leverage the 3402 information to mount effective attacks such as focusing on high-cost 3403 links. 3405 Revealing some endpoint properties may also reveal additional 3406 information than the Provider intended. For example, when adding the 3407 line bitrate as one endpoint property, such information may be 3408 potentially linked to the income of the habitants at the network 3409 location of an endpoint. 3411 In [RFC6708] Section 5.2.1, three types of risks associated with the 3412 confidentiality of ALTO Information Resources are identified: risk 3413 type (1) Excess disclosure of the ALTO service provider's data to an 3414 authorized ALTO Client; risk type (2) Disclosure of the ALTO service 3415 provider's data (e.g., network topology information or endpoint 3416 addresses) to an unauthorized third party; and risk type (3) Excess 3417 retrieval of the ALTO service provider's data by collaborating ALTO 3418 Clients. [I-D.ietf-alto-deployments] also discusses information 3419 leakage from ALTO. 3421 15.3.2. Protection Strategies 3423 To address risk types (1) and (3), the Provider of an ALTO Server 3424 must be cognizant that the network topology and provisioning 3425 information provided through ALTO may lead to attacks. ALTO does not 3426 require any particular level of details of information disclosure, 3427 and hence the Provider should evaluate how much information is 3428 revealed and the associated risks. 3430 To address risk type (2), the ALTO Protocol needs confidentiality. 3431 Since ALTO requires that HTTP over TLS must be supported, the 3432 confidentiality mechanism is provided by HTTP over TLS. 3434 For deployment scenarios where client authentication is desired to 3435 address risk type (2), ALTO requires that HTTP Digestion 3436 Authentication is supported to achieve ALTO Client Authentication to 3437 limit the number of parties with whom ALTO information is directly 3438 shared. TLS Client Authentication may also be supported. Depending 3439 on the use-case and scenario, an ALTO Server may apply other access 3440 control techniques to restrict access to its services. Access 3441 control can also help to prevent Denial-of-Service attacks by 3442 arbitrary hosts from the Internet. See [I-D.ietf-alto-deployments] 3443 for a more detailed discussion on this issue. 3445 See Section 14.3 on guidelines when registering Endpoint Properties 3446 to protect endpoint privacy. 3448 15.3.3. Limitations 3450 ALTO Information Providers should be cognizant that encryption only 3451 protects ALTO information until it is decrypted by the intended ALTO 3452 Client. Digital Rights Management (DRM) techniques and legal 3453 agreements protecting ALTO information are outside of the scope of 3454 this document. 3456 15.4. Privacy for ALTO Users 3458 15.4.1. Risk Scenarios 3460 The ALTO Protocol provides mechanisms in which the ALTO Client 3461 serving a user can send messages containing Network Location 3462 Identifiers (IP addresses or fine-grained PIDs) to the ALTO Server. 3463 This is particularly true for the Endpoint Property, Endpoint Cost, 3464 and fine-grained Filtered Map services. The ALTO Server or a third- 3465 party who is able to intercept such messages can store and process 3466 obtained information in order to analyze user behaviors and 3467 communication patterns. The analysis may correlate information 3468 collected from multiple clients to deduce additional application/ 3469 content information. Such analysis can lead to privacy risks. For a 3470 more comprehensive classification of related risk scenarios, see 3471 cases 4, 5, and 6 in [RFC6708], Section 5.2. 3473 15.4.2. Protection Strategies 3475 To protect user privacy, an ALTO Client should be cognizant about 3476 potential ALTO Server tracking through client queries, e.g., by using 3477 HTTP cookies. The ALTO Protocol as defined by this document does not 3478 rely on HTTP cookies. ALTO Clients MAY decide to not return cookies 3479 received from the server, in order to make tracking more difficult. 3480 However, this might break protocol extensions that are beyond the 3481 scope of this document. 3483 An ALTO Client may consider the possibility of relying only on 3484 Network Map for PIDs and Cost Map amongst PIDs to avoid passing IP 3485 addresses of other endpoints (e.g., peers) to the ALTO Server. When 3486 specific IP addresses are needed (e.g., when using the Endpoint Cost 3487 Service), an ALTO Client SHOULD minimize the amount of information 3488 sent in IP addresses. For example, the ALTO Client may consider 3489 obfuscation techniques such as specifying a broader address range 3490 (i.e., a shorter prefix length) or by zeroing out or randomizing the 3491 last few bits of IP addresses. Note that obfuscation may yield less 3492 accurate results. 3494 15.5. Availability of ALTO Service 3496 15.5.1. Risk Scenarios 3498 An attacker may want to disable ALTO Service as a way to disable 3499 network guidance to large scale applications.In particular, queries 3500 which can be generated with low effort but result in expensive 3501 workloads at the ALTO Server could be exploited for Denial-of-Service 3502 attacks. For instance, a simple ALTO query with n Source Network 3503 Locations and m Destination Network Locations can be generated fairly 3504 easily but results in the computation of n*m Path Costs between pairs 3505 by the ALTO Server (see Section 5.2). 3507 15.5.2. Protection Strategies 3509 ALTO Provider should be cognizant of the workload at the ALTO Server 3510 generated by certain ALTO Queries, such as certain queries to the Map 3511 Service, the Map Filtering Service and the Endpoint Cost (Ranking) 3512 Service. One way to limit Denial-of-Service attacks is to employ 3513 access control to the ALTO Server. The ALTO Server can also indicate 3514 overload and reject repeated requests that can cause availability 3515 problems. More advanced protection schemes such as computational 3516 puzzles [I-D.jennings-sip-hashcash] may be considered in an extension 3517 document. 3519 An ALTO Provider should also leverage the fact that the Map Service 3520 allows ALTO Servers to pre-generate maps that can be distributed to 3521 many ALTO Clients. 3523 16. Manageability Considerations 3525 This section details operations and management considerations based 3526 on existing deployments and discussions during protocol development. 3527 It also indicates where extension documents are expected to provide 3528 appropriate functionality discussed in [RFC5706] as additional 3529 deployment experience becomes available. 3531 16.1. Operations 3533 16.1.1. Installation and Initial Setup 3535 The ALTO Protocol is based on HTTP. Thus, configuring an ALTO Server 3536 may require configuring the underlying HTTP server implementation to 3537 define appropriate security policies, caching policies, performance 3538 settings, etc. 3540 Additionally, an ALTO Service Provider will need to configure the 3541 ALTO information to be provided by the ALTO Server. The granularity 3542 of the topological map and the cost map is left to the specific 3543 policies of the ALTO Service Provider. However, a reasonable default 3544 may include two PIDs, one to hold the endpoints in the provider's 3545 network and the second PID to represent full IPv4 and IPv6 3546 reachability (see Section 11.2.2), with the cost between each source/ 3547 destination PID set to 1. Another operational issue that the ALTO 3548 Service Provider needs to consider is that the filtering service can 3549 degenerate into a full map service when the filtering input is empty. 3550 Although this choice as the degeneration behavior provides 3551 continuity, the computational and network load of serving full maps 3552 to a large number of ALTO Clients should be considered. 3554 Implementers employing an ALTO Client should attempt to automatically 3555 discover an appropriate ALTO Server. Manual configuration of the 3556 ALTO Server location may be used where automatic discovery is not 3557 appropriate. Methods for automatic discovery and manual 3558 configuration are discussed in [I-D.ietf-alto-server-discovery]. 3560 Specifications for underlying protocols (e.g., TCP, HTTP, TLS) should 3561 be consulted for their available settings and proposed default 3562 configurations. 3564 16.1.2. Migration Path 3566 This document does not detail a migration path for ALTO Servers since 3567 there is no previous standard protocol providing the similar 3568 functionality. 3570 There are existing applications making use of network information 3571 discovered from other entities such as whois, geo-location databases, 3572 or round-trip time measurements, etc. Such applications should 3573 consider using ALTO as an additional source of information; ALTO need 3574 not be the sole source of network information. 3576 16.1.3. Dependencies on Other Protocols and Functional Components 3578 The ALTO Protocol assumes that HTTP client and server implementations 3579 exist. It also assumes that JSON encoder and decoder implementations 3580 exist. 3582 An ALTO Server assumes that it can gather sufficient information to 3583 populate Network and Cost maps. "Sufficient information" is 3584 dependent on the information being exposed, but likely includes 3585 information gathered from protocols such as IGP and EGP Routing 3586 Information Bases (see Figure 1). Specific mechanisms have been 3587 proposed (e.g., [I-D.medved-alto-svr-apis]) and are expected to be 3588 provided in extension documents. 3590 16.1.4. Impact and Observation on Network Operation 3592 ALTO presents a new opportunity for managing network traffic by 3593 providing additional information to clients. In particular, the 3594 deployment of an ALTO Server may shift network traffic patterns, and 3595 the potential impact to network operation can be large. An ALTO 3596 Service Provider should ensure that appropriate information is being 3597 exposed. Privacy implications for ISPs are discussed in 3598 Section 15.3. 3600 An ALTO Service Provider should consider how to measure impacts on 3601 (or integration with) traffic engineering, in addition to monitoring 3602 correctness and responsiveness of ALTO Servers. The measurement of 3603 impacts can be challenging because ALTO-enabled applications may not 3604 provide related information back to the ALTO Service Provider. 3605 Furthermore, the measurement of an ALTO Service Provider may show 3606 that ALTO Clients are not bound to ALTO Server guidance as ALTO is 3607 only one source of information. 3609 While it can be challenging to measure the impact of ALTO guidance, 3610 there exist some possible techniques. In certain trusted deployment 3611 environments, it may be possible to collect information directly from 3612 ALTO clients. It may also be possible to vary or selectively disable 3613 ALTO guidance for a portion of ALTO clients either by time, 3614 geographical region, or some other criteria to compare the network 3615 traffic characteristics with and without ALTO. 3617 Both ALTO Service Providers and those using ALTO Clients should be 3618 aware of the impact of incorrect or faked guidance (see 3619 [I-D.ietf-alto-deployments]). 3621 16.2. Management 3623 16.2.1. Management Interoperability 3625 A common management API would be desirable given that ALTO Servers 3626 may typically be configured with dynamic data from various sources, 3627 and ALTO Servers are intended to scale horizontally for fault- 3628 tolerance and reliability. A specific API or protocol is outside the 3629 scope of this document, but may be provided by an extension document. 3631 Logging is an important functionality for ALTO Servers and, depending 3632 on the deployment, ALTO Clients. Logging should be done via syslog 3633 [RFC5424]. 3635 16.2.2. Management Information 3637 A Management Information Model (see Section 3.2 of [RFC5706]) is not 3638 provided by this document, but should be included or referenced by 3639 any extension documenting an ALTO-related management API or protocol. 3641 16.2.3. Fault Management 3643 An ALTO Service Provider should monitor whether any ALTO Servers have 3644 failed. See Section 16.2.5 for related metrics which may indicate 3645 server failures. 3647 16.2.4. Configuration Management 3649 Standardized approaches and protocols to configuration management for 3650 ALTO are outside the scope of this document, but this document does 3651 outline high-level principles suggested for future standardization 3652 efforts. 3654 An ALTO Server requires at least the following logical inputs: 3656 o Data sources from which ALTO Information is derived. This can 3657 either be raw network information (e.g., from routing elements) or 3658 pre-processed ALTO-level information in the form of a Network Map, 3659 Cost Map, etc. 3661 o Algorithms for computing the ALTO information returned to clients. 3662 These could either return information from a database, or 3663 information customized for each client. 3665 o Security policies mapping potential clients to the information 3666 that they have privilege to access. 3668 Multiple ALTO Servers can be deployed for scalability. A centralized 3669 configuration database may be used to ensure they are providing the 3670 desired ALTO information with appropriate security controls. The 3671 ALTO information (e.g., Network Maps and Cost Maps) being served by 3672 each ALTO Server, as well as security policies (HTTP authentication, 3673 TLS client and server authentication, TLS encryption parameters) 3674 intended to serve the same information should be monitored for 3675 consistency. 3677 16.2.5. Performance Management 3679 An exhaustive list of desirable performance information from ALTO 3680 Servers and ALTO Clients are outside of the scope of this document. 3681 The following is a list of suggested ALTO-specific metrics to be 3682 monitored based on the existing deployment and protocol development 3683 experience: 3685 o Requests and responses for each service listed in a Information 3686 Directory (total counts and size in bytes). 3688 o CPU and memory utilization 3690 o ALTO map updates 3692 o Number of PIDs 3694 o ALTO map sizes (in-memory size, encoded size, number of entries) 3696 16.2.6. Security Management 3698 Section 15 documents ALTO-specific security considerations. 3699 Operators should configure security policies with those in mind. 3700 Readers should refer to HTTP [RFC2616] and TLS [RFC5246] and related 3701 documents for mechanisms available for configuring security policies. 3702 Other appropriate security mechanisms (e.g., physical security, 3703 firewalls, etc) should also be considered. 3705 17. References 3707 17.1. Normative References 3709 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", 3710 RFC 1812, June 1995. 3712 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 3713 Extensions (MIME) Part Two: Media Types", RFC 2046, 3714 November 1996. 3716 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3717 Requirement Levels", BCP 14, RFC 2119, March 1997. 3719 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 3720 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 3721 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 3723 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 3724 Resource Identifier (URI): Generic Syntax", STD 66, 3725 RFC 3986, January 2005. 3727 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 3728 (CIDR): The Internet Address Assignment and Aggregation 3729 Plan", BCP 122, RFC 4632, August 2006. 3731 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 3732 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 3733 May 2008. 3735 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3736 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 3738 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 3739 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 3740 October 2008. 3742 [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009. 3744 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 3745 Address Text Representation", RFC 5952, August 2010. 3747 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 3748 Verification of Domain-Based Application Service Identity 3749 within Internet Public Key Infrastructure Using X.509 3750 (PKIX) Certificates in the Context of Transport Layer 3751 Security (TLS)", RFC 6125, March 2011. 3753 17.2. Informative References 3755 [BitTorrent] 3756 "Bittorrent Protocol Specification v1.0", 3757 . 3759 [Fielding-Thesis] 3760 Fielding, R., "Architectural Styles and the Design of 3761 Network-based Software Architectures", University of 3762 California, Irvine, Dissertation 2000, 2000. 3764 [I-D.akonjang-alto-proxidor] 3765 Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D. 3766 Saucez, "The PROXIDOR Service", 3767 draft-akonjang-alto-proxidor-00 (work in progress), 3768 March 2009. 3770 [I-D.ietf-alto-deployments] 3771 Stiemerling, M., Kiesel, S., Previdi, S., and M. Scharf, 3772 "ALTO Deployment Considerations", 3773 draft-ietf-alto-deployments-09 (work in progress), 3774 February 2014. 3776 [I-D.ietf-alto-server-discovery] 3777 Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and 3778 S. Yongchao, "ALTO Server Discovery", 3779 draft-ietf-alto-server-discovery-10 (work in progress), 3780 September 2013. 3782 [I-D.ietf-httpbis-p2-semantics] 3783 Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 3784 (HTTP/1.1): Semantics and Content", 3785 draft-ietf-httpbis-p2-semantics-26 (work in progress), 3786 February 2014. 3788 [I-D.jenkins-alto-cdn-use-cases] 3789 Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and 3790 S. Previdi, "Use Cases for ALTO within CDNs", 3791 draft-jenkins-alto-cdn-use-cases-03 (work in progress), 3792 June 2012. 3794 [I-D.jennings-sip-hashcash] 3795 Jennings, C., "Computational Puzzles for SPAM Reduction in 3796 SIP", draft-jennings-sip-hashcash-06 (work in progress), 3797 July 2007. 3799 [I-D.medved-alto-svr-apis] 3800 Medved, J., Ward, D., Peterson, J., Woundy, R., and D. 3801 McDysan, "ALTO Network-Server and Server-Server APIs", 3802 draft-medved-alto-svr-apis-00 (work in progress), 3803 March 2011. 3805 [I-D.p4p-framework] 3806 Alimi, R., Pasko, D., Popkin, L., Wang, Y., and Y. Yang, 3807 "P4P: Provider Portal for P2P Applications", 3808 draft-p4p-framework-00 (work in progress), November 2008. 3810 [I-D.saumitra-alto-multi-ps] 3811 Das, S., Narayanan, V., and L. Dondeti, "ALTO: A Multi 3812 Dimensional Peer Selection Problem", 3813 draft-saumitra-alto-multi-ps-00 (work in progress), 3814 October 2008. 3816 [I-D.saumitra-alto-queryresponse] 3817 Das, S. and V. Narayanan, "A Client to Service Query 3818 Response Protocol for ALTO", 3819 draft-saumitra-alto-queryresponse-00 (work in progress), 3820 March 2009. 3822 [I-D.shalunov-alto-infoexport] 3823 Shalunov, S., Penno, R., and R. Woundy, "ALTO Information 3824 Export Service", draft-shalunov-alto-infoexport-00 (work 3825 in progress), October 2008. 3827 [I-D.wang-alto-p4p-specification] 3828 Wang, Y., Alimi, R., Pasko, D., Popkin, L., and Y. Yang, 3829 "P4P Protocol Specification", 3830 draft-wang-alto-p4p-specification-00 (work in progress), 3831 March 2009. 3833 [IEEE.754.2008] 3834 Institute of Electrical and Electronics Engineers, 3835 "Standard for Binary Floating-Point Arithmetic", IEEE 3836 Standard 754, August 2008. 3838 [P4P-SIGCOMM08] 3839 Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A. 3840 Silberschatz, "P4P: Provider Portal for (P2P) 3841 Applications", SIGCOMM 2008, August 2008. 3843 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 3845 [RFC4627] Crockford, D., "The application/json Media Type for 3846 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 3848 [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic 3849 Optimization (ALTO) Problem Statement", RFC 5693, 3850 October 2009. 3852 [RFC5706] Harrington, D., "Guidelines for Considering Operations and 3853 Management of New Protocols and Protocol Extensions", 3854 RFC 5706, November 2009. 3856 [RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for 3857 IPv4/IPv6 Translation", RFC 6144, April 2011. 3859 [RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix 3860 Translation", RFC 6296, June 2011. 3862 [RFC6708] Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and 3863 Y. Yang, "Application-Layer Traffic Optimization (ALTO) 3864 Requirements", RFC 6708, September 2012. 3866 Appendix A. Acknowledgments 3868 Thank you to Sebastian Kiesel (University of Stuttgart) and Jan 3869 Seedorf (NEC) for substantial contributions to the Security 3870 Considerations section. Ben Niven-Jenkins (Velocix), Michael Scharf 3871 and Sabine Randriamasy (Alcatel-Lucent) gave substantial feedback and 3872 suggestions on the protocol design. We are particularly grateful to 3873 the substantial contributions of Wendy Roome (Alcatel-Lucent). 3875 We would like to thank the following people whose input and 3876 involvement was indispensable in achieving this merged proposal: 3878 Obi Akonjang (DT Labs/TU Berlin), 3880 Saumitra M. Das (Qualcomm Inc.), 3882 Syon Ding (China Telecom), 3884 Doug Pasko (Verizon), 3886 Laird Popkin (Pando Networks), 3888 Satish Raghunath (Juniper Networks), 3890 Albert Tian (Ericsson/Redback), 3892 Yu-Shun Wang (Microsoft), 3894 David Zhang (PPLive), 3896 Yunfei Zhang (China Mobile). 3898 We would also like to thank the following additional people who were 3899 involved in the projects that contributed to this merged document: 3900 Alex Gerber (ATT), Chris Griffiths (Comcast), Ramit Hora (Pando 3901 Networks), Arvind Krishnamurthy (University of Washington), Marty 3902 Lafferty (DCIA), Erran Li (Bell Labs), Jin Li (Microsoft), Y. Grace 3903 Liu (IBM Watson), Jason Livingood (Comcast), Michael Merritt (ATT), 3904 Ingmar Poese (DT Labs/TU Berlin), James Royalty (Pando Networks), 3905 Damien Saucez (UCL) Thomas Scholl (ATT), Emilio Sepulveda 3906 (Telefonica), Avi Silberschatz (Yale University), Hassan Sipra (Bell 3907 Canada), Georgios Smaragdakis (DT Labs/TU Berlin), Haibin Song 3908 (Huawei), Oliver Spatscheck (ATT), See-Mong Tang (Microsoft), Jia 3909 Wang (ATT), Hao Wang (Yale University), Ye Wang (Yale University), 3910 Haiyong Xie (Yale University). 3912 Appendix B. Design History and Merged Proposals 3914 The ALTO Protocol specified in this document consists of 3915 contributions from 3917 o P4P [I-D.p4p-framework], [P4P-SIGCOMM08], 3918 [I-D.wang-alto-p4p-specification]; 3920 o ALTO Info-Export [I-D.shalunov-alto-infoexport]; 3922 o Query/Response [I-D.saumitra-alto-queryresponse], 3923 [I-D.saumitra-alto-multi-ps]; and 3925 o Proxidor [I-D.akonjang-alto-proxidor]. 3927 Appendix C. Authors 3929 [[CmtAuthors: RFC Editor: Please move information in this section to 3930 the Authors' Addresses section at publication time.]] 3932 Sebastian Kiesel 3933 University of Stuttgart Computing Center 3934 Networks and Communication Systems Department 3935 Allmandring 30 3936 70550 Stuttgart 3937 Germany 3939 Email: ietf-alto@skiesel.de 3941 Stefano Previdi 3942 Cisco 3944 Email: sprevidi@cisco.com 3946 Wendy Roome 3947 Alcatel Lucent 3949 Email: w.roome@alcatel-lucent.com 3950 Stanislav Shalunov 3951 BitTorrent 3953 Email: shalunov@bittorrent.com 3955 Richard Woundy 3956 Comcast 3958 Richard_Woundy@cable.comcast.com 3960 Authors' Addresses 3962 Richard Alimi (editor) 3963 Google 3964 1600 Amphitheatre Parkway 3965 Mountain View CA 3966 USA 3968 Email: ralimi@google.com 3970 Reinaldo Penno (editor) 3971 Cisco Systems 3972 170 West Tasman Dr 3973 San Jose CA 3974 USA 3976 Email: repenno@cisco.com 3978 Y. Richard Yang (editor) 3979 Yale University 3980 51 Prospect St 3981 New Haven CT 3982 USA 3984 Email: yry@cs.yale.edu