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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: June 12, 2014 Cisco Systems 6 Y. Yang, Ed. 7 Yale University 8 December 9, 2013 10 ALTO Protocol 11 draft-ietf-alto-protocol-23.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 June 12, 2014. 63 Copyright Notice 65 Copyright (c) 2013 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. HTTP Cookies . . . . . . . . . . . . . . . . . . . . . 23 124 8.3.8. Parsing of Unknown Fields . . . . . . . . . . . . . . 23 125 8.4. Server Response Encoding . . . . . . . . . . . . . . . . . 24 126 8.4.1. Meta Information . . . . . . . . . . . . . . . . . . . 24 127 8.4.2. Data Information . . . . . . . . . . . . . . . . . . . 24 128 8.5. Protocol Errors . . . . . . . . . . . . . . . . . . . . . 24 129 8.5.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 25 130 8.5.2. Response Format and Error Codes . . . . . . . . . . . 25 131 8.5.3. Overload Conditions and Server Unavailability . . . . 27 132 9. Protocol Specification: Information Resource Directory . . . . 27 133 9.1. Information Resource Attributes . . . . . . . . . . . . . 27 134 9.1.1. Resource ID . . . . . . . . . . . . . . . . . . . . . 27 135 9.1.2. Media Type . . . . . . . . . . . . . . . . . . . . . . 28 136 9.1.3. Capabilities . . . . . . . . . . . . . . . . . . . . . 28 137 9.1.4. Accepts Input Parameters . . . . . . . . . . . . . . . 28 138 9.1.5. Dependent Resources . . . . . . . . . . . . . . . . . 28 139 9.2. Information Resource Directory (IRD) . . . . . . . . . . . 28 140 9.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 29 141 9.2.2. Encoding . . . . . . . . . . . . . . . . . . . . . . . 29 142 9.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 31 143 9.2.4. Delegation using IRD . . . . . . . . . . . . . . . . . 34 144 9.2.5. Considerations of Using IRD . . . . . . . . . . . . . 36 145 10. Protocol Specification: Basic Data Types . . . . . . . . . . . 36 146 10.1. PID Name . . . . . . . . . . . . . . . . . . . . . . . . . 36 147 10.2. Resource ID . . . . . . . . . . . . . . . . . . . . . . . 37 148 10.3. Version Tag . . . . . . . . . . . . . . . . . . . . . . . 37 149 10.4. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 37 150 10.4.1. Typed Endpoint Addresses . . . . . . . . . . . . . . . 38 151 10.4.2. Address Type . . . . . . . . . . . . . . . . . . . . . 38 152 10.4.3. Endpoint Address . . . . . . . . . . . . . . . . . . . 38 153 10.4.4. Endpoint Prefixes . . . . . . . . . . . . . . . . . . 38 154 10.4.5. Endpoint Address Group . . . . . . . . . . . . . . . . 39 155 10.5. Cost Mode . . . . . . . . . . . . . . . . . . . . . . . . 40 156 10.6. Cost Metric . . . . . . . . . . . . . . . . . . . . . . . 40 157 10.7. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . 40 158 10.8. Endpoint Property . . . . . . . . . . . . . . . . . . . . 41 159 10.8.1. Resource Specific Endpoint Properties . . . . . . . . 41 160 10.8.2. Global Endpoint Properties . . . . . . . . . . . . . . 41 161 11. Protocol Specification: Service Information Resources . . . . 41 162 11.1. Meta Information . . . . . . . . . . . . . . . . . . . . . 42 163 11.2. Map Service . . . . . . . . . . . . . . . . . . . . . . . 42 164 11.2.1. Network Map . . . . . . . . . . . . . . . . . . . . . 42 165 11.2.2. Mapping IP Addresses to PIDs for 'ipv4'/'ipv6' 166 Network Maps . . . . . . . . . . . . . . . . . . . . . 45 167 11.2.3. Cost Map . . . . . . . . . . . . . . . . . . . . . . . 46 168 11.3. Map Filtering Service . . . . . . . . . . . . . . . . . . 49 169 11.3.1. Filtered Network Map . . . . . . . . . . . . . . . . . 49 170 11.3.2. Filtered Cost Map . . . . . . . . . . . . . . . . . . 51 171 11.4. Endpoint Property Service . . . . . . . . . . . . . . . . 55 172 11.4.1. Endpoint Property . . . . . . . . . . . . . . . . . . 56 173 11.5. Endpoint Cost Service . . . . . . . . . . . . . . . . . . 59 174 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 . . . . . . . . . . . . . . . . 71 189 14.5. ALTO Error Code Registry . . . . . . . . . . . . . . . . . 73 190 15. Security Considerations . . . . . . . . . . . . . . . . . . . 73 191 15.1. Authenticity and Integrity of ALTO Information . . . . . . 73 192 15.1.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 73 193 15.1.2. Protection Strategies . . . . . . . . . . . . . . . . 73 194 15.1.3. Limitations . . . . . . . . . . . . . . . . . . . . . 74 195 15.2. Potential Undesirable Guidance from Authenticated ALTO 196 Information . . . . . . . . . . . . . . . . . . . . . . . 74 197 15.2.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 74 198 15.2.2. Protection Strategies . . . . . . . . . . . . . . . . 75 199 15.3. Confidentiality of ALTO Information . . . . . . . . . . . 75 200 15.3.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 75 201 15.3.2. Protection Strategies . . . . . . . . . . . . . . . . 76 202 15.3.3. Limitations . . . . . . . . . . . . . . . . . . . . . 76 203 15.4. Privacy for ALTO Users . . . . . . . . . . . . . . . . . . 76 204 15.4.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 76 205 15.4.2. Protection Strategies . . . . . . . . . . . . . . . . 77 206 15.5. Availability of ALTO Service . . . . . . . . . . . . . . . 77 207 15.5.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 77 208 15.5.2. Protection Strategies . . . . . . . . . . . . . . . . 77 209 16. Manageability Considerations . . . . . . . . . . . . . . . . . 78 210 16.1. Operations . . . . . . . . . . . . . . . . . . . . . . . . 78 211 16.1.1. Installation and Initial Setup . . . . . . . . . . . . 78 212 16.1.2. Migration Path . . . . . . . . . . . . . . . . . . . . 78 213 16.1.3. Requirements on Other Protocols and Functional 214 Components . . . . . . . . . . . . . . . . . . . . . . 79 215 16.1.4. Impact and Observation on Network Operation . . . . . 79 216 16.2. Management . . . . . . . . . . . . . . . . . . . . . . . . 79 217 16.2.1. Management Interoperability . . . . . . . . . . . . . 79 218 16.2.2. Management Information . . . . . . . . . . . . . . . . 80 219 16.2.3. Fault Management . . . . . . . . . . . . . . . . . . . 80 220 16.2.4. Configuration Management . . . . . . . . . . . . . . . 80 221 16.2.5. Performance Management . . . . . . . . . . . . . . . . 81 222 16.2.6. Security Management . . . . . . . . . . . . . . . . . 81 223 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 81 224 17.1. Normative References . . . . . . . . . . . . . . . . . . . 81 225 17.2. Informative References . . . . . . . . . . . . . . . . . . 82 226 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 84 227 Appendix B. Design History and Merged Proposals . . . . . . . . . 85 228 Appendix C. Specifying the "value" Key for 229 E_INVALID_FIELD_VALUE . . . . . . . . . . . . . . . . 86 230 Appendix D. Authors . . . . . . . . . . . . . . . . . . . . . . . 86 231 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 87 233 1. Introduction 235 1.1. Problem Statement 237 This document defines the ALTO Protocol, which provides a solution 238 for the problem stated in [RFC5693]. Specifically, in today's 239 networks, network information such as network topologies, link 240 availability, routing policies, and path costs are hidden from the 241 application layer, and many applications benefited from such hiding 242 of network complexity. However, new applications, such as 243 application-layer overlays, can benefit from information about the 244 underlying network infrastructure. In particular, these modern 245 network applications can be adaptive, and hence become more network- 246 efficient (e.g., reduce network resource consumption) and achieve 247 better application performance (e.g., accelerated download rate), by 248 leveraging network-provided information. 250 At a high level, the ALTO Protocol specified in this document is a 251 unidirectional interface that allows a network to publish its network 252 information such as network locations, costs between them at 253 configurable granularities, and endhost properties to network 254 applications. The information published by the ALTO Protocol should 255 benefit both the network and the applications (i.e., the consumers of 256 the information). Either the operator of the network or a third- 257 party (e.g., an information aggregator) can retrieve or derive 258 related information of the network and publish it using the ALTO 259 Protocol. When a network provides information through the ALTO 260 Protocol, we say that the network provides the ALTO Service. 262 To better understand the goal of the ALTO Protocol, we provide a 263 short, non-normative overview of the benefits of ALTO to both 264 networks and applications: 266 o A network that provides an ALTO Service can achieve better 267 utilization of its networking infrastructure. For example, by 268 using ALTO as a tool to interact with applications, a network is 269 able to provide network information to applications so that the 270 applications can better manage traffic on more expensive or 271 difficult-to-provision links such as long distance, transit or 272 backup links. During the interaction, the network can choose to 273 protect its sensitive and confidential network state information, 274 by abstracting real metric values into non-real numerical scores 275 or ordinal ranking. 277 o An application that uses an ALTO Service can benefit from better 278 knowledge of the network to avoid network bottlenecks. For 279 example, an overlay application can use information provided by 280 the ALTO Service to avoid selecting peers connected via high-delay 281 links (e.g., some intercontinental links). Using ALTO to 282 initialize each node with promising ("better-than-random") peers, 283 an adaptive peer-to-peer overlay may achieve faster, better 284 convergence. 286 1.2. Design Overview 288 The ALTO Protocol specified in this document meets the ALTO 289 requirements specified in [RFC5693], and unifies multiple protocols 290 previously designed with similar intentions. See Appendix A for a 291 list of people and Appendix B for a list of proposals that have made 292 significant contributions to this effort. 294 The ALTO Protocol uses a REST-ful design [Fielding-Thesis], and 295 encodes its requests and responses using JSON [RFC4627]. These 296 designs are chosen because of their flexibility and extensibility. 297 In addition, these designs make it possible for ALTO to be deployed 298 at scale by leveraging existing HTTP [RFC2616] implementations, 299 infrastructures and deployment experience. 301 2. Terminology 303 We use the following terms defined in [RFC5693]: Application, Overlay 304 Network, Peer, Resource, Resource Identifier, Resource Provider, 305 Resource Consumer, Resource Directory, Transport Address, Host 306 Location Attribute, ALTO Service, ALTO Server, ALTO Client, ALTO 307 Query, ALTO Reply, ALTO Transaction, Local Traffic, Peering Traffic, 308 Transit Traffic. 310 We also use the following additional terms: Endpoint Address, Network 311 Location, ALTO Information, ALTO Information Base, and ALTO Service. 313 2.1. Endpoint 315 An Endpoint is an application or host that is capable of 316 communicating (sending and/or receiving messages) on a network. 318 An Endpoint is typically either a Resource Provider or Resource 319 Consumer. 321 2.2. Endpoint Address 323 An Endpoint Address represents the communication address of an 324 endpoint. Common forms of Endpoint Addresses include IP address, MAC 325 address, overlay ID, and phone number. An Endpoint Address can be 326 network-attachment based (e.g., IP address) or network-attachment 327 agnostic (e.g., MAC address). 329 Each Endpoint Address has an associated Address Type, which indicates 330 both its syntax and semantics. 332 2.3. Network Location 334 Network Location is a generic term denoting a single Endpoint or a 335 group of Endpoints. For instance, it can be a single IPv4 or IPv6 336 address, an IPv4 or IPv6 prefix, or a set of prefixes. 338 2.4. ALTO Information 340 ALTO Information is a generic term referring to the network 341 information sent by an ALTO Server. 343 2.5. ALTO Information Base 345 We use the term ALTO Information Base to refer to the internal 346 representation of ALTO Information maintained by an ALTO Server. 347 Note that the structure of this internal representation is not 348 defined by this document. 350 2.6. ALTO Service 352 A network that provides ALTO Information through the ALTO Protocol is 353 said to provide the ALTO Service. 355 3. Architecture 357 We now define the ALTO architecture and the ALTO Protocol's place in 358 the overall architecture. 360 3.1. ALTO Service and Protocol Scope 362 Each network region in the global Internet can provide its ALTO 363 Service, which conveys network information from the perspective of 364 that network region. A network region in this context can be an 365 Autonomous System (AS), an ISP, a region smaller than an AS or ISP, 366 or a set of ISPs. The specific network region that an ALTO Service 367 represents will depend on the ALTO deployment scenario and ALTO 368 service discovery mechanism. 370 The ALTO Service specified in this document defines network Endpoints 371 (and aggregations thereof) and generic costs amongst them from the 372 region's perspective. The network Endpoints may include all 373 Endpoints in the global Internet. Hence, we say that the network 374 information provided by the ALTO Service of a network region 375 represents the "my-Internet view" of the network region. One may 376 note that the "my-Internet view" defined in this document does not 377 specify the internal topology of a network, and hence, we say that it 378 provides a "single-switch" abstraction. Extensions to this document 379 may 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 groupings. 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 US-ASCII string of type 570 PIDName (see Section 10.1) and its associated set of Endpoint 571 Addresses. As we discussed above, there can be many different ways 572 of grouping the endpoints and assigning PIDs. For example, a PID may 573 denote a subnet, a set of subnets, a metropolitan area, a PoP, an 574 autonomous system, or a set of autonomous systems. Interpreting the 575 PIDs defined in a Network Map using the "single-switch" abstraction, 576 one can 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. 816 8. Protocol Specification: General Processing 818 This section first specifies general client and server processing. 819 The details of specific services will be covered in the following 820 sections. 822 8.1. Overall Design 824 The ALTO Protocol uses a REST-ful design. There are two primary 825 components to this design: 827 o Information Resources: An ALTO Server provides a set of network 828 information resources. Each information resource has a media type 829 [RFC2046]. An ALTO Client may construct an HTTP request for a 830 particular information resource (including any parameters, if 831 necessary), and the ALTO Server returns the requested information 832 resource in an HTTP response. 834 o Information Resource Directory (IRD): An ALTO Server provides to 835 ALTO Clients a list of available information resources and the URI 836 at which each is provided. This document refers to this list as 837 the Information Resource Directory. ALTO Clients consult the 838 directory to determine the services provided by an ALTO Server. 840 8.2. Notation 842 This document uses 'JSONString', 'JSONNumber', 'JSONBool' to indicate 843 the JSON string, number, and boolean types, respectively. The type 844 'JSONValue' indicates a JSON value, as specified in Section 2.1 of 845 [RFC4627]. 847 We use an adaptation of the C-style struct notation to define the 848 fields (names/values) of JSON objects. An optional field is enclosed 849 by [ ], and an array is indicated by two numbers in angle brackets, 850 , where m indicates the minimal number of values, and n is the 851 maximum. When we write * for n, it means no upper bound. In the 852 definitions, the JSON names of the fields are case sensitive. 854 For example, the definition below defines a new type Type4, with 855 three field members (or fields for short) named "name1", "name2", and 856 "name3" respectively. The field named "name3" is optional, and the 857 field named "name2" is an array of at least one value. 858 object { Type1 name1; Type2 name2<1..*>; [Type3 name3;] 859 } Type4; 861 We also define dictionary maps (or maps for short) from strings to 862 JSON values. For example, the definition below defines a Type3 863 object as a map. Type1 must be defined as string, and Type2 can be 864 defined as any type. 865 object-map { Type1 -> Type2; } Type3; 867 We use subtyping to denote that one type is derived from another 868 type. The example below denotes that TypeDerived is derived from 869 TypeBase. TypeDerived includes all fields defined in TypeBase. If 870 TypeBase does not have a field named "name1", TypeDerived will have a 871 new field named "name1". If TypeBase already has a field named 872 "name1" but with a different type, TypeDerived will have a field 873 named "name1" with the type defined in TypeDerived (i.e., Type1 in 874 the example). 875 object { Type1 name1; } TypeDerived : TypeBase; 877 Note that despite the notation, no standard, machine-readable 878 interface definition or schema is provided in this document. 879 Extension documents may document these as necessary. 881 8.3. Basic Operations 883 The ALTO Protocol employs standard HTTP [RFC2616]. It is used for 884 discovering available Information Resources at an ALTO Server and 885 retrieving Information Resources. ALTO Clients and ALTO Servers use 886 HTTP requests and responses carrying ALTO-specific content with 887 encoding as specified in this document, and MUST be compliant with 889 [RFC2616]. 891 Instead of specifying the generic application/json Media Type for all 892 ALTO request parameters (if any) and responses, ALTO Clients and 893 Servers use multiple, specific JSON-based Media Types (e.g., 894 application/alto-networkmap+json, application/alto-costmap+json) to 895 indicate content types; see Table 2 for a list of Media Types defined 896 in this document. This allows easy extensibility while maintaining 897 clear semantics and versioning. For example, a new version of a 898 component of the ALTO Protocol (e.g., a new version of the Network 899 Map) can be defined by simply introducing a new Media Type (e.g., 900 application/alto-networkmap-v2+json). 902 8.3.1. Client Discovering Information Resources 904 To discover available Information Resources, an ALTO Client requests 905 Information Resource Directories. Informally, an Information 906 Resource Directory enumerates URIs at which an ALTO Server offers 907 Information Resources. 909 Specifically, using the ALTO Discovery protocol, an ALTO Client 910 obtains a URI through which it can request an Information Resource 911 Directory (IRD). We refer to this IRD as the Root IRD of the ALTO 912 Client. Each entry in an IRD indicates a URI at which an ALTO Server 913 accepts requests, and returns either an Information Resource or an 914 Information Resource Directory that references additional Information 915 Resources. Beginning with its Root IRD and following links to IRDs 916 recursively, an ALTO Client can discover all Information Resources 917 available to it. We refer to this set of Information Resources as 918 the Information Resource Closure of the ALTO Client. By inspecting 919 its Information Resource Closure, an ALTO Client can determine 920 whether an ALTO Server supports the desired Information Resource, and 921 if it is supported, the URI at which it is available. 923 See Section 9.2 for a detailed specification on IRDs. 925 8.3.2. Client Requesting Information Resources 927 Where possible, the ALTO Protocol uses the HTTP GET method to request 928 resources. However, some ALTO services provide Information Resources 929 that are the function of one or more input parameters. Input 930 parameters are encoded in the HTTP request's entity body, and the 931 ALTO Client MUST use the HTTP POST method to send the parameters. 933 When requesting an ALTO Information Resource that requires input 934 parameters specified in a HTTP POST request, an ALTO Client MUST set 935 the Content-Type HTTP header to the media type corresponding to the 936 format of the supplied input parameters. 938 8.3.3. Server Responding to IR Request 940 Upon receiving a request for an Information Resource that the ALTO 941 Server can provide, the ALTO Server MUST return the requested 942 Information Resource. In other cases, to be more informative 943 ([I-D.ietf-httpbis-p2-semantics]), the ALTO Server MAY provide the 944 ALTO Client with an Information Resource Directory indicating how to 945 reach the desired information resource, or return an ALTO error 946 object; see Section 8.5 for more details on ALTO error handling. 948 It is possible for an ALTO Server to leverage caching HTTP 949 intermediaries to respond to both GET and POST requests by including 950 explicit freshness information (see Section 14 of [RFC2616]). 951 Caching of POST requests is not widely implemented by HTTP 952 intermediaries, however an alternative approach is for an ALTO 953 Server, in response to POST requests, to return an HTTP 303 status 954 code ("See Other") indicating to the ALTO Client that the resulting 955 Information Resource is available via a GET request to an alternate 956 URL. HTTP intermediaries that do not support caching of POST 957 requests could then cache the response to the GET request from the 958 ALTO Client following the alternate URL in the 303 response if the 959 response to the subsequent GET request contains explicit freshness 960 information. 962 The ALTO Server MUST indicate the type of its response using a media 963 type (i.e., the Content-Type HTTP header of the response). 965 8.3.4. Client Handling Server Response 967 8.3.4.1. Using Information Resources 969 This specification does not indicate any required actions taken by 970 ALTO Clients upon successfully receiving an Information Resource from 971 an ALTO Server. Although ALTO Clients are suggested to interpret the 972 received ALTO Information and adapt application behavior, ALTO 973 Clients are not required to do so. 975 8.3.4.2. Handling Server Response and IRD 977 After receiving an Information Resource Directory, the Client can 978 consult it to determine if any of the offered URIs contain the 979 desired Information Resource. However, an ALTO Client MUST NOT 980 assume that the media type returned by the ALTO Server for a request 981 to a URI is the media type advertised in the IRD or specified in its 982 request (i.e., the client must still check the Content-Type header). 983 The expectation is that the media type returned should normally be 984 the media type advertised and requested, but in some cases it may 985 legitimately not be so. 987 In particular, it is possible for an ALTO Client to receive an 988 Information Resource Directory from an ALTO Server as a response to 989 its request for a specific Information Resource. In this case, the 990 ALTO Client may ignore the response or still parse the response. To 991 indicate that an ALTO Client will always check if a response is an 992 Information Resource Directory, the ALTO Client can indicate in the 993 "Accept" header of a HTTP request that it can accept Information 994 Resource Directory; see Section 9.2 for the media type. 996 8.3.4.3. Handling Error Conditions 998 If an ALTO Client does not successfully receive a desired Information 999 Resource from a particular ALTO Server (i.e., server response 1000 indicates error or there is no response), the Client can either 1001 choose another server (if one is available) or fall back to a default 1002 behavior (e.g., perform peer selection without the use of ALTO 1003 information, when used in a peer-to-peer system). 1005 8.3.5. Authentication and Encryption 1007 When server and/or client authentication, encryption, and/or 1008 integrity protection are required, an ALTO Server MUST support SSL/ 1009 TLS [RFC5246] as a mechanism. For cases such as a public ALTO 1010 service or deployment scenarios where there is an implicit trust 1011 relationship between the client and the server and the network 1012 infrastructure connecting them is secure, SSL/TLS may not be 1013 necessary. See [RFC6125] for considerations regarding verification 1014 of server identity. 1016 8.3.6. Information Refreshing 1018 An ALTO Client MAY determine the frequency at which ALTO Information 1019 is refreshed based on information made available via HTTP. 1021 8.3.7. HTTP Cookies 1023 If cookies are included in an HTTP request received by an ALTO 1024 Server, they MUST be ignored. 1026 8.3.8. 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: InforResourceDirectory 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 defined in Table 1. Note that the ALTO Error Codes defined in 1091 Table 1 are limited to support the error conditions needed for 1092 purposes of this document. Additional status codes may be defined in 1093 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. See Appendix C for the rules to specify the "value" 1176 key. 1178 If multiple errors are present in a single request (e.g., a request 1179 uses a JSONString when a JSONNumber is expected and a required field 1180 is missing), then the ALTO Server MUST return exactly one of the 1181 detected errors. However, the reported error is implementation 1182 defined, since specifying a particular order for message processing 1183 encroaches needlessly on implementation techniques. 1185 8.5.3. Overload Conditions and Server Unavailability 1187 If an ALTO Server detects that it cannot handle a request from an 1188 ALTO Client due to excessive load, technical problems, or system 1189 maintenance, it SHOULD do one of the following: 1191 o Return an HTTP 503 ("Service Unavailable") status code to the ALTO 1192 Client. As indicated by [RFC2616], a the Retry-After HTTP header 1193 may be used to indicate when the ALTO Client should retry the 1194 request. 1196 o Return an HTTP 307 ("Temporary Redirect") status code indicating 1197 an alternate ALTO Server that may be able to satisfy the request. 1199 The ALTO Server MAY also terminate the connection with the ALTO 1200 Client. 1202 The particular policy applied by an ALTO Server to determine that it 1203 cannot service a request is outside of the scope of this document. 1205 9. Protocol Specification: Information Resource Directory 1207 As we discussed, an ALTO Client starts by retrieving an Information 1208 Resource Directory, which specifies the attributes of individual 1209 Information Resources that an ALTO Server provides. 1211 9.1. Information Resource Attributes 1213 In this document, each Information Resource has five attributes 1214 associated with it, including its assigned ID, its response format, 1215 its capabilities, its accepted input parameters, and other resources 1216 that it may depend on. The function of an Information Resource 1217 Directory is to publishes these attributes. 1219 9.1.1. Resource ID 1221 Each Information Resource that an ALTO Client can request MUST be 1222 assigned an ID that is unique amongst all Information Resources in 1223 the Information Resource Closure of the client. The ID SHOULD remain 1224 stable even when the data provided by that resource changes. For 1225 example, even though the number of PIDs in a Network Map may be 1226 adjusted, its Resource ID should remain the same. Similarly, if the 1227 entries in a Cost Map are updated, its Resource ID should remain the 1228 same. IDs SHOULD NOT be re-used for different resources over time. 1230 9.1.2. Media Type 1232 ALTO uses Media Type [RFC2046] to uniquely indicate the data format 1233 used to encode the content to be transmitted between an ALTO Server 1234 and an ALTO Client in the HTTP entity body. 1236 9.1.3. Capabilities 1238 The Capabilities attribute of an Information Resource indicates 1239 specific capabilities that the server can provide. For example, if 1240 an ALTO Server allows an ALTO Client to specify cost constraints when 1241 the Client requests a Cost Map Information Resource, then the Server 1242 advertises the cost-constraints capability of the Cost Map 1243 Information Resource. 1245 9.1.4. Accepts Input Parameters 1247 An ALTO Server may allow an ALTO Client to supply input parameters 1248 when requesting certain Information Resources. The associated 1249 accepts attribute of an Information Resource is a Media Type, which 1250 indicates how the Client specifies the input parameters as contained 1251 in the entity body of the HTTP POST request. 1253 9.1.5. Dependent Resources 1255 The information provided in an Information Resource may use 1256 information provided in some other resources (e.g., a Cost Map uses 1257 the PIDs defined in a Network Map). The uses attribute conveys such 1258 information. 1260 9.2. Information Resource Directory (IRD) 1262 An ALTO Server uses Information Resource Directory to publish 1263 available Information Resources and their aforementioned attributes. 1264 Since resource selection happens after consumption of the Information 1265 Resource Directory, the format of the Information Resource Directory 1266 is designed to be simple with the intention of future ALTO Protocol 1267 versions maintaining backwards compatibility. Future extensions or 1268 versions of the ALTO Protocol SHOULD be accomplished by extending 1269 existing media types or adding new media types, but retaining the 1270 same format for the Information Resource Directory. 1272 An ALTO Server MUST make an Information Resource Directory available 1273 via the HTTP GET method to a URI discoverable by an ALTO Client. 1274 Discovery of this URI is out of scope of this document, but could be 1275 accomplished by manual configuration or by returning the URI of an 1276 Information Resource Directory from the ALTO Discovery Protocol 1277 [I-D.ietf-alto-server-discovery]. For recommendations on how the URI 1278 may look like, see [I-D.ietf-alto-server-discovery]. 1280 9.2.1. Media Type 1282 The media type to indicate an information directory is "application/ 1283 alto-directory+json". 1285 9.2.2. Encoding 1287 An Information Resource Directory response may include in "meta" the 1288 "cost-types" key, whose value is of type IRDMetaCostTypes defined 1289 below, where CostType is defined in Section 10.7: 1291 object-map { 1292 JSONString -> CostType; 1293 } IRDMetaCostTypes; 1295 The function of "cost-types" is to assign names to a set of CostTypes 1296 that can be used in one or more "resources" entries in the IRD to 1297 simplify specification. The names defined in "cost-types" in an IRD 1298 are local to the IRD. 1300 For a Root IRD, "meta" MUST include the "default-alto-network-map" 1301 key, which specifies the Resource ID of a Network Map. When there are 1302 multiple Network Maps defined in an IRD (e.g., with different levels 1303 of granularity), the "default-alto-network-map" key provides a 1304 guideline to simple clients that use only one Network Map. 1306 The data component of an Information Resource Directory response is 1307 named "resources", which is a JSON object of type IRDResourceEntries: 1309 object { 1310 IRDResourceEntries resources; 1311 } InfoResourceDirectory : ResponseEntityBase; 1313 object-map { 1314 ResourceID -> IRDResourceEntry; 1315 } IRDResourceEntries; 1317 object { 1318 JSONString uri; 1319 JSONString media-type; 1320 [JSONString accepts;] 1321 [Capabilities capabilities;] 1322 [ResourceID uses<0..*>;] 1323 } IRDResourceEntry; 1325 object { 1326 ... 1327 } Capabilities; 1329 An IRDResourceEntries object is a dictionary map keyed by 1330 ResourceIDs, where ResourceID is defined in Section 10.2. The value 1331 of each entry specifies: 1333 uri A URI at which the ALTO Server provides one or more Information 1334 Resources, or an Information Resource Directory indicating 1335 additional Information Resources. URIs can be relative to the URI 1336 of the IRD and MUST be resolved according to Section 5 of 1337 [RFC3986]. 1339 media-type The media type of Information Resource (see 1340 Section 9.1.2) available via GET or POST requests to the 1341 corresponding URI or "application/alto-directory+json", which 1342 indicates that the response for a request to the URI will be an 1343 Information Resource Directory for URIs discoverable via the URI. 1345 accepts The media type of input parameters (see Section 9.1.4) 1346 accepted by POST requests to the corresponding URI. If this field 1347 is not present, it MUST be assumed to be empty. 1349 capabilities A JSON Object enumerating capabilities of an ALTO 1350 Server in providing the Information Resource at the corresponding 1351 URI and Information Resources discoverable via the URI. If this 1352 field is not present, it MUST be assumed to be an empty object. 1354 If a capability for one of the offered Information Resources is 1355 not explicitly listed here, an ALTO Client may either issue an 1356 OPTIONS HTTP request to the corresponding URI to determine if the 1357 capability is supported, or assume its default value documented in 1358 this specification or an extension document describing the 1359 capability. 1361 uses A list of Resource IDs, defined in the same IRD, that define 1362 the resources on which this resource directly depends. An ALTO 1363 Server SHOULD include in this list any resources that the ALTO 1364 Client would need to retrieve in order to interpret the contents 1365 of this resource. For example, a Cost Map resource should include 1366 in this list the Network Map on which it depends. ALTO Clients 1367 may wish to consult this list in order to pre-fetch necessary 1368 resources. 1370 If an entry has an empty list for "accepts", then the corresponding 1371 URI MUST support GET requests. If an entry has a non-empty 1372 "accepts", then the corresponding URI MUST support POST requests. If 1373 an ALTO Server wishes to support both GET and POST on a single URI, 1374 it MUST specify two entries in the Information Resource Directory. 1376 9.2.3. Example 1378 The following is an example Information Resource Directory returned 1379 by an ALTO Server to an ALTO Client. Assume it is the Root IRD of 1380 the Client. 1382 GET /directory HTTP/1.1 1383 Host: alto.example.com 1384 Accept: application/alto-directory+json,application/alto-error+json 1386 HTTP/1.1 200 OK 1387 Content-Length: TBA 1388 Content-Type: application/alto-directory+json 1390 { 1391 "meta" : { 1392 "cost-types": { 1393 "num-routing": { 1394 "cost-mode" : "numerical", 1395 "cost-metric": "routingcost", 1396 "description": "My default" 1397 }, 1398 "num-hop": { 1399 "cost-mode" : "numerical", 1400 "cost-metric": "hopcount" 1401 }, 1402 "ord-routing": { 1403 "cost-mode" : "ordinal", 1404 "cost-metric": "routingcost" 1405 }, 1406 "ord-hop": { 1407 "cost-mode" : "ordinal", 1408 "cost-metric": "hopcount" 1409 } 1410 }, 1411 "default-alto-network-map" : "my-default-network-map" 1412 }, 1413 "resources" : { 1414 "my-default-network-map" : { 1415 "uri" : "http://alto.example.com/networkmap", 1416 "media-type" : "application/alto-networkmap+json" 1417 }, 1418 "numerical-routing-cost-map" : { 1419 "uri" : "http://alto.example.com/costmap/num/routingcost", 1420 "media-type" : "application/alto-costmap+json", 1421 "capabilities" : { 1422 "cost-type-names" : [ "num-routing" ] 1423 }, 1424 "uses": [ "my-default-network-map" ] 1425 }, 1426 "numerical-hopcount-cost-map" : { 1427 "uri" : "http://alto.example.com/costmap/num/hopcount", 1428 "media-type" : "application/alto-costmap+json", 1429 "capabilities" : { 1430 "cost-type-names" : [ "num-hop" ] 1431 }, 1432 "uses": [ "my-default-network-map" ] 1433 }, 1434 "custom-maps-resources" : { 1435 "uri" : "http://custom.alto.example.com/maps", 1436 "media-type" : "application/alto-directory+json" 1437 }, 1438 "endpoint-property" : { 1439 "uri" : "http://alto.example.com/endpointprop/lookup", 1440 "media-type" : "application/alto-endpointprop+json", 1441 "accepts" : "application/alto-endpointpropparams+json", 1442 "capabilities" : { 1443 "prop-types" : [ "my-default-network-map.pid", 1444 "priv:ietf-example-prop" ] 1445 }, 1447 }, 1448 "endpoint-cost" : { 1449 "uri" : "http://alto.example.com/endpointcost/lookup", 1450 "media-type" : "application/alto-endpointcost+json", 1451 "accepts" : "application/alto-endpointcostparams+json", 1452 "capabilities" : { 1453 "cost-constraints" : true, 1454 "cost-type-names" : [ "num-routing", "num-hop", 1455 "ord-routing", "ord-hop"] 1456 } 1457 } 1458 } 1459 } 1461 Specifically, the "cost-types" key of "meta" of the example IRD 1462 defines names for four cost types in this IRD. For example, "num- 1463 routing" in the example is the name that refers to a Cost Type with 1464 Cost Mode being "numerical" and Cost Metric being "routingcost". 1465 This name is used in the second entry of "resources", which defines a 1466 Cost Map. In particular, the "cost-type-names" of its "capabilities" 1467 specifies that this resource supports a Cost Type named as "num- 1468 routing". The ALTO Client looks up the name "num-routing" in "cost- 1469 types" of the IRD to obtain the Cost Type named as "num-routing". 1470 The last entry of "resources" uses all four names defined in "cost- 1471 types". 1473 Another key defined in "meta" of the example IRD is "default-alto- 1474 network-map", which has value "my-default-network-map", which is the 1475 Resource ID of a Network Map that will be defined in "resources". 1477 The "resources" field of the example IRD defines six Information 1478 Resources. For example, the second entry, which is assigned a 1479 Resource ID "numerical-routing-cost-map", provides a Cost Map, as 1480 indicated by the media-type "application/alto-costmap+json". The 1481 Cost Map is based on the Network Map defined with Resource ID "my- 1482 default-network-map". As another example, the last entry, which is 1483 assigned Resource ID "endpoint-cost", provides the Endpoint Cost 1484 Service, which is indicated by the media-type "application/ 1485 alto-endpointcost+json". An ALTO Client should use uri 1486 "http://alto.example.com/endpointcost/lookup" to access the service. 1487 The ALTO Client should format its request body to be the 1488 "application/alto-endpointcostparams+json" media type, as specified 1489 by the "accepts" attribute of the Information Resource. The "cost- 1490 type-names" field of the "capabilities" attribute of the Information 1491 Resource includes four defined cost types specified in the "cost- 1492 types" key of "meta" of the IRD. Hence, one can verify that the 1493 Endpoint Cost Information Resource supports both Cost Metrics 1494 'routingcost' and 'hopcount', each available for both 'numerical' and 1495 'ordinal'. When requesting the Information Resource, an ALTO Client 1496 can specify cost constraints, as indicated by the "cost-constraints" 1497 field of the "capabilities" attribute. 1499 9.2.4. Delegation using IRD 1501 ALTO Information Resource Directory provides flexibility to provide 1502 ALTO Service (e.g., delegation to another domain). Consider the 1503 preceding example. Assume that the ALTO Server running at 1504 alto.example.com wants to delegate some Information Resources to a 1505 separate subdomain: "custom.alto.example.com". In particular, assume 1506 that the maps available via this subdomain are filtered Network Maps, 1507 filtered Cost Maps, and some pre-generated maps for the "hopcount" 1508 and "routingcost" Cost Metrics in the "ordinal" Cost Mode. The 1509 fourth entry of "resources" in the preceding example IRD implements 1510 the delegation. The entry has a media-type of "application/ 1511 alto-directory+json", and an ALTO Client can discover the Information 1512 Resources available at "custom.alto.example.com" if its request to 1513 "http://custom.alto.example.com/maps" is successful: 1515 GET /maps HTTP/1.1 1516 Host: custom.alto.example.com 1517 Accept: application/alto-directory+json,application/alto-error+json 1519 HTTP/1.1 200 OK 1520 Content-Length: TBA 1521 Content-Type: application/alto-directory+json 1523 { 1524 "meta" : { 1525 "cost-types": { 1526 "num-routing": { 1527 "cost-mode" : "numerical", 1528 "cost-metric": "routingcost", 1529 "description": "My default" 1530 }, 1531 "num-hop": { 1532 "cost-mode" : "numerical", 1533 "cost-metric": "hopcount" 1534 }, 1535 "ord-routing": { 1536 "cost-mode" : "ordinal", 1537 "cost-metric": "routingcost" 1539 }, 1540 "ord-hop": { 1541 "cost-mode" : "ordinal", 1542 "cost-metric": "hopcount" 1543 } 1544 } 1545 }, 1546 "resources" : { 1547 "filtered-network-map" : { 1548 "uri" : "http://custom.alto.example.com/networkmap/filtered", 1549 "media-type" : "application/alto-networkmap+json", 1550 "accepts" : "application/alto-networkmapfilter+json", 1551 "uses": [ "my-default-network-map" ] 1552 }, 1553 "filtered-cost-map" : { 1554 "uri" : "http://custom.alto.example.com/costmap/filtered", 1555 "media-type" : "application/alto-costmap+json", 1556 "accepts" : "application/alto-costmapfilter+json", 1557 "capabilities" : { 1558 "cost-constraints" : true, 1559 "cost-type-names" : [ "num-routing", "num-hop", 1560 "ord-routing", "ord-hop" ] 1561 }, 1562 "uses": [ "my-default-network-map" ] 1563 }, 1564 "ordinal-routing-cost-map" : { 1565 "uri" : "http://custom.alto.example.com/ord/routingcost", 1566 "media-type" : "application/alto-costmap+json", 1567 "capabilities" : { 1568 "cost-type-names" : [ "ord-routing" ] 1569 }, 1570 "uses": [ "my-default-network-map" ] 1571 }, 1572 "ordinal-hopcount-cost-map" : { 1573 "uri" : "http://custom.alto.example.com/ord/hopcount", 1574 "media-type" : "application/alto-costmap+json", 1575 "capabilities" : { 1576 "cost-type-names" : [ "ord-hop" ], 1577 }, 1578 "uses": [ "my-default-network-map" ] 1579 } 1580 } 1581 } 1583 Note that the subdomain does not define Network Map, and uses the 1584 Network Map with Resource ID "my-default-network-map" defined in the 1585 Root IRD. 1587 9.2.5. Considerations of Using IRD 1589 9.2.5.1. ALTO Client 1591 This document specifies no requirements or constraints on ALTO 1592 Clients with regards to how they process an Information Resource 1593 Directory to identify the URI corresponding to a desired Information 1594 Resource. However, some advice is provided for implementors. 1596 It is possible that multiple entries in the directory match a desired 1597 Information Resource. For instance, in the example in Section 9.2.3, 1598 a full Cost Map with "numerical" Cost Mode and "routingcost" Cost 1599 Metric could be retrieved via a GET request to 1600 "http://alto.example.com/costmap/num/routingcost", or via a POST 1601 request to "http://custom.alto.example.com/costmap/filtered". 1603 In general, it is preferred for ALTO Clients to use GET requests 1604 where appropriate, since it is more likely for responses to be 1605 cachable. However, an ALTO Client may need to use POST, for example, 1606 to get ALTO costs or properties that are for a restricted set of PIDs 1607 or Endpoints, or to update cached information previously acquired via 1608 GET requests." 1610 9.2.5.2. ALTO Server 1612 This document indicates that an ALTO Server may or may not provide 1613 the Information Resources specified in the Map Filtering Service. If 1614 these resources are not provided, it is indicated to an ALTO Client 1615 by the absence of a Network Map or Cost Map with any media types 1616 listed under "accepts". 1618 10. Protocol Specification: Basic Data Types 1620 This section details the format of basic data types. 1622 10.1. PID Name 1624 A PID Name is encoded as a US-ASCII string. The string MUST be no 1625 more than 64 characters, and MUST NOT contain characters other than 1626 alphanumeric characters (code points 0x30-0x39, 0x41-0x5A, and 0x61- 1627 0x7A), the hyphen ('-', code point 0x2D), the colon (':', code point 1628 0x3A), the at ('@', code point 0x40), the underline ('_', code point 1629 0x5F), or the '.' separator (code point 0x2E). The '.' separator is 1630 reserved for future use and MUST NOT be used unless specifically 1631 indicated in this document, or an extension document. 1633 The type 'PIDName' is used in this document to indicate a string of 1634 this format. 1636 10.2. Resource ID 1638 A Resource ID uniquely identifies an particular resource (e.g., a 1639 Network Map) within an ALTO Server (see Section 9.2). 1641 A Resource ID is encoded as a US-ASCII string with the same format as 1642 that of PIDName. 1644 The type 'ResourceID' is used in this document to indicate a string 1645 of this format. 1647 10.3. Version Tag 1649 A Version Tag is defined as: 1651 object { 1652 ResourceID resource-id; 1653 JSONString tag; 1654 } VersionTag; 1656 The 'resource-id' attribute is the Resource ID of a resource (e.g., a 1657 Network Map) defined in the Information Resource Directory, and 'tag' 1658 is a case-sensitive US-ASCII string. The 'tag' string MUST be no 1659 more than 64 characters, and MUST NOT contain any ASCII character 1660 below 0x21 or above 0x7E. 1662 Two values of the VersionTag are equal if and only if both the the 1663 'resource-id' attributes are byte-for-byte equal and the 'tag' 1664 attributes are byte-for-byte equal. 1666 10.4. Endpoints 1668 This section defines formats used to encode addresses for Endpoints. 1669 In a case that multiple textual representations encode the same 1670 Endpoint address or prefix (within the guidelines outlined in this 1671 document), the ALTO Protocol does not require ALTO Clients or ALTO 1672 Servers to use a particular textual representation, nor does it 1673 require that ALTO Servers reply to requests using the same textual 1674 representation used by requesting ALTO Clients. ALTO Clients must be 1675 cognizant of this. 1677 10.4.1. Typed Endpoint Addresses 1679 When an Endpoint Address is used, an ALTO implementation must be able 1680 to determine its type. For this purpose, the ALTO Protocol allows 1681 endpoint addresses to also explicitly indicate their types. We refer 1682 to such addresses as Typed Endpoint Addresses. 1684 Typed Endpoint Addresses are encoded as US-ASCII strings of the 1685 format 'AddressType:EndpointAddr' (with the ':' character as a 1686 separator). The type 'TypedEndpointAddr' is used to indicate a 1687 string of this format. 1689 10.4.2. Address Type 1691 The AddressType component of TypedEndPointAddr is defined as an US- 1692 ASCII string consisting of only alphanumeric characters (code points 1693 0x30-0x39, 0x41-0x5A, and 0x61-0x7A). The type 'AddressType' is used 1694 in this document to indicate a string of this format. 1696 This document defines two values for AddressType: 'ipv4' to refer to 1697 IPv4 addresses, and 'ipv6' to refer to IPv6 addresses. All 1698 AddressType identifiers appearing in an HTTP request or response with 1699 an 'application/alto-*' media type MUST be registered in the ALTO 1700 Address Type registry (see Section 14.4). 1702 10.4.3. Endpoint Address 1704 The EndpointAddr component of TypedEndPointAddr is also encoded as an 1705 US-ASCII string. The exact characters and format depend on 1706 AddressType. This document defines EndpointAddr when AddressType is 1707 'ipv4' or 'ipv6'. 1709 10.4.3.1. IPv4 1711 IPv4 Endpoint Addresses are encoded as specified by the 'IPv4address' 1712 rule in Section 3.2.2 of [RFC3986]. 1714 10.4.3.2. IPv6 1716 IPv6 Endpoint Addresses are encoded as specified in Section 4 of 1717 [RFC5952]. 1719 10.4.4. Endpoint Prefixes 1721 For efficiency, it is useful to denote a set of Endpoint Addresses 1722 using a special notation (if one exists). This specification makes 1723 use of the prefix notations for both IPv4 and IPv6 for this purpose. 1725 Endpoint Prefixes are encoded as US-ASCII strings. The exact 1726 characters and format depend on the type of endpoint address. 1728 The type 'EndpointPrefix' is used in this document to indicate a 1729 string of this format. 1731 10.4.4.1. IPv4 1733 IPv4 Endpoint Prefixes are encoded as specified in Section 3.1 of 1734 [RFC4632]. 1736 10.4.4.2. IPv6 1738 IPv6 Endpoint Prefixes are encoded as specified in Section 7 of 1739 [RFC5952]. 1741 10.4.5. Endpoint Address Group 1743 The ALTO Protocol includes messages that specify potentially large 1744 sets of endpoint addresses. Endpoint Address Groups provide a more 1745 efficient way to encode such sets, even when the set contains 1746 endpoint addresses of different types. 1748 An Endpoint Address Group is defined as: 1750 object-map { 1751 AddressType -> EndpointPrefix<0..*>; 1752 } EndpointAddrGroup; 1754 In particular, an Endpoint Address Group is a JSON object 1755 representing a map, where each key is the string corresponding to an 1756 address type, and the corresponding value is an array listing 1757 prefixes of addresses of that type. 1759 The following is an example with both IPv4 and IPv6 endpoint 1760 addresses: 1762 { 1763 "ipv4": [ 1764 "192.0.2.0/24", 1765 "198.51.100.0/25" 1766 ], 1767 "ipv6": [ 1768 "2001:db8:0:1::/64", 1769 "2001:db8:0:2::/64" 1771 ] 1772 } 1774 10.5. Cost Mode 1776 A Cost Mode is encoded as a US-ASCII string. The string MUST either 1777 have the value 'numerical' or 'ordinal'. 1779 The type 'CostMode' is used in this document to indicate a string of 1780 this format. 1782 10.6. Cost Metric 1784 A Cost Metric is encoded as a US-ASCII string. The string MUST be no 1785 more than 32 characters, and MUST NOT contain characters other than 1786 alphanumeric characters (code points 0x30-0x39, 0x41-0x5A, and 0x61- 1787 0x7A), the hyphen ('-', code point 0x2D), the colon (':', code point 1788 0x3A), the underline ('_', code point 0x5F), or the '.' separator 1789 (0x2E). The '.' separator is reserved for future use and MUST NOT be 1790 used unless specifically indicated by a companion or extension 1791 document. 1793 Identifiers prefixed with 'priv:' are reserved for Private Use 1794 [RFC5226]. Identifiers prefixed with 'exp:' are reserved for 1795 Experimental use. For an identifier with the 'priv:' or 'exp:' 1796 prefix, an additional string (e.g., company identifier or random 1797 string) MUST follow to reduce potential collisions. For example, a 1798 short string after 'exp:' to indicate the starting time of a specific 1799 experiment is recommended. All other identifiers that appear in an 1800 HTTP request or response with an 'application/alto-*' media type and 1801 indicate Cost Metrics MUST be registered in the ALTO Cost Metrics 1802 registry Section 14.2. 1804 The type 'CostMetric' is used in this document to indicate a string 1805 of this format. 1807 10.7. Cost Type 1809 The combination of a CostMetric and a CostMode defines a CostType: 1811 object { 1812 CostMetric cost-metric; 1813 CostMode cost-mode; 1814 [JSONString description;] 1815 } CostType; 1816 'description', if present, MUST contain a US-ASCII string with a 1817 human-readable description of the cost-metric and cost-mode. An ALTO 1818 Client MAY present this string to a developer, as part of a discovery 1819 process. But the field SHOULD NOT be interpreted by an ALTO Client. 1821 10.8. Endpoint Property 1823 We distinguish two types of Endpoint Properties: Resource Specific 1824 Endpoint Properties and Global Endpoint Properties. The type 1825 'EndpointPropertyType' is used in this document to indicate a US- 1826 ASCII string denoting either a Resource Specific Endpoint Property or 1827 a Global Endpoint Property. 1829 10.8.1. Resource Specific Endpoint Properties 1831 We define only one Resource Specific Endpoint Property in this 1832 document: pid. It has the following format: a Resource ID, followed 1833 by the '.' separator (0x2E), followed by "pid". An example is "my- 1834 default-networkmap.pid". 1836 10.8.2. Global Endpoint Properties 1838 An Global Endpoint Property is encoded as a US-ASCII string. The 1839 string MUST be no more than 32 characters, and MUST NOT contain 1840 characters other than alphanumeric characters (code points 0x30-0x39, 1841 0x41-0x5A, and 0x61-0x7A), the hyphen ('-', code point 0x2D), the 1842 colon (':', code point 0x3A), or the underline ('_', code point 1843 0x5F). Note that the '.' separator is not allowed so that there is 1844 no ambiguity on whether an endpoint property is global or resource 1845 specific. 1847 Identifiers prefixed with 'priv:' are reserved for Private Use 1848 [RFC5226]. Identifiers prefixed with 'exp:' are reserved for 1849 Experimental use. For an identifier with the 'priv:' or 'exp:' 1850 prefix, an additional string (e.g., company identifier or random 1851 string) MUST follow to reduce potential collisions. For example, a 1852 short string after 'exp:' to indicate the starting time of a specific 1853 experiment is recommended. All other identifiers for Endpoint 1854 Properties appearing in an HTTP request or response with an 1855 'application/alto-*' media type MUST be registered in the ALTO 1856 Endpoint Property registry Section 14.3. 1858 11. Protocol Specification: Service Information Resources 1860 This section documents the individual Information Resources defined 1861 to provide the services defined in this document. 1863 11.1. Meta Information 1865 For the "meta" field of the response to an individual Information 1866 Resource, we define two generic keys: "vtag", which is the Version 1867 Tag (see Section 10.3) of the current Information Resource; and 1868 "dependent-vtags", which is an array of Version Tags, to indicate the 1869 Version Tags of the resources that this resource depends on. 1871 11.2. Map Service 1873 The Map Service provides batch information to ALTO Clients in the 1874 form of two types of maps: a Network Map and Cost Map. 1876 11.2.1. Network Map 1878 A Network Map Information Resource defines a set of PIDs, and for 1879 each PID, lists the network locations (endpoints) within the PID. An 1880 ALTO Server MUST provide at least one Network Map. 1882 11.2.1.1. Media Type 1884 The media type of Network Map is "application/alto-networkmap+json". 1886 11.2.1.2. HTTP Method 1888 A Network Map resource is requested using the HTTP GET method. 1890 11.2.1.3. Accept Input Parameters 1892 None. 1894 11.2.1.4. Capabilities 1896 None. 1898 11.2.1.5. Uses 1900 None. 1902 11.2.1.6. Response 1904 The "meta" field of a Network Map response MUST include "vtag", which 1905 is the Version Tag of the retrieved Network Map. 1907 The data component of a Network Map response is named "network-map", 1908 which is a JSON object of type NetworkMapData: 1910 object { 1911 NetworkMapData network-map; 1912 } InfoResourceNetworkMap : ResponseEntityBase; 1914 object-map { 1915 PIDName -> EndpointAddrGroup; 1916 } NetworkMapData; 1918 Specifically, a NetworkMapData object is a dictionary map keyed by 1919 PIDs, and each value representing the associated set of endpoint 1920 addresses of a PID. 1922 The returned Network Map MUST include all PIDs known to the ALTO 1923 Server. 1925 11.2.1.7. Example 1927 GET /networkmap HTTP/1.1 1928 Host: alto.example.com 1929 Accept: application/alto-networkmap+json,application/alto-error+json 1930 HTTP/1.1 200 OK 1931 Content-Length: TBA 1932 Content-Type: application/alto-networkmap+json 1934 { 1935 "meta" : { 1936 "vtag": { 1937 "resource-id": "my-default-network-map", 1938 "tag": "1266506139" 1939 } 1940 }, 1941 "network-map" : { 1942 "PID1" : { 1943 "ipv4" : [ 1944 "192.0.2.0/24", 1945 "198.51.100.0/25" 1946 ] 1947 }, 1948 "PID2" : { 1949 "ipv4" : [ 1950 "198.51.100.128/25" 1951 ] 1952 }, 1953 "PID3" : { 1954 "ipv4" : [ 1955 "0.0.0.0/0" 1956 ], 1957 "ipv6" : [ 1958 "::/0" 1959 ] 1960 } 1961 } 1962 } 1964 When parsing a Network Map, an ALTO Client MUST ignore any 1965 EndpointAddressGroup whose address type it does not recognize. If as 1966 a result a PID does not have any address types known to the client, 1967 the client still MUST recognize that PID name as valid, even though 1968 the PID then contains no endpoints. 1970 Note that the encoding of a Network Map response was chosen for 1971 readability and compactness. If lookup efficiency at runtime is 1972 crucial, then the returned Network Map can be transformed into data 1973 structures offering more efficient lookup. For example, one may 1974 store the Network Map as a trie-based data structure, which may allow 1975 efficient longest-prefix matching of IP addresses. 1977 11.2.2. Mapping IP Addresses to PIDs for 'ipv4'/'ipv6' Network Maps 1979 A key usage of a Network Map is to map Endpoint Addresses to PIDs. 1980 For Network Maps containing the 'ipv4' and 'ipv6' address types 1981 defined in this document, when either an ALTO Client or an ALTO 1982 Server needs to compute the mapping from IP addresses to PIDs, the 1983 longest-prefix matching algorithm [RFC1812] MUST be used. 1985 To ensure that the longest-prefix matching algorithm yields one and 1986 only one PID, Network Maps containing the 'ipv4/'ipv6' address types 1987 MUST satisfy the following two requirements. 1989 First, such a Network Map MUST define a PID for each possible address 1990 in the IP address space for all of the address types contained in the 1991 map. We refer to this as the completeness property of such a Network 1992 Map. A RECOMMENDED way to satisfy this property is to define a PID 1993 with the shortest enclosing prefix of the addresses provided in the 1994 map. For a map with full IPv4 reachability, this would mean 1995 including the 0.0.0.0/0 prefix in a PID; for full IPv6 reachability, 1996 this would be the ::/0 prefix. 1998 Second, such a Network Map MUST NOT define two or more PIDs that 1999 contain an identical IP prefix, in order to ensure that the longest- 2000 prefix matching algorithm maps each IP addresses into exactly one 2001 PID. We refer to this as the non-overlapping property of such a 2002 Network Map. Specifically, to map an IP address to its PID in a non- 2003 overlapping Network Map, one considers the set S which consists of 2004 all prefixes defined in the Network Map, applies the longest-prefix 2005 mapping algorithm to S to identify the longest prefix containing the 2006 IP address, and assigns that the IP address belongs to the PID 2007 containing the identified longest prefix. 2009 The following example shows a complete and non-overlapping Network 2010 Map: 2012 "network-map" : { 2013 "PID0" : { "ipv6" : [ "::/0" ] }, 2014 "PID1" : { "ipv4" : [ "0.0.0.0/0" ] }, 2015 "PID2" : { "ipv4" : [ "192.0.2.0/24", "198.51.100.0/24" ] }, 2016 "PID3" : { "ipv4" : [ "192.0.2.0/25", "192.0.2.128/25" ] } 2017 } 2019 The IP address 192.0.2.1 should be mapped to PID3. 2021 If, however, the two adjacent prefixes in PID3 were combined as a 2022 single prefix, then PID3 was changed to 2024 "PID3" : { "ipv4" : [ "192.0.2.0/24" ] } 2026 The new map is no longer non-overlapping, and 192.0.2.1 could no 2027 longer be mapped unambiguously to a PID by means of longest-prefix 2028 matching. 2030 Extension documents may define techniques to allow a single IP 2031 address being mapped to multiple PIDs, when a need is identified. 2033 11.2.3. Cost Map 2035 A Cost Map resource lists the Path Cost for each pair of source/ 2036 destination PID defined by the ALTO Server for a given Cost Metric 2037 and Cost Mode. This resource MUST be provided for at least the 2038 'routingcost' Cost Metric. 2040 11.2.3.1. Media Type 2042 The media type of Cost Map is "application/alto-costmap+json". 2044 11.2.3.2. HTTP Method 2046 A Cost Map resource is requested using the HTTP GET method. 2048 11.2.3.3. Accept Input Parameters 2050 None. 2052 11.2.3.4. Capabilities 2054 The capabilities of an ALTO Server URI providing an unfiltered cost 2055 map is a JSON Object of type CostMapCapabilities: 2057 object { 2058 JSONString cost-type-names<1..1>; 2059 } CostMapCapabilities; 2061 with field: 2063 cost-type-names Note that the array MUST include a single CostType 2064 name defined by key "cost-types" in "meta" of the IRD. This is 2065 because an unfiltered Cost Map (accept == "") is requested via an 2066 HTTP GET that accepts no input parameters. As a contrast, for 2067 filtered cost maps (see Section 11.3.2), the array can have 2068 multiple elements. 2070 11.2.3.5. Uses 2072 The Resource ID of the Network Map based on which the Cost Map will 2073 be defined. Recall (Section 6) that the combination of a Network Map 2074 and a CostType defines a key. In other words, an ALTO Server MUST 2075 NOT define two Cost Maps with the same Cost Type, Network Map pair. 2077 11.2.3.6. Response 2079 The "meta" field of a Cost Map response MUST include the "dependent- 2080 vtags" key, whose value is a single-element array to indicate the 2081 Version Tag of the Network Map used, where the Network Map is 2082 specified in "uses" of the IRD. The "meta" MUST also include "cost- 2083 type", to indicate the Cost Type (Section 10.7) of the Cost Map. 2085 The data component of a Cost Map response is named "cost-map", which 2086 is a JSON object of type CostMapData: 2088 object { 2089 CostMapData cost-map; 2090 } InfoResourceCostMap : ResponseEntityBase; 2092 object-map { 2093 PIDName -> DstCosts; 2094 } CostMapData; 2096 object-map { 2097 PIDName -> JSONValue; 2098 } DstCosts; 2100 Specifically, a CostMapData object is a dictionary map object, with 2101 each key being the PIDName string identifying the corresponding 2102 Source PID, and value being a type of DstCosts, which denotes the 2103 associated costs from the Source PID to a set of destination PIDs ( 2104 Section 6.2). An implementation of the protocol in this document 2105 SHOULD assume that the cost is a JSONNumber and fail to parse if it 2106 is not, unless the implementation is using an extension to this 2107 document that indicates when and how costs of other data types are 2108 signaled. 2110 The returned Cost Map MUST include the Path Cost for each (Source 2111 PID, Destination PID) pair for which a Path Cost is defined. An ALTO 2112 Server MAY omit entries for which a Path Cost is not defined (e.g., 2113 both the Source and Destination PIDs contain addresses outside of the 2114 Network Provider's administrative domain). 2116 Similar to Network Map, the encoding of Cost Map was chosen for 2117 readability and compactness. If lookup efficiency at runtime is 2118 crucial, then the returned Cost Map can be transformed into data 2119 structures offering more efficient lookup. For example, one may 2120 store a Cost Map as a matrix. 2122 11.2.3.7. Example 2124 GET /costmap/num/routingcost HTTP/1.1 2125 Host: alto.example.com 2126 Accept: application/alto-costmap+json,application/alto-error+json 2128 HTTP/1.1 200 OK 2129 Content-Length: TBA 2130 Content-Type: application/alto-costmap+json 2132 { 2133 "meta" : { 2134 "dependent-vtags" : [ 2135 {"resource-id": "my-default-network-map", 2136 "tag": "1266506139" 2137 } 2138 ], 2139 "cost-type" : {"cost-mode" : "numerical", 2140 "cost-metric": "routingcost" 2141 } 2142 }, 2143 "cost-map" : { 2144 "PID1": { "PID1": 1, "PID2": 5, "PID3": 10 }, 2145 "PID2": { "PID1": 5, "PID2": 1, "PID3": 15 }, 2146 "PID3": { "PID1": 20, "PID2": 15 } 2147 } 2148 } 2150 Similar to the Network Map case, we considered array-based encoding 2151 for "map", but chose the current encoding for clarity. 2153 11.3. Map Filtering Service 2155 The Map Filtering Service allows ALTO Clients to specify filtering 2156 criteria to return a subset of the full maps available in the Map 2157 Service. 2159 11.3.1. Filtered Network Map 2161 A Filtered Network Map is a Network Map Information Resource 2162 (Section 11.2.1) for which an ALTO Client may supply a list of PIDs 2163 to be included. A Filtered Network Map MAY be provided by an ALTO 2164 Server. 2166 11.3.1.1. Media Type 2168 Since a Filtered Network Map is still a Network Map, it uses the 2169 media type defined for Network Map at Section 11.2.1.1. 2171 11.3.1.2. HTTP Method 2173 A Filtered Network Map is requested using the HTTP POST method. 2175 11.3.1.3. Accept Input Parameters 2177 An ALTO Client supplies filtering parameters by specifying media type 2178 "application/alto-networkmapfilter+json" with HTTP POST body 2179 containing a JSON Object of type ReqFilteredNetworkMap, where: 2181 object { 2182 PIDName pids<0..*>; 2183 [AddressType address-types<0..*>;] 2184 } ReqFilteredNetworkMap; 2186 with fields: 2188 pids Specifies list of PIDs to be included in the returned Filtered 2189 Network Map. If the list of PIDs is empty, the ALTO Server MUST 2190 interpret the list as if it contained a list of all currently- 2191 defined PIDs. The ALTO Server MUST interpret entries appearing 2192 multiple times as if they appeared only once. 2194 address-types Specifies list of address types to be included in the 2195 returned Filtered Network Map. If the "address-types" field is not 2196 specified, or the list of address types is empty, the ALTO Server 2197 MUST interpret the list as if it contained a list of all address 2198 types known to the ALTO Server. The ALTO Server MUST interpret 2199 entries appearing multiple times as if they appeared only once. 2201 11.3.1.4. Capabilities 2203 None. 2205 11.3.1.5. Uses 2207 The Resource ID of the Network Map based on which the filtering is 2208 performed. 2210 11.3.1.6. Response 2212 The format is the same as unfiltered Network Map. See 2213 Section 11.2.1.6 for the format. 2215 The ALTO Server MUST only include PIDs in the response that were 2216 specified (implicitly or explicitly) in the request. If the input 2217 parameters contain a PID name that is not currently defined by the 2218 ALTO Server, the ALTO Server MUST behave as if the PID did not appear 2219 in the input parameters. Similarly, the ALTO Server MUST only 2220 enumerate addresses within each PID that have types which were 2221 specified (implicitly or explicitly) in the request. If the input 2222 parameters contain an address type that is not currently known to the 2223 ALTO Server, the ALTO Server MUST behave as if the address type did 2224 not appear in the input parameters. 2226 The Version Tag included in the "vtag" of the response MUST 2227 correspond to the full (unfiltered) Network Map Information Resource 2228 from which the filtered information is provided. This ensures that a 2229 single, canonical Version Tag is used independent of any filtering 2230 that is requested by an ALTO Client. 2232 11.3.1.7. Example 2234 POST /networkmap/filtered HTTP/1.1 2235 Host: custom.alto.example.com 2236 Content-Length: TBA 2237 Content-Type: application/alto-networkmapfilter+json 2238 Accept: application/alto-networkmap+json,application/alto-error+json 2240 { 2241 "pids": [ "PID1", "PID2" ] 2242 } 2244 HTTP/1.1 200 OK 2245 Content-Length: TBA 2246 Content-Type: application/alto-networkmap+json 2248 { 2249 "meta" : { 2250 "vtag" : { 2251 "resource-id": "my-default-network-map", 2252 "tag": "1266506139" 2253 } 2254 }, 2255 "network-map" : { 2256 "PID1" : { 2257 "ipv4" : [ 2258 "192.0.2.0/24", 2259 "198.51.100.0/24" 2260 ] 2261 }, 2262 "PID2" : { 2263 "ipv4": [ 2264 "198.51.100.128/24" 2265 ] 2266 } 2267 } 2268 } 2270 11.3.2. Filtered Cost Map 2272 A Filtered Cost Map is a Cost Map Information Resource 2273 (Section 11.2.3) for which an ALTO Client may supply additional 2274 parameters limiting the scope of the resulting Cost Map. A Filtered 2275 Cost Map MAY be provided by an ALTO Server. 2277 11.3.2.1. Media Type 2279 Since a Filtered Cost Map is still a Cost Map, it uses the media type 2280 defined for Cost Map at Section 11.2.3.1. 2282 11.3.2.2. HTTP Method 2284 A Filtered Cost Map is requested using the HTTP POST method. 2286 11.3.2.3. Accept Input Parameters 2288 The input parameters for a Filtered Map are supplied in the entity 2289 body of the POST request. This document specifies the input 2290 parameters with a data format indicated by the media type 2291 "application/alto-costmapfilter+json", which is a JSON Object of type 2292 ReqFilteredCostMap, where: 2294 object { 2295 CostType cost-type; 2296 [JSONString constraints<0..*>;] 2297 [PIDFilter pids;] 2298 } ReqFilteredCostMap; 2300 object { 2301 PIDName srcs<0..*>; 2302 PIDName dsts<0..*>; 2303 } PIDFilter; 2305 with fields: 2307 cost-type The CostType (Section 10.7) for the returned costs. The 2308 cost-metric and cost-mode fields MUST match one of the supported 2309 Cost Types indicated in this resource's capabilities 2310 (Section 11.3.2.4). The ALTO Client SHOULD omit the description 2311 field, and if present, the ALTO Server MUST ignore the description 2312 field. 2314 constraints Defines a list of additional constraints on which 2315 elements of the Cost Map are returned. This parameter MUST NOT be 2316 specified if this resource's capabilities ( Section 11.3.2.4) 2317 indicate that constraint support is not available. A constraint 2318 contains two entities separated by whitespace: (1) an operator, 2319 'gt' for greater than, 'lt' for less than, 'ge' for greater than 2320 or equal to, 'le' for less than or equal to, or 'eq' for equal to; 2321 (2) a target cost value. The cost value is a number that MUST be 2322 defined in the same units as the Cost Metric indicated by the 2323 cost-metric parameter. ALTO Servers SHOULD use at least IEEE 754 2324 double-precision floating point [IEEE.754.2008] to store the cost 2325 value, and SHOULD perform internal computations using double- 2326 precision floating-point arithmetic. If multiple 'constraint' 2327 parameters are specified, they are interpreted as being related to 2328 each other with a logical AND. 2330 pids A list of Source PIDs and a list of Destination PIDs for which 2331 Path Costs are to be returned. If a list is empty, the ALTO 2332 Server MUST interpret it as the full set of currently-defined 2333 PIDs. The ALTO Server MUST interpret entries appearing in a list 2334 multiple times as if they appeared only once. If the "pids" field 2335 is not present, both lists MUST be interpreted by the ALTO Server 2336 as containing the full set of currently-defined PIDs. 2338 11.3.2.4. Capabilities 2340 The URI providing this resource supports all capabilities documented 2341 in Section 11.2.3.4 (with identical semantics), plus additional 2342 capabilities. In particular, the capabilities are defined by a JSON 2343 object of type FilteredCostMapCapabilities: 2345 object { 2346 JSONString cost-type-names<1..*>; 2347 JSONBool cost-constraints; 2348 } FilteredCostMapCapabilities; 2350 with fields: 2352 cost-type-names See Section 11.2.3.4 and note that the array can 2353 have 1 to many cost types. 2355 cost-constraints If true, then the ALTO Server allows cost 2356 constraints to be included in requests to the corresponding URI. 2357 If not present, this field MUST be interpreted as if it specified 2358 false. ALTO Clients should be aware that constraints may not have 2359 the intended effect for cost maps with the 'ordinal' Cost Mode 2360 since ordinal costs are not restricted to being sequential 2361 integers. 2363 11.3.2.5. Uses 2365 The Resource ID of the Network Map based on which the Cost Map will 2366 be filtered. 2368 11.3.2.6. Response 2370 The format is the same as an unfiltered Cost Map. See 2371 Section 11.2.3.6 for the format. 2373 The "dependent-vtags" key in the "meta" field is an array consisting 2374 of a single element, which is the Version Tag of the Network Map used 2375 in filtering. ALTO Clients should verify that the Version Tag 2376 included in the response is consistent with the Version Tag of the 2377 Network Map used to generate the request (if applicable). If it is 2378 not, the ALTO Client may wish to request an updated Network Map, 2379 identify changes, and consider requesting a new Filtered Cost Map. 2381 The returned Cost Map MUST contain only source/destination pairs that 2382 have been indicated (implicitly or explicitly) in the input 2383 parameters. If the input parameters contain a PID name that is not 2384 currently defined by the ALTO Server, the ALTO Server MUST behave as 2385 if the PID did not appear in the input parameters. 2387 If any constraints are specified, Source/Destination pairs for which 2388 the Path Costs do not meet the constraints MUST NOT be included in 2389 the returned Cost Map. If no constraints were specified, then all 2390 Path Costs are assumed to meet the constraints. 2392 11.3.2.7. Example 2394 POST /costmap/filtered HTTP/1.1 2395 Host: custom.alto.example.com 2396 Content-Type: application/alto-costmapfilter+json 2397 Accept: application/alto-costmap+json,application/alto-error+json 2399 { 2400 "cost-type" : {"cost-mode": "numerical", 2401 "cost-metric": "routingcost" 2402 }, 2403 "pids" : { 2404 "srcs" : [ "PID1" ], 2405 "dsts" : [ "PID1", "PID2", "PID3" ] 2406 } 2407 } 2409 HTTP/1.1 200 OK 2410 Content-Length: TBA 2411 Content-Type: application/alto-costmap+json 2413 { 2414 "meta" : { 2415 "dependent-vtags" : [ 2416 {"resource-id": "my-default-network-map", 2417 "tag": "1266506139" 2418 } 2419 ], 2420 "cost-type": {"cost-mode" : "numerical", 2421 "cost-metric" : "routingcost" 2422 } 2423 }, 2424 "cost-map" : { 2425 "PID1": { "PID1": 0, "PID2": 1, "PID3": 2 } 2426 } 2427 } 2429 11.4. Endpoint Property Service 2431 The Endpoint Property Service provides information about Endpoint 2432 properties to ALTO Clients. 2434 11.4.1. Endpoint Property 2436 An Endpoint Property resource provides information about properties 2437 for individual endpoints. It MAY be provided by an ALTO Server. 2439 11.4.1.1. Media Type 2441 The media type of Endpoint Property is "application/ 2442 alto-endpointprop+json". 2444 11.4.1.2. HTTP Method 2446 The Endpoint Property resource is requested using the HTTP POST 2447 method. 2449 11.4.1.3. Accept Input Parameters 2451 An ALTO Client supplies the endpoint properties to be queried through 2452 a media type "application/alto-endpointpropparams+json", and 2453 specifies in the HTTP POST entity body a JSON Object of type 2454 ReqEndpointProp: 2456 object { 2457 EndpointPropertyType properties<1..*>; 2458 TypedEndpointAddr endpoints<1..*>; 2459 } ReqEndpointProp; 2461 with fields: 2463 properties List of endpoint properties to be returned for each 2464 endpoint. Each specified property MUST be included in the list of 2465 supported properties indicated by this resource's capabilities 2466 (Section 11.4.1.4). The ALTO Server MUST interpret entries 2467 appearing multiple times as if they appeared only once. 2469 endpoints List of endpoint addresses for which the specified 2470 properties are to be returned. The ALTO Server MUST interpret 2471 entries appearing multiple times as if they appeared only once. 2473 11.4.1.4. Capabilities 2475 This resource may be defined across multiple types of endpoint 2476 properties. The capabilities of an ALTO Server URI providing 2477 Endpoint Properties are defined by a JSON Object of type 2478 EndpointPropertyCapabilities: 2480 object { 2481 EndpointPropertyType prop-types<1..*>; 2482 } EndpointPropertyCapabilities; 2484 with field: 2486 prop-types The Endpoint Properties (see Section 10.8) supported by 2487 the corresponding URI. 2489 In particular, the Information Resource Closure MUST provide the look 2490 up of pid for every Network Map defined. 2492 11.4.1.5. Uses 2494 None. 2496 11.4.1.6. Response 2498 The "dependent-vtags" key in the "meta" field of the response MUST be 2499 an array that includes the Version Tags of all Network Maps whose 2500 'pid' is queried. 2502 The data component of an Endpoint Properties response is named 2503 "endpoint-properties", which is a JSON object of type 2504 EndpointPropertyMapData, where: 2506 object { 2507 EndpointPropertyMapData endpoint-properties; 2508 } InfoResourceEndpointProperties : ResponseEntityBase; 2510 object-map { 2511 TypedEndpointAddr -> EndpointProps; 2512 } EndpointPropertyMapData; 2514 object { 2515 EndpointPropertyType -> JSONValue; 2516 } EndpointProps; 2518 Specifically, an EndpointPropertyMapData object has one member for 2519 each endpoint indicated in the input parameters (with the name being 2520 the endpoint encoded as a TypedEndpointAddr). The requested 2521 properties for each endpoint are encoded in a corresponding 2522 EndpointProps object, which encodes one name/value pair for each 2523 requested property, where the property names are encoded as strings 2524 of type EndpointPropertyType. An implementation of the protocol in 2525 this document SHOULD assume that the property value is a JSONString 2526 and fail to parse if it is not, unless the implementation is using an 2527 extension to this document that indicates when and how property 2528 values of other data types are signaled. 2530 The ALTO Server returns the value for each of the requested endpoint 2531 properties for each of the endpoints listed in the input parameters. 2533 If the ALTO Server does not define a requested property's value for a 2534 particular endpoint, then it MUST omit that property from the 2535 response for only that endpoint. 2537 11.4.1.7. Example 2539 POST /endpointprop/lookup HTTP/1.1 2540 Host: alto.example.com 2541 Content-Length: TBA 2542 Content-Type: application/alto-endpointpropparams+json 2543 Accept: application/alto-endpointprop+json,application/alto-error+json 2545 { 2546 "properties" : [ "my-default-networkmap.pid", 2547 "priv:ietf-example-prop" ], 2548 "endpoints" : [ "ipv4:192.0.2.34", 2549 "ipv4:203.0.113.129" ] 2550 } 2552 HTTP/1.1 200 OK 2553 Content-Length: TBA 2554 Content-Type: application/alto-endpointprop+json 2556 { 2557 "meta" : { 2558 "dependent-vtags" : [ 2559 {"resource-id": "my-default-network-map", 2560 "tag": "1266506139" 2561 } 2562 ] 2563 }, 2564 "endpoint-properties": { 2565 "ipv4:192.0.2.34" : { "my-default-network-map.pid": "PID1", 2566 "priv:ietf-example-prop": "1" }, 2567 "ipv4:203.0.113.129" : { "my-default-network-map.pid": "PID3" } 2568 } 2569 } 2571 11.5. Endpoint Cost Service 2573 The Endpoint Cost Service provides information about costs between 2574 individual endpoints. 2576 In particular, this service allows lists of Endpoint prefixes (and 2577 addresses, as a special case) to be ranked (ordered) by an ALTO 2578 Server. 2580 11.5.1. Endpoint Cost 2582 An Endpoint Cost resource provides information about costs between 2583 individual endpoints. It MAY be provided by an ALTO Server. 2585 It is important to note that although this resource allows an ALTO 2586 Server to reveal costs between individual endpoints, an ALTO Server 2587 is not required to do so. A simple alternative would be to compute 2588 the cost between two endpoints as the cost between the PIDs 2589 corresponding to the endpoints. See Section 15.3 for additional 2590 details. 2592 11.5.1.1. Media Type 2594 The media type of Endpoint Cost is "application/ 2595 alto-endpointcost+json". 2597 11.5.1.2. HTTP Method 2599 The Endpoint Cost resource is requested using the HTTP POST method. 2601 11.5.1.3. Accept Input Parameters 2603 An ALTO Client supplies the endpoint cost parameters through a media 2604 type "application/alto-endpointcostparams+json", with an HTTP POST 2605 entity body of a JSON Object of type ReqEndpointCostMap: 2607 object { 2608 CostType cost-type; 2609 [JSONString constraints<0..*>;] 2610 EndpointFilter endpoints; 2611 } ReqEndpointCostMap; 2613 object { 2614 [TypedEndpointAddr srcs<0..*>;] 2615 [TypedEndpointAddr dsts<0..*>;] 2616 } EndpointFilter; 2617 with fields: 2619 cost-type The Cost Type (Section 10.7) to use for returned costs. 2620 The cost-metric and cost-mode fields MUST match one of the 2621 supported Cost Types indicated in this resource's capabilities ( 2622 Section 11.5.1.4). The ALTO Client SHOULD omit the description 2623 field, and if present, the ALTO Server MUST ignore the description 2624 field. 2626 constraints Defined equivalently to the "constraints" input 2627 parameter of a Filtered Cost Map (see Section 11.3.2). 2629 endpoints A list of Source Endpoints and Destination Endpoints for 2630 which Path Costs are to be returned. If the list of Source or 2631 Destination Endpoints is empty (or not included), the ALTO Server 2632 MUST interpret it as if it contained the Endpoint Address 2633 corresponding to the client IP address from the incoming 2634 connection (see Section 13.3 for discussion and considerations 2635 regarding this mode). The Source and Destination Endpoint lists 2636 MUST NOT be both empty. The ALTO Server MUST interpret entries 2637 appearing multiple times in a list as if they appeared only once. 2639 11.5.1.4. Capabilities 2641 In this document, we define EndpointCostCapabilities the same as 2642 FilteredCostMapCapabilities. See Section 11.3.2.4. 2644 11.5.1.5. Uses 2646 It is important to note that although this resource allows an ALTO 2647 Server to reveal costs between individual endpoints, an ALTO Server 2648 is not required to do so. A simple implementation of an ECS resource 2649 may compute the cost between two endpoints as the cost between the 2650 PIDs corresponding to the endpoints, using one of the exposed network 2651 and cost maps defined by the server. However, to preserve 2652 flexibility, the ECS resource MAY omit declaring in the "uses" 2653 attribute the network map and/or cost map on which it depends. 2655 11.5.1.6. Response 2657 The "meta" field of an Endpoint Cost response MUST include the "cost- 2658 type" key, to indicate the Cost Type used. 2660 The data component of an Endpoint Cost response is named "endpoint- 2661 cost-map", which is a JSON object of type EndpointCostMapData: 2663 object { 2664 EndpointCostMapData endpoint-cost-map; 2665 } InfoResourceEndpointCostMap : ResponseEntityBase; 2667 object-map { 2668 TypedEndpointAddr -> EndpointDstCosts; 2669 } EndpointCostMapData; 2671 object-map { 2672 TypedEndpointAddr -> JSONValue; 2673 } EndpointDstCosts; 2675 Specifically, an EndpointCostMapData object is a dictionary map with 2676 each key representing a TypedEndpointAddr string identifying the 2677 Source Endpoint specified in the input parameters. For each Source 2678 Endpoint, a EndpointDstCosts dictionary map object denotes the 2679 associated cost to each Destination Endpoint specified in input 2680 parameters. An implementation of the protocol in this document 2681 SHOULD assume that the cost value is a JSONNumber and fail to parse 2682 if it is not, unless the implementation is using an extension to this 2683 document that indicates when and how costs of other data types are 2684 signaled. If the ALTO Server does not define a cost value from a 2685 Source Endpoint to a particular Destination Endpoint, it MAY be 2686 omitted from the response. 2688 11.5.1.7. Example 2690 POST /endpointcost/lookup HTTP/1.1 2691 Host: alto.example.com 2692 Content-Length: TBA 2693 Content-Type: application/alto-endpointcostparams+json 2694 Accept: application/alto-endpointcost+json,application/alto-error+json 2696 { 2697 "cost-type": {"cost-mode" : "ordinal", 2698 "cost-metric" : "routingcost"}, 2699 "endpoints" : { 2700 "srcs": [ "ipv4:192.0.2.2" ], 2701 "dsts": [ 2702 "ipv4:192.0.2.89", 2703 "ipv4:198.51.100.34", 2704 "ipv4:203.0.113.45" 2705 ] 2706 } 2707 } 2709 HTTP/1.1 200 OK 2710 Content-Length: TBA 2711 Content-Type: application/alto-endpointcost+json 2713 { 2714 "meta" : { 2715 "cost-type": {"cost-mode" : "ordinal", 2716 "cost-metric" : "routingcost" 2717 } 2718 }, 2719 "endpoint-cost-map" : { 2720 "ipv4:192.0.2.2": { 2721 "ipv4:192.0.2.89" : 1, 2722 "ipv4:198.51.100.34" : 2, 2723 "ipv4:203.0.113.45" : 3 2724 } 2725 } 2726 } 2728 12. Use Cases 2730 The sections below depict typical use cases. While these use cases 2731 focus on peer-to-peer applications, ALTO can be applied to other 2732 environments such as CDNs [I-D.jenkins-alto-cdn-use-cases]. 2734 12.1. ALTO Client Embedded in P2P Tracker 2736 Many currently-deployed P2P systems use a Tracker to manage swarms 2737 and perform peer selection. Such a P2P Tracker can already use a 2738 variety of information to perform peer selection to meet application- 2739 specific goals. By acting as an ALTO Client, the P2P Tracker can use 2740 ALTO information as an additional information source to enable more 2741 network-efficient traffic patterns and improve application 2742 performance. 2744 A particular requirement of many P2P trackers is that they must 2745 handle a large number of P2P clients. A P2P tracker can obtain and 2746 locally store ALTO information (the Network Map and Cost Map) from 2747 the ISPs containing the P2P clients, and benefit from the same 2748 aggregation of network locations done by ALTO Servers. 2750 .---------. (1) Get Network Map .---------------. 2751 | | <----------------------> | | 2752 | ALTO | | P2P Tracker | 2753 | Server | (2) Get Cost Map | (ALTO Client) | 2754 | | <----------------------> | | 2755 `---------' `---------------' 2756 ^ | 2757 (3) Get Peers | | (4) Selected Peer 2758 | v List 2759 .---------. .-----------. 2760 | Peer 1 | <-------------- | P2P | 2761 `---------' | Client | 2762 . (5) Connect to `-----------' 2763 . Selected Peers / 2764 .---------. / 2765 | Peer 50 | <------------------ 2766 `---------' 2768 Figure 4: ALTO Client Embedded in P2P Tracker 2770 Figure 4 shows an example use case where a P2P tracker is an ALTO 2771 Client and applies ALTO information when selecting peers for its P2P 2772 clients. The example proceeds as follows: 2774 1. The P2P Tracker requests from the ALTO Server using the Network 2775 Map query the Network Map covering all PIDs. The Network Map 2776 includes the IP prefixes contained in each PID, allowing the P2P 2777 tracker to locally map P2P clients into PIDs. 2779 2. The P2P Tracker requests from the ALTO Server the Cost Map 2780 amongst all PIDs identified in the preceding step. 2782 3. A P2P Client joins the swarm, and requests a peer list from the 2783 P2P Tracker. 2785 4. The P2P Tracker returns a peer list to the P2P client. The 2786 returned peer list is computed based on the Network Map and Cost 2787 Map returned by the ALTO Server, and possibly other information 2788 sources. Note that it is possible that a tracker may use only 2789 the Network Map to implement hierarchical peer selection by 2790 preferring peers within the same PID and ISP. 2792 5. The P2P Client connects to the selected peers. 2794 Note that the P2P tracker may provide peer lists to P2P clients 2795 distributed across multiple ISPs. In such a case, the P2P tracker 2796 may communicate with multiple ALTO Servers. 2798 12.2. ALTO Client Embedded in P2P Client: Numerical Costs 2800 P2P clients may also utilize ALTO information themselves when 2801 selecting from available peers. It is important to note that not all 2802 P2P systems use a P2P tracker for peer discovery and selection. 2803 Furthermore, even when a P2P tracker is used, the P2P clients may 2804 rely on other sources, such as peer exchange and DHTs, to discover 2805 peers. 2807 When an P2P Client uses ALTO information, it typically queries only 2808 the ALTO Server servicing its own ISP. The my-Internet view provided 2809 by its ISP's ALTO Server can include preferences to all potential 2810 peers. 2812 .---------. (1) Get Network Map .---------------. 2813 | | <----------------------> | | 2814 | ALTO | | P2P Client | 2815 | Server | (2) Get Cost Map | (ALTO Client) | 2816 | | <----------------------> | | .---------. 2817 `---------' `---------------' <- | P2P | 2818 .---------. / | ^ ^ | Tracker | 2819 | Peer 1 | <-------------- | | \ `---------' 2820 `---------' | (3) Gather Peers 2821 . (4) Select Peers | | \ 2822 . and Connect / .--------. .--------. 2823 .---------. / | P2P | | DHT | 2824 | Peer 50 | <---------------- | Client | `--------' 2825 `---------' | (PEX) | 2826 `--------' 2828 Figure 5: ALTO Client Embedded in P2P Client 2830 Figure 5 shows an example use case where a P2P Client locally applies 2831 ALTO information to select peers. The use case proceeds as follows: 2833 1. The P2P Client requests the Network Map covering all PIDs from 2834 the ALTO Server servicing its own ISP. 2836 2. The P2P Client requests the Cost Map amongst all PIDs from the 2837 ALTO Server. The Cost Map by default specifies numerical costs. 2839 3. The P2P Client discovers peers from sources such as Peer Exchange 2840 (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and 2841 P2P Trackers. 2843 4. The P2P Client uses ALTO information as part of the algorithm for 2844 selecting new peers, and connects to the selected peers. 2846 12.3. ALTO Client Embedded in P2P Client: Ranking 2848 It is also possible for a P2P Client to offload the selection and 2849 ranking process to an ALTO Server. In this use case, the ALTO Client 2850 gathers a list of known peers in the swarm, and asks the ALTO Server 2851 to rank them. 2853 As in the use case using numerical costs, the P2P Client typically 2854 only queries the ALTO Server servicing its own ISP. 2856 .---------. .---------------. 2857 | | | | 2858 | ALTO | (2) Get Endpoint Ranking | P2P Client | 2859 | Server | <----------------------> | (ALTO Client) | 2860 | | | | .---------. 2861 `---------' `---------------' <- | P2P | 2862 .---------. / | ^ ^ | Tracker | 2863 | Peer 1 | <-------------- | | \ `---------' 2864 `---------' | (1) Gather Peers 2865 . (3) Connect to | | \ 2866 . Selected Peers / .--------. .--------. 2867 .---------. / | P2P | | DHT | 2868 | Peer 50 | <---------------- | Client | `--------' 2869 `---------' | (PEX) | 2870 `--------' 2872 Figure 6: ALTO Client Embedded in P2P Client: Ranking 2874 Figure 6 shows an example of this scenario. The use case proceeds as 2875 follows: 2877 1. The P2P Client discovers peers from sources such as Peer Exchange 2878 (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and 2879 P2P Trackers. 2881 2. The P2P Client queries the ALTO Server's Ranking Service, 2882 including discovered peers as the set of Destination Endpoints, 2883 and indicates the 'ordinal' Cost Mode. The response indicates 2884 the ranking of the candidate peers. 2886 3. The P2P Client connects to the peers in the order specified in 2887 the ranking. 2889 13. Discussions 2891 13.1. Discovery 2893 The discovery mechanism by which an ALTO Client locates an 2894 appropriate ALTO Server is out of scope for this document. This 2895 document assumes that an ALTO Client can discover an appropriate ALTO 2896 Server. Once it has done so, the ALTO Client may use the Information 2897 Resource Directory (see Section 9.2) to locate an Information 2898 Resource with the desired ALTO Information. 2900 13.2. Hosts with Multiple Endpoint Addresses 2902 In practical deployments, a particular host can be reachable using 2903 multiple addresses (e.g., a wireless IPv4 connection, a wireline IPv4 2904 connection, and a wireline IPv6 connection). In general, the 2905 particular network path followed when sending packets to the host 2906 will depend on the address that is used. Network providers may 2907 prefer one path over another. An additional consideration may be how 2908 to handle private address spaces (e.g., behind carrier-grade NATs). 2910 To support such behavior, this document allows multiple endpoint 2911 addresses and address types. With this support, the ALTO Protocol 2912 allows an ALTO Service Provider the flexibility to indicate 2913 preferences for paths from an endpoint address of one type to an 2914 endpoint address of a different type. 2916 13.3. Network Address Translation Considerations 2918 At this day and age of NAT v4<->v4, v4<->v6 [RFC6144], and possibly 2919 v6<->v6 [RFC6296], a protocol should strive to be NAT friendly and 2920 minimize carrying IP addresses in the payload, or provide a mode of 2921 operation where the source IP address provide the information 2922 necessary to the server. 2924 The protocol specified in this document provides a mode of operation 2925 where the source network location is computed by the ALTO Server 2926 (i.e., the the Endpoint Cost Service) from the source IP address 2927 found in the ALTO Client query packets. This is similar to how some 2928 P2P Trackers (e.g., BitTorrent Trackers - see "Tracker HTTP/HTTPS 2929 Protocol" in [BitTorrent]) operate. 2931 There may be cases where an ALTO Client needs to determine its own IP 2932 address, such as when specifying a source Endpoint Address in the 2933 Endpoint Cost Service. It is possible that an ALTO Client has 2934 multiple network interface addresses, and that some or all of them 2935 may require NAT for connectivity to the public Internet. 2937 If a public IP address is required for a network interface, the ALTO 2938 Client SHOULD use the Session Traversal Utilities for NAT (STUN) 2939 [RFC5389]. If using this method, the host MUST use the "Binding 2940 Request" message and the resulting "XOR-MAPPED-ADDRESS" parameter 2941 that is returned in the response. Using STUN requires cooperation 2942 from a publicly accessible STUN server. Thus, the ALTO Client also 2943 requires configuration information that identifies the STUN server, 2944 or a domain name that can be used for STUN server discovery. To be 2945 selected for this purpose, the STUN server needs to provide the 2946 public reflexive transport address of the host. 2948 ALTO Clients should be cognizant that the network path between 2949 Endpoints can depend on multiple factors, e.g., source address, and 2950 destination address used for communication. An ALTO Server provides 2951 information based on Endpoint Addresses (more generally, Network 2952 Locations), but the mechanisms used for determining existence of 2953 connectivity or usage of NAT between Endpoints are out of scope of 2954 this document. 2956 13.4. Endpoint and Path Properties 2958 An ALTO Server could make available many properties about Endpoints 2959 beyond their network location or grouping. For example, connection 2960 type, geographical location, and others may be useful to 2961 applications. This specification focuses on network location and 2962 grouping, but the protocol may be extended to handle other Endpoint 2963 properties. 2965 14. IANA Considerations 2967 This document defines registries for application/alto-* Media Types, 2968 ALTO Cost Metric, ALTO Endpoint Property Types, ALTO Address Types, 2969 and ALTO Error Codes. Initial values for the registries are given 2970 below; future assignments are to be made through the IANA Policy of 2971 Standards Action, defined in [RFC5226]. 2973 14.1. application/alto-* Media Types 2975 This document requests the registration of multiple media types, 2976 listed in Table 2. 2978 +-------------+------------------------------+----------------+ 2979 | Type | Subtype | Specification | 2980 +-------------+------------------------------+----------------+ 2981 | application | alto-directory+json | Section 9.2 | 2982 | application | alto-networkmap+json | Section 11.2.1 | 2983 | application | alto-networkmapfilter+json | Section 11.3.1 | 2984 | application | alto-costmap+json | Section 11.2.3 | 2985 | application | alto-costmapfilter+json | Section 11.3.2 | 2986 | application | alto-endpointprop+json | Section 11.4.1 | 2987 | application | alto-endpointpropparams+json | Section 11.4.1 | 2988 | application | alto-endpointcost+json | Section 11.5.1 | 2989 | application | alto-endpointcostparams+json | Section 11.5.1 | 2990 | application | alto-error+json | Section 8.5 | 2991 +-------------+------------------------------+----------------+ 2993 Table 2: ALTO Protocol Media Types. 2995 Type name: application 2997 Subtype name: This documents requests the registration of multiple 2998 subtypes, as listed in Table 2. 3000 Required parameters: n/a 3002 Optional parameters: n/a 3004 Encoding considerations: Encoding considerations are identical to 3005 those specified for the 'application/json' media type. See 3006 [RFC4627]. 3008 Security considerations: Security considerations relating to the 3009 generation and consumption of ALTO Protocol messages are discussed 3010 in Section 15. 3012 Interoperability considerations: This document specifies format of 3013 conforming messages and the interpretation thereof. 3015 Published specification: This document is the specification for 3016 these media types; see Table 2 for the section documenting each 3017 media type. 3019 Applications that use this media type: ALTO Servers and ALTO Clients 3020 either standalone or embedded within other applications. 3022 Additional information: 3024 Magic number(s): n/a 3026 File extension(s): This document uses the mime type to refer to 3027 protocol messages and thus does not require a file extension. 3029 Macintosh file type code(s): n/a 3031 Person & email address to contact for further information: See 3032 "Authors' Addresses" section. 3034 Intended usage: COMMON 3036 Restrictions on usage: n/a 3038 Author: See "Authors' Addresses" section. 3040 Change controller: Internet Engineering Task Force 3041 (mailto:iesg@ietf.org). 3043 14.2. ALTO Cost Metric Registry 3045 This document requests the creation of an ALTO Cost Metric registry, 3046 listed in Table 3, to be maintained by IANA. 3048 +-------------+---------------------+ 3049 | Identifier | Intended Semantics | 3050 +-------------+---------------------+ 3051 | routingcost | See Section 6.1.1.1 | 3052 | priv: | Private use | 3053 | exp: | Experimental use | 3054 +-------------+---------------------+ 3056 Table 3: ALTO Cost Metrics. 3058 This registry serves two purposes. First, it ensures uniqueness of 3059 identifiers referring to ALTO Cost Metrics. Second, it provides 3060 references to particular semantics of allocated Cost Metrics to be 3061 applied by both ALTO Servers and applications utilizing ALTO Clients. 3063 New ALTO Cost Metrics are assigned after Expert Review [RFC5226]. 3064 The Expert Reviewer will generally consult the ALTO Working Group or 3065 its successor. Expert Review is used to ensure that proper 3066 documentation regarding ALTO Cost Metric semantics and security 3067 considerations has been provided. The provided documentation should 3068 be detailed enough to provide guidance to both ALTO Service Providers 3069 and applications utilizing ALTO Clients as to how values of the 3070 registered ALTO Cost Metric should be interpreted. Updates and 3071 deletions of ALTO Cost Metrics follow the same procedure. 3073 Registered ALTO Cost Metric identifiers MUST conform to the 3074 syntactical requirements specified in Section 10.6. Identifiers are 3075 to be recorded and displayed as ASCII strings. 3077 Identifiers prefixed with 'priv:' are reserved for Private Use. 3078 Identifiers prefixed with 'exp:' are reserved for Experimental use. 3080 Requests to add a new value to the registry MUST include the 3081 following information: 3083 o Identifier: The name of the desired ALTO Cost Metric. 3085 o Intended Semantics: ALTO Costs carry with them semantics to guide 3086 their usage by ALTO Clients. For example, if a value refers to a 3087 measurement, the measurement units must be documented. For proper 3088 implementation of the ordinal Cost Mode (e.g., by a third-party 3089 service), it should be documented whether higher or lower values 3090 of the cost are more preferred. 3092 o Security Considerations: ALTO Costs expose information to ALTO 3093 Clients. As such, proper usage of a particular Cost Metric may 3094 require certain information to be exposed by an ALTO Service 3095 Provider. Since network information is frequently regarded as 3096 proprietary or confidential, ALTO Service Providers should be made 3097 aware of the security ramifications related to usage of a Cost 3098 Metric. 3100 This specification requests registration of the identifier 3101 'routingcost'. Semantics for the this Cost Metric are documented in 3102 Section 6.1.1.1, and security considerations are documented in 3103 Section 15.3. 3105 14.3. ALTO Endpoint Property Type Registry 3107 This document requests the creation of an ALTO Endpoint Property 3108 Types registry, listed in Table 4, to be maintained by IANA. 3110 +------------+--------------------+ 3111 | Identifier | Intended Semantics | 3112 +------------+--------------------+ 3113 | pid | See Section 7.1.1 | 3114 | priv: | Private use | 3115 | exp: | Experimental use | 3116 +------------+--------------------+ 3118 Table 4: ALTO Endpoint Property Types. 3120 The maintenance of this registry is similar to that of the preceding 3121 ALTO Cost Metrics. 3123 14.4. ALTO Address Type Registry 3125 This document requests the creation of an ALTO Address Type registry, 3126 listed in Table 5, to be maintained by IANA. 3128 +------------+-----------------+-----------------+------------------+ 3129 | Identifier | Address | Prefix Encoding | Mapping to/from | 3130 | | Encoding | | IPv4/v6 | 3131 +------------+-----------------+-----------------+------------------+ 3132 | ipv4 | See | See | Direct mapping | 3133 | | Section 10.4.3 | Section 10.4.4 | to IPv4 | 3134 | ipv6 | See | See | Direct mapping | 3135 | | Section 10.4.3 | Section 10.4.4 | to IPv6 | 3136 +------------+-----------------+-----------------+------------------+ 3138 Table 5: ALTO Address Types. 3140 This registry serves two purposes. First, it ensures uniqueness of 3141 identifiers referring to ALTO Address Types. Second, it states the 3142 requirements for allocated Address Type identifiers. 3144 New ALTO Address Types are assigned after Expert Review [RFC5226]. 3145 The Expert Reviewer will generally consult the ALTO Working Group or 3146 its successor. Expert Review is used to ensure that proper 3147 documentation regarding the new ALTO Address Types and their security 3148 considerations has been provided. The provided documentation should 3149 indicate how an address of a registered type is encoded as an 3150 EndpointAddr and, if possible, a compact method (e.g., IPv4 and IPv6 3151 prefixes) for encoding a set of addresses as an EndpointPrefix. 3152 Updates and deletions of ALTO Address Types follow the same 3153 procedure. 3155 Registered ALTO Address Type identifiers MUST conform to the 3156 syntactical requirements specified in Section 10.4.2. Identifiers 3157 are to be recorded and displayed as ASCII strings. 3159 Requests to add a new value to the registry MUST include the 3160 following information: 3162 o Identifier: The name of the desired ALTO Address Type. 3164 o Endpoint Address Encoding: The procedure for encoding an address 3165 of the registered type as an EndpointAddr (see Section 10.4.3). 3167 o Endpoint Prefix Encoding: The procedure for encoding a set of 3168 addresses of the registered type as an EndpointPrefix (see 3169 Section 10.4.4). If no such compact encoding is available, the 3170 same encoding used for a singular address may be used. In such a 3171 case, it must be documented that sets of addresses of this type 3172 always have exactly one element. 3174 o Mapping to/from IPv4/IPv6 Addresses: If possible, a mechanism to 3175 map addresses of the registered type to and from IPv4 or IPv6 3176 addresses should be specified. 3178 o Security Considerations: In some usage scenarios, Endpoint 3179 Addresses carried in ALTO Protocol messages may reveal information 3180 about an ALTO Client or an ALTO Service Provider. Applications 3181 and ALTO Service Providers using addresses of the registered type 3182 should be made aware of how (or if) the addressing scheme relates 3183 to private information and network proximity. 3185 This specification requests registration of the identifiers 'ipv4' 3186 and 'ipv6', as shown in Table 5. 3188 14.5. ALTO Error Code Registry 3190 This document requests the creation of an ALTO Error Code registry, 3191 listed in Table 1, to be maintained by IANA. 3193 15. Security Considerations 3195 Some environments and use cases of ALTO require consideration of 3196 security attacks on ALTO Servers and Clients. In order to support 3197 those environments interoperably, the ALTO requirements document 3198 [RFC6708] outlines minimum-to-implement authentication and other 3199 security requirements. Below we consider the threats and protection 3200 strategies. 3202 15.1. Authenticity and Integrity of ALTO Information 3204 15.1.1. Risk Scenarios 3206 An attacker may want to provide false or modified ALTO Information 3207 Resources or Information Resource Directory to ALTO Clients to 3208 achieve certain malicious goals. As an example, an attacker may 3209 provide false endpoint properties. For example, suppose that a 3210 network supports an endpoint property named "hasQuota" which reports 3211 if the endpoint has usage quota. An attacker may want to generate a 3212 false reply to lead to unexpected charges to the endpoint. An attack 3213 may also want to provide false Cost Map. For example, by faking a 3214 Cost Map that highly prefers a small address range or a single 3215 address, the attacker may be able to turn a distributed application 3216 into a Distributed Denial of Service (DDoS) tool. 3218 Depending on the network scenario, an attacker can attack 3219 authenticity and integrity of ALTO Information Resources using 3220 various techniques, including, but not limited to, sending forged 3221 DHCP replies in an Ethernet, DNS poisoning, and installing a 3222 transparent HTTP proxy that does some modifications. 3224 15.1.2. Protection Strategies 3226 ALTO protects the authenticity and integrity of ALTO Information 3227 (both Information Directory and individual Information Resources) by 3228 leveraging the authenticity and integrity mechanisms in TLS. In 3229 particular, the ALTO Protocol requires that HTTP over TLS [RFC2818] 3230 MUST be supported, when protecting the authenticity and integrity of 3231 ALTO Information is required. The rules in [RFC2818] for a client to 3232 verify server identity using server certificates MUST be supported. 3233 ALTO Providers who request server certificates and certification 3234 authorities who issue ALTO-specific certificates SHOULD consider the 3235 recommendations and guidelines defined in [RFC6125] 3237 Software engineers developing and service providers deploying ALTO 3238 should make themselves familiar with up-to-date Best Current 3239 Practices on configuring HTTP over TLS. 3241 15.1.3. Limitations 3243 The protection of HTTP over TLS for ALTO depends on that the domain 3244 name in the URI for the Information Resources is not comprised. This 3245 will depend on the protection implemented by service discovery. 3247 A deployment scenario may require redistribution of ALTO information 3248 to improve scalability. When authenticity and integrity of ALTO 3249 information are still required, then ALTO Clients obtaining ALTO 3250 information through redistribution must be able to validate the 3251 received ALTO information. Support for this validation is not 3252 provided in this document, but may be provided by extension 3253 documents. 3255 15.2. Potential Undesirable Guidance from Authenticated ALTO 3256 Information 3258 15.2.1. Risk Scenarios 3260 The ALTO Service makes it possible for an ALTO Provider to influence 3261 the behavior of network applications. An ALTO Provider may be 3262 hostile to some applications and hence try to use ALTO Information 3263 Resources to achieve certain goals [RFC5693]: "redirecting 3264 applications to corrupted mediators providing malicious content, or 3265 applying policies in computing Cost Map based on criteria other than 3266 network efficiency." See [I-D.ietf-alto-deployments] for additional 3267 discussions on faked ALTO Guidance. 3269 A related scenario is that an ALTO Server could unintentionally give 3270 "bad" guidance. For example, if many ALTO Clients follow the Cost 3271 Map or Endpoint Cost guidance without doing additional sanity checks 3272 or adaptation, more preferable hosts and/or links could get 3273 overloaded while less preferable ones remain idle; see AR-14 of 3274 [RFC6708] for related application considerations. 3276 15.2.2. Protection Strategies 3278 To protect applications from undesirable ALTO Information Resources, 3279 it is important to note that there is no protocol mechanism to 3280 require conforming behaviors on how applications use ALTO Information 3281 Resources. An application using ALTO may consider including a 3282 mechanism to detect misleading or undesirable results from using ALTO 3283 Information Resources. For example, if throughput measurements do 3284 not show "better-than-random" results when using the Cost Map to 3285 select resource providers, the application may want to disable ALTO 3286 usage or switch to an external ALTO Server provided by an 3287 "independent organization" (see AR-20 and AR-21 in [RFC6708]). If 3288 the first ALTO Server is provided by the access network service 3289 provider and the access network service provider tries to redirect 3290 access to the external ALTO Server back to the provider's ALTO Server 3291 or try to tamper with the responses, the preceding authentication and 3292 integrity protection can detect such a behavior. 3294 15.3. Confidentiality of ALTO Information 3296 15.3.1. Risk Scenarios 3298 Although in many cases ALTO Information Resources may be regarded as 3299 non-confidential information, there are deployment cases where ALTO 3300 Information Resources can be sensitive information that can pose 3301 risks if exposed to unauthorized parties. We discuss the risks and 3302 protection strategies for such deployment scenarios. 3304 For example, an attacker may infer details regarding the topology, 3305 status, and operational policies of a network through the Network and 3306 Cost Maps. As a result, a sophisticated attacker may be able to 3307 infer more fine-graind topology information than an ISP hosting an 3308 ALTO Server intends to disclose. The attacker can leverage the 3309 information to mount effective attacks such as focusing on high-cost 3310 links. 3312 Revealing some endpoint properties may also reveal additional 3313 information than the Provider intended. For example, when adding the 3314 line bitrate as one endpoint property, such information may be 3315 potentially linked to the income of the habitants at the network 3316 location of an endpoint. 3318 In [RFC6708] Section 5.2.1, three types of risks associated with the 3319 confidentiality of ALTO Information Resources are identified: risk 3320 type (1) Excess disclosure of the ALTO service provider's data to an 3321 authorized ALTO Client; risk type (2) Disclosure of the ALTO service 3322 provider's data (e.g., network topology information) to an 3323 unauthorized third party; and risk type (3) Excess retrieval of the 3324 ALTO service provider's data by collaborating ALTO Clients. 3325 [I-D.ietf-alto-deployments] also discusses information leakage from 3326 ALTO. 3328 15.3.2. Protection Strategies 3330 To address risk types (1) and (3), the Provider of an ALTO Server 3331 must be cognizant that the network topology and provisioning 3332 information provided through ALTO may lead to attacks. ALTO does not 3333 require any particular level of details of information disclosure, 3334 and hence the Provider should evaluate how much information is 3335 revealed and the associated risks. 3337 To address risk type (2), the ALTO Protocol need confidentiality. 3338 Since ALTO requires that HTTP over TLS MUST be supported, the 3339 confidentiality mechanism is provided by HTTP over TLS. 3341 For deployment scenarios where client authentication is desired to 3342 address risk type (2), ALTO requires that HTTP Digestion 3343 Authentication MUST be supported to achieve ALTO Client 3344 Authentication to limit the number of parties with whom ALTO 3345 information is directly shared. Depending on the use-case and 3346 scenario, an ALTO Server may apply other access control techniques to 3347 restrict access to its services. Access control can also help to 3348 prevent Denial-of-Service attacks by arbitrary hosts from the 3349 Internet. See [I-D.ietf-alto-deployments] for a more detailed 3350 discussion on this issue. 3352 15.3.3. Limitations 3354 ALTO Information Providers should be cognizant that encryption only 3355 protects ALTO information until it is decrypted by the intended ALTO 3356 Client. Digital Rights Management (DRM) techniques and legal 3357 agreements protecting ALTO information are outside of the scope of 3358 this document. 3360 15.4. Privacy for ALTO Users 3362 15.4.1. Risk Scenarios 3364 The ALTO Protocol provides mechanisms in which the ALTO Client 3365 serving a user can send messages containing Network Location 3366 Identifiers (IP addresses or fine-grained PIDs) to the ALTO Server. 3367 This is particularly true for the Endpoint Property, Endpoint Cost, 3368 and fine-grained Filtered Map services. The ALTO Server or a third- 3369 party who is able to intercept such messages can store and process 3370 obtained information in order to analyze user behaviors and 3371 communication patterns. The analysis may correlate information 3372 collected from multiple clients to deduce additional application/ 3373 content information. Such analysis can lead to privacy risks. For a 3374 more comprehensive classification of related risk scenarios, see 3375 cases 4, 5, and 6 in [RFC6708], Section 5.2. 3377 15.4.2. Protection Strategies 3379 To protect user privacy, an ALTO Client should be cognizant about 3380 potential ALTO Server tracking through client queries. An ALTO 3381 Client may consider the possibility of relying only on Network Map 3382 for PIDs and Cost Map amongst PIDs to avoid passing IP addresses of 3383 other endpoints (e.g., peers) to the ALTO Server. When specific IP 3384 addresses are needed (e.g., when using the Endpoint Cost Service), an 3385 ALTO Client may consider obfuscation techniques such as specifying a 3386 broader address range (i.e., a shorter prefix length) or by zeroing 3387 out or randomizing the last few bits of IP addresses. Note that 3388 obfuscation may yield less accurate results. 3390 15.5. Availability of ALTO Service 3392 15.5.1. Risk Scenarios 3394 An attacker may want to disable ALTO Service as a way to disable 3395 network guidance to large scale applications.In particular, queries 3396 which can be generated with low effort but result in expensive 3397 workloads at the ALTO Server could be exploited for Denial-of-Service 3398 attacks. For instance, a simple ALTO query with n Source Network 3399 Locations and m Destination Network Locations can be generated fairly 3400 easily but results in the computation of n*m Path Costs between pairs 3401 by the ALTO Server (see Section 5.2). 3403 15.5.2. Protection Strategies 3405 ALTO Provider should be cognizant of the workload at the ALTO Server 3406 generated by certain ALTO Queries, such as certain queries to the Map 3407 Service, the Map Filtering Service and the Endpoint Cost (Ranking) 3408 Service. One way to limit Denial-of-Service attacks is to employ 3409 access control to the ALTO Server. The ALTO Server can also indicate 3410 overload and reject repeated requests that can cause availability 3411 problems. More advanced protection schemes such as computational 3412 puzzles [I-D.jennings-sip-hashcash] may be considered in an extension 3413 document. 3415 An ALTO Provider should also leverage the fact that the Map Service 3416 allows ALTO Servers to pre-generate maps that can be distributed to 3417 many ALTO Clients. 3419 16. Manageability Considerations 3421 This section details operations and management considerations based 3422 on existing deployments and discussions during protocol development. 3423 It also indicates where extension documents are expected to provide 3424 appropriate functionality discussed in [RFC5706] as additional 3425 deployment experience becomes available. 3427 16.1. Operations 3429 16.1.1. Installation and Initial Setup 3431 The ALTO Protocol is based on HTTP. Thus, configuring an ALTO Server 3432 may require configuring the underlying HTTP server implementation to 3433 define appropriate security policies, caching policies, performance 3434 settings, etc. 3436 Additionally, an ALTO Service Provider will need to configure the 3437 ALTO information to be provided by the ALTO Server. The granularity 3438 of the topological map and the cost map is left to the specific 3439 policies of the ALTO Service Provider. However, a reasonable default 3440 may include two PIDs, one to hold the endpoints in the provider's 3441 network and the second PID to represent full IPv4 and IPv6 3442 reachability (see Section 11.2.2), with the cost between each source/ 3443 destination PID set to 1. Another operational issue that the ALTO 3444 Service Provider needs to consider is that the filtering service can 3445 degenerate into a full map service when the filtering input is empty. 3446 Although this choice as the degeneration behavior provides 3447 continuity, the operational impact should be considered. 3449 Implementers employing an ALTO Client should attempt to automatically 3450 discover an appropriate ALTO Server. Manual configuration of the 3451 ALTO Server location may be used where automatic discovery is not 3452 appropriate. Methods for automatic discovery and manual 3453 configuration are discussed in [I-D.ietf-alto-server-discovery]. 3455 Specifications for underlying protocols (e.g., TCP, HTTP, SSL/TLS) 3456 should be consulted for their available settings and proposed default 3457 configurations. 3459 16.1.2. Migration Path 3461 This document does not detail a migration path for ALTO Servers since 3462 there is no previous standard protocol providing the similar 3463 functionality. 3465 There are existing applications making use of network information 3466 discovered from other entities such as whois, geo-location databases, 3467 or round-trip time measurements, etc. Such applications should 3468 consider using ALTO as an additional source of information; ALTO need 3469 not be the sole source of network information. 3471 16.1.3. Requirements on Other Protocols and Functional Components 3473 The ALTO Protocol assumes that HTTP client and server implementations 3474 exist. It also assumes that JSON encoder and decoder implementations 3475 exist. 3477 An ALTO Server assumes that it can gather sufficient information to 3478 populate Network and Cost maps. "Sufficient information" is 3479 dependent on the information being exposed, but likely includes 3480 information gathered from protocols such as IGP and EGP Routing 3481 Information Bases (see Figure 1). Specific mechanisms have been 3482 proposed (e.g., [I-D.medved-alto-svr-apis]) and are expected to be 3483 provided in extension documents. 3485 16.1.4. Impact and Observation on Network Operation 3487 ALTO presents a new opportunity for managing network traffic by 3488 providing additional information to clients. The potential impact to 3489 network operation is large. 3491 Deployment of an ALTO Server may shift network traffic patterns. 3492 Thus, an ALTO Service Provider should consider impacts on (or 3493 integration with) traffic engineering and the deployment of a 3494 monitoring service to observe the effects of ALTO operations. Note 3495 that ALTO-specific monitoring and metrics are discussed in 3496 [I-D.ietf-alto-deployments]. In particular, an ALTO Service Provider 3497 may observe that ALTO Clients are not bound to ALTO Server guidance 3498 as ALTO is only one source of information. 3500 An ALTO Service Provider should ensure that appropriate information 3501 is being exposed. Privacy implications for ISPs are discussed in 3502 Section 15.3. Both ALTO Service Providers and those using ALTO 3503 Clients should be aware of the impact of incorrect or faked guidance 3504 (see [I-D.ietf-alto-deployments]). 3506 16.2. Management 3508 16.2.1. Management Interoperability 3510 A common management API would be desirable given that ALTO Servers 3511 may typically be configured with dynamic data from various sources, 3512 and ALTO Servers are intended to scale horizontally for fault- 3513 tolerance and reliability. A specific API or protocol is outside the 3514 scope of this document, but may be provided by an extension document. 3516 Logging is an important functionality for ALTO Servers and, depending 3517 on the deployment, ALTO Clients. Logging should be done via syslog 3518 [RFC5424]. 3520 16.2.2. Management Information 3522 A Management Information Model (see Section 3.2 of [RFC5706] is not 3523 provided by this document, but should be included or referenced by 3524 any extension documenting an ALTO-related management API or protocol. 3526 16.2.3. Fault Management 3528 Monitoring ALTO Servers and Clients is described in 3529 [I-D.ietf-alto-deployments]. 3531 16.2.4. Configuration Management 3533 Standardized approaches and protocols to configuration management for 3534 ALTO are outside the scope of this document, but this document does 3535 outline high-level principles suggested for future standardization 3536 efforts. 3538 An ALTO Server requires at least the following logical inputs: 3540 o Data sources from which ALTO Information is derived. This can 3541 either be raw network information (e.g., from routing elements) or 3542 pre-processed ALTO-level information in the form of a Network Map, 3543 Cost Map, etc. 3545 o Algorithms for computing the ALTO information returned to clients. 3546 These could either return information from a database, or 3547 information customized for each client. 3549 o Security policies mapping potential clients to the information 3550 that they have privilege to access. 3552 Multiple ALTO Servers can be deployed for scalability. A centralized 3553 configuration database may be used to ensure they are providing the 3554 desired ALTO information with appropriate security controls. The 3555 ALTO information (e.g., Network Maps and Cost Maps) being served by 3556 each ALTO Server, as well as security policies (HTTP authentication, 3557 SSL/TLS client and server authentication, SSL/TLS encryption 3558 parameters) intended to serve the same information should be 3559 monitored for consistency. 3561 16.2.5. Performance Management 3563 An exhaustive list of desirable performance information from a ALTO 3564 Servers and ALTO Clients are outside of the scope of this document. 3565 The following is a list of suggested ALTO-specific to be monitored 3566 based on the existing deployment and protocol development experience: 3568 o Requests and responses for each service listed in a Information 3569 Directory (total counts and size in bytes). 3571 o CPU and memory utilization 3573 o ALTO map updates 3575 o Number of PIDs 3577 o ALTO map sizes (in-memory size, encoded size, number of entries) 3579 16.2.6. Security Management 3581 Section 15 documents ALTO-specific security considerations. 3582 Operators should configure security policies with those in mind. 3583 Readers should refer to HTTP [RFC2616] and SSL/TLS [RFC5246] and 3584 related documents for mechanisms available for configuring security 3585 policies. Other appropriate security mechanisms (e.g., physical 3586 security, firewalls, etc) should also be considered. 3588 17. References 3590 17.1. Normative References 3592 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", 3593 RFC 1812, June 1995. 3595 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 3596 Extensions (MIME) Part Two: Media Types", RFC 2046, 3597 November 1996. 3599 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3600 Requirement Levels", BCP 14, RFC 2119, March 1997. 3602 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 3603 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 3604 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 3606 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 3607 Resource Identifier (URI): Generic Syntax", STD 66, 3608 RFC 3986, January 2005. 3610 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 3611 (CIDR): The Internet Address Assignment and Aggregation 3612 Plan", BCP 122, RFC 4632, August 2006. 3614 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 3615 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 3616 May 2008. 3618 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3619 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 3621 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 3622 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 3623 October 2008. 3625 [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009. 3627 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 3628 Address Text Representation", RFC 5952, August 2010. 3630 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 3631 Verification of Domain-Based Application Service Identity 3632 within Internet Public Key Infrastructure Using X.509 3633 (PKIX) Certificates in the Context of Transport Layer 3634 Security (TLS)", RFC 6125, March 2011. 3636 17.2. Informative References 3638 [BitTorrent] 3639 "Bittorrent Protocol Specification v1.0", 3640 . 3642 [Fielding-Thesis] 3643 Fielding, R., "Architectural Styles and the Design of 3644 Network-based Software Architectures", University of 3645 California, Irvine, Dissertation 2000, 2000. 3647 [I-D.akonjang-alto-proxidor] 3648 Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D. 3649 Saucez, "The PROXIDOR Service", 3650 draft-akonjang-alto-proxidor-00 (work in progress), 3651 March 2009. 3653 [I-D.ietf-alto-deployments] 3654 Stiemerling, M., Kiesel, S., Previdi, S., and M. Scharf, 3655 "ALTO Deployment Considerations", 3656 draft-ietf-alto-deployments-08 (work in progress), 3657 October 2013. 3659 [I-D.ietf-alto-server-discovery] 3660 Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and 3661 S. Yongchao, "ALTO Server Discovery", 3662 draft-ietf-alto-server-discovery-10 (work in progress), 3663 September 2013. 3665 [I-D.ietf-httpbis-p2-semantics] 3666 Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 3667 (HTTP/1.1): Semantics and Content", 3668 draft-ietf-httpbis-p2-semantics-25 (work in progress), 3669 November 2013. 3671 [I-D.jenkins-alto-cdn-use-cases] 3672 Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and 3673 S. Previdi, "Use Cases for ALTO within CDNs", 3674 draft-jenkins-alto-cdn-use-cases-03 (work in progress), 3675 June 2012. 3677 [I-D.jennings-sip-hashcash] 3678 Jennings, C., "Computational Puzzles for SPAM Reduction in 3679 SIP", draft-jennings-sip-hashcash-06 (work in progress), 3680 July 2007. 3682 [I-D.medved-alto-svr-apis] 3683 Medved, J., Ward, D., Peterson, J., Woundy, R., and D. 3684 McDysan, "ALTO Network-Server and Server-Server APIs", 3685 draft-medved-alto-svr-apis-00 (work in progress), 3686 March 2011. 3688 [I-D.p4p-framework] 3689 Alimi, R., Pasko, D., Popkin, L., Wang, Y., and Y. Yang, 3690 "P4P: Provider Portal for P2P Applications", 3691 draft-p4p-framework-00 (work in progress), November 2008. 3693 [I-D.saumitra-alto-multi-ps] 3694 Das, S., Narayanan, V., and L. Dondeti, "ALTO: A Multi 3695 Dimensional Peer Selection Problem", 3696 draft-saumitra-alto-multi-ps-00 (work in progress), 3697 October 2008. 3699 [I-D.saumitra-alto-queryresponse] 3700 Das, S. and V. Narayanan, "A Client to Service Query 3701 Response Protocol for ALTO", 3702 draft-saumitra-alto-queryresponse-00 (work in progress), 3703 March 2009. 3705 [I-D.shalunov-alto-infoexport] 3706 Shalunov, S., Penno, R., and R. Woundy, "ALTO Information 3707 Export Service", draft-shalunov-alto-infoexport-00 (work 3708 in progress), October 2008. 3710 [I-D.wang-alto-p4p-specification] 3711 Wang, Y., Alimi, R., Pasko, D., Popkin, L., and Y. Yang, 3712 "P4P Protocol Specification", 3713 draft-wang-alto-p4p-specification-00 (work in progress), 3714 March 2009. 3716 [IEEE.754.2008] 3717 Institute of Electrical and Electronics Engineers, 3718 "Standard for Binary Floating-Point Arithmetic", IEEE 3719 Standard 754, August 2008. 3721 [P4P-SIGCOMM08] 3722 Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A. 3723 Silberschatz, "P4P: Provider Portal for (P2P) 3724 Applications", SIGCOMM 2008, August 2008. 3726 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 3728 [RFC4627] Crockford, D., "The application/json Media Type for 3729 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 3731 [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic 3732 Optimization (ALTO) Problem Statement", RFC 5693, 3733 October 2009. 3735 [RFC5706] Harrington, D., "Guidelines for Considering Operations and 3736 Management of New Protocols and Protocol Extensions", 3737 RFC 5706, November 2009. 3739 [RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for 3740 IPv4/IPv6 Translation", RFC 6144, April 2011. 3742 [RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix 3743 Translation", RFC 6296, June 2011. 3745 [RFC6708] Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and 3746 Y. Yang, "Application-Layer Traffic Optimization (ALTO) 3747 Requirements", RFC 6708, September 2012. 3749 Appendix A. Acknowledgments 3751 Thank you to Sebastian Kiesel (University of Stuttgart) and Jan 3752 Seedorf (NEC) for substantial contributions to the Security 3753 Considerations section. Ben Niven-Jenkins (Velocix), Michael Scharf 3754 and Sabine Randriamasy (Alcatel-Lucent) gave substantial feedback and 3755 suggestions on the protocol design. We are particularly grateful to 3756 the substantial contributions of Wendy Roome (Alcatel-Lucent). 3758 We would like to thank the following people whose input and 3759 involvement was indispensable in achieving this merged proposal: 3761 Obi Akonjang (DT Labs/TU Berlin), 3763 Saumitra M. Das (Qualcomm Inc.), 3765 Syon Ding (China Telecom), 3767 Doug Pasko (Verizon), 3769 Laird Popkin (Pando Networks), 3771 Satish Raghunath (Juniper Networks), 3773 Albert Tian (Ericsson/Redback), 3775 Yu-Shun Wang (Microsoft), 3777 David Zhang (PPLive), 3779 Yunfei Zhang (China Mobile). 3781 We would also like to thank the following additional people who were 3782 involved in the projects that contributed to this merged document: 3783 Alex Gerber (ATT), Chris Griffiths (Comcast), Ramit Hora (Pando 3784 Networks), Arvind Krishnamurthy (University of Washington), Marty 3785 Lafferty (DCIA), Erran Li (Bell Labs), Jin Li (Microsoft), Y. Grace 3786 Liu (IBM Watson), Jason Livingood (Comcast), Michael Merritt (ATT), 3787 Ingmar Poese (DT Labs/TU Berlin), James Royalty (Pando Networks), 3788 Damien Saucez (UCL) Thomas Scholl (ATT), Emilio Sepulveda 3789 (Telefonica), Avi Silberschatz (Yale University), Hassan Sipra (Bell 3790 Canada), Georgios Smaragdakis (DT Labs/TU Berlin), Haibin Song 3791 (Huawei), Oliver Spatscheck (ATT), See-Mong Tang (Microsoft), Jia 3792 Wang (ATT), Hao Wang (Yale University), Ye Wang (Yale University), 3793 Haiyong Xie (Yale University). 3795 Appendix B. Design History and Merged Proposals 3797 The ALTO Protocol specified in this document consists of 3798 contributions from 3799 o P4P [I-D.p4p-framework], [P4P-SIGCOMM08], 3800 [I-D.wang-alto-p4p-specification]; 3802 o ALTO Info-Export [I-D.shalunov-alto-infoexport]; 3804 o Query/Response [I-D.saumitra-alto-queryresponse], 3805 [I-D.saumitra-alto-multi-ps]; and 3807 o Proxidor [I-D.akonjang-alto-proxidor]. 3809 Appendix C. Specifying the "value" Key for E_INVALID_FIELD_VALUE 3811 In Section 8.5.2, an ALTO Server may specify an optional "value" key 3812 to indicate the invalid value that triggerred an 3813 E_INVALID_FIELD_VALUE error. The "value" key must specify a 3814 JSONString, but the invalid value may not be a simple JSONString. 3815 Below are the rule to specify the "value" key: 3817 o If the invalid value is a string, "value" is that string; 3819 o If the invalid value is a number, "value" must be the invalid 3820 number as a string; 3822 o If the invalid value is a subfield, the server must set the 3823 "field" key to the full path of the field name and "value" to the 3824 invalid subfield value, converting it to a string if needed. For 3825 example, if the "cost-mode" subfield of the "cost-type" field is 3826 an invalid mode "foo", the server should set "value" to "foo", and 3827 "field" to "cost-mode/cost-type"; 3829 o If an element of a JSON array has an invalid value, the server 3830 sets "value" to the value of the invalid element, as a string, and 3831 "field" to the name of the array. An array element of the wrong 3832 type (e.g., a number in what is supposed to be an array of 3833 strings) is an invalid value error, not an invalid type error. 3834 The server sets "value" to the string version of the incorrect 3835 element, and "field" to the name of the array. 3837 Appendix D. Authors 3839 [[CmtAuthors: RFC Editor: Please move information in this section to 3840 the Authors' Addresses section at publication time.]] 3841 Sebastian Kiesel 3842 University of Stuttgart Computing Center 3843 Networks and Communication Systems Department 3844 Allmandring 30 3845 70550 Stuttgart 3846 Germany 3848 Email: ietf-alto@skiesel.de 3850 Stefano Previdi 3851 Cisco 3853 Email: sprevidi@cisco.com 3855 Wendy Roome 3856 Alcatel Lucent 3858 Email: w.roome@alcatel-lucent.com 3860 Stanislav Shalunov 3861 BitTorrent 3863 Email: shalunov@bittorrent.com 3865 Richard Woundy 3866 Comcast 3868 Richard_Woundy@cable.comcast.com 3870 Authors' Addresses 3872 Richard Alimi (editor) 3873 Google 3874 1600 Amphitheatre Parkway 3875 Mountain View CA 3876 USA 3878 Email: ralimi@google.com 3879 Reinaldo Penno (editor) 3880 Cisco Systems 3881 170 West Tasman Dr 3882 San Jose CA 3883 USA 3885 Email: repenno@cisco.com 3887 Y. Richard Yang (editor) 3888 Yale University 3889 51 Prospect St 3890 New Haven CT 3891 USA 3893 Email: yry@cs.yale.edu