ALTO WG R. Alimi, Ed. Internet-Draft Google Intended status: Standards Track R. Penno, Ed. Expires: November 21, 2011 Juniper Networks Y. Yang, Ed. Yale University May 20, 2011 ALTO Protocol draft-ietf-alto-protocol-08.txt Abstract Networking applications today already have access to a great amount of Inter-Provider network topology information. For example, views of the Internet routing table are easily available at looking glass servers and entirely practical to be downloaded by clients. What is missing is knowledge of the underlying network topology from the ISP or Content Provider (henceforth referred as Provider) point of view. In other words, what a Provider prefers in terms of traffic optimization -- and a way to distribute it. The ALTO Service provides information such as preferences of network resources with the goal of modifying network resource consumption patterns while maintaining or improving application performance. This document describes a protocol implementing the ALTO Service. While such service would primarily be provided by the network (i.e., the ISP), content providers and third parties could also operate this service. Applications that could use this service are those that have a choice in connection endpoints. Examples of such applications are peer-to-peer (P2P) and content delivery networks. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Alimi, et al. Expires November 21, 2011 [Page 1] Internet-Draft ALTO Protocol May 2011 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 21, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Alimi, et al. Expires November 21, 2011 [Page 2] Internet-Draft ALTO Protocol May 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1. Background and Problem Statement . . . . . . . . . . . . . 6 1.2. Design History and Merged Proposals . . . . . . . . . . . 6 1.3. Solution Benefits . . . . . . . . . . . . . . . . . . . . 6 1.3.1. Service Providers . . . . . . . . . . . . . . . . . . 7 1.3.2. Applications . . . . . . . . . . . . . . . . . . . . . 7 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1. Endpoint Address . . . . . . . . . . . . . . . . . . . 7 2.1.2. ASN . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3. Network Location . . . . . . . . . . . . . . . . . . . 8 2.1.4. ALTO Information . . . . . . . . . . . . . . . . . . . 8 2.1.5. ALTO Information Base . . . . . . . . . . . . . . . . 8 2.2. ALTO Service and Protocol Scope . . . . . . . . . . . . . 8 3. Protocol Structure . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Server Information Service . . . . . . . . . . . . . . . . 11 3.2. ALTO Information Services . . . . . . . . . . . . . . . . 11 3.2.1. Map Service . . . . . . . . . . . . . . . . . . . . . 11 3.2.2. Map Filtering Service . . . . . . . . . . . . . . . . 11 3.2.3. Endpoint Property Service . . . . . . . . . . . . . . 11 3.2.4. Endpoint Cost Service . . . . . . . . . . . . . . . . 12 4. Network Map . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. PID . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2. Endpoint Addresses . . . . . . . . . . . . . . . . . . . . 13 4.2.1. IP Addresses . . . . . . . . . . . . . . . . . . . . . 13 4.3. Example Network Map . . . . . . . . . . . . . . . . . . . 13 5. Cost Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.1. Cost Attributes . . . . . . . . . . . . . . . . . . . . . 14 5.1.1. Cost Type . . . . . . . . . . . . . . . . . . . . . . 15 5.1.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 15 5.2. Cost Map Structure . . . . . . . . . . . . . . . . . . . . 16 5.3. Network Map and Cost Map Dependency . . . . . . . . . . . 16 6. Protocol Design Overview . . . . . . . . . . . . . . . . . . . 17 6.1. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.1.1. Existing Infrastructure . . . . . . . . . . . . . . . 17 6.1.2. ALTO Information Reuse and Redistribution . . . . . . 17 6.2. Protocol Design . . . . . . . . . . . . . . . . . . . . . 18 7. Protocol Specification . . . . . . . . . . . . . . . . . . . . 18 7.1. Notation . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.2. Basic Operation . . . . . . . . . . . . . . . . . . . . . 19 7.2.1. Discovering Information Resources . . . . . . . . . . 19 7.2.2. Requesting Information Resources . . . . . . . . . . . 19 7.2.3. Response . . . . . . . . . . . . . . . . . . . . . . . 20 7.2.4. Client Behavior . . . . . . . . . . . . . . . . . . . 20 7.2.5. Authentication and Encryption . . . . . . . . . . . . 20 7.2.6. HTTP Cookies . . . . . . . . . . . . . . . . . . . . . 20 Alimi, et al. Expires November 21, 2011 [Page 3] Internet-Draft ALTO Protocol May 2011 7.2.7. Parsing . . . . . . . . . . . . . . . . . . . . . . . 21 7.3. Information Resource . . . . . . . . . . . . . . . . . . . 21 7.3.1. Capabilities . . . . . . . . . . . . . . . . . . . . . 21 7.3.2. Input Parameters Media Type . . . . . . . . . . . . . 21 7.3.3. Media Type . . . . . . . . . . . . . . . . . . . . . . 21 7.3.4. Encoding . . . . . . . . . . . . . . . . . . . . . . . 21 7.4. ALTO Errors . . . . . . . . . . . . . . . . . . . . . . . 23 7.4.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 23 7.4.2. Resource Format . . . . . . . . . . . . . . . . . . . 23 7.4.3. Error Codes . . . . . . . . . . . . . . . . . . . . . 24 7.5. ALTO Types . . . . . . . . . . . . . . . . . . . . . . . . 25 7.5.1. PID Name . . . . . . . . . . . . . . . . . . . . . . . 25 7.5.2. Endpoints . . . . . . . . . . . . . . . . . . . . . . 25 7.5.3. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 27 7.5.4. Cost Type . . . . . . . . . . . . . . . . . . . . . . 27 7.5.5. Endpoint Property . . . . . . . . . . . . . . . . . . 27 7.6. Information Resource Directory . . . . . . . . . . . . . . 28 7.6.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 28 7.6.2. Encoding . . . . . . . . . . . . . . . . . . . . . . . 28 7.6.3. Example . . . . . . . . . . . . . . . . . . . . . . . 30 7.6.4. Usage Considerations . . . . . . . . . . . . . . . . . 33 7.7. Information Resources . . . . . . . . . . . . . . . . . . 34 7.7.1. Server Information Service . . . . . . . . . . . . . . 34 7.7.2. Map Service . . . . . . . . . . . . . . . . . . . . . 36 7.7.3. Map Filtering Service . . . . . . . . . . . . . . . . 41 7.7.4. Endpoint Property Service . . . . . . . . . . . . . . 46 7.7.5. Endpoint Cost Service . . . . . . . . . . . . . . . . 49 8. Redistributable Responses . . . . . . . . . . . . . . . . . . 52 8.1. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 53 8.1.1. Service ID . . . . . . . . . . . . . . . . . . . . . . 53 8.1.2. Expiration Time . . . . . . . . . . . . . . . . . . . 54 8.1.3. Signature . . . . . . . . . . . . . . . . . . . . . . 54 8.2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 56 8.2.1. Response Redistribution Descriptor Fields . . . . . . 57 8.2.2. Signature . . . . . . . . . . . . . . . . . . . . . . 57 9. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 58 9.1. ALTO Client Embedded in P2P Tracker . . . . . . . . . . . 58 9.2. ALTO Client Embedded in P2P Client: Numerical Costs . . . 59 9.3. ALTO Client Embedded in P2P Client: Ranking . . . . . . . 60 10. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 61 10.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 61 10.2. Hosts with Multiple Endpoint Addresses . . . . . . . . . . 62 10.3. Network Address Translation Considerations . . . . . . . . 62 10.4. Mapping IPs to ASNs . . . . . . . . . . . . . . . . . . . 63 10.5. Endpoint and Path Properties . . . . . . . . . . . . . . . 63 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63 11.1. application/alto-* Media Types . . . . . . . . . . . . . . 63 11.2. ALTO Cost Type Registry . . . . . . . . . . . . . . . . . 65 Alimi, et al. Expires November 21, 2011 [Page 4] Internet-Draft ALTO Protocol May 2011 11.3. ALTO Endpoint Property Registry . . . . . . . . . . . . . 66 12. Security Considerations . . . . . . . . . . . . . . . . . . . 67 12.1. Privacy Considerations for ISPs . . . . . . . . . . . . . 67 12.2. ALTO Clients . . . . . . . . . . . . . . . . . . . . . . . 68 12.3. Authentication, Integrity Protection, and Encryption . . . 68 12.4. ALTO Information Redistribution . . . . . . . . . . . . . 69 12.5. Denial of Service . . . . . . . . . . . . . . . . . . . . 69 12.6. ALTO Server Access Control . . . . . . . . . . . . . . . . 70 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 70 13.1. Normative References . . . . . . . . . . . . . . . . . . . 70 13.2. Informative References . . . . . . . . . . . . . . . . . . 71 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 73 Appendix B. Authors . . . . . . . . . . . . . . . . . . . . . . . 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 74 Alimi, et al. Expires November 21, 2011 [Page 5] Internet-Draft ALTO Protocol May 2011 1. Introduction 1.1. Background and Problem Statement Today, network information available to applications is mostly from the view of endhosts. There is no clear mechanism to convey information about the network's preferences to applications. By leveraging better network-provided information, applications have the potential to become more network-efficient (e.g., reduce network resource consumption) and achieve better application performance (e.g., accelerated download rate). The ALTO Service intends to provide a simple way to convey network information to applications. The goal of this document is to specify a simple and unified protocol that meets the ALTO requirements [I-D.ietf-alto-reqs] while providing a migration path for Internet Service Providers (ISP), Content Providers, and clients that have deployed protocols with similar intentions (see below). This document is a work in progress and will be updated with further developments. 1.2. Design History and Merged Proposals The protocol specified here consists of contributions from o P4P [I-D.p4p-framework], [P4P-SIGCOMM08], [I-D.wang-alto-p4p-specification]; o ALTO Info-Export [I-D.shalunov-alto-infoexport]; o Query/Response [I-D.saumitra-alto-queryresponse], [I-D.saumitra-alto-multi-ps]; o ATTP [ATTP]; o Proxidor [I-D.akonjang-alto-proxidor]. See Appendix A for a list of people that have contributed significantly to this effort and the projects and proposals listed above. 1.3. Solution Benefits The ALTO Service offers many benefits to both end-users (consumers of the service) and Internet Service Providers (providers of the service). Alimi, et al. Expires November 21, 2011 [Page 6] Internet-Draft ALTO Protocol May 2011 1.3.1. Service Providers The ALTO Service enables ISPs to influence the peer selection process in distributed applications in order to increase locality of traffic, improve user-experience, amongst others. It also helps ISPs to efficiently manage traffic that traverses more expensive links such as transit and backup links, thus allowing a better provisioning of the networking infrastructure. 1.3.2. Applications Applications that use the ALTO Service can benefit in multiple ways. For example, they may no longer need to infer topology information, and some applications can reduce reliance on measuring path performance metrics themselves. They can take advantage of the ISP's knowledge to avoid bottlenecks and boost performance. An example type of application is a Peer-to-Peer overlay where peer selection can be improved by including ALTO information in the selection process. 2. Architecture Two key design objectives of the ALTO Protocol are simplicity and extensibility. At the same time, it introduces additional techniques to address potential scalability and privacy issues. This section first introduces the terminology, and then defines the ALTO architecture and the ALTO Protocol's place in the overall architecture. 2.1. Terminology We use the following terms defined in [RFC5693]: Application, Overlay Network, Peer, Resource, Resource Identifier, Resource Provider, Resource Consumer, Resource Directory, Transport Address, Host Location Attribute, ALTO Service, ALTO Server, ALTO Client, ALTO Query, ALTO Reply, ALTO Transaction, Local Traffic, Peering Traffic, Transit Traffic. We also use the following additional terms: Endpoint Address, Autonomous System Number (ASN), and Network Location. 2.1.1. Endpoint Address An endpoint address represents the communication address of an endpoint. An endpoint address can be network-attachment based (IP address) or network-attachment agnostic. Common forms of endpoint Alimi, et al. Expires November 21, 2011 [Page 7] Internet-Draft ALTO Protocol May 2011 addresses include IP address, MAC address, overlay ID, and phone number. Each Endpoint Address has an associated Address Type, which indicates both its syntax and semantics. 2.1.2. ASN An Autonomous System Number. 2.1.3. Network Location Network Location is a generic term denoting a single endpoint or group of endpoints. 2.1.4. ALTO Information ALTO Information is a generic term referring to the network information sent by an ALTO Server. 2.1.5. ALTO Information Base Internal representation of the ALTO Information maintained by the ALTO Server. Note that the structure of this internal representation is not defined by this document. 2.2. ALTO Service and Protocol Scope An ALTO Server conveys the network information from the perspective of a network region; the ALTO Server presents its "my-Internet View" of the network region. In particular, an ALTO Server defines network Endpoints (and aggregations thereof) and generic costs amongst them, both from the network region's own perspective. A network region in this context can be an Autonomous System, an ISP, or perhaps a smaller region or set of ISPs; the details depend on the deployment scenario and discovery mechanism. To better understand the ALTO Service and the role of the ALTO Protocol, we show in Figure 1 the overall system architecture. In this architecture, an ALTO Server prepares ALTO Information; an ALTO Client uses ALTO Service Discovery to identify an appropriate ALTO Server; and the ALTO Client requests available ALTO Information from the ALTO Server using the ALTO Protocol. The ALTO Information provided by the ALTO Server can be updated dynamically based on network conditions, or can be seen as a policy which is updated at a larger time-scale. Alimi, et al. Expires November 21, 2011 [Page 8] Internet-Draft ALTO Protocol May 2011 More specifically, the ALTO Information provided by an ALTO Server may be influenced (at the operator's discretion) by other systems. Examples include (but are not limited to) static network configuration databases, dynamic network information, routing protocols, provisioning policies, and interfaces to outside parties. These components are shown in the figure for completeness but outside the scope of this specification. Note that it may also be possible for ALTO Servers to exchange network information with other ALTO Servers (either within the same administrative domain or another administrative domain with the consent of both parties) in order to adjust exported ALTO Information. Such a protocol is also outside the scope of this specification. +-------------------------------------------------------------------+ | ISP | | | | +-----------+ | | | Routing | | | +--------------+ | Protocols | | | | Provisioning | +-----------+ | | | Policy | | | | +--------------+\ | | | \ | | | \ | | | +-----------+ \+---------+ +--------+ | | |Dynamic | | ALTO | ALTO Protocol | ALTO | | | |Network |.......| Server | -------------------- | Client | | | |Information| +---------+ +--------+ | | +-----------+ / / | | / ALTO SD Query/Response / | | / / | | +----------+ +--------------+ | | | External | | ALTO Service | | | | Interface| | Discovery | | | +----------+ +--------------+ | | | | +-------------------------------------------------------------------+ | +------------------+ | Third Parties | | | | Content Providers| +------------------+ Figure 1: Basic ALTO Architecture. Alimi, et al. Expires November 21, 2011 [Page 9] Internet-Draft ALTO Protocol May 2011 3. Protocol Structure The ALTO Protocol uses a simple extensible framework to convey network information. In the general framework, the ALTO protocol will convey properties on both Network Locations and the paths between Network Locations. In this document, we focus on a particular Endpoint property to denote the location of an endpoint, and provider-defined costs for paths between pairs of Network Locations. The ALTO Protocol is built on a common transport protocol, messaging structure and encoding, and transaction model. The protocol is subdivided into services of related functionality. ALTO-Core provides the Server Information Service and the Map Service to provide ALTO Information. Other ALTO Information services can provide additional functionality. There are three such services defined in this document: the Map Filtering Service, Endpoint Property Service, and Endpoint Cost Service. Additional services may be defined in companion documents. Note that functionality offered in different services are not totally non-overlapping (e.g., the Map Service and Map Filtering Service). .------------------------------------------------------------. | | | .----------. .-----------------------------------------. | | | | | ALTO Info Services | | | | | | .-----------. .----------. .----------. | | | | | | | Map | | Endpoint | | Endpoint | | | | | | | | Filtering | | Property | | Cost | | | | | | | | Service | | Service | | Service | | | | | Server | | `-----------' `----------' `----------' | | | | Info. | | .-------------------------------------. | | | | Service | | | Map Service | | | | | | | | .-------------. .--------------. | | | | | | | | | Network Map | | Cost Map | | | | | | | | | `-------------' `--------------' | | | | | | | `-------------------------------------' | | | `----------' `-----------------------------------------' | | | `------------------------------------------------------------' Figure 2: ALTO Protocol Structure Alimi, et al. Expires November 21, 2011 [Page 10] Internet-Draft ALTO Protocol May 2011 3.1. Server Information Service The Server Information Service lists the details on the information that can be provided by an ALTO Server and perhaps other ALTO Servers maintained by the network provider. The configuration includes, for example, details about the operations and cost metrics supported by the ALTO Server and other related ALTO Servers that may be usable by an ALTO Client. 3.2. ALTO Information Services Multiple, distinct services are defined to allow ALTO Clients to query ALTO Information from an ALTO Server. The ALTO Server internally maintains an ALTO Information Base that encodes the network provider's preferences. The ALTO Information Base encodes the Network Locations defined by the ALTO Server (and their corresponding properties), as well as the provider-defined costs between pairs of Network Locations. 3.2.1. Map Service The Map Service provides batch information to ALTO Clients in the form of Network Map and Cost Map. The Network Map (See Section 4) provides the full set of Network Location groupings defined by the ALTO Server and the endpoints contained with each grouping. The Cost Map (see Section 5) provides costs between the defined groupings. These two maps can be thought of (and implemented as) as simple files with appropriate encoding provided by the ALTO Server. 3.2.2. Map Filtering Service Resource constrained ALTO Clients may benefit from query results being filtered at the ALTO Server. This avoids an ALTO Client spending network bandwidth or CPU collecting results and performing client-side filtering. The Map Filtering Service allows ALTO Clients to query for the ALTO Server Network Map and Cost Map based on additional parameters. 3.2.3. Endpoint Property Service This service allows ALTO Clients to look up properties for individual endpoints. An example endpoint property is its Network Location (its grouping defined by the ALTO Server) or connectivity type (e.g., ADSL, Cable, or FTTH). Alimi, et al. Expires November 21, 2011 [Page 11] Internet-Draft ALTO Protocol May 2011 3.2.4. Endpoint Cost Service Some ALTO Clients may also benefit from querying for costs and rankings based on endpoints. The Endpoint Cost Service allows an ALTO Server to return either numerical costs or ordinal costs (rankings) directly amongst Endpoints. 4. Network Map In reality, many endpoints are very close to one another in terms of network connectivity, for example, endpoints on the same site of an enterprise. By treating a group of endpoints together as a single entity in ALTO, we can achieve much greater scalability without losing critical information. The Network Location endpoint property allows an ALTO Server to group endpoints together to indicate their proximity. The resulting set of groupings is called the ALTO Network Map. The definition of proximity varies depending on the granularity of the ALTO information configured by the provider. In one deployment, endpoints on the same subnet may be considered close; while in another deployment, endpoints connected to the same PoP may be considered close. As used in this document, the Network Map refers to the syntax and semantics of the information distributed by the ALTO Server. This document does not discuss the internal representation of this data structure within the ALTO Server. 4.1. PID Each group of Endpoints is identified by a provider-defined Network Location identifier called a PID. There can be many different ways of grouping the endpoints and assigning PIDs. A PID is an identifier that provides an indirect and network-agnostic way to specify an aggregation of network endpoints that may be treated similarly, based on network topology, type, or other properties. For example, a PID may be defined by the ALTO service provider to denote a subnet, a set of subnets, a metropolitan area, a PoP, an autonomous system, or a set of autonomous systems. Aggregation of endpoints into PIDs can indicate proximity and can improve scalability. In particular, network preferences (costs) may be specified between PIDs, allowing cost information to be more compactly represented and updated at a faster time scale than the network aggregations themselves. Alimi, et al. Expires November 21, 2011 [Page 12] Internet-Draft ALTO Protocol May 2011 Using PIDs, the Network Map may also be used to communicate simple preferences with only minimal information from the Cost Map. For example, an ISP may prefer that endpoints associated with the same PoP (Point-of-Presence) in a P2P application communicate locally instead of communicating with endpoints in other PoPs. The ISP may aggregate endhosts within a PoP into a single PID in the Network Map. The Cost Map may be encoded to indicate that peering within the same PID is preferred; for example, cost(PID_i, PID_i) == c* and cost(PID_i, PID_j) > c* for i != j. Section 5 provides further details about Cost Map structure. 4.2. Endpoint Addresses Communicating endpoints may have many types of addresses, such as IP addresses, MAC addresses, or overlay IDs. The current specification only considers IP addresses. 4.2.1. IP Addresses The endpoints aggregated into a PID are denoted by a list of IP prefixes. When either an ALTO Client or ALTO Server needs to determine which PID in a Network Map contains a particular IP address, longest-prefix matching MUST be used. A Network Map MUST define a PID for each possible address in the IP address space for all of the address types contained in the map. A RECOMMENDED way to satisfy this property is to define a PID that contains the 0.0.0.0/0 prefix for IPv4 or ::/0 (for IPv6). Each endpoint MUST map into exactly one PID. Since longest-prefix matching is used to map an endpoint to a PID, this can be accomplished by ensuring that no two PIDs contain an identical IP prefix. 4.3. Example Network Map Figure 3 illustrates an example Network Map. PIDs are used to identify network-agnostic aggregations. Alimi, et al. Expires November 21, 2011 [Page 13] Internet-Draft ALTO Protocol May 2011 .-----------------------------------------------------------. | ALTO Network Map | | | | .-----------------------------------. .---------------. | | | NetLoc: PID-1 | | NetLoc: PID-2 | | | | .------------------------------. | | ... | | | | | 192.0.2.0/24 | | `---------------` | | | | .--------------------------. | | | | | | | Endpoint: 192.0.2.34 | | | .---------------. | | | | `--------------------------` | | | NetLoc: PID-3 | | | | `------------------------------` | | ... | | | | .------------------------------. | `---------------` | | | | 198.51.100.0/25 | | | | | | .--------------------------. | | .---------------. | | | | | Endpoint: 198.51.100.100 | | | | NetLoc: PID-4 | | | | | `--------------------------` | | | ... | | | | `------------------------------` | `---------------` | | `-----------------------------------` | | | `-----------------------------------------------------------` Figure 3: Example Network Map 5. Cost Map An ALTO Server indicates preferences amongst network locations in the form of Path Costs. Path Costs are generic costs and can be internally computed by a network provider according to its own needs. An ALTO Cost Map defines Path Costs pairwise amongst sets of source and destination Network Locations. One advantage of separating ALTO information into a Network Map and a Cost Map is that the two components can be updated at different time scales. For example, Network Maps may be stable for a longer time while Cost Maps may be updated to reflect dynamic network conditions. As used in this document, the Cost Map refers to the syntax and semantics of the information distributed by the ALTO Server. This document does not discuss the internal representation of this data structure within the ALTO Server. 5.1. Cost Attributes Path Costs have attributes: Alimi, et al. Expires November 21, 2011 [Page 14] Internet-Draft ALTO Protocol May 2011 o Type: identifies what the costs represent; o Mode: identifies how the costs should be interpreted. Certain queries for Cost Maps allow the ALTO Client to indicate the desired Type and Mode. 5.1.1. Cost Type The Type attribute indicates what the cost represents. For example, an ALTO Server could define costs representing air-miles, hop-counts, or generic routing costs. Cost types are indicated in protocol messages as strings. 5.1.1.1. Cost Type: routingcost An ALTO Server MUST define the 'routingcost' Cost Type. This Cost Type conveys a generic measure for the cost of routing traffic from a source to a destination. Lower values indicate a higher preference for traffic to be sent from a source to a destination. Note that an ISP may internally compute routing cost using any method it chooses (e.g., air-miles or hop-count) as long as it conforms to these semantics. 5.1.2. Cost Mode The Mode attribute indicates how costs should be interpreted. Specifically, the Mode attribute indicates whether returned costs should be interpreted as numerical values or ordinal rankings. It is important to communicate such information to ALTO Clients, as certain operations may not be valid on certain costs returned by an ALTO Server. For example, it is possible for an ALTO Server to return a set of IP addresses with costs indicating a ranking of the IP addresses. Arithmetic operations, such as summation, that would make sense for numerical values, do not make sense for ordinal rankings. ALTO Clients may handle such costs differently. Cost Modes are indicated in protocol messages as strings. An ALTO Server MUST support at least one of 'numerical' and 'ordinal' costs. ALTO Clients SHOULD be cognizant of operations when a desired cost mode is not supported. For example, an ALTO Client desiring numerical costs may adjust behavior if only the ordinal Cost Mode is Alimi, et al. Expires November 21, 2011 [Page 15] Internet-Draft ALTO Protocol May 2011 available. Alternatively, an ALTO Client desiring ordinal costs may construct ordinal costs given numerical values if only the numerical Cost Mode is available. 5.1.2.1. Cost Mode: numerical This Cost Mode is indicated by the string 'numerical'. This mode indicates that it is safe to perform numerical operations (e.g. summation) on the returned costs. 5.1.2.2. Cost Mode: ordinal This Cost Mode is indicated by the string 'ordinal'. This mode indicates that the costs values to a set of Destination Network Locations from a particular Source Network Location are a ranking, with lower values indicating a higher preference. It is important to note that the values in the Cost Map provided with the ordinal Cost Mode are not necessarily the actual cost known to the ALTO Server. 5.2. Cost Map Structure A query for a Cost Map either explicitly or implicitly includes a list of Source Network Locations and a list of Destination Network Locations. (Recall that a Network Location can be an endpoint address or a PID.) Specifically, assume that a query has a list of multiple Source Network Locations, say [Src_1, Src_2, ..., Src_m], and a list of multiple Destination Network Locations, say [Dst_1, Dst_2, ..., Dst_n]. The ALTO Server will return the Path Cost for each communicating pair (i.e., Src_1 -> Dst_1, ..., Src_1 -> Dst_n, ..., Src_m -> Dst_1, ..., Src_m -> Dst_n). We refer to this structure as a Cost Map. If the Cost Mode is 'ordinal', the Path Cost of each communicating pair is relative to the m*n entries. 5.3. Network Map and Cost Map Dependency If a Cost Map contains PIDs in the list of Source Network Locations or the list of Destination Network Locations, the Path Costs are generated based on a particular Network Map (which defines the PIDs). Version Tags are introduced to ensure that ALTO Clients are able to use consistent information even though the information is provided in two maps. Alimi, et al. Expires November 21, 2011 [Page 16] Internet-Draft ALTO Protocol May 2011 A Version Tag is an opaque string associated with a Network Map maintained by the ALTO Server. When the Network Map changes, the Version Tag MUST also be changed. (Thus, the Version Tag is defined similarly to HTTP's Entity Tags; see Section 3.11 of [RFC2616].) Possibilities for generating a Version Tag include the last-modified timestamp for the Network Map, or a hash of its contents. A Network Map distributed by the ALTO Server includes its Version Tag. A Cost Map referring to PIDs also includes the Version Tag of the Network Map on which it is based. 6. Protocol Design Overview The ALTO Protocol design uses a REST-ful design with the goal of leveraging current HTTP [RFC2616] implementations and infrastructure. The REST-ful design supports flexible deployment strategies and provides extensibility. ALTO requests and responses are encoded with JSON [RFC4627]. 6.1. Benefits Benefits enabled by these design choices include easier understanding and debugging, mature libraries, tools, infrastructure, and caching and redistribution of ALTO information for increased scalability. 6.1.1. Existing Infrastructure HTTP is a natural choice for integration with existing applications and infrastructure. In particular, the ALTO Protocol design leverages: o the huge installed base of infrastructure, including HTTP caches, o mature software implementations, o the fact that many P2P clients already have an embedded HTTP client, and o authentication and encryption mechanisms in HTTP and SSL/TLS. 6.1.2. ALTO Information Reuse and Redistribution ALTO information may be useful to a large number of applications and users. For example, an identical Network Map may be used by all ALTO Clients querying a particular ALTO Server. At the same time, distributing ALTO information must be efficient and not become a bottleneck. Alimi, et al. Expires November 21, 2011 [Page 17] Internet-Draft ALTO Protocol May 2011 Beyond integration with existing HTTP caching infrastructure, ALTO information may also be cached or redistributed using application- dependent mechanisms, such as P2P DHTs or P2P file-sharing. This document does not define particular mechanisms for such redistribution, but it does define the primitives (e.g., digital signatures) needed to support such a mechanism. See [I-D.gu-alto-redistribution] for further discussion. Note that if caching or redistribution is used, the response message may be returned from another (possibly third-party) entity. Reuse and Redistribution is further discussed in Section 12.4. Protocol support for redistribution is specified in Section 8. 6.2. Protocol Design The ALTO Protocol uses a REST-ful design. There are two primary components to this design: o Information Resources: Each service provides network information as a set of resources, which are distinguished by their media types [RFC2046]. An ALTO Client may construct an HTTP request for a particular resource (including any parameters, if necessary), and an ALTO Server returns the requested resource in an HTTP response. o Information Resource Directory: An ALTO Server provides to ALTO Clients a list of available resources and the URI at which each is provided. This document refers to this list as the Information Resource Directory. This directory is the single entry point to an ALTO Service. ALTO Clients consult the directory to determine the services provided by an ALTO Server. 7. Protocol Specification This section first specifies general client and server processing, followed by a detailed specification for each ALTO Information Resource. 7.1. Notation This document uses an adaptation of the C-style struct notation to define the required and optional members of JSON objects. Unless explicitly noted, each member of a struct is REQUIRED. The types 'JSONString', 'JSONNumber', 'JSONBool' indicate the JSON string, number, and boolean types, respectively. Alimi, et al. Expires November 21, 2011 [Page 18] Internet-Draft ALTO Protocol May 2011 Note that no standard, machine-readable interface definition or schema is provided. Extension documents may document these as necessary. 7.2. Basic Operation The ALTO Protocol employs standard HTTP [RFC2616]. It is used for discovering available Information Resources at an ALTO Server and retrieving Information Resources. ALTO Clients and ALTO Servers use HTTP requests and responses carrying ALTO-specific content with encoding as specified in this document, and MUST be compliant with [RFC2616]. 7.2.1. Discovering Information Resources To discover available resources, an ALTO Client may request the Information Resource Directory, which an ALTO Server provides at the URI found by the ALTO Discovery protocol. Informally, an Information Resource Directory enumerates URIs at which an ALTO Server offers Information Resources. Each entry in the directory indicates a URI at which an ALTO Server accepts requests, and returns either the requested Information Resource or an Information Resource Directory that references additional Information Resources. See Section 7.6 for a detailed specification. 7.2.2. Requesting Information Resources Through the retrieved Information Resource Directories, an ALTO Client can determine whether an ALTO Server supports the desired Information Resource, and if it is supported, the URI at which it is available. Where possible, the ALTO Protocol uses the HTTP GET method to request resources. However, some ALTO services provide Information Resources that are the function of one or more input parameters. Input parameters are encoded in the HTTP request's entity body, and the request uses the HTTP POST method. Note that it is possible for an ALTO Server to employ caching for the response to a POST request. This can be accomplished by returning an HTTP 303 status code ("See Other") indicating to the ALTO Client that the resulting Cost Map is available via a GET request to an alternate URL (which may be cached). When requesting an ALTO Information Resource that requires input parameters specified in a HTTP POST request, an ALTO Client MUST set the Content-Type HTTP header to the media type corresponding to the Alimi, et al. Expires November 21, 2011 [Page 19] Internet-Draft ALTO Protocol May 2011 format of the supplied input parameters. 7.2.3. Response Upon receiving a request, an ALTO server either returns the requested resource, provides the ALTO Client an Information Resource Directory indicating how to reach the desired resource, or returns an error. The type of response MUST be indicated by the media type attached to the response (the Content-Type HTTP header). If an ALTO Client receives an Information Resource Directory, it can consult the received directory to determine if any of the offered URIs contain the desired Information Resource. The generic encoding for an Information Resource is specified in Section 7.3. Errors are indicated via either ALTO-level error codes, or via HTTP status codes; see Section 7.4. 7.2.4. Client Behavior 7.2.4.1. Using Information Resources This specification does not indicate any required actions taken by ALTO Clients upon successfully receiving an Information Resource from an ALTO Server. Although ALTO Clients are suggested to interpret the received ALTO Information and adapt application behavior, ALTO Clients are not required to do so. 7.2.4.2. Error Conditions If an ALTO Client does not successfully receive a desired Information Resource from a particular ALTO Server, it can either choose another server (if one is available) or fall back to a default behavior (e.g., perform peer selection without the use of ALTO information). An ALTO Client may also retry the request at a later time. 7.2.5. Authentication and Encryption An ALTO Server MAY support SSL/TLS to implement server and/or client authentication, as well as encryption. See [RFC6125] for considerations regarding verification of server identity. 7.2.6. HTTP Cookies If cookies are included in an HTTP request received by an ALTO Server, they MUST be ignored. Alimi, et al. Expires November 21, 2011 [Page 20] Internet-Draft ALTO Protocol May 2011 7.2.7. Parsing This document only details object members used by this specification. Extensions may include additional members within JSON objects defined in this document. ALTO implementations MUST ignore such unknown fields when processing ALTO messages. 7.3. Information Resource An Information Resource is an HTTP entity body received by an ALTO Server that encodes the ALTO Information desired by an ALTO Client. This document specifies multiple Information Resources that can be provided by an ALTO Server. Each Information Resource has certain attributes associated with it, indicating its data format, the input parameters it supports, and format of the input parameters. 7.3.1. Capabilities An ALTO Server may advertise to an ALTO Client that it supports certain capabilities in requests for an Information Resource. For example, if an ALTO Server allows requests for a Cost Map to include constraints, it may advertise that it supports this capability. 7.3.2. Input Parameters Media Type An ALTO Server may allow an ALTO Client to supply input parameters when requesting certain Information Resources. The format of the input parameters (i.e., as contained in the entity body of the HTTP POST request) is indicated by the media type [RFC2046]. 7.3.3. Media Type The media type [RFC2046] uniquely indicates the data format of the Information Resource as returned by an ALTO Server in the HTTP entity body. 7.3.4. Encoding Though each Information Resource may have a distinct syntax, they are designed to have a common structure containing generic ALTO-layer metadata about the resource, as well as data itself. An Information Resource has a single top-level JSON object of type InfoResourceEntity: Alimi, et al. Expires November 21, 2011 [Page 21] Internet-Draft ALTO Protocol May 2011 object { InfoResourceMetaData meta; [InfoResourceDataType] data; } InfoResourceEntity; with members: meta meta-information pertaining to the Information Resource data the data contained in the Information Resource 7.3.4.1. Meta Information Meta information is encoded as a JSON object with type InfoResourceMetaData: object { InfoResourceRedistDesc redistribution; [OPTIONAL] } InfoResourceMetaData; with members: redistribution Additional data for use in Information Resources that may be redistributed amongst ALTO Clients. See Section 8. 7.3.4.2. ALTO Information The "data" member of the InfoResourceEntity encodes the resource- specific data; the structure of this member is detailed later in this section for each particular Information Resource. 7.3.4.3. Signature An ALTO Server MAY additionally supply a signature asserting that it generated a particular response. See Section 8.2.2. 7.3.4.4. Example The following is an example of the encoding for an Information Resource: Alimi, et al. Expires November 21, 2011 [Page 22] Internet-Draft ALTO Protocol May 2011 HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-costmap+json { "meta" : { "redistribution" : { ... } }, "data" : { ... } } 7.4. ALTO Errors If there is an error processing a request, an ALTO Server SHOULD return additional ALTO-layer information, if it is available, in the form of an ALTO Error Resource encoded in the HTTP response's entity body. If no ALTO-layer information is available, an ALTO Server may omit an ALTO Error resource from the response. An appropriate HTTP status code MUST be set. It is important to note that the HTTP Status Code and ALTO Error Code have distinct roles. An ALTO Error Code provides detailed information about the why a particular request for an ALTO Resource was not successful. The HTTP status code indicates to HTTP processing elements (e.g., intermediaries and clients) how the response should be treated. 7.4.1. Media Type The media type for an Error Resource is "application/ alto-error+json". 7.4.2. Resource Format An Error Resource has the format: object { JSONString code; JSONString reason; [OPTIONAL] } ErrorResourceEntity; Alimi, et al. Expires November 21, 2011 [Page 23] Internet-Draft ALTO Protocol May 2011 where: code An ALTO Error Code defined in Table 1 reason A (free-form) human-readable explanation of the particular error 7.4.3. Error Codes This document defines ALTO Error Codes to support the error conditions needed for purposes of this document. Additional status codes may be defined in companion or extension documents. The HTTP status codes corresponding to each ALTO Error Code are defined to provide correct behavior with HTTP intermediaries and clients. When an ALTO Server returns a particular ALTO Error Code, it MUST indicate one of the corresponding HTTP status codes in Table 1in the HTTP response. If multiple errors are present in a single request (e.g., a request uses a JSONString when a JSONInteger is expected and a required field is missing), then the ALTO Server MUST return exactly one of the detected errors. However, the reported error is implementation defined, since specifying a particular order for message processing encroaches needlessly on implementation technique. +-------------------------+-----------------+-----------------------+ | ALTO Error Code | HTTP Status | Description | | | Code(s) | | +-------------------------+-----------------+-----------------------+ | E_JSON_SYNTAX | 400 | JSON parsing error in | | | | request | | | | | | E_JSON_FIELD_MISSING | 400 | Required field | | | | missing | | | | | | E_JSON_VALUE_TYPE | 400 | JSON Value of | | | | unexpected type | | | | | | E_INVALID_COST_MODE | 400 | Invalid cost mode | | | | | | E_INVALID_COST_TYPE | 400 | Invalid cost type | | | | | | E_INVALID_PROPERTY_TYPE | 400 | Invalid property type | +-------------------------+-----------------+-----------------------+ Table 1: Defined ALTO Error Codes Alimi, et al. Expires November 21, 2011 [Page 24] Internet-Draft ALTO Protocol May 2011 7.5. ALTO Types This section details the format for particular data values used in the ALTO Protocol. 7.5.1. PID Name A PID Name is encoded as a US-ASCII string. The string MUST be no more than 64 characters, and MUST NOT contain characters other than alphanumeric characters or the '.' separator. The '.' separator is reserved for future use and MUST NOT be used unless specifically indicated by a companion or extension document. The type 'PIDName' is used in this document to indicate a string of this format. 7.5.2. Endpoints 7.5.2.1. Address Type Address Types are encoded as US-ASCII strings consisting of only alphanumeric characters. This document defines the address type "ipv4" to refer to IPv4 addresses, and "ipv6" to refer to IPv6 addresses. Extension documents may define additional Address Types. The type 'AddressType' is used in this document to indicate a string of this format. 7.5.2.2. Endpoint Address Endpoint Addresses are encoded as US-ASCII strings. The exact characters and format depend on the type of endpoint address. The type 'EndpointAddr' is used in this document to indicate a string of this format. 7.5.2.2.1. IPv4 IPv4 Endpoint Addresses are encoded as specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986]. 7.5.2.2.2. IPv6 IPv6 Endpoint Addresses are encoded as specified in Section 4 of [RFC5952]. Alimi, et al. Expires November 21, 2011 [Page 25] Internet-Draft ALTO Protocol May 2011 7.5.2.2.3. Typed Endpoint Addresses When an Endpoint Address is used, an ALTO implementation must be able to determine its type. For this purpose, the ALTO Protocol allows endpoint addresses to also explicitly indicate their type. Typed Endpoint Addresses are encoded as US-ASCII strings of the format 'AddressType:EndpointAddr' (with the ':' character as a separator). The type 'TypedEndpointAddr' is used to indicate a string of this format. 7.5.2.3. Endpoint Prefixes For efficiency, it is useful to denote a set of Endpoint Addresses using a special notation (if one exists). This specification makes use of the prefix notations for both IPv4 and IPv6 for this purpose. Endpoint Prefixes are encoded as US-ASCII strings. The exact characters and format depend on the type of endpoint address. The type 'EndpointPrefix' is used in this document to indicate a string of this format. 7.5.2.3.1. IPv4 IPv4 Endpoint Prefixes are encoded as specified in Section 3.1 of [RFC4632]. 7.5.2.3.2. IPv6 IPv6 Endpoint Prefixes are encoded as specified in Section 7 of [RFC5952]. 7.5.2.4. Endpoint Address Group The ALTO Protocol includes messages that specify potentially large sets of endpoint addresses. Endpoint Address Groups provide a more efficient way to encode such sets, even when the set contains endpoint addresses of different types. An Endpoint Address Group is defined as: object { EndpointPrefix [AddressType]<0..*>; ... } EndpointAddrGroup; Alimi, et al. Expires November 21, 2011 [Page 26] Internet-Draft ALTO Protocol May 2011 In particular, an Endpoint Address Group is a JSON object with the name of each member being the string corresponding to the address type, and the member's corresponding value being a list of prefixes of addresses of that type. The following is an example with both IPv4 and IPv6 endpoint addresses: { "ipv4": [ "192.0.2.0/24", "198.51.100.0/25" ], "ipv6": [ "2001:db8:0:1::/64", "2001:db8:0:2::/64" ] } 7.5.3. Cost Mode A Cost Mode is encoded as a US-ASCII string. The string MUST either have the value 'numerical' or 'ordinal'. The type 'CostMode' is used in this document to indicate a string of this format. 7.5.4. Cost Type A Cost Type is encoded as a US-ASCII string. The string MUST be no more than 32 characters, and MUST NOT contain characters other than alphanumeric characters, the hyphen ('-'), or the ':' separator. Identifiers prefixed with 'priv:' are reserved for Private Use [RFC5226]. Identifiers prefixed with 'exp:' are reserved for Experimental use. All other identifiers appearing in an HTTP request or response with an 'application/alto-*' media type MUST be registered in the ALTO Cost Types registry Section 11.2. The type 'CostType' is used in this document to indicate a string of this format. 7.5.5. Endpoint Property An Endpoint Property is encoded as a US-ASCII string. The string MUST be no more than 32 characters, and MUST NOT contain characters Alimi, et al. Expires November 21, 2011 [Page 27] Internet-Draft ALTO Protocol May 2011 other than alphanumeric characters, the hyphen ('-'), or the ':' separator. Identifiers prefixed with 'priv:' are reserved for Private Use [RFC5226]. Identifiers prefixed with 'exp:' are reserved for Experimental use. All other identifiers appearing in an HTTP request or response with an 'application/alto-*' media type MUST be registered in the ALTO Endpoint Property registry Section 11.3. The type 'EndpointProperty' is used in this document to indicate a string of this format. 7.6. Information Resource Directory An Information Resource Directory indicates to ALTO Clients which Information Resources are made available by an ALTO Server. Since resource selection happens after consumption of the Information Resource Directory, the format of the Information Resource Directory is designed to be simple with the intention of future ALTO Protocol versions maintaining backwards compatibility. Future extensions or versions of the ALTO Protocol SHOULD be accomplished by extending existing media types or adding new media types, but retaining the same format for the Information Resource Directory. An ALTO Server MUST make an Information Resource Directory available via the HTTP GET method to a URI discoverable by an ALTO Client. Discovery of this URI is out of scope of this document, but could be accomplished by manual configuration or by returning the URI of an Information Resource Directory from the ALTO Discovery Protocol [I-D.ietf-alto-server-discovery]. 7.6.1. Media Type The media type is "application/alto-directory+json". 7.6.2. Encoding An Information Resource Directory is a JSON object of type InfoResourceDirectory: Alimi, et al. Expires November 21, 2011 [Page 28] Internet-Draft ALTO Protocol May 2011 object { ... } Capabilities; object { JSONString uri; JSONString media-types<1..*>; JSONString accepts<0..*>; [OPTIONAL] Capabilities capabilities; [OPTIONAL] } ResourceEntry; object { ResourceEntry resources<0..*>; } InfoResourceDirectory; where the "resources" array indicates a list of Information Resources provided by an ALTO Server. Note that the list of available resources is enclosed in a JSON object for extensibility; future protocol versions may specify additional members in the InfoResourceDirectory object. Each entry MUST indicate a URI that either directly provides the indicated Information Resource, or responds to a HTTP OPTIONS request which provides an Information Resource Directory with entries of additional Information Resources. If an ALTO Client makes a GET or POST request to a URI that does not directly provide an indicated Information Resource, the ALTO Server MUST either reply with an HTTP 300 status code ("Multiple Choices") and an Information Resource Directory in the HTTP response's entity body, or indicate an appropriate HTTP status code. A URI that directly provides an Information Resource MAY also respond to HTTP OPTIONS requests, but it is not required to do so (in which case, it MUST respond with HTTP 405 status code ("Method Not Allowed"). This allows certain Information Resources to be configured as static files with minimal configuration on some HTTP servers. Each entry in the directory specifies: uri A URI at which the ALTO Server provides one or more Information Resources, or an Information Resource Directory indicating additional Information Resources. Alimi, et al. Expires November 21, 2011 [Page 29] Internet-Draft ALTO Protocol May 2011 media-types The list of all media types of Information Resources (see Section 7.3.3) available via GET or POST requests to the corresponding URI or URIs discoverable via the URI. accepts The list of all media types of input parameters (see Section 7.3.2) accepted by POST requests to the corresponding URI or URIs discoverable via the URI. If this member is not present, it MUST be assumed to be an empty array. capabilities A JSON Object enumerating capabilities of an ALTO Server in providing the Information Resource at the corresponding URI and Information Resources discoverable via the URI. If this member is not present, it MUST be assumed to be an empty array. If a capability for one of the offered Information Resources is not explicitly listed here, an ALTO Client may either issue an OPTIONS HTTP request to the corresponding URI to determine if the capability is supported, or assume its default value. 7.6.3. Example The following is an example Information Resource Directory returned by an ALTO Server. In this example, the ALTO Server provides additional Network and Cost Maps via a separate subdomain, "custom.alto.example.com". The maps available via this subdomain are Filtered Network and Cost Maps as well as pre-generated maps for the "hopcount" and "routingcost" Cost Types in the "ordinal" Cost Mode. An ALTO Client could discover the maps available via "custom.alto.example.com" by either: o Successfully performing an OPTIONS request to "http://custom.alto.example.com/maps", or o Attempting a POST request for a desired Network or Cost Map to "http://custom.alto.example.com/maps" and receiving a HTTP 300 status code ("Multiple Choices") response with an Information Resource Directory. GET /directory HTTP/1.1 Host: alto.example.com Accept: application/alto-directory+json HTTP/1.1 200 OK Alimi, et al. Expires November 21, 2011 [Page 30] Internet-Draft ALTO Protocol May 2011 Content-Length: [TODO] Content-Type: application/alto-directory+json { "resources" : [ { "uri" : "http://alto.example.com/serverinfo", "media-types" : [ "application/alto-serverinfo+json" ] }, { "uri" : "http://alto.example.com/networkmap", "media-types" : [ "application/alto-networkmap+json" ] }, { "uri" : "http://alto.example.com/costmap/num/routingcost", "media-types" : [ "application/alto-costmap+json" ], "capabilities" : { "cost-modes" : [ "numerical" ], "cost-types" : [ "routingcost" ] } }, { "uri" : "http://alto.example.com/costmap/num/hopcount", "media-types" : [ "application/alto-costmap+json" ], "capabilities" : { "cost-modes" : [ "numerical" ], "cost-types" : [ "hopcount" ] } }, { "uri" : "http://custom.alto.example.com/maps", "media-types" : [ "application/alto-networkmap+json", "application/alto-costmap+json" ], "accepts" : [ "application/alto-networkmapfilter+json", "application/alto-costmapfilter+json" ], }, { "uri" : "http://alto.example.com/endpointprop/lookup", "media-types" : [ "application/alto-endpointprop+json" ], "accepts" : [ "application/alto-endpointpropparams+json" ], "capabilities" : { "prop-types" : [ "pid" ] } }, { "uri" : "http://alto.example.com/endpointcost/lookup", "media-types" : [ "application/alto-endpointcost+json" ], "accepts" : [ "application/alto-endpointcostparams+json" ], "capabilities" : { "cost-constraints" : true, Alimi, et al. Expires November 21, 2011 [Page 31] Internet-Draft ALTO Protocol May 2011 "cost-modes" : [ "ordinal", "numerical" ], "cost-types" : [ "routingcost", "hopcount" ] } } ] } OPTIONS /maps HTTP/1.1 Host: custom.alto.example.com Accept: application/alto-directory+json Alimi, et al. Expires November 21, 2011 [Page 32] Internet-Draft ALTO Protocol May 2011 HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-directory+json { "resources" : [ { "uri" : "http://custom.alto.example.com/networkmap/filtered", "media-types" : [ "application/alto-networkmap+json" ], "accepts" : [ "application/alto-networkmapfilter+json" ] }, { "uri" : "http://custom.alto.example.com/costmap/filtered", "media-types" : [ "application/alto-costmap+json" ], "accepts" : [ "application/alto-costmapfilter+json" ], "capabilities" : { "cost-constraints" : true, "cost-modes" : [ "ordinal", "numerical" ], "cost-types" : [ "routingcost", "hopcount" ] } }, { "uri" : "http://custom.alto.example.com/ord/routingcost", "media-types" : [ "application/alto-costmap+json" ], "capabilities" : { "cost-modes" : [ "ordinal" ], "cost-types" : [ "routingcost" ] } }, { "uri" : "http://custom.alto.example.com/ord/hopcount", "media-types" : [ "application/alto-costmap+json" ], "capabilities" : { "cost-modes" : [ "ordinal" ], "cost-types" : [ "hopcount" ] } } ] } 7.6.4. Usage Considerations 7.6.4.1. ALTO Client This document specifies no requirements or constraints on ALTO Clients with regards to how they process an Information Resource Directory to identify the URI corresponding to a desired Information Resource. However, some advice is provided for implementors. It is possible that multiple entries in the directory match a desired Alimi, et al. Expires November 21, 2011 [Page 33] Internet-Draft ALTO Protocol May 2011 Information Resource. For instance, in the example in Section 7.6.3, a full Cost Map with "numerical" Cost Mode and "routingcost" Cost Type could be retrieved via a GET request to "http://alto.example.com/costmap/num/routingcost", or via a POST request to "http://custom.alto.example.com/costmap/filtered". In general, it is preferred for ALTO Clients to use GET requests where appropriate, since it is more likely for responses to be cacheable. 7.6.4.2. ALTO Server This document indicates that an ALTO Server may or may not provide the Information Resources specified in the Map Filtering Service. If these resources are not provided, it is indicated to an ALTO Client by the absence of a Network Map or Cost Map with any media types listed under "accepts". 7.7. Information Resources This section documents the individual Information Resources defined in the ALTO Protocol. 7.7.1. Server Information Service The Server Information Service provides generic information about an ALTO Server. 7.7.1.1. Server Info This Information Resource MUST be provided by an ALTO Server. 7.7.1.1.1. Media Type The media type is "application/alto-serverinfo+json". 7.7.1.1.2. HTTP Method This resource is requested using the HTTP GET method. 7.7.1.1.3. Input Parameters None. 7.7.1.1.4. Capabilities None. Alimi, et al. Expires November 21, 2011 [Page 34] Internet-Draft ALTO Protocol May 2011 7.7.1.1.5. Response The returned InfoResourceEntity object has "data" member of type InfoResourceServerInfo: object { JSONString service-id; [OPTIONAL] JSONString certificates<0..*>; [OPTIONAL] } InfoResourceServerInfo; which has members: service-id UUID [RFC4122] indicating an one or more ALTO Servers serving equivalent ALTO Information. certificates List of PEM-encoded X.509 certificates used by the ALTO Server in the signing of responses. If an ALTO Server has the possibility of marking any response as redistributable, the 'service-id' and 'certificates' fields are REQUIRED instead of OPTIONAL. See Section 8&$160;for detailed specification. 7.7.1.1.6. Example GET /serverinfo HTTP/1.1 Host: alto.example.com Accept: application/alto-serverinfo+json HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-serverinfo+json { "meta" : {}, "data" : { "service-id" : "c89ca72f-dead-41b5-9e2b-b65455ace1ee", "certificates" : [ ... ] } } Alimi, et al. Expires November 21, 2011 [Page 35] Internet-Draft ALTO Protocol May 2011 7.7.2. Map Service The Map Service provides batch information to ALTO Clients in the form of two types of maps: a Network Map and Cost Map. 7.7.2.1. Network Map The Network Map Information Resource lists for each PID, the network locations (endpoints) within the PID. It MUST be provided by an ALTO Server. 7.7.2.1.1. Media Type The media type is "application/alto-networkmap+json". 7.7.2.1.2. HTTP Method This resource is requested using the HTTP GET method. 7.7.2.1.3. Input Parameters None. 7.7.2.1.4. Capabilities None. 7.7.2.1.5. Response The returned InfoResourceEntity object "data" member of type InfoResourceNetworkMap: object { EndpointAddrGroup [pidname]<0..*>; ... } NetworkMapData; object { JSONString map-vtag; NetworkMapData map; } InfoResourceNetworkMap; with members: Alimi, et al. Expires November 21, 2011 [Page 36] Internet-Draft ALTO Protocol May 2011 map-vtag The Version Tag (Section 5.3) of the Network Map. map The Network Map data itself. NetworkMapData is a JSON object with each member representing a single PID and its associated set of endpoint addresses. A member's name is a string of type PIDName. The returned Network Map MUST include all PIDs known to the ALTO Server. 7.7.2.1.6. Example GET /networkmap HTTP/1.1 Host: alto.example.com Accept: application/alto-networkmap+json Alimi, et al. Expires November 21, 2011 [Page 37] Internet-Draft ALTO Protocol May 2011 HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-networkmap+json { "meta" : {}, "data" : { "map-vtag" : "1266506139", "map" : { "PID1" : { "ipv4" : [ "192.0.2.0/24", "198.51.100.0/25" ] }, "PID2" : { "ipv4" : [ "198.51.100.128/25" ] }, "PID3" : { "ipv4" : [ "0.0.0.0/0" ], "ipv6" : [ "::/0" ] ] } } } 7.7.2.2. Cost Map The Cost Map resource lists the Path Cost for each pair of source/ destination PID defined by the ALTO Server for a given Cost Type and Cost Mode. This resource MUST be provided for at least the 'routingcost' Cost Type and 'numerical' Cost Mode. Note that since this resource, an unfiltered Cost Map requested by an HTTP GET, does not indicate the desired Cost Mode or Cost Type as input parameters, an ALTO Server MUST indicate in an Information Resource Directory a unfiltered Cost Map Information Resource by specifying the capabilities (Section 7.7.2.2.4) with "cost-types" and "cost-modes" members each having a single element. This technique will allow an ALTO Client to determine a URI for an unfiltered Cost Map of the desired Cost Mode and Cost Type. Alimi, et al. Expires November 21, 2011 [Page 38] Internet-Draft ALTO Protocol May 2011 7.7.2.2.1. Media Type The media type is "application/alto-costmap+json". 7.7.2.2.2. HTTP Method This resource is requested using the HTTP GET method. 7.7.2.2.3. Input Parameters None. 7.7.2.2.4. Capabilities This resource may be defined for across multiple Cost Types and Cost Modes. The capabilities of an ALTO Server URI providing this resource are defined by a JSON Object of type CostMapCapability: object { CostMode cost-modes<0..*>; CostType cost-types<0..*>; } CostMapCapability; with members: cost-modes The Cost Modes ( Section 5.1.2) supported by the corresponding URI. If not present, this member MUST be interpreted as an empty array. cost-types The Cost Types ( Section 5.1.1) supported by the corresponding URI. If not present, this member MUST be interpreted as an empty array. An ALTO Server MUST support all of the Cost Types listed here for each of the listed Cost Modes. Note that an ALTO Server may provide multiple Cost Map Information Resources, each with different capabilities. 7.7.2.2.5. Response The returned InfoResourceEntity object has "data" member of type InfoResourceCostMap: Alimi, et al. Expires November 21, 2011 [Page 39] Internet-Draft ALTO Protocol May 2011 object DstCosts { JSONNumber [PIDName]; ... }; object { DstCosts [PIDName]<0..*>; ... } CostMapData; object { CostMode cost-mode; CostType cost-type; JSONString map-vtag; CostMapData map; } InfoResourceCostMap; with members: cost-mode Cost Mode (Section 5.1.2) used in the Cost Map. cost-type Cost Type (Section 5.1.1) used in the Cost Map. map-vtag The Version Tag (Section 5.3) of the Network Map used to generate the Cost Map. map The Cost Map data itself. CostMapData is a JSON object with each member representing a single Source PID; the name for a member is the PIDName string identifying the corresponding Source PID. For each Source PID, a DstCosts object denotes the associated cost to a set of destination PIDs ( Section 5.2); the name for each member in the object is the PIDName string identifying the corresponding Destination PID. DstCosts MUST have a single member for each Destination PID in the map. The returned Cost Map MUST include Path Costs for each pair of Source PID and Destination PID known to the ALTO Server. 7.7.2.2.6. Example GET /costmap/num/routingcost HTTP/1.1 Host: alto.example.com Accept: application/alto-costmap+json Alimi, et al. Expires November 21, 2011 [Page 40] Internet-Draft ALTO Protocol May 2011 HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-costmap+json { "meta" : {}, "data" : { "cost-mode" : "numerical", "cost-type" : "routingcost", "map-vtag" : "1266506139", "map" : { "PID1": { "PID1": 1, "PID2": 5, "PID3": 10 }, "PID2": { "PID1": 5, "PID2": 1, "PID3": 15 }, "PID3": { "PID1": 20, "PID2": 15, "PID3": 1 } } } } 7.7.3. Map Filtering Service The Map Filtering Service allows ALTO Clients to specify filtering criteria to return a subset of the full maps available in the Map Service. 7.7.3.1. Filtered Network Map A Filtered Network Map is a Network Map Information Resource (Section 7.7.2.1) for which an ALTO Client may supply a list of PIDs to be included. A Filtered Network Map MAY be provided by an ALTO Server. 7.7.3.1.1. Media Type See Section 7.7.2.1.1. 7.7.3.1.2. HTTP Method This resource is requested using the HTTP POST method. 7.7.3.1.3. Input Parameters Input parameters are supplied in the entity body of the POST request. This document specifies the input parameters with a data format indicated by the media type "application/alto-networkmapfilter+json", which is a JSON Object of type ReqFilteredNetworkMap, where: Alimi, et al. Expires November 21, 2011 [Page 41] Internet-Draft ALTO Protocol May 2011 object { PIDName pids<0..*>; } ReqFilteredNetworkMap; with members: pids Specifies list of PIDs to be included in the returned Filtered Network Map. If the list of PIDs is empty, the ALTO Server MUST interpret the list as if it contained a list of all currently- defined PIDs. 7.7.3.1.4. Capabilities None. 7.7.3.1.5. Response See Section 7.7.2.1.5 for the format. The ALTO Server MUST only include PIDs in the response that were specified (implicitly or explicitly) in the request. If the input parameters contain a PID name that is not currently defined by the ALTO Server, the ALTO Server MUST behave as if the PID did not appear in the input parameters. Alimi, et al. Expires November 21, 2011 [Page 42] Internet-Draft ALTO Protocol May 2011 7.7.3.1.6. Example POST /networkmap/filtered HTTP/1.1 Host: custom.alto.example.com Content-Length: [TODO] Content-Type: application/alto-networkmapfilter+json Accept: application/alto-networkmap+json { pids: [ "PID1", "PID2" ] } HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-networkmap+json { "meta" : {}, "data" : { "map-vtag" : "1266506139", "map" : { "PID1" : { "ipv4" : [ "192.0.2.0/24", "198.51.100.0/24" ] }, "PID2" : { "ipv4": [ "198.51.100.128/24" ] } } } } 7.7.3.2. Filtered Cost Map A Filtered Cost Map is a Cost Map Information Resource (Section 7.7.2.2) for which an ALTO Client may supply additional parameters limiting the scope of the resulting Cost Map. A Filtered Cost Map MAY be provided by an ALTO Server. Alimi, et al. Expires November 21, 2011 [Page 43] Internet-Draft ALTO Protocol May 2011 7.7.3.2.1. Media Type See Section 7.7.2.2.1. 7.7.3.2.2. HTTP Method This resource is requested using the HTTP POST method. 7.7.3.2.3. Input Parameters Input parameters are supplied in the entity body of the POST request. This document specifies the input parameters with a data format indicated by the media type "application/alto-costmapfilter+json", which is a JSON Object of type ReqFilteredCostMap, where: object { PIDName srcs<0..*>; PIDName dsts<0..*>; } PIDFilter; object { CostMode cost-mode; CostType cost-type; JSONString constraints<0..*>; [OPTIONAL] PIDFilter pids; [OPTIONAL] } ReqFilteredCostMap; with members: cost-type The Cost Type ( Section 5.1.1) for the returned costs. This MUST be one of the supported Cost Types indicated in this resource's capabilities ( Section 7.7.3.2.4). cost-mode The Cost Mode ( Section 5.1.2) for the returned costs. This MUST be one of the supported Cost Modes indicated in this resource's capabilities ( Section 7.7.3.2.4). constraints Defines a list of additional constraints on which elements of the Cost Map are returned. This parameter MUST NOT be specified if this resource's capabilities ( Section 7.7.3.2.4) indicate that constraint support is not available. A constraint contains two entities separated by whitespace: (1) an operator either 'gt' for greater than or 'lt' for less than (2) a target numerical cost. The numerical cost is a number that MUST be defined in the same units as the Cost Type indicated by the cost- type parameter. ALTO Servers SHOULD use at least IEEE 754 double- Alimi, et al. Expires November 21, 2011 [Page 44] Internet-Draft ALTO Protocol May 2011 precision floating point [IEEE.754.2008] to store the numerical cost, and SHOULD perform internal computations using double- precision floating-point arithmetic. If multiple 'constraint' parameters are specified, they are interpreted as being related to each other with a logical AND. pids A list of Source PIDs and a list of Destination PIDs for which Path Costs are to be returned. If a list is empty, the ALTO Server MUST interpret it as the full set of currently-defined PIDs. If the "pids" member is not present, both lists MUST be interpreted by the ALTO Server as containing the full set of currently-defined PIDs. 7.7.3.2.4. Capabilities See Section 7.7.2.2.4. 7.7.3.2.5. Response See Section 7.7.2.2.5 for the format. The returned Cost Map MUST NOT contain any source/destination pair that was not indicated (implicitly or explicitly) in the input parameters. If the input parameters contain a PID name that is not currently defined by the ALTO Server, the ALTO Server MUST behave as if the PID did not appear in the input parameters. If any constraints are specified, Source/Destination pairs that do for which the Path Costs do not meet the constraints MUST NOT be included in the returned Cost Map. If no constraints were specified, then all Path Costs are assumed to meet the constraints. Alimi, et al. Expires November 21, 2011 [Page 45] Internet-Draft ALTO Protocol May 2011 7.7.3.2.6. Example POST /costmap/filtered HTTP/1.1 Host: custom.alto.example.com Content-Type: application/alto-costmapfilter+json Accept: application/alto-costmap+json { "cost-mode" : "numerical", "cost-type" : "routingcost", "pids" : { "srcs" : [ "PID1" ], "dsts" : [ "PID1", "PID2", "PID3" ] } } HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-costmap+json { "meta" : {}, "data" : { "cost-mode" : "numerical", "cost-type" : "routingcost", "map-vtag" : "1266506139", "map" : { "PID1": { "PID1": 0, "PID2": 1, "PID3": 2 } } } } 7.7.4. Endpoint Property Service The Endpoint Property Service provides information about Endpoint properties to ALTO Clients. 7.7.4.1. Endpoint Property The Endpoint Property resource provides information about properties for individual endpoints. It MAY be provided by an ALTO Server. If an ALTO Server provides the Endpoint Property resource, it MUST provide and define at least the 'pid' property for each Endpoint. Alimi, et al. Expires November 21, 2011 [Page 46] Internet-Draft ALTO Protocol May 2011 7.7.4.1.1. Media Type The media type is "application/alto-endpointprop+json". 7.7.4.1.2. HTTP Method This resource is requested using the HTTP POST method. 7.7.4.1.3. Input Parameters Input parameters are supplied in the entity body of the POST request. This document specifies the data format of input parameteres with the media type "application/alto-endpointpropparams+json", which is a JSON Object of type ReqEndpointProp: object { EndpointProperty properties<0..*>; TypedEndpointAddr endpoints<0..*>; } ReqEndpointProp; with members: properties List of endpoint properties to returned for each endpoint. Each specified property MUST be included in the list of supported properties indicated by this resource's capabilities ( Section 7.7.4.1.4). endpoints List of endpoint addresses for which the specified properties are to be returned. 7.7.4.1.4. Capabilities This resource may be defined across multiple types of endpoint properties. The capabilities of an ALTO Server URI providing Endpoint Properties are defined by a JSON Object of type EndpointPropertyCapability: object { EndpointProperty prop-types<0..*>; } EndpointPropertyCapability; with members: Alimi, et al. Expires November 21, 2011 [Page 47] Internet-Draft ALTO Protocol May 2011 prop-types The Endpoint Property Types ( Section 3.2.3) supported by the corresponding URI. If not present, this member MUST be interpreted as an empty array. 7.7.4.1.5. Response The returned InfoResourceEntity object has "data" member of type InfoResourceEndpointProperty, where: object { JSONString [EndpointProperty]; ... } EndpointProps; object { EndpointProps [TypedEndpointAddr]<0..*>; ... } InfoResourceEndpointProperty; InfoResourceEndpointProperty has one member for each endpoint indicated in the input parameters (with the name being the endpoint encoded as a TypedEndpointAddr). The requested properties for each endpoint are encoded in a corresponding EndpointProps object, which encodes one name/value pair for each requested property, where the property names are encoded as strings of type EndpointProperty and the property values encoded as JSON Strings. The ALTO Server returns the value for each of the requested endpoint properties for each of the endpoints listed in the input parameters. If the ALTO Server does not define a requested property for a particular endpoint, then it MUST omit it from the response for only that endpoint. Alimi, et al. Expires November 21, 2011 [Page 48] Internet-Draft ALTO Protocol May 2011 7.7.4.1.6. Example POST /endpointprop/lookup HTTP/1.1 Host: alto.example.com Content-Length: [TODO] Content-Type: application/alto-endpointpropparams+json Accept: application/alto-endpointprop+json { "properties" : [ "pid" ], "endpoints" : [ "ipv4:192.0.2.34", "ipv4:203.0.113.129" ] } HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-endpointprop+json { "meta" : {}, "data": { "ipv4:192.0.2.34" : { "pid": "PID1" }, "ipv4:203.0.113.129" : { "pid": "PID3" } } } 7.7.5. Endpoint Cost Service The Endpoint Cost Service provides information about costs between individual endpoints. In particular, this service allows lists of Endpoint prefixes (and addresses, as a special case) to be ranked (ordered) by an ALTO Server. 7.7.5.1. Endpoint Cost The Endpoint Cost resource provides information about costs between individual endpoints. It MAY be provided by an ALTO Server. If it is provided. It is important to note that although this resource allows an ALTO Server to reveal costs between individual endpoints, an ALTO Server is not required to do so. A simple alternative would be to compute the cost between two endpoints as the cost between the PIDs corresponding to the endpoints. See Section 12.1 for additional Alimi, et al. Expires November 21, 2011 [Page 49] Internet-Draft ALTO Protocol May 2011 details. 7.7.5.1.1. Media Type The media type is "application/alto-endpointcost+json". 7.7.5.1.2. HTTP Method This resource is requested using the HTTP POST method. 7.7.5.1.3. Input Parameters Input parameters are supplied in the entity body of the POST request. This document specifies input parameters with a data format indicated by media type "application/alto-endpointcostparams+json", which is a JSON Object of type ReqEndpointCostMap: object { TypedEndpointAddr srcs<0..*>; [OPTIONAL] TypedEndpointAddr dsts<1..*>; } EndpointFilter; object { CostMode cost-mode; CostType cost-type; JSONString constraints; [OPTIONAL] EndpointFilter endpoints; } ReqEndpointCostMap; with members: cost-mode The Cost Mode ( Section 5.1.2) to use for returned costs. This MUST be one of the Cost Modes indicated in this resource's capabilities ( Section 7.7.5.1.4). cost-type The Cost Type ( Section 5.1.1) to use for returned costs. This MUST be one of the Cost Types indicated in this resource's capabilities ( Section 7.7.5.1.4). constraints Defined equivalently to the "constraints" input parameter of a Filtered Cost Map (see Section 7.7.3.2). endpoints A list of Source Endpoints and Destination Endpoints for which Path Costs are to be returned. If the list of Source Endpoints is empty (or not included), the ALTO Server MUST interpret it as if it contained the Endpoint Address of the Alimi, et al. Expires November 21, 2011 [Page 50] Internet-Draft ALTO Protocol May 2011 requesting client. The list of destination Endpoints MUST NOT be empty. 7.7.5.1.4. Capabilities See Section 7.7.2.2.4. 7.7.5.1.5. Response The returned InfoResourceEntity object has "data" member equal to InfoResourceEndpointCostMap, where: object EndpointDstCosts { JSONNumber [TypedEndpointAddr]; ... }; object { EndpointDstCosts [TypedEndpointAddr]<0..*>; ... } EndpointCostMapData; object { CostMode cost-mode; CostType cost-type; EndpointCostMapData map; } InfoResourceEndpointCostMap; InfoResourceEndpointCostMap has members: cost-mode The Cost Mode used in the returned Cost Map. cost-type The Cost Type used in the returned Cost Map. map The Endpoint Cost Map data itself. EndpointCostMapData is a JSON object with each member representing a single Source Endpoint specified in the input parameters; the name for a member is the TypedEndpointAddr string identifying the corresponding Source Endpoint. For each Source Endpoint, a EndpointDstCosts object denotes the associated cost to each Destination Endpoint specified in the input parameters; the name for each member in the object is the TypedEndpointAddr string identifying the corresponding Destination Endpoint. Alimi, et al. Expires November 21, 2011 [Page 51] Internet-Draft ALTO Protocol May 2011 7.7.5.1.6. Example POST /endpointcost/lookup HTTP/1.1 Host: alto.example.com Content-Length: [TODO] Content-Type: application/alto-endpointcostparams+json Accept: application/alto-endpointcost+json { "cost-mode" : "ordinal", "cost-type" : "routingcost", "endpoints" : { "srcs": [ "ipv4:192.0.2.2" ], "dsts": [ "ipv4:192.0.2.89", "ipv4:198.51.100.34", "ipv4:203.0.113.45" ] } } HTTP/1.1 200 OK Content-Length: [TODO] Content-Type: application/alto-endpointcost+json { "meta" : {}, "data" : { "map" : { "ipv4:192.0.2.2": { "ipv4:192.0.2.89" : 1, "ipv4:198.51.100.34" : 2, "ipv4:203.0.113.45" : 3 } } } } 8. Redistributable Responses This section defines how an ALTO Server enables certain Information Resources to be redistributed by ALTO Clients. Concepts are first introduced, followed by the protocol specification. Alimi, et al. Expires November 21, 2011 [Page 52] Internet-Draft ALTO Protocol May 2011 8.1. Concepts 8.1.1. Service ID The Service ID is a UUID that identifies a set of ALTO Servers that would provide semantically-identical Information Resources for any request for any ALTO Client. Each ALTO Server within such a set is configured with an identical Service ID. If a pair of ALTO Servers would provide an identical Information Resource (same information sources, configuration, internal computations, update timescales, etc) in response to any particular ALTO Client request, then the pair of ALTO Servers MAY have the same Service ID. If this condition is not true, the pair of ALTO Servers MUST have a different Service ID. 8.1.1.1. Rationale For scalability and fault tolerance, multiple ALTO Servers may be deployed to serve equivalent ALTO Information. In such a scenario, Information Resources from any such redundant server should be seen as equivalent for the purposes of redistribution. For example, if two ALTO Servers A and B are deployed by the service provider to distribute equivalent ALTO Information, then clients contacting Server A should be able to redistribute Information Resources to clients contacting Server B. To accomplish this behavior, ALTO Clients must be able to determine that Server A and Server B serve identical ALTO Information. One technique would be to rely on the ALTO Server's DNS name. However, such an approach would mandate that all ALTO Servers resolved by a particular DNS name would need to provide equivalent ALTO information, which may be unnecessarily restrictive. Another technique would be to rely on the server's IP address. However, this suffers similar problems as the DNS name in deployment scenarios using IP Anycast. To avoid such restrictions, the ALTO Protocol allows an ALTO Service Provider to explicitly denote ALTO Servers that provide equivalent ALTO Information by giving them identical Service IDs. Service IDs decouple the identification of equivalent ALTO Servers from the discovery process. 8.1.1.2. Server Information Resource If an ALTO Server generates redistributable responses, the Server Information resource's 'service-id' field MUST be set to the ALTO Server's Service ID. Alimi, et al. Expires November 21, 2011 [Page 53] Internet-Draft ALTO Protocol May 2011 8.1.1.3. Configuration To help prevent ALTO Servers from mistakenly claiming to distribute equivalent ALTO Information, ALTO Server implementations SHOULD by default generate a new UUID at installation time or startup if one has not explicitly been configured. 8.1.2. Expiration Time Information Resources marked as redistributable should indicate a time after which the information is considered stale and should be refreshed from the ALTO Server (or possibly another ALTO Client). If an expiration time is present, the ALTO Server SHOULD ensure that it is reasonably consistent with the expiration time that would be computed by HTTP header fields. This specification makes no recommendation on which expiration time takes precedence, but implementers should be cognizant that HTTP intermediaries will obey only the HTTP header fields. 8.1.3. Signature Information Resources marked as redistributable include a signature used to assert that the ALTO Server Provider generated the ALTO Information. 8.1.3.1. Rationale Verification of the signature requires the ALTO Client to retrieve the ALTO Server's public key. To reduce requirements on the underlying transport (i.e., requiring SSL/TLS), an ALTO Client retrieves the public key as part of an X.509 certificate from the ALTO Server's Server Information resource. 8.1.3.2. Certificates 8.1.3.2.1. Local Certificate The ALTO Server's public key is encoded within an X.509 certificate. The corresponding private key MUST be used to sign redistributable responses. This certificate is termed the Local Certificate for an ALTO Server. 8.1.3.2.2. Certificate Chain To ease key provisioning, the ALTO Protocol is designed such that each ALTO Server with an identical Service ID may have a unique private key (and hence certificate). Alimi, et al. Expires November 21, 2011 [Page 54] Internet-Draft ALTO Protocol May 2011 The ALTO Service Provider may configure a certificate chain at each such ALTO Server. The Local Certificate for a single ALTO Server is the bottom-most certificate in the chain. The Certificate Chains of each ALTO Server with an identical Service ID MUST share a common Root Certificate. Note that there are two simple deployment scenarios: o One-Level Certificate Chain (Local Certificate Only): In this deployment scenario, each ALTO Server with an identical Service ID may provisioned with an identical Local Certificate. o Two-Level Certificate Chain: In this deployment scenario, a Root Certificate is maintained for a set of ALTO Servers with the same Service ID. A unique Local Certificate signed by this CA is provisioned to each ALTO Server. There are advantages to using a Certificate Chain instead of deploying the same Local Certificate to each ALTO Server. Specifically, it avoids storage of the CA's private key at ALTO Servers. It is possible to revoke and re-issue a key to a single ALTO Server. 8.1.3.2.3. Server Information Resource If an ALTO Server generates redistributable responses, the Server Information resource's 'certificates' field MUST be populated with the ALTO Server's full certificate chain. The first element MUST be the ALTO Server's Local Certificate, followed by the remaining Certificate Chain in ascending order to the Root Certificate. 8.1.3.3. Signature Verification ALTO Clients SHOULD verify the signature on any ALTO information received via redistribution before adjusting application behavior based on it. An ALTO Client SHOULD cache its ALTO Server's Service ID and corresponding Certificate Chain included in the Server Information resource. Recall that the last certificate in this chain is the Root Certificate. The retrieval of the Service ID and certificates SHOULD be secured using HTTPS with proper validation of the server endpoint of the SSL/TLS connection [RFC6125]. An Information Resource received via redistribution from Service ID S is declared valid if an ALTO Client can construct a transitive certificate chain from the certificate (public key) used to sign the Information Resource to the Root Certificate corresponding to Service Alimi, et al. Expires November 21, 2011 [Page 55] Internet-Draft ALTO Protocol May 2011 ID S obtained by the ALTO Client in a Server Information resource. To properly construct the chain and complete this validation, an ALTO Client may need to request additional certificates from other ALTO Clients. A simple mechanism is to request the certificate chain from the ALTO Client that received the Information Resource. Note that these additional received certificates may be cached locally by an ALTO Client. ALTO Clients SHOULD verify Information Resources received via redistribution. 8.1.3.4. Redistribution by ALTO Clients ALTO Clients SHOULD pass the ALTO Server Certificate, Signature, and Signature Algorithm along with the Information Resource. The mechanism for redistributing such information is not specified by the ALTO Protocol, but one possibility is to add additional messages or fields to the application's native protocol. 8.2. Protocol An ALTO Server MAY indicate that a response is suitable for redistribution by including the "redistribution" member in the RspMetaData JSON object of an Information Resource. This additional member, called the Response Redistribution Descriptor, has type RspRedistDesc: object { JSONString service-id; JSONString request-uri; JSONValue request-body; JSONString media-type; JSONString expires; } RspRedistDesc; The fields encoded in the Response Redistribution Descriptor allows an ALTO Client receiving redistributed ALTO Information to understand the context of the query (the ALTO Service generating the response and any input parameters) and to interpret the results. Information about ALTO Client performing the request and any HTTP Headers passed in the request are not included in the Response Redistribution Descriptor. If any such information or headers influence the response generated by the ALTO Server, the response SHOULD NOT be indicated as redistributable. Alimi, et al. Expires November 21, 2011 [Page 56] Internet-Draft ALTO Protocol May 2011 8.2.1. Response Redistribution Descriptor Fields This section defines the fields of the Response Redistribution Descriptor. 8.2.1.1. Service ID The 'service-id' member is REQUIRED and MUST have a value equal to the ALTO Server's Service ID. 8.2.1.2. Request URI The 'request-uri' member is REQUIRED and MUST specify the HTTP Request-URI that was passed in the HTTP request. 8.2.1.3. Request Body If the HTTP request's entity body was non-empty, the 'request-body' member MUST specify full JSON value passed in the HTTP request's entity body (note that whitespace may differ, as long as the JSON Value is identical). If the HTTP request was empty, then the 'request-body' MUST NOT be included. 8.2.1.4. Response Media Type The 'media-type' member is REQUIRED and MUST specify the same HTTP Content-Type that is used in the HTTP response. 8.2.1.5. Expiration Time The 'expires' element is RECOMMENDED and, if present, MUST specify a time in UTC formatted according to [RFC3339]. 8.2.2. Signature The Hash Algorithm, Signature Algorithm, and Signature are included as either HTTP Headers or Trailers. Headers may be useful if Information Resources are pre-generated, while Trailers may be useful if Information Resources are dynamically generated (e.g., to avoid buffering large responses in memory while the hash value is computed). The following HTTP Headers (the ALTO Server MAY specify them as HTTP Trailers instead) MUST be used to encode the Signature parameters for redistributable Information Resources: ALTO-HashAlgorithm: ALTO-SignatureAlgorithm: Alimi, et al. Expires November 21, 2011 [Page 57] Internet-Draft ALTO Protocol May 2011 ALTO-SignatureDigest: where and are an integer values from the IANA TLS HashAlgorithm and SignatureAlgorithm registries, and is the corresponding Base64-encoded signature. 9. Use Cases The sections below depict typical use cases. 9.1. ALTO Client Embedded in P2P Tracker Many P2P currently-deployed P2P systems use a Tracker to manage swarms and perform peer selection. P2P trackers may currently use a variety of information to perform peer selection to meet application- specific goals. By acting as an ALTO Client, an P2P tracker can use ALTO information as an additional information source to enable more network-efficient traffic patterns and improve application performance. A particular requirement of many P2P trackers is that they must handle a large number of P2P clients. A P2P tracker can obtain and locally store ALTO information (the Network Map and Cost Map) from the ISPs containing the P2P clients, and benefit from the same aggregation of network locations done by ALTO Servers. .---------. (1) Get Network Map .---------------. | | <----------------------> | | | ALTO | | P2P Tracker | | Server | (2) Get Cost Map | (ALTO Client) | | | <----------------------> | | `---------' `---------------' ^ | (3) Get Peers | | (4) Selected Peer | v List .---------. .-----------. | Peer 1 | <-------------- | P2P | `---------' | Client | . (5) Connect to `-----------' . Selected Peers / .---------. / | Peer 50 | <------------------ `---------' Figure 4: ALTO Client Embedded in P2P Tracker Figure 4 shows an example use case where a P2P tracker is an ALTO Alimi, et al. Expires November 21, 2011 [Page 58] Internet-Draft ALTO Protocol May 2011 Client and applies ALTO information when selecting peers for its P2P clients. The example proceeds as follows: 1. The P2P Tracker requests the Network Map covering all PIDs from the ALTO Server using the Network Map query. The Network Map includes the IP prefixes contained in each PID, allowing the P2P tracker to locally map P2P clients into a PIDs. 2. The P2P Tracker requests the Cost Map amongst all PIDs from the ALTO Server. 3. A P2P Client joins the swarm, and requests a peer list from the P2P Tracker. 4. The P2P Tracker returns a peer list to the P2P client. The returned peer list is computed based on the Network Map and Cost Map returned by the ALTO Server, and possibly other information sources. Note that it is possible that a tracker may use only the Network Map to implement hierarchical peer selection by preferring peers within the same PID and ISP. 5. The P2P Client connects to the selected peers. Note that the P2P tracker may provide peer lists to P2P clients distributed across multiple ISPs. In such a case, the P2P tracker may communicate with multiple ALTO Servers. 9.2. ALTO Client Embedded in P2P Client: Numerical Costs P2P clients may also utilize ALTO information themselves when selecting from available peers. It is important to note that not all P2P systems use a P2P tracker for peer discovery and selection. Furthermore, even when a P2P tracker is used, the P2P clients may rely on other sources, such as peer exchange and DHTs, to discover peers. When an P2P Client uses ALTO information, it typically queries only the ALTO Server servicing its own ISP. The my-Internet view provided by its ISP's ALTO Server can include preferences to all potential peers. Alimi, et al. Expires November 21, 2011 [Page 59] Internet-Draft ALTO Protocol May 2011 .---------. (1) Get Network Map .---------------. | | <----------------------> | | | ALTO | | P2P Client | | Server | (2) Get Cost Map | (ALTO Client) | | | <----------------------> | | .---------. `---------' `---------------' <- | P2P | .---------. / | ^ ^ | Tracker | | Peer 1 | <-------------- | | \ `---------' `---------' | (3) Gather Peers . (4) Select Peers | | \ . and Connect / .--------. .--------. .---------. / | P2P | | DHT | | Peer 50 | <---------------- | Client | `--------' `---------' | (PEX) | `--------' Figure 5: ALTO Client Embedded in P2P Client Figure 5 shows an example use case where a P2P Client locally applies ALTO information to select peers. The use case proceeds as follows: 1. The P2P Client requests the Network Map covering all PIDs from the ALTO Server servicing its own ISP. 2. The P2P Client requests the Cost Map amongst all PIDs from the ALTO Server. The Cost Map by default specifies numerical costs. 3. The P2P Client discovers peers from sources such as Peer Exchange (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and P2P Trackers. 4. The P2P Client uses ALTO information as part of the algorithm for selecting new peers, and connects to the selected peers. 9.3. ALTO Client Embedded in P2P Client: Ranking It is also possible for a P2P Client to offload the selection and ranking process to an ALTO Server. In this use case, the ALTO Client gathers a list of known peers in the swarm, and asks the ALTO Server to rank them. As in the use case using numerical costs, the P2P Client typically only queries the ALTO Server servicing its own ISP. Alimi, et al. Expires November 21, 2011 [Page 60] Internet-Draft ALTO Protocol May 2011 .---------. .---------------. | | | | | ALTO | (2) Get Endpoint Ranking | P2P Client | | Server | <----------------------> | (ALTO Client) | | | | | .---------. `---------' `---------------' <- | P2P | .---------. / | ^ ^ | Tracker | | Peer 1 | <-------------- | | \ `---------' `---------' | (1) Gather Peers . (3) Connect to | | \ . Selected Peers / .--------. .--------. .---------. / | P2P | | DHT | | Peer 50 | <---------------- | Client | `--------' `---------' | (PEX) | `--------' Figure 6: ALTO Client Embedded in P2P Client: Ranking Figure 6 shows an example of this scenario. The use case proceeds as follows: 1. The P2P Client discovers peers from sources such as Peer Exchange (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and P2P Trackers. 2. The P2P Client queries the ALTO Server's Ranking Service, including discovered peers as the set of Destination Endpoints, and indicates the 'ordinal' Cost Mode. The response indicates the ranking of the candidate peers. 3. The P2P Client connects to the peers in the order specified in the ranking. 10. Discussions 10.1. Discovery The discovery mechanism by which an ALTO Client locates an appropriate ALTO Server is out of scope for this document. This document assumes that an ALTO Client can discover an appropriate ALTO Server. Once it has done so, the ALTO Client may use the Information Resource Directory (see Section 7.6) to locate an Information Resource with the desired ALTO Information. Alimi, et al. Expires November 21, 2011 [Page 61] Internet-Draft ALTO Protocol May 2011 10.2. Hosts with Multiple Endpoint Addresses In practical deployments, especially during the transition from IPv4 to IPv6, a particular host may be reachable using multiple addresses. Furthermore, the particular network path followed when sending packets to the host may differ based on the address that is used. Network providers may prefer one path over another (e.g., one path my have a NAT64 middlebox). An additional consideration may be how to handle private address spaces (e.g., behind carrier-grade NATs). To support such behavior, this document allows multiple types of endpoint addresses. In supporting multiple address types, the ALTO Protocol also allows ALTO Service Provider the flexibility to indicate preferences for paths from an endpoint address of one type to an endpoint address of a different type. Note that in general, the path through the network may differ dependent on the types of addresses that are used. Note that there are limitations as to what information ALTO can provide in this regard. In particular, a particular ALTO Service provider may not be able to determine if connectivity with a particular endhost will succeed over IPv4 or IPv6, as this may depend upon information unknown to the ISP such as particular application implementations. 10.3. Network Address Translation Considerations At this day and age of NAT v4<->v4, v4<->v6 [RFC6144], and possibly v6<->v6[I-D.mrw-nat66], a protocol should strive to be NAT friendly and minimize carrying IP addresses in the payload, or provide a mode of operation where the source IP address provide the information necessary to the server. The protocol specified in this document provides a mode of operation where the source network location is computed by the ALTO Server (via the Endpoint Property Lookup interface) from the source IP address found in the ALTO Client query packets. This is similar to how some P2P Trackers (e.g., BitTorrent Trackers - see "Tracker HTTP/HTTPS Protocol" in [BitTorrent]) operate. The ALTO client SHOULD use the Session Traversal Utilities for NAT (STUN) [RFC5389] to determine a public IP address to use as a source Endpoint address. If using this method, the host MUST use the "Binding Request" message and the resulting "XOR-MAPPED-ADDRESS" parameter that is returned in the response. Using STUN requires cooperation from a publicly accessible STUN server. Thus, the ALTO client also requires configuration information that identifies the STUN server, or a domain name that can be used for STUN server Alimi, et al. Expires November 21, 2011 [Page 62] Internet-Draft ALTO Protocol May 2011 discovery. To be selected for this purpose, the STUN server needs to provide the public reflexive transport address of the host. 10.4. Mapping IPs to ASNs It may be desired for the ALTO Protocol to provide ALTO information including ASNs. Thus, ALTO Clients may need to identify the ASN for a Resource Provider to determine the cost to that Resource Provider. Applications can already map IPs to ASNs using information from a BGP Looking Glass. To do so, they must download a file of about 1.5MB when compressed (as of October 2008, with all information not needed for IP to ASN mapping removed) and periodically (perhaps monthly) refresh it. Alternatively, the Network Map query in the Map Filtering Service defined in this document could be extended to map ASNs into a set of IP prefixes. The mappings provided by the ISP would be both smaller and more authoritative. For simplicity of implementation, it's highly desirable that clients only have to implement exactly one mechanism of mapping IPs to ASNs. 10.5. Endpoint and Path Properties An ALTO Server could make available many properties about Endpoints beyond their network location or grouping. For example, connection type, geographical location, and others may be useful to applications. This specification focuses on network location and grouping, but the protocol may be extended to handle other Endpoint properties. 11. IANA Considerations 11.1. application/alto-* Media Types This document requests the registration of multiple media types, listed in Table 2. Alimi, et al. Expires November 21, 2011 [Page 63] Internet-Draft ALTO Protocol May 2011 +-------------+------------------------------+-----------------+ | Type | Subtype | Specification | +-------------+------------------------------+-----------------+ | application | alto-directory+json | Section 7.6 | | application | alto-serverinfo+json | Section 7.7.1.1 | | application | alto-networkmap+json | Section 7.7.2.1 | | application | alto-networkmapfilter+json | Section 7.7.3.1 | | application | alto-costmap+json | Section 7.7.2.2 | | application | alto-costmapfilter+json | Section 7.7.3.2 | | application | alto-endpointprop+json | Section 7.7.4.1 | | application | alto-endpointpropparams+json | Section 7.7.4.1 | | application | alto-endpointcost+json | Section 7.7.5.1 | | application | alto-endpointcostparams+json | Section 7.7.5.1 | | application | alto-error+json | Section 7.4 | +-------------+------------------------------+-----------------+ Table 2: ALTO Protocol Media Types Type name: application Subtype name: This documents requests the registration of multiple subtypes, as listed in Table 2. Required parameters: n/a Optional parameters: n/a Encoding considerations: Encoding considerations are identical to those specified for the 'application/json' media type. See [RFC4627]. Security considerations: Security considerations relating to the generation and consumption of ALTO protocol messages are discussed in Section 12. Interoperability considerations: This document specifies format of conforming messages and the interpretation thereof. Published specification: This document is the specification for these media types; see Table 2for the section documenting each media type. Applications that use this media type: ALTO Servers and ALTO Clients either standalone or embedded within other applications. Alimi, et al. Expires November 21, 2011 [Page 64] Internet-Draft ALTO Protocol May 2011 Additional information: Magic number(s): n/a File extension(s): This document uses the mime type to refer to protocol messages and thus does not require a file extension. Macintosh file type code(s): n/a Person & email address to contact for further information: See "Authors' Addresses" section. Intended usage: COMMON Restrictions on usage: n/a Author: See "Authors' Addresses" section. Change controller: See "Authors' Addresses" section. 11.2. ALTO Cost Type Registry This document requests the creation of an ALTO Cost Type registry to be maintained by IANA. This registry serves two purposes. First, it ensures uniqueness of identifiers referring to ALTO Cost Types. Second, it provides references to particular semantics of allocated Cost Types to be applied by both ALTO Servers and applications utilizing ALTO Clients. New ALTO Cost Types are assigned after Expert Review [RFC5226]. The Expert Reviewer will generally consult the ALTO Working Group or its successor. Expert Review is used to ensure that proper documentation regarding ALTO Cost Type semantics and security considerations has been provided. The provided documentation should be detailed enough to provide guidance to both ALTO Service Providers and applications utilizing ALTO Clients as to how values of the registered ALTO Cost Type should be interpreted. Updates and deletions of ALTO Cost Types follow the same procedure. Registered ALTO Cost Type identifiers MUST conform to the syntatical requirements specified in Section 7.5.4. Identifiers are to be recorded and displayed as ASCII strings. Identifiers prefixed with 'priv:' are reserved for Private Use. Identifiers prefixed with 'exp:' are reserved for Experimental use. Requests to add a new value to the registry MUST include the Alimi, et al. Expires November 21, 2011 [Page 65] Internet-Draft ALTO Protocol May 2011 following information: o Identifier: The name of the desired ALTO Cost Type. o Intended Semantics: ALTO Costs carry with them semantics to guide their usage by ALTO Clients. For example, if a value refers to a measurement, the measurement units must be documented. For proper implementation of the ordinal Cost Mode (e.g., by a third-party service), it should be documented whether higher or lower values of the cost are more preferred. o Security Considerations: ALTO Costs expose information to ALTO Clients. As such, proper usage of a particular Cost Type may require certain information to be exposed by an ALTO Service Provider. Since network information is frequently regarded as proprietary or confidential, ALTO Service Providers should be made aware of the security ramifications related to usage of a Cost Type. This specification requests registration of the identifier 'routingcost'. Semantics for the this Cost Type are documented in Section 5.1.1.1, and security considerations are documented in Section 12.1. 11.3. ALTO Endpoint Property Registry This document requests the creation of an ALTO Endpoint Property registry to be maintained by IANA. This registry serves two purposes. First, it ensures uniqueness of identifiers referring to ALTO Endpoint Properties. Second, it provides references to particular semantics of allocated Endpoint Properties to be applied by both ALTO Servers and applications utilizing ALTO Clients. New ALTO Endpoint Properties are assigned after Expert Review [RFC5226]. The Expert Reviewer will generally consult the ALTO Working Group or its successor. Expert Review is used to ensure that proper documentation regarding ALTO Endpoint Property semantics and security considerations has been provided. The provided documentation should be detailed enough to provide guidance to both ALTO Service Providers and applications utilizing ALTO Clients as to how values of the registered ALTO Endpoint Properties should be interpreted. Updates and deletions of ALTO Endpoint Properties follow the same procedure. Registered ALTO Endpoint Property identifiers MUST conform to the syntatical requirements specified in Section 7.5.5. Identifiers are Alimi, et al. Expires November 21, 2011 [Page 66] Internet-Draft ALTO Protocol May 2011 to be recorded and displayed as ASCII strings. Identifiers prefixed with 'priv:' are reserved for Private Use. Identifiers prefixed with 'exp:' are reserved for Experimental use. Requests to add a new value to the registry MUST include the following information: o Identifier: The name of the desired ALTO Endpoint Property. o Intended Semantics: ALTO Endpoint Properties carry with them semantics to guide their usage by ALTO Clients. For example, if a value refers to a measurement, the measurement units must be documented. For proper implementation of the ordinal Cost Mode (e.g., by a third-party service), it should be documented whether higher or lower values of the cost are more preferred. o Security Considerations: ALTO Endpoint Properties expose information to ALTO Clients. As such, proper usage of a particular Endpoint Properties may require certain information to be exposed by an ALTO Service Provider. Since network information is frequently regarded as proprietary or confidential, ALTO Service Providers should be made aware of the security ramifications related to usage of an Endpoint Property. This specification requests registration of the identifier 'pid'. Semantics for the this Endpoint Property are documented in Section 4.1, and security considerations are documented in Section 12.1. 12. Security Considerations 12.1. Privacy Considerations for ISPs ISPs must be cognizant of the network topology and provisioning information provided through ALTO Interfaces. ISPs should evaluate how much information is revealed and the associated risks. On the one hand, providing overly fine-grained information may make it easier for attackers to infer network topology. In particular, attackers may try to infer details regarding ISPs' operational policies or inter-ISP business relationships by intentionally posting a multitude of selective queries to an ALTO server and analyzing the responses. Such sophisticated attacks may reveal more information than an ISP hosting an ALTO server intends to disclose. On the other hand, revealing overly coarse-grained information may not provide benefits to network efficiency or performance improvements to ALTO Clients. Alimi, et al. Expires November 21, 2011 [Page 67] Internet-Draft ALTO Protocol May 2011 12.2. ALTO Clients Applications using the information must be cognizant of the possibility that the information is malformed or incorrect. Even if an ALTO Server has been properly authenticated by the ALTO Client, the information provided may be malicious because the ALTO Server and its credentials have been compromised (e.g., through malware). Other considerations (e.g., relating to application performance) can be found in Section 6 of [RFC5693]. ALTO Clients should also be cognizant of revealing Network Location Identifiers (IP addresses or fine-grained PIDs) to the ALTO Server, as doing so may allow the ALTO Server to infer communication patterns. One possibility is for the ALTO Client to only rely on Network Map for PIDs and Cost Map amongst PIDs to avoid passing IP addresses of their peers to the ALTO Server. In addition, ALTO clients should be cautious not to unintentionally or indirectly disclose the resource identifier (of which they try to improve the retrieval through ALTO-guidance), e.g., the name/ identifier of a certain video stream in P2P live streaming, to the ALTO server. Note that the ALTO Protocol specified in this document does not explicitly reveal any resource identifier to the ALTO Server. However, for instance, depending on the popularity or other specifics (such as language) of the resource, an ALTO server could potentially deduce information about the desired resource from information such as the Network Locations the client sends as part of its request to the server. 12.3. Authentication, Integrity Protection, and Encryption SSL/TLS can provide encryption of transmitted messages as well as authentication of the ALTO Client and Server. HTTP Basic or Digest authentication can provide authentication of the client (combined with SSL/TLS, it can additionally provide encryption and authentication of the server). An ALTO Server may optionally use authentication (and potentially encryption) to protect ALTO information it provides. This can be achieved by digitally signing a hash of the ALTO information itself and attaching the signature to the ALTO information. There may be special use cases where encryption of ALTO information is desirable. In many cases, however, information sent out by an ALTO Server may be regarded as non-confidential information. ISPs should be cognizant that encryption only protects ALTO information until it is decrypted by the intended ALTO Client. Digital Rights Management (DRM) techniques and legal agreements Alimi, et al. Expires November 21, 2011 [Page 68] Internet-Draft ALTO Protocol May 2011 protecting ALTO information are outside of the scope of this document. 12.4. ALTO Information Redistribution It is possible for applications to redistribute ALTO information to improve scalability. Even with such a distribution scheme, ALTO Clients obtaining ALTO information must be able to validate the received ALTO information to ensure that it was generated by an appropriate ALTO Server. Further, to prevent the ALTO Server from being a target of attack, the verification scheme must not require ALTO Clients to contact the ALTO Server to validate every set of information. Contacting an ALTO server for information validation would also undermine the intended effect of redistribution and is therefore not desirable. Note that the redistribution scheme must additionally handle details such as ensuring ALTO Clients retrieve ALTO information from the correct ALTO Server. See [I-D.gu-alto-redistribution] for further discussion. Details of a particular redistribution scheme are outside the scope of this document. To fulfill these requirements, ALTO Information meant to be redistributable contains a digital signature which includes a hash of the ALTO information signed by the ALTO Server with its private key. The corresponding public key is included in the Server Information resource Section 7.7.1.1, along with the certificate chain to a Root Certificate generated by the ALTO Service Provider. To prevent man- in-the-middle attacks, an ALTO Client SHOULD perform the Server Information resource request over SSL/TLS and verify the server identity according to [RFC6125]. The signature verification algorithm is detailed in Section 8.1.3.3. 12.5. Denial of Service ISPs should be cognizant of the workload at the ALTO Server generated by certain ALTO Queries, such as certain queries to the Map Filtering Service and Ranking Service. In particular, queries which can be generated with low effort but result in expensive workloads at the ALTO Server could be exploited for Denial-of-Service attacks. For instance, a simple ALTO query with n Source Network Locations and m Destination Network Locations can be generated fairly easily but results in the computation of n*m Path Costs between pairs by the ALTO Server (see Section 5.2). One way to limit Denial-of-Service attacks is to employ access control to the ALTO server. Another possible mechanism for an ALTO Server to protect itself against a multitude of computationally expensive bogus requests is to demand Alimi, et al. Expires November 21, 2011 [Page 69] Internet-Draft ALTO Protocol May 2011 that each ALTO Client to solve a computational puzzle first before allocating resources for answering a request (see, e.g., [I-D.jennings-sip-hashcash]). The current specification does not use such computational puzzles, and discussion regarding tradeoffs of such an approach would be needed before including such a technique in the ALTO Protocol. ISPs should also leverage the fact that the the Map Service allows ALTO Servers to pre-generate maps that can be useful to many ALTO Clients. 12.6. ALTO Server Access Control In order to limit access to an ALTO server (e.g., for an ISP to only allow its users to access its ALTO server, or to prevent Denial-of- Service attacks by arbitrary hosts from the Internet), an ALTO server may employ access control policies. Depending on the use-case and scenario, an ALTO server may restrict access to its services more strictly or rather openly (see [I-D.stiemerling-alto-deployments] for a more detailed discussion on this issue). 13. References 13.1. Normative References [IEEE.754.2008] Institute of Electrical and Electronics Engineers, "Standard for Binary Floating-Point Arithmetic", IEEE Standard 754, August 2008. [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. Alimi, et al. Expires November 21, 2011 [Page 70] Internet-Draft ALTO Protocol May 2011 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005. [RFC4627] Crockford, D., "The application/json Media Type for JavaScript Object Notation (JSON)", RFC 4627, July 2006. [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, August 2006. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, October 2008. [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010. [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, March 2011. 13.2. Informative References [BitTorrent] "Bittorrent Protocol Specification v1.0", . [I-D.akonjang-alto-proxidor] Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D. Saucez, "The PROXIDOR Service", draft-akonjang-alto-proxidor-00 (work in progress), March 2009. [I-D.gu-alto-redistribution] Yingjie, G., Alimi, R., and R. Even, "ALTO Information Redistribution", draft-gu-alto-redistribution-03 (work in progress), July 2010. [I-D.ietf-alto-reqs] Previdi, S., Stiemerling, M., Woundy, R., and Y. Yang, "Application-Layer Traffic Optimization (ALTO) Alimi, et al. Expires November 21, 2011 [Page 71] Internet-Draft ALTO Protocol May 2011 Requirements", draft-ietf-alto-reqs-08 (work in progress), March 2011. [I-D.ietf-alto-server-discovery] Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and S. Yongchao, "ALTO Server Discovery", draft-ietf-alto-server-discovery-00 (work in progress), May 2011. [I-D.jennings-sip-hashcash] Jennings, C., "Computational Puzzles for SPAM Reduction in SIP", draft-jennings-sip-hashcash-06 (work in progress), July 2007. [I-D.mrw-nat66] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix Translation", draft-mrw-nat66-16 (work in progress), April 2011. [I-D.p4p-framework] Alimi, R., Pasko, D., Popkin, L., Wang, Y., and Y. Yang, "P4P: Provider Portal for P2P Applications", draft-p4p-framework-00 (work in progress), November 2008. [I-D.saumitra-alto-multi-ps] Das, S., Narayanan, V., and L. Dondeti, "ALTO: A Multi Dimensional Peer Selection Problem", draft-saumitra-alto-multi-ps-00 (work in progress), October 2008. [I-D.saumitra-alto-queryresponse] Das, S. and V. Narayanan, "A Client to Service Query Response Protocol for ALTO", draft-saumitra-alto-queryresponse-00 (work in progress), March 2009. [I-D.shalunov-alto-infoexport] Shalunov, S., Penno, R., and R. Woundy, "ALTO Information Export Service", draft-shalunov-alto-infoexport-00 (work in progress), October 2008. [I-D.stiemerling-alto-deployments] Stiemerling, M. and S. Kiesel, "ALTO Deployment Considerations", draft-stiemerling-alto-deployments-06 (work in progress), January 2011. [I-D.wang-alto-p4p-specification] Wang, Y., Alimi, R., Pasko, D., Popkin, L., and Y. Yang, Alimi, et al. Expires November 21, 2011 [Page 72] Internet-Draft ALTO Protocol May 2011 "P4P Protocol Specification", draft-wang-alto-p4p-specification-00 (work in progress), March 2009. [P4P-SIGCOMM08] Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A. Silberschatz, "P4P: Provider Portal for (P2P) Applications", SIGCOMM 2008, August 2008. [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic Optimization (ALTO) Problem Statement", RFC 5693, October 2009. [RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for IPv4/IPv6 Translation", RFC 6144, April 2011. Appendix A. Acknowledgments Thank you to Jan Seedorf for contributions to the Security Considerations section. We would like to thank Yingjie Gu and Roni Even for helpful input and design concerning ALTO Information redistribution. We would like to thank the following people whose input and involvement was indispensable in achieving this merged proposal: Obi Akonjang (DT Labs/TU Berlin), Saumitra M. Das (Qualcomm Inc.), Syon Ding (China Telecom), Doug Pasko (Verizon), Laird Popkin (Pando Networks), Satish Raghunath (Juniper Networks), Albert Tian (Ericsson/Redback), Yu-Shun Wang (Microsoft), David Zhang (PPLive), Yunfei Zhang (China Mobile). We would also like to thank the following additional people who were Alimi, et al. Expires November 21, 2011 [Page 73] Internet-Draft ALTO Protocol May 2011 involved in the projects that contributed to this merged document: Alex Gerber (AT&T), Chris Griffiths (Comcast), Ramit Hora (Pando Networks), Arvind Krishnamurthy (University of Washington), Marty Lafferty (DCIA), Erran Li (Bell Labs), Jin Li (Microsoft), Y. Grace Liu (IBM Watson), Jason Livingood (Comcast), Michael Merritt (AT&T), Ingmar Poese (DT Labs/TU Berlin), James Royalty (Pando Networks), Damien Saucez (UCL) Thomas Scholl (AT&T), Emilio Sepulveda (Telefonica), Avi Silberschatz (Yale University), Hassan Sipra (Bell Canada), Georgios Smaragdakis (DT Labs/TU Berlin), Haibin Song (Huawei), Oliver Spatscheck (AT&T), See-Mong Tang (Microsoft), Jia Wang (AT&T), Hao Wang (Yale University), Ye Wang (Yale University), Haiyong Xie (Yale University). Appendix B. Authors [[CmtAuthors: RFC Editor: Please move information in this section to the Authors' Addresses section at publication time.]] Stefano Previdi Cisco Email: sprevidi@cisco.com Stanislav Shalunov BitTorrent Email: shalunov@bittorrent.com Richard Woundy Comcast Richard_Woundy@cable.comcast.com Authors' Addresses Richard Alimi (editor) Google 1600 Amphitheatre Parkway Mountain View CA USA Email: ralimi@google.com Alimi, et al. Expires November 21, 2011 [Page 74] Internet-Draft ALTO Protocol May 2011 Reinaldo Penno (editor) Juniper Networks 1194 N Mathilda Avenue Sunnyvale CA USA Email: rpenno@juniper.net Y. Richard Yang (editor) Yale University 51 Prospect St New Haven CT USA Email: yry@cs.yale.edu Alimi, et al. Expires November 21, 2011 [Page 75]