ALTO Extension: Entity Property Maps
draft-ietf-alto-unified-props-new-17

Document Type Active Internet-Draft (alto WG)
Authors Wendy Roome  , Sabine Randriamasy  , Y. Yang  , Jingxuan Zhang  , Kai Gao 
Last updated 2021-06-15 (latest revision 2021-04-16)
Replaces draft-roome-alto-unified-props-new
Stream Internet Engineering Task Force (IETF)
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Stream WG state Submitted to IESG for Publication (wg milestone: Jul 2020 - Submit endpoint prop... )
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Send notices to Vijay Gurbani <vijay.gurbani@gmail.com>
ALTO WG                                                         W. Roome
Internet-Draft                                            S. Randriamasy
Intended status: Standards Track                         Nokia Bell Labs
Expires: 18 October 2021                                         Y. Yang
                                                         Yale University
                                                                J. Zhang
                                                       Tongji University
                                                                  K. Gao
                                                      Sichuan University
                                                           16 April 2021

                  ALTO Extension: Entity Property Maps
                  draft-ietf-alto-unified-props-new-17

Abstract

   This document extends the base Application-Layer Traffic Optimization
   (ALTO) Protocol by generalizing the concept of "endpoint properties"
   as applied to endpoints as defined by IP addresses to endpoints
   defined by a wider set of objects.  Further, these properties are
   presented as maps, similar to the network and cost maps in the base
   ALTO protocol.  The protocol is extended in two major directions.
   First, from endpoints restricted to IP addresses to entities covering
   a wider and extensible set of objects; second, from properties on
   specific endpoints to entire entity property maps.  These extensions
   introduce additional features allowing entities and property values
   to be specific to a given information resource.  This is made
   possible by a generic and flexible design of entity and property
   types.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on 18 October 2021.

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Copyright Notice

   Copyright (c) 2021 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 (https://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 Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   6
   3.  Basic Features of the Entity Property Map Extension . . . . .   7
     3.1.  Entity  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Entity Domain . . . . . . . . . . . . . . . . . . . . . .   8
       3.2.1.  Entity Domain Type  . . . . . . . . . . . . . . . . .   8
       3.2.2.  Entity Domain Name  . . . . . . . . . . . . . . . . .   9
     3.3.  Entity Property Type  . . . . . . . . . . . . . . . . . .   9
     3.4.  New information resource and media type: ALTO Property
           Map . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   4.  Advanced Features of the Entity Property Map Extension  . . .  11
     4.1.  Entity Identifier and Entity Domain Name  . . . . . . . .  11
     4.2.  Resource-Specific Entity Domain Name  . . . . . . . . . .  11
     4.3.  Resource-Specific Entity Property Value . . . . . . . . .  12
     4.4.  Entity Hierarchy and Property Inheritance . . . . . . . .  13
       4.4.1.  Entity Hierarchy  . . . . . . . . . . . . . . . . . .  14
       4.4.2.  Property Inheritance  . . . . . . . . . . . . . . . .  14
       4.4.3.  Property Value Unicity  . . . . . . . . . . . . . . .  14
     4.5.  Supported Properties on Entity Domains in Property Map
           Capabilities  . . . . . . . . . . . . . . . . . . . . . .  15
     4.6.  Defining Information Resource for Resource-Specific Entity
           Domains . . . . . . . . . . . . . . . . . . . . . . . . .  16
       4.6.1.  Defining Information Resource and its Media Type  . .  17
       4.6.2.  Examples of Defining Information Resources and Their
               Media Types . . . . . . . . . . . . . . . . . . . . .  18
     4.7.  Defining Information Resource for Resource-Specific
           Property Values . . . . . . . . . . . . . . . . . . . . .  18
   5.  Protocol Specification: Basic Data Types  . . . . . . . . . .  19
     5.1.  Entity Domain . . . . . . . . . . . . . . . . . . . . . .  19
       5.1.1.  Entity Domain Type  . . . . . . . . . . . . . . . . .  19
       5.1.2.  Entity Domain Name  . . . . . . . . . . . . . . . . .  20

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       5.1.3.  Entity Identifier . . . . . . . . . . . . . . . . . .  22
       5.1.4.  Hierarchy and Inheritance . . . . . . . . . . . . . .  22
     5.2.  Entity Property . . . . . . . . . . . . . . . . . . . . .  23
       5.2.1.  Entity Property Type  . . . . . . . . . . . . . . . .  23
       5.2.2.  Entity Property Name  . . . . . . . . . . . . . . . .  24
       5.2.3.  Format for Entity Property Value  . . . . . . . . . .  24
   6.  Entity Domain Types Defined in this Document  . . . . . . . .  24
     6.1.  Internet Address Domain Types . . . . . . . . . . . . . .  25
       6.1.1.  Entity Domain Type: IPv4  . . . . . . . . . . . . . .  25
       6.1.2.  Entity Domain Type: IPv6  . . . . . . . . . . . . . .  25
       6.1.3.  Hierarchy and Inheritance of Internet Address
               Domains . . . . . . . . . . . . . . . . . . . . . . .  26
       6.1.4.  Defining Information Resource Media Type for domain
               types IPv4 and IPv6 . . . . . . . . . . . . . . . . .  27
     6.2.  Entity Domain Type: PID . . . . . . . . . . . . . . . . .  27
       6.2.1.  Entity Domain Type Identifier . . . . . . . . . . . .  27
       6.2.2.  Domain-Specific Entity Identifiers  . . . . . . . . .  27
       6.2.3.  Hierarchy and Inheritance . . . . . . . . . . . . . .  28
       6.2.4.  Defining Information Resource Media Type for Domain
               Type PID  . . . . . . . . . . . . . . . . . . . . . .  28
       6.2.5.  Relationship To Internet Addresses Domains  . . . . .  28
     6.3.  Internet Address Properties vs. PID Properties  . . . . .  28
   7.  Property Map  . . . . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  29
     7.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  29
     7.3.  Accept Input Parameters . . . . . . . . . . . . . . . . .  29
     7.4.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  29
     7.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     7.6.  Response  . . . . . . . . . . . . . . . . . . . . . . . .  30
   8.  Filtered Property Map . . . . . . . . . . . . . . . . . . . .  31
     8.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  31
     8.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  31
     8.3.  Accept Input Parameters . . . . . . . . . . . . . . . . .  31
     8.4.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  32
     8.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . .  32
     8.6.  Filtered Property Map Response  . . . . . . . . . . . . .  32
     8.7.  Entity property type defined in this document . . . . . .  34
       8.7.1.  Entity Property Type: pid . . . . . . . . . . . . . .  34
   9.  Impact on Legacy ALTO Servers and ALTO Clients  . . . . . . .  34
     9.1.  Impact on Endpoint Property Service . . . . . . . . . . .  35
     9.2.  Impact on Resource-Specific Properties  . . . . . . . . .  35
     9.3.  Impact on Other Properties  . . . . . . . . . . . . . . .  35
   10. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  35
     10.1.  Network Map  . . . . . . . . . . . . . . . . . . . . . .  35
     10.2.  Property Definitions . . . . . . . . . . . . . . . . . .  36
     10.3.  Information Resource Directory (IRD) . . . . . . . . . .  37
     10.4.  Full Property Map Example  . . . . . . . . . . . . . . .  39
     10.5.  Filtered Property Map Example #1 . . . . . . . . . . . .  40

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     10.6.  Filtered Property Map Example #2 . . . . . . . . . . . .  41
     10.7.  Filtered Property Map Example #3 . . . . . . . . . . . .  43
     10.8.  Filtered Property Map Example #4 . . . . . . . . . . . .  44
     10.9.  Filtered Property Map for ANEs Example #5  . . . . . . .  45
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  46
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  48
     12.1.  application/alto-* Media Types . . . . . . . . . . . . .  48
     12.2.  ALTO Entity Domain Type Registry . . . . . . . . . . . .  50
       12.2.1.  Consistency Procedure between ALTO Address Type
               Registry and ALTO Entity Domain Type Registry . . . .  51
       12.2.2.  ALTO Entity Domain Type Registration Process . . . .  52
     12.3.  ALTO Entity Property Type Registry . . . . . . . . . . .  54
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  55
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  55
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  55
     14.2.  Informative References . . . . . . . . . . . . . . . . .  56
   Appendix A.  Features introduced with the Entity Property Maps
           extension . . . . . . . . . . . . . . . . . . . . . . . .  57
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  58

1.  Introduction

   The ALTO protocol [RFC7285] introduces the concept of "properties"
   attached to "endpoint addresses", and defines the Endpoint Property
   Service (EPS) to allow ALTO clients to retrieve those properties.
   While useful, the EPS, as defined in [RFC7285], has at least three
   limitations.

   First, the EPS allows properties to be associated with only endpoints
   that are identified by individual communication addresses like IPv4
   and IPv6 addresses.  It is reasonable to think that collections of
   endpoints, as defined by CIDRs [RFC4632] or PIDs, may also have
   properties.  Furthermore, recent ALTO use cases show that properties
   of entities such as network flows [RFC7011] and routing elements
   [RFC7921] are also useful.  Such cases are documented in
   [I-D.gao-alto-fcs].  The current EPS however is restricted to
   individual endpoints and cannot be applied to those entities.

   Second, the EPS only allows endpoints identified by global
   communication addresses.  However, an endpoint address may be a local
   IP address or an anycast IP address that may not be globally unique.
   Additionally, an entity such as a PID may have an identifier that is
   not globally unique.  That is, a same PID identifier may be used in
   multiple network maps, while in each network map, this PID identifier
   points to a different set of addresses.  For example, PID "mypid10"
   may be defined in "netmap1" and "netmap2" while in each network map,
   "mypid10" covers a different set of addresses.

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   Third, the EPS is only defined as a POST-mode service.  Clients must
   request the properties for an explicit set of endpoint addresses.  By
   contrast, [RFC7285] defines a GET-mode cost map resource which
   returns all available costs, so a client can get a full set of costs
   once, and then process cost lookups without querying the ALTO server.
   [RFC7285] does not define a similar service for endpoint properties.
   At first, a map of endpoint properties might seem impractical,
   because it could require enumerating the property value for every
   possible endpoint.  However, in practice, it is highly unlikely that
   properties will be defined for every endpoint address.  It is much
   more likely that properties may be defined for only a subset of
   endpoint addresses, and the specification of properties uses an
   aggregation representation to allow enumeration.  This is
   particularly true if blocks of endpoint addresses with a common
   prefix (e.g., a CIDR) have the same value for a property.  Entities
   in other domains may very well allow aggregated representation and
   hence be enumerable as well.

   To address the three limitations, this document specifies a protocol
   extension for defining and retrieving ALTO properties:

   *  The first limitation is addressed by introducing a generic concept
      called ALTO Entity, which generalizes an endpoint and may
      represent a PID, a network element, a cell in a cellular network,
      an abstracted network element as defined in
      [I-D.ietf-alto-path-vector], or other physical or logical objects
      involved in a network topology.  Each entity is included in a
      collection called an ALTO Entity Domain.  Since each ALTO Entity
      Domain includes only one type of entities, each Entity Domain can
      be classified by the type of entities in it.

   *  The second limitation is addressed by using resource-specific
      entity domains.  A resource-specific entity domain contains
      entities that are defined and identified with respect to a given
      ALTO information resource, which provides scoping.  For example,
      an entity domain containing PIDs is identified with respect to the
      network map in which these PIDs are defined.  Likewise, an entity
      domain containing local IP addresses may be defined with respect
      to a local network map.

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   *  The third limitation is addressed by defining two new types of
      ALTO information resources: Property Map, detailed in Section 7
      and Filtered Property Map, detailed in Section 8.  The former is a
      GET-mode resource that returns the property values for all
      entities in one or more entity domains, and is analogous to a
      network map or a cost map in [RFC7285].  The latter is a POST-mode
      resource that returns the values for sets of properties and
      entities requested by the client, and is analogous to a filtered
      network map or a filtered cost map.

   The protocol extension defined in this document is augmentable.  New
   entity domain types can be defined without revising the specification
   defined in this document.  Similarly, new cost metrics and new
   endpoint properties can be defined in other documents without
   revising the protocol specification defined in [RFC7285].

1.1.  Terminology

   This document uses the following terms and abbreviations, that will
   be further defined in the document.  While this document introduces
   the feature "entity property map", it will use both the term
   "property map" and "entity property map" to refer to this feature.

   *  Transaction: A request/response exchange between an ALTO client
      and an ALTO server.

   *  Client: When used with a capital "C", this term refers to an ALTO
      client.  Note that expressions "ALTO client" and "ALTO Client" are
      equivalent.

   *  Server: When used with a capital "S", this term refers to an ALTO
      server.  Note that expressions "ALTO server" and "ALTO Server" are
      equivalent.

   *  EPM: An abbreviation for entity property map.

   *  FPM: An abbreviation for filtered property map.

   *  EPS: An abbreviation for Endpoint Property Service.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.  When the words appear in lower case, they
   are to be interpreted with their natural language meanings.

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3.  Basic Features of the Entity Property Map Extension

   This section gives a high-level overview of the basic features
   involved in ALTO Entity Property Maps.  It assumes the reader is
   familiar with the ALTO protocol [RFC7285].  The purpose of this
   extension is to allow conveying properties on objects that extend
   ALTO Endpoints and are called ALTO Entities, or entities for short.

   The features introduced in this section can be used as standalone.
   However, in some cases, these features may depend on particular
   information resources and need to be defined with respect to them.
   To this end, Section 4 introduces additional features that extend the
   ones presented in the present section.

   The Entity Property Maps extension described in this document
   introduces a number of features that are summarized in Appendix A,
   where Table 4 lists the features and references the sections in this
   document that give a high-level and normative description thereof.

3.1.  Entity

   The concept of an ALTO Entity generalizes the concept of an ALTO
   Endpoint defined in Section 2.1 of [RFC7285].  An entity is an object
   that can be an endpoint that is defined by its network address, but
   can also be an object that has a defined mapping to a set of one or
   more network addresses or an object that is not even related to any
   network address.  Thus, whereas all endpoints are entities, not all
   entities are endpoints.

   Examples of entities are:

   *  an ALTO endpoint, defined in [RFC7285], that represents an
      application or a host identified by a communication address (e.g.,
      an IPv4 or IPv6 address) in a network,

   *  a PID, defined in [RFC7285], that has a provider defined human-
      readable identifier specified by an ALTO network map, which maps a
      PID to a set of IPv4 and IPv6 addresses,

   *  an autonomous system (AS), that has an AS number (ASN) as its
      identifier and maps to a set of IPv4 and IPv6 addresses,

   *  a country with a code as specified in [ISO3166-1], to which
      applications such as CDN providers associate properties and
      capabilities,

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   *  a TCP/IP network flow, that is identified by a TCP/IP 5-Tuple
      specifying its source and destination addresses and port numbers
      and the utilized protocol,

   *  a routing element, that is specified in [RFC7921] and is
      associated with routing capabilities information,

   *  an abstract network element, that represents an abstraction of a
      network part such as a router, one or more links, a network domain
      or their aggregation.

3.2.  Entity Domain

   An entity domain defines a set of entities of the same semantic type.
   An entity domain is characterized by its type and identified by its
   name.

   In this document, an entity is owned by exactly one entity domain
   name.  An entity identifier points to exactly one entity.  If two
   entities in two different entity domains refer to the same physical
   or logical object, they are treated as different entities.  For
   example, if an end host has both an IPv4 and an IPv6 address, these
   two addresses will be treated as two entities, defined respectively
   in the "ipv4" and "ipv6" entity domains.

3.2.1.  Entity Domain Type

   The type of an entity domain type defines the semantics of a type of
   entity.  Entity domain types can be defined in different documents.
   For example: the present document defines entity domain types "ipv4",
   "ipv6" and "pid" in sections Section 6.1 and Section 6.2.  The entity
   domain type "ane", that defines Abstract Network Elements (ANEs), is
   introduced in [I-D.ietf-alto-path-vector].  The entity domain type
   that defines country codes is introduced in
   [I-D.ietf-alto-cdni-request-routing-alto].  An entity domain type
   MUST be registered at the IANA, as specified in section
   Section 12.2.2 and similarly to an ALTO address type.

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3.2.2.  Entity Domain Name

   The name of an entity domain is defined in the scope of an ALTO
   server.  An entity domain name can sometimes be identical to the name
   of its relevant entity domain type.  This is the case when the
   entities of a domain have an identifier that points to the same
   object throughout all the information resources of the Server that
   provide entity properties for this domain.  For example, a domain of
   type "ipv4" containing entities identified by a public IPv4 address
   can be named "ipv4" because its entities are uniquely identified by
   all the Server resources.

   In some cases the name of an entity domain needs to be different from
   simply its entity domain type.  Indeed, for some domain types,
   entities are defined relative to a given information resource.  This
   is the case for entities of domain type "pid".  A PID is defined
   relative to a network map.  For example: an entity "mypid10" of
   domain type "pid" may be defined in a given network map and be
   undefined in other network maps.  Or "mypid10" may even be defined in
   two different network maps and map, in each of these network maps, to
   a different set of endpoint addresses.  In this case, naming an
   entity domain only by its type "pid" does not guarantee that its set
   of entities is owned by exactly one entity domain.

   Section 4.2 and Section 5.1.2 of this document describe how a domain
   is uniquely identified, across the ALTO Server, by a name that
   associates the domain type and the related information resource.

3.3.  Entity Property Type

   An entity property defines a property of an entity.  This is similar
   to the endpoint property defined in Section 7.1 of [RFC7285].  An
   entity property can convey either network-aware or network-agnostic
   information.  Similarly to an entity domain, an entity property is
   characterized by its type and identified by its name.  An entity
   property type MUST be registered at the IANA, as specified in section
   Section 12.3.

   Below are some examples with real and fictitious entity domain and
   property names:

   *  an entity in the "ipv4" domain type may have a property whose
      value is an Autonomous System (AS) number indicating the AS that
      owns this IPv4 address and another property named "countrycode"
      indicating a country code mapping to this address,

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   *  an entity identified by its country code in the entity domain type
      "countrycode", defined in
      [I-D.ietf-alto-cdni-request-routing-alto] may have a property
      indicating what delivery protocol is used by a CDN,

   *  an entity in the "netmap1.pid" domain may have a property that
      indicates the central geographical location of the endpoints it
      includes.

   It should be noted that some identifiers may be used for both an
   entity domain type and a property type.  For example:

   *  the identifier "countrycode" may point to both the entity domain
      type "countrycode" and the fictitious property type "countrycode".

   *  the identifier "pid" may point to both the entity domain type
      "pid" and the property type "pid".

   Likewise, a same identifier may point to both a domain name and a
   property name.  For example: the identifier "netmap10.pid" may point
   to either the domain defined by the PIDs of network map "netmap10" or
   to a property that returns, for an entity defined by its IPv4
   address, the PID of netmap10 that contains this entity.  Such cases
   will be further explained in Section 4.

3.4.  New information resource and media type: ALTO Property Map

   This document introduces a new ALTO information resource named
   Property Map. An ALTO property map provides a set of properties on
   one or more sets of entities.  A property may apply to different
   entity domain types and names.  For example, an ALTO property map may
   define the "ASN" property for both "ipv4" and "ipv6" entity domains.

   The present extension also introduces a new media type.

   This document uses the same definition of an information resource as
   Section 9.1 of [RFC7285].  ALTO uses media types to uniquely indicate
   the data format used to encode the content to be transmitted between
   an ALTO server and an ALTO client in the HTTP entity body.  In the
   present case, an ALTO property map resource is defined by the media
   type "application/alto-propmap+json".

   A Property Map can be queried as a GET-mode resource, thus conveying
   all properties on all entities indicated in its capabilities.  It can
   also be queried as a POST-mode resource, thus conveying a selection
   of properties on a selection of entities.

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4.  Advanced Features of the Entity Property Map Extension

   This section gives a high-level overview of the advanced features
   involved in ALTO Entity Property Maps.  Most of these features are
   defined to extend the ones defined in Section 3.

4.1.  Entity Identifier and Entity Domain Name

   In [RFC7285], an endpoint has an identifier that is explicitly
   associated with the "ipv4" or "ipv6" address domain.  Examples are
   "ipv4:192.0.2.14" and "ipv6:2001:db8::12".

   In this document, an entity must be owned by exactly one entity
   domain name and an entity identifier must point to exactly one
   entity.  To ensure this, an entity identifier is explicitly attached
   to the name of its entity domain and an entity domain type
   characterizes the semantics and identifier format of its entities.

   The encoding format of an entity identifier is further specified in
   Section 5.1.3 of this document.

   For instance:

   *  if an entity is an endpoint with example routable IPv4 address
      "192.0.2.14", its identifier is associated with domain name "ipv4"
      and is "ipv4:192.0.2.14",

   *  if an entity is a PID named "mypid10" in network map resource
      "netmap2", its identifier is associated with domain name
      "netmap2.pid" and is "netmap2.pid:mypid10".

4.2.  Resource-Specific Entity Domain Name

   Some entities are defined and identified uniquely and globally.  This
   is the case for instance when entities are endpoints that are
   identified by a routable IPv4 or IPv6 address.  The entity domain for
   such entities can be globally defined and named "ipv4" or "ipv6".
   Those entity domains are called resource-agnostic entity domains in
   this document, as they are not associated with any specific ALTO
   information resources.

   Some other entities and entity types are only defined relatively to a
   given information resource.  This is the case for entities of domain
   type "pid", that can only be understood with respect to the network
   map where they are defined.  For example, a PID named "mypid10" may
   be defined to represent a set S1 of IP addresses in a network map
   resource named "netmap1".  Another network map "netmap2" may use the
   same name "mypid10" and define it to represent another set S2 of IP

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   addresses.  The identifier "pid:mypid10" may thus point to different
   objects because the information on the originating information
   resource is lost.

   To solve this ambiguity, the present extension introduces the concept
   of resources-specific entity domain.  This concept applies to domain
   types where entities are defined relatively to a given information
   resource.  It can also apply to entity domains that are defined
   locally, such as local networks of objects identified with a local
   IPv4 address.

   In such cases, an entity domain type is explicitly associated with an
   identifier of the information resource where these entities are
   defined.  Such an information resource is referred to as the
   "specific information resource".  Using a resource-aware entity
   domain name, an ALTO property map can unambiguously identify distinct
   entity domains of the same type, on which entity properties may be
   queried.  Examples of resource-specific entity domain names may look
   like: "netmap1.pid" or "netmap2.pid".  Thus, a name association such
   as "netmap1.pid:mypid10" and "netmap2.pid:mypid10" allows to
   distinguish the two abovementioned PIDs that are both named "mypid10"
   but in two different resources, "netmap1" and "netmap2".

   An information resource is defined in the scope of an ALTO Server and
   so is an entity domain name.  The format of a resource-specific
   entity domain name is further specified in Section 5.1.2.

4.3.  Resource-Specific Entity Property Value

   Like entity domains, some types of properties are defined relatively
   to an information resource.  That is, an entity may have a property
   of a given type, whose values are associated to different information
   resources.

   For example, suppose entity "192.0.2.34" defined in the "ipv4" domain
   has a property of type "pid", whose value is the PID to which address
   "192.0.2.34" is attached in a network map.  The mapping of network
   addresses to PIDs is specific to a network map and probably different
   from one network map resource to another one.  Thus, if a property
   "pid" is defined for entity "192.0.2.34" in two different network
   maps "netmap1" and "netmap2", the value for this property will likely
   be a different value in "netmap1" and "netmap2".

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   To support information resource dependent property values, this
   document uses the same approach as in Section 10.8.1 of [RFC7285]
   entitled "Resource-Specific Endpoint Properties".  When a property
   value depends on a given information resource, the name of this
   property MUST be explicitly associated with the information resource
   that defines it.

   For example, the property "pid" queried on entity "ipv4:192.0.2.34"
   and defined in both "netmap1" and "netmap2", can be named
   "netmap1.pid" and "netmap2.pid".  This allows a Client to get a
   property of the same type but defined in different information
   resources with a single query.  Specifications on the property name
   format are provided in Section 5.2.

4.4.  Entity Hierarchy and Property Inheritance

   For some domain types, entities can be grouped in a set and be
   defined by the identifier of this set.  This is the case for domain
   types "ipv4" and "ipv6", where individual Internet addresses can be
   grouped in blocks.  When a same property value applies to a whole
   set, a Server can define a property for the identifier of this set
   instead of enumerating all the entities and their properties.  This
   allows a substantial reduction of transmission payload both for the
   Server and the Client.  For example, all the entities included in the
   set defined by the address block "ipv6:2001:db8::1/64" share the same
   properties and values defined for this block.

   Additionally, entity sets sometimes are related by inclusion,
   hierarchy or other relations.  This allows defining inheritance rules
   for entity properties that propagate properties among related entity
   sets.  The Server and the Client can use these inheritance rules for
   further payload savings.  Entity hierarchy and property inheritance
   rules are specified in the documents that define the applicable
   domain types.  The present document defines these rules for the
   "ipv4" and "ipv6" domain types.

   This document introduces, for applicable domain types, "Entity
   Property Inheritance rules", with the following concepts: Entity
   Hierarchy, Property Inheritance and Property Value Unicity.  A
   detailed specification of entity hierarchy and property inheritance
   rules is provided in Section 5.1.4.

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4.4.1.  Entity Hierarchy

   An entity domain may allow using a single identifier to identify a
   set of individual entities.  For example, a CIDR block can be used to
   identify a set of IPv4 or IPv6 entities.  A CIDR block is called a
   hierarchical entity identifier, as it can reflect inclusion relations
   among entity sets.  That is, in an entity hierarchy, "supersets" are
   defined at upper levels and include "subsets" defined at lower
   levels."  For example, the CIDR "ipv4:192.0.1.0/24" includes all the
   individual IPv4 entities identified by the CIDR "ipv4:192.0.1.0/26".

4.4.2.  Property Inheritance

   A property may be defined for a hierarchical entity identifier, while
   it may be undefined for individual entities covered by this
   identifier.  In this case, these individual entities inherit the
   property value defined for the identifier that covers them.  For
   example, suppose a property map defines a property P for which it
   assigns value V1 only for the hierarchical entity identifier
   "ipv4:192.0.1.0/24" but not for individual entities in this block.
   Suppose also that inheritance rules are specified for CIDR blocks in
   the "ipv4" domain type.  When receiving this property map, a Client
   can infer that entity "ipv4:192.0.1.1" inherits the property value V1
   of block "ipv4:192.0.1.0/24" because the address "ipv4:192.0.1.1" is
   included in the CIDR block "ipv4:192.0.1.0/24".

   Property value inheritance rules also apply among entity sets.  A
   property map may define values for an entity set belonging to a
   hierarchy but not for "subsets" that are covered by this set
   identifier.  In this case, inheritance rules must specify how
   entities in "subsets" inherit property values from their "superset".
   For instance, if a property P is defined only for the entity set
   identified by address block "ipv4:192.0.1.0/24", the entity set
   identified by "ipv4:192.0.1.0/30" and thus included in the former
   set, may inherit the property P value from set "ipv4:192.0.1.0/24".

4.4.3.  Property Value Unicity

   The inheritance rules must ensure that an entity belonging to a
   hierarchical set of entities inherits no more than one property
   value, for the sake of consistency.  Indeed, a property map may
   define a property on a hierarchy of entity sets that inherit property
   values from one or more supersets (located at upper levels).  On the
   other hand, a property value, defined on a subset (located at a lower
   level) may be different from the value defined on a superset.  In
   such a case, subsets may potentially end up with different property
   values.  This may be the case for address blocs with increasing
   prefix length, on which a property value gets increasingly accurate

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   and thus may differ.  For example, a fictitious property such as
   "geo-location" or "average transfer volume" may be defined at a
   progressively finer grain for lower level subsets of entities,
   defined with progressively longer CIDR prefixes.  It seems more
   interesting to have property values of progressively higher accuracy.
   A unicity rule, applied to the entity domain type must specify an
   arbitration rule among the different property values for an entity.
   An example illustrating the need for such rules is provided in
   Section 6.1.3.

4.5.  Supported Properties on Entity Domains in Property Map
      Capabilities

   A property type is not necessarily applicable to any domain type, or
   an ALTO Server may choose not to provide a property on all applicable
   domains.  For instance, a property type reflecting link bandwidth is
   likely not defined on entities of a domain of type "country-code".
   Therefore an ALTO server providing Property Maps needs to specify the
   properties that can be queried on the different entity domains it
   supports.

   This document explains how the Information Resources Directory (IRD)
   capabilities of a Property Map resource unambiguously expose what
   properties a Client can query on a given entity domain.

   *  a field named "mappings" lists the names of the entity domains
      supported by the Property Map,

   *  for each listed entity domain, a list of the names of the
      applicable properties is provided.

   An example is provided in Section 10.3.  The "mappings" field
   associates entity domains and properties that can be resource-
   agnostic or resource-specific.  This allows a Client to formulate
   compact and unambiguous entity property queries, possibly relating to
   one or more information resources.  In particular:

   *  it avoids a Client to query a property on entity domains on which
      it is not defined,

   *  it allows a Client to query, for an entity E, values for a
      property P that are defined in several information resources,

   *  it allows a Client to query a property P on entities that are
      defined in several information resources.

   Further specifications are provided in Section 7.4.

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4.6.  Defining Information Resource for Resource-Specific Entity Domains

   A Client willing to query properties on entities belonging to a
   domain needs to know how to retrieve these entities.  To this end,
   the Client can look up the "mappings" field exposed in IRD
   capabilities of a property map, see Section 4.5.  This field, in its
   keys, exposes all the entity domains supported by the property map.
   The syntax of the entity domain identifier specified in Section 5.1.2
   allows the client to infer whether the entity domain is resource-
   specific or not.  The Client can extract, if applicable, the
   identifier of the specific resource, query the resource and retrieve
   the entities.  For example:

   *  an entity domain named "netmap1.ipv4" includes the IPv4 addresses
      that appear in the "ipv4" field of the endpoint address group of
      each PID in the network map "netmap1", and that cannot be
      recognized outside "netmap1" because, for instance, these are
      local non-routable addresses,

   *  an entity domain named "netmap1.pid" includes the PIDs listed in
      network map "netmap1".

   *  an entity domain named "ipv4" is resource-agnostic and covers all
      the routable IPv4 addresses.

   Besides, it is also necessary to inform a Client about which
   associations of specific resources and entity domain types are
   allowed, because it is not possible to prevent a Server from exposing
   inappropriate associations.  An informed Client will just ignore
   inappropriate associations exposed by a Server and avoid error-prone
   transactions with the Server.

   For example, the association "costmap3.pid" is not allowed for the
   following reason: although a cost map exposes PID identifiers, it
   does not define the set of addresses included in this PID.  Neither
   does a cost map list all the PIDs on which properties can be queried,
   because a cost map only exposes PID pairs on which a queried cost
   type is defined.  Therefore, the resource "costmap3" does not enable
   a Client to extract information on the existing PID entities or on
   the addresses they contain.

   Instead, the cost map uses a network map, where all the PIDs used in
   a cost map are defined together with the addresses contained by the
   PIDs.  This network map is qualified in this document as the Defining
   Information Resource for the entity domain of type "pid" and this
   concept is explained in Section 4.6.1.

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4.6.1.  Defining Information Resource and its Media Type

   For the reasons explained in the previous section, this document
   introduces the concept of "Defining Information Resource and its
   Media Type".

   A defining information resource for an entity domain D is the
   information resource where entities of D are defined.  That is, all
   the information on the entities of D can be retrieved in this
   resource.  This concept applies to resource-specific entity domains.
   This is useful for entity domain types that are by essence domain-
   specific, such as "pid" and "ane" domain types.  It is also useful
   for resource-specific entity domains constructed from resource-
   agnostic domain types, such as network map specific domains of local
   IPv4 addresses.

   The defining information resource of a resource-specific entity
   domain D is unique and has the following specificities:

   *  it has an entry in the IRD,

   *  it defines the entities of D,

   *  it does not use another information resource that defines these
      entities,

   *  it defines and exposes entity identifiers that are all persistent.

   *  its media type is unique and equal to the one that is specified
      for the defining information resource of an entity domain type.

   A fundamental attribute of a defining information resource is its
   media type.  There is a unique association between an entity domain
   type and the media type of its defining information resource.  When
   an entity domain type allows associations with defining information
   resources, the media type of the potential defining information
   resource MUST be specified:

   *  in the document that defines this entity domain type,

   *  in the IANA ALTO Entity Domain Type Registry and related
      information.

   When the Client wants to use a resource-specific entity domain, it
   needs to be cognizant of the media-type of its defining information
   resource.  If the Server exposes a resource-specific entity domain
   with a non-compliant media type for the defining resource, the Client
   MUST ignore the entities from that entity domain to avoid errors.

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4.6.2.  Examples of Defining Information Resources and Their Media Types

   Here are examples of defining information resource types and their
   media types associated to different entity domain types.

   *  For entity domain type "pid": the media type of the specific
      resource is "application/alto-networkmap+json", because PIDs are
      defined in network map resources.

   *  For entity domain types "ipv4" and "ipv6": the media type of the
      specific resource is "application/alto-networkmap+json", because
      IPv4 and IPv6 addresses covered by the Server are defined in
      network map resources.

   *  For entities of domain type "ane": [I-D.ietf-alto-path-vector]
      defines entities named "ANE", where ANE stands for Abstracted
      Network Element, and the entity domain type "ane".  An ANE may
      have a persistent identifier, say, "entity-4", that is provided by
      the Server as a value of the "persistent-entity-id" property of
      this ANE.  Further properties may then be queried on an ANE by
      using its persistent entity ID.  These properties are available
      from a persistent property map, that defines properties on a
      specific "ane" domain.  Together with the persistent identifier,
      the Server also provides the property map resource identifier
      where the "ane" domain containing "entity-4" is defined.  The
      definition of the "ane" entity domain containing "entity-4" is
      thus specific to the property map.  Therefore, for entities of
      domain type "ane" that have a persitent identifier, the media type
      of the specific information resource is "application/alto-
      propmap+json".

   *  Last, the entity domain types "asn" and "countrycode" defined in
      [I-D.ietf-alto-cdni-request-routing-alto] do not have a defining
      information resource.  Indeed, the entity identifiers in these two
      entity domain types are already standardized in documents that the
      Client can use.

4.7.  Defining Information Resource for Resource-Specific Property
      Values

   As explained in Section 4.3, a property type may take values that are
   resource-specific.  This is the case for property type "pid", whose
   values are by essence defined relatively to a specific network map.
   That is, the PID value returned for an IPv4 address is specific to
   the network map defining this PID and may differ from one network map
   to another one.

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   Another example is provided in
   [I-D.ietf-alto-cdni-request-routing-alto] that defines property type
   "cdni-capabilities".  The value of this property is specific to a
   CDNI Advertisement resource, that provides a list of CDNI
   capabilities.  The property is provided for entity domain types
   "ipv4", "ipv6", "asn" and "countrycode".  A CDNI Advertisement
   resource does however not define PID values for IPv4 addresses while
   a network map does not define CDNI capabilities for IPv4 addresses.

   Similarly to resource-specific entity domains, the Client needs to be
   cognizant of appropriate associations of information resource and
   property types.  Therefore, when specifying and registering a
   property type whose values are resource-specific, the media type of
   its defining information resource needs to be specified.  For
   example:

   *  The media type of the defining information resource for property
      type "pid" is "application/alto-networkmap+json".

   *  The media type of the defining information resource for property
      type "cdni-capabilities" defined in
      [I-D.ietf-alto-cdni-request-routing-alto] is "application/alto-
      cdni+json".

5.  Protocol Specification: Basic Data Types

5.1.  Entity Domain

5.1.1.  Entity Domain Type

   An entity domain has a type, which is uniquely identified by a string
   that MUST be no more than 64 characters, and MUST NOT contain
   characters other than US-ASCII alphanumeric characters
   (U+0030-U+0039, U+0041-U+005A, and U+0061-U+007A), the hyphen ('-',
   U+002D), or the low line ('_', U+005F).

   For example, the strings "ipv4", "ipv6", and "pid" are valid entity
   domain types. "ipv4.anycast" and "pid.local" are invalid.

   The type EntityDomainType is used in this document to denote a JSON
   string meeting the preceding requirements.

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   An entity domain type defines the semantics of a type of entity,
   independently of any specifying resource.  Each entity domain type
   MUST be registered with the IANA, following the procedure specified
   in Section 12.2.2 of this document.  The format of the entity
   identifiers (see Section 5.1.3) in that type of entity domain, as
   well as any hierarchical or inheritance rules (see Section 5.1.4) for
   those entities, MUST be specified at the same time.

5.1.2.  Entity Domain Name

   As said in Section 3.2 when introducing entity domains, an entity
   domain is characterized by its type and identified by its name.

   This document distinguishes three categories of entity domains:
   resource-specific entity domains, resource-agnostic entity domains
   and self-defined entity domains.  Their entity domain names are
   constructed as specified in the following sub-sections.

   Each entity domain is identified by a unique entity domain name which
   is a string of the following format:

       EntityDomainName ::= [ [ ResourceID ] '.' ] EntityDomainType

   Where the presence and construction of component:

       "[ [ ResourceID ] '.' ]"

   depends on the category of entity domain.

   Note that the '.' separator is not allowed in EntityDomainType and
   hence there is no ambiguity on whether an entity domain name refers
   to a resource-agnostic entity domain or a resource-specific entity
   domain.

   Note also that Section 10.1 of [RFC7285] specifies the format of the
   PID Name which is the format of the resource ID including the
   following specification: "the '.' separator is reserved for future
   use and MUST NOT be used unless specifically indicated in this
   document, or an extension document".  The present extension keeps the
   format specification of [RFC7285], hence the '.' separator MUST NOT
   be used in an information resource ID.

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5.1.2.1.  Resource-specific Entity Domain

   A resource-specific entity domain is identified by an entity domain
   name constructed as follows.  It MUST start with a resource ID using
   the ResourceID type defined in Section 10.2 of [RFC7285], followed by
   the '.' separator (U+002E), followed by a string of the type
   EntityDomainType specified in Section 5.1.1.

   For example, if an ALTO server provides two network maps "netmap-1"
   and "netmap-2", these network maps can define two resource-specific
   domains of type "pid", respectively identified by "netmap-1.pid" and
   "netmap-2.pid".

5.1.2.2.  Resource-agnostic Entity Domain

   A resource-agnostic entity domain contains entities that are
   identified independently of any information resource.  Hence, the
   identifier of a resource-agnostic entity domain is simply the
   identifier of its entity domain type.  For example, "ipv4" and "ipv6"
   identify the two resource-agnostic Internet address entity domains
   defined in Section 6.1.

5.1.2.3.  Self-defined Entity Domain

   A property map can define properties on entities that are specific to
   a unique information resource, which is the property map itself.
   This may be the case when an ALTO Server provides properties on a set
   of entities that are defined only in this property map, are not
   relevant to another one and do not depend on another specific
   resource.

   For example: a specialised property map may define a domain of type
   "ane", defined in [I-D.ietf-alto-path-vector], that contains a set of
   ANEs representing data centers, that each have a persistent
   identifier and are relevant only to this property map.

   In this case, the entity domain is qualified as "self-defined".  The
   identifier of a self-defined entity domain can be of the format:

       EntityDomainName ::= '.' EntityDomainType

   where '.' indicates that the entity domain only exists within the
   property map resource using it.

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   A self-defined entity domain can be viewed as a particular case of
   resource-specific entity domain, where the specific resource is the
   current resource that uses this entity domain.  In that case, for the
   sake of simplification, the component "ResourceID" SHOULD be omitted
   in its entity domain name.

5.1.3.  Entity Identifier

   Entities in an entity domain are identified by entity identifiers
   (EntityID) of the following format:

   EntityID ::= EntityDomainName ':' DomainTypeSpecificEntityID

   Examples from the Internet address entity domains include individual
   IP addresses such as "net1.ipv4:192.0.2.14" and
   "net1.ipv6:2001:db8::12", as well as address blocks such as
   "net1.ipv4:192.0.2.0/26" and "net1.ipv6:2001:db8::1/48".

   The format of the second part of an entity identifier depends on the
   entity domain type, and MUST be specified when defining a new entity
   domain type and registering it with the IANA.  Identifiers MAY be
   hierarchical, and properties MAY be inherited based on that
   hierarchy.  The rules defining any hierarchy or inheritance MUST be
   defined when the entity domain type is registered.

   The type EntityID is used in this document to denote a JSON string
   representing an entity identifier in this format.

   Note that two entity identifiers with different valid textual
   representations may refer to the same entity, for a given entity
   domain.  For example, the strings "net1.ipv6:2001:db8::1" and
   "net1.ipv6:2001:db8:0:0:0:0:0:1" refer to the same entity in the
   "ipv6" entity domain.  Such equivalences should be established by the
   object represented by DomainTypeSpecificEntityID, for example,
   [RFC5952] establishes equivalence for IPv6 addresses, while [RFC4632]
   does so for IPv4 addresses.

5.1.4.  Hierarchy and Inheritance

   To simplify the representation, some types of entity domains allow
   the ALTO Client and Server to use a hierarchical entity identifier
   format to represent a block of individual entities.  For instance, in
   an IPv4 domain "net1.ipv4", a CIDR "net1.ipv4:192.0.2.0/26" covers 64
   individual IPv4 entities.  In this case, the corresponding property
   inheritance rule MUST be defined for the entity domain type.  The
   hierarchy and inheritance rule MUST have no ambiguity.

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5.2.  Entity Property

   Each entity property has a type to indicate the encoding and the
   semantics of the value of this entity property, and has a name to
   identify it.

5.2.1.  Entity Property Type

   The type EntityPropertyType is used in this document to indicate a
   string denoting an entity property type.  The string MUST be no more
   than 32 characters, and it MUST NOT contain characters other than US-
   ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and
   U+0061-U+007A), the hyphen ('-', U+002D), the colon (':', U+003A), or
   the low line ('_', U+005F).  Note that the '.' separator is not
   allowed because it is reserved to separate an entity property type
   and an information resource identifier when an entity property is
   resource-specific.

   Each entity property type MUST be registered with the IANA, following
   the procedure specified in Section 12.3 of this document.  The
   intended semantics of the entity property type MUST be specified at
   the same time.

   Identifiers prefixed with "priv:" are reserved for Private Use
   [RFC8126] without a need to register with IANA.  All other
   identifiers for entity property types appearing in an HTTP request or
   response with an "application/alto-*" media type MUST be registered
   in the "ALTO Entity Property Type Registry", defined in Section 12.3.
   For an entity property identifier with the "priv:" prefix, an
   additional string (e.g., company identifier or random string) MUST
   follow the prefix to reduce potential collisions, that is, the string
   "priv:" alone is not a valid endpoint property identifier.

   To distinguish from the endpoint property type, the entity property
   type has the following characteristics:

   *  Some entity property types are applicable to entities in
      particular entity domain types only.  For example, the property
      type "pid" is applicable to entities in the entity domain types
      "ipv4" or "ipv6" while is not applicable to entities in an entity
      domain of type "pid".

   *  The intended semantics of the value of an entity property may also
      depend on the entity domain type.  For example, suppose that a
      property named "geo-location" is defined as the coordinates of a
      point, encoded as: "latitude longitude [altitude]."  When applied
      to an entity that represents a specific host computer, identified
      by an address in an entity domain of type "ipv4" or "ipv6", the

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      "geo-location" property would define the host's location.
      However, when applied to an entity in a "pid" domain type, the
      property would indicate the location of the center of all hosts in
      this "pid" entity.

5.2.2.  Entity Property Name

   Each entity property is identified by an entity property name, which
   is a string of the following format:

   EntityPropertyName ::= [ ResourceID ] '.' EntityPropertyType

   Similar to the endpoint property type defined in Section 10.8 of
   [RFC7285], each entity property may be defined by either the property
   map itself (self-defined) or some other specific information resource
   (resource-specific).

   The entity property name of a resource-specific entity property
   starts with a string of the type ResourceID defined in [RFC7285],
   followed by the '.' separator (U+002E) and a EntityDomainType typed
   string.  For example, the "pid" properties of an "ipv4" entity
   defined by two different maps "net-map-1" and "net-map-2" are
   identified by "net-map-1.pid" and "net-map-2.pid" respectively.

   The specific information resource of an entity property may be the
   current information resource itself, that is, the property map
   defining the property.  In that case, the ResourceID in the property
   name SHOULD be ignored.  For example, the property name ".asn"
   applied to an entity identitifed by its IPv4 address, indicates the
   AS number of the AS that "owns" the entity, where the returned AS
   number is defined by the property map itself.

5.2.3.  Format for Entity Property Value

   [RFC7285] in Section 11.4.1.6, specifies that an implementation of
   the Endpoint Property Service specified in [RFC7285] SHOULD assume
   that the property value is a JSONString and fail to parse if it is
   not.  This document extends the format of a property value by
   allowing it to be a JSONValue instead of just a JSONString.

6.  Entity Domain Types Defined in this Document

   This document requires the definition of each entity domain type MUST
   include (1) the entity domain type name and (2) domain-specific
   entity identifiers, and MAY include (3) hierarchy and inheritance
   semantics optionally.  This document defines three initial entity
   domain types as follows.

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6.1.  Internet Address Domain Types

   The document defines two entity domain types (IPv4 and IPv6) for
   Internet addresses.  Both types are resource-agnostic entity domain
   types and hence define corresponding resource-agnostic entity domains
   as well.  Since the two domains use the same hierarchy and
   inheritance semantics, we define the semantics together, instead of
   repeating for each.

6.1.1.  Entity Domain Type: IPv4

6.1.1.1.  Entity Domain Type Identifier

   ipv4

6.1.1.2.  Domain-Specific Entity Identifiers

   Individual addresses are strings as specified by the IPv4Addresses
   rule of Section 3.2.2 of [RFC3986]; Hierarchical addresses are
   prefix-match strings as specified in Section 3.1 of [RFC4632].  To
   define properties, an individual Internet address and the
   corresponding full-length prefix are considered aliases for the same
   entity.  An individual Internet address and the corresponding full-
   length prefix are considered aliases for the same entity on which to
   define properties.  Thus, "ipv4:192.0.2.0" and "ipv4:192.0.2.0/32"
   are equivalent.

6.1.2.  Entity Domain Type: IPv6

6.1.2.1.  Entity Domain Type Identifier

   ipv6

6.1.2.2.  Domain-Specific Entity Identifiers

   Individual addresses are strings as specified by Section 4 of
   [RFC5952]; Hierarchical addresses are prefix-match strings as
   specified in Section 7 of [RFC5952].  To define properties, an
   individual Internet address and the corresponding 128-bit prefix are
   considered aliases for the same entity.  That is, "ipv6:2001:db8::1"
   and "ipv6:2001:db8::1/128" are equivalent, and have the same set of
   properties.

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6.1.3.  Hierarchy and Inheritance of Internet Address Domains

   Both Internet address domains allow property values to be inherited.
   Specifically, if a property P is not defined for a specific Internet
   address I, but P is defined for a hierarchical Internet address C
   which prefix-matches I, then the address I inherits the value of P
   defined for the hierarchical address C.  If more than one such
   hierarchical addresses define a value for P, I inherits the value of
   P in the hierarchical address with the longest prefix.  Note that
   this longest prefix rule ensures no multiple value inheritances, and
   hence no ambiguity.

   Hierarchical addresses can also inherit properties: if a property P
   is not defined for the hierarchical address C, but is defined for
   another hierarchical address C' which covers all IP addresses in C,
   and C' has a shorter prefix length than C, then C MAY inherit the
   property from C'.  If there are multiple such hierarchical addresses
   like C', C MUST inherit from the hierarchical address having the
   longest prefix length.

   As an example, suppose that a server defines a property P for the
   following entities:

                             ipv4:192.0.2.0/26: P=v1
                             ipv4:192.0.2.0/28: P=v2
                             ipv4:192.0.2.0/30: P=v3
                             ipv4:192.0.2.0:    P=v4

                     Figure 1: Defined Property Values.

   Then the following entities have the indicated values:

                         ipv4:192.0.2.0:    P=v4
                         ipv4:192.0.2.1:    P=v3
                         ipv4:192.0.2.16:   P=v1
                         ipv4:192.0.2.32:   P=v1
                         ipv4:192.0.2.64:   (not defined)
                         ipv4:192.0.2.0/32: P=v4
                         ipv4:192.0.2.0/31: P=v3
                         ipv4:192.0.2.0/29: P=v2
                         ipv4:192.0.2.0/27: P=v1
                         ipv4:192.0.2.0/25: (not defined)

                    Figure 2: Inherited Property Values.

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   An ALTO server MAY explicitly indicate a property as not having a
   value for a particular entity.  That is, a server MAY say that
   property P of entity X is "defined to have no value", instead of
   "undefined".  To indicate "no value", a server MAY perform different
   behaviours:

   *  If that entity would inherit a value for that property, then the
      ALTO server MUST return a "null" value for that property.  In this
      case, the ALTO client MUST recognize a "null" value as "no value"
      and "do not apply the inheritance rules for this property."

   *  If the entity would not inherit a value, then the ALTO server MAY
      return "null" or just omit the property.  In this case, the ALTO
      client cannot infer the value for this property of this entity
      from the Inheritance rules.  So the client MUST interpret that
      this property has no value.

   If the ALTO server does not define any properties for an entity, then
   the server MAY omit that entity from the response.

6.1.4.  Defining Information Resource Media Type for domain types IPv4
        and IPv6

   Entity domain types "ipv4" and "ipv6" both allow to define resource
   specific entity domains.  When resource specific domains are defined
   with entities of domain type "ipv4" or "ipv6", the defining
   information resource for an entity domain of type "ipv4" or "ipv6"
   MUST be a Network Map. The media type of a defining information
   resource is therefore:

   application/alto-networkmap+json

6.2.  Entity Domain Type: PID

   The PID domain associates property values with the PIDs in a network
   map.  Accordingly, this entity domain always depends on a network
   map.

6.2.1.  Entity Domain Type Identifier

   pid

6.2.2.  Domain-Specific Entity Identifiers

   The entity identifiers are the PID names of the associated network
   map.

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6.2.3.  Hierarchy and Inheritance

   There is no hierarchy or inheritance for properties associated with
   PIDs.

6.2.4.  Defining Information Resource Media Type for Domain Type PID

   The entity domain type "pid" allows to define resource specific
   entity domains.  When resource specific domains are defined with
   entities of domain type "pid", the defining information resource for
   entity domain type "pid" MUST be a Network Map. The media type of a
   defining information resource is therefore:

   application/alto-networkmap+json

6.2.5.  Relationship To Internet Addresses Domains

   The PID domain and the Internet address domains are completely
   independent; the properties associated with a PID have no relation to
   the properties associated with the prefixes or endpoint addresses in
   that PID.  An ALTO server MAY choose to assign all the properties of
   a PID to the prefixes in that PID or only some of these properties.

   For example, suppose "PID1" consists of the prefix
   "ipv4:192.0.2.0/24", and has the property "P" with value "v1".  The
   Internet address entities "ipv4:192.0.2.0" and "ipv4:192.0.2.0/24" in
   the IPv4 domain MAY have a value for the property "P", and if they
   do, it is not necessarily "v1".

6.3.  Internet Address Properties vs. PID Properties

   Because the Internet address and PID domains relate to completely
   distinct domain types, the question may arise as to which entity
   domain type is the best for a property.  In general, the Internet
   address domain types are RECOMMENDED for properties that are closely
   related to the Internet address, or are associated with, and
   inherited through, hierarchical addresses.

   The PID domain type is RECOMMENDED for properties that arise from the
   definition of the PID, rather than from the Internet address prefixes
   in that PID.

   For example, because Internet addresses are allocated to service
   providers by blocks of prefixes, an "ISP" property would be best
   associated with Internet address domain types.  On the other hand, a
   property that explains why a PID was formed, or how it relates to a
   provider's network, would best be associated with the PID domain
   type.

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7.  Property Map

   A property map returns the properties defined for all entities in one
   or more domains, e.g., the "location" property of entities in "pid"
   domain, and the "ASN" property of entities in "ipv4" and "ipv6"
   domains.

   Section 10.4 gives an example of a property map request and its
   response.

7.1.  Media Type

   The media type of a property map is "application/alto-propmap+json".

7.2.  HTTP Method

   The property map is requested using the HTTP GET method.

7.3.  Accept Input Parameters

   None.

7.4.  Capabilities

   The capabilities are defined by an object of type
   PropertyMapCapabilities:

       object {
         EntityPropertyMapping mappings;
       } PropertyMapCapabilities;

       object-map {
         EntityDomainName -> EntityPropertyName<1..*>;
       } EntityPropertyMapping

   with fields:

   mappings:  A JSON object whose keys are names of entity domains and
      values are the supported entity properties of the corresponding
      entity domains.

7.5.  Uses

   The "uses" field of a property map resource in an IRD entry specifies
   dependent resources of this property map.  It is an array of the
   resource ID(s) of the resource(s).

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7.6.  Response

   If the entity domains in this property map depend on other resources,
   the "dependent-vtags" field in the "meta" field of the response MUST
   be an array that includes the version tags of those resources, and
   the order MUST be consistent with the "uses" field of this property
   map resource.  The data component of a property map response is named
   "property-map", which is a JSON object of type PropertyMapData,
   where:

       object {
         PropertyMapData property-map;
       } InfoResourceProperties : ResponseEntityBase;

       object-map {
         EntityID -> EntityProps;
       } PropertyMapData;

       object {
         EntityPropertyName -> JSONValue;
       } EntityProps;

   The ResponseEntityBase type is defined in Section 8.4 of [RFC7285].

   Specifically, a PropertyMapData object has one member for each entity
   in the property map.  The entity's properties are encoded in the
   corresponding EntityProps object.  EntityProps encodes one name/value
   pair for each property, where the property names are encoded as
   strings of type PropertyName.  A protocol implementation SHOULD
   assume that the property value is either a JSONString or a JSON
   "null" value, and fail to parse if it is not, unless the
   implementation is using an extension to this document that indicates
   when and how property values of other data types are signaled.

   For each entity in the property map:

   *  If the entity is in a resource-specific entity domain, the ALTO
      server SHOULD only return self-defined properties and resource-
      specific properties which depend on the same resource as the
      entity does.  The ALTO client SHOULD ignore the resource-specific
      property in this entity if their mapping is not registered in the
      ALTO Resource Entity Property Transfer Registry of the type of the
      corresponding resource.

   *  If the entity is in a shared entity domain, the ALTO server SHOULD
      return self-defined properties and all resource-specific
      properties defined for all resource-specific entities which have
      the same domain-specific entity identifier as this entity does.

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   For efficiency, the ALTO server SHOULD omit property values that are
   inherited rather than explicitly defined; if a client needs inherited
   values, the client SHOULD use the entity domain's inheritance rules
   to deduce those values.

8.  Filtered Property Map

   A filtered property map returns the values of a set of properties for
   a set of entities selected by the client.

   Section 10.5, Section 10.6, Section 10.7 and Section 10.8 give
   examples of filtered property map requests and responses.

8.1.  Media Type

   The media type of a property map resource is "application/alto-
   propmap+json".

8.2.  HTTP Method

   The filtered property map is requested using the HTTP POST method.

8.3.  Accept Input Parameters

   The input parameters for a filtered property map request 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-propmapparams+json", which is a JSON object of type
   ReqFilteredPropertyMap:

     object {
       EntityID             entities<1..*>;
       EntityPropertyName   properties<1..*>;
     } ReqFilteredPropertyMap;

   with fields:

   entities:  List of entity identifiers for which the specified
      properties are to be returned.  The ALTO server MUST interpret
      entries appearing multiple times as if they appeared only once.
      The domain of each entity MUST be included in the list of entity
      domains in this resource's "capabilities" field (see Section 8.4).

   properties:  List of properties to be returned for each entity.  Each

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      specified property MUST be included in the list of properties in
      this resource's "capabilities" field (see Section 8.4).  The ALTO
      server MUST interpret entries appearing multiple times as if they
      appeared only once.  Note that the "entities" and "properties"
      fields MUST have at least one entry each.

8.4.  Capabilities

   The capabilities are defined by an object of type
   PropertyMapCapabilities, as defined in Section 7.4.

8.5.  Uses

   Same to the "uses" field of the Property Map resource (see
   Section 7.5).

8.6.  Filtered Property Map Response

   The response MUST indicate an error, using ALTO protocol error
   handling, as defined in Section 8.5 of [RFC7285], if the request is
   invalid.

   Specifically, a filtered property map request can be invalid in the
   following cases:

   *  An entity identifier in the "entities" field of the request is
      invalid if:

      -  The domain of this entity is not defined in the "entity-
         domains" capability of this resource in the IRD,

      -  The entity identifier is not valid for the entity domain.

      A valid entity identifier does never generate an error, even if
      the filtered property map resource does not define any properties
      for it.

      If an entity identifier in the "entities" field of the request is
      invalid, the ALTO server MUST return an "E_INVALID_FIELD_VALUE"
      error defined in Section 8.5.2 of [RFC7285], and the "value" field
      of the error message SHOULD indicate the provided invalid entity
      identifier.

   *  A property name in the "properties" field of the request is
      invalid if this property name is not defined in the "properties"
      capability of this resource in the IRD.

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      When a filtered property map resource does not define a value for
      a property requested on a particular entity, it is not an error.
      In this case, the ALTO server MUST omit that property from the
      response for that endpoint.

      If a property name in "properties" in the request is invalid, the
      ALTO server MUST return an "E_INVALID_FIELD_VALUE" error defined
      in Section 8.5.2 of [RFC7285].  The "value" field of the error
      message SHOULD indicate the property name.

   The response to a valid request is the same as for the Property Map
   (see Section 7.6), except that:

   *  If the requested entities include entities in the shared entity
      domain, the "dependent-vtags" field in its "meta" field MUST
      include version tags of all dependent resources appearing in the
      "uses" field.

   *  If the requested entities only include entities in resource-
      specific entity domains, the "dependent-vtags" field in its "meta"
      field MUST include the version tags of the resources on which the
      requested resource-specific entity domains and the requested
      resource-specific properties are dependent on.

   *  The response only includes the entities and properties requested
      by the client.  If an entity in the request is identified by a
      hierarchical identifier (e.g., a "ipv4" or "ipv6" prefix), the
      response MUST cover properties for all identifiers in this
      hierarchical identifier.

   The filtered property map response MUST include all the inherited
   property values for the requested entities and all the entities which
   are able to inherit property values from the requested entities.  To
   achieve this goal, the ALTO server MAY follow three rules:

   *  If a property for a requested entity is inherited from another
      entity not included in the request, the response SHOULD include
      this property for the requested entity.  For example, A full
      property map may skip a property P for an entity A (e.g.,
      ipv4:192.0.2.0/31) if P can be derived using inheritance from
      another entity B (e.g., ipv4:192.0.2.0/30).  A filtered property
      map request may include only A but not B.  In such a case, the
      property P SHOULD be included in the response for A.

   *  If there are entities covered by a requested entity but having
      different values for the requested properties, the response SHOULD
      include all those entities and the different property values for
      them.  For example, considering a request for property P of entity

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      A (e.g., ipv4:192.0.2.0/31), if P has value v1 for
      A1=ipv4:192.0.2.0/32 and v2 for A2=ipv4:192.0.2.1/32, then, the
      response SHOULD include A1 and A2.

   *  If an entity identifier in the response is already covered by
      other entities identifiers in the same response, it SHOULD be
      removed from the response, for the sake of compactness.  In the
      previous example, the entity A = ipv4:192.0.2.0/31 SHOULD be
      removed because A1 and A2 cover all the addresses in A.

   An ALTO client should be aware that the entities in the response MAY
   be different from the entities in its request.

8.7.  Entity property type defined in this document

   This document defines the entity property type "pid".  This property
   type extends the ALTO Endpoint Property Type "pid" defined in section
   7.1.1 of [RFC7285] as follows: the property has the same semantics
   and applies to IPv4 and IPv6 addresses; the difference is that the
   IPv4 and IPv6 addresses have evolved from the status of endpoints to
   the status of entities.

   The defining information resource for property type MUST be a network
   map.  This document requests a IANA registration for this property

8.7.1.  Entity Property Type: pid

   1.  Identifier: pid

   2.  Semantics: the intended semantics are the same as in [RFC7285]
       for the ALTO Endpoint Property Type "pid"

   3.  Media type of defining information resource: application/alto-
       networkmap+json

   4.  Security considerations: for entity property type "pid" are the
       same as documented in [RFC7285] for the ALTO Endpoint Property
       Type "pid".

9.  Impact on Legacy ALTO Servers and ALTO Clients

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9.1.  Impact on Endpoint Property Service

   Since the Property Map and the Filtered Property Map defined in this
   document provide a functionality that covers the Endpoint Property
   Service (EPS) defined in Section 11.4 of [RFC7285], ALTO servers may
   prefer to provide Property Map and Filtered Property Map in place of
   EPS.  However, for the legacy endpoint properties, it is recommended
   that ALTO servers also provide EPS so that legacy clients can still
   be supported.

9.2.  Impact on Resource-Specific Properties

   Section 10.8 of [RFC7285] defines two categories of endpoint
   properties: "resource-specific" and "global".  Resource-specific
   property names are prefixed with the ID of the resource they depend
   on, while global property names have no such prefix.  The property
   map and the filtered property map defined in this document define
   similar categories of entity properties.  The difference is that
   entity property maps do not define "global" entity properties.
   Instead, they define "self-defined" entity properties as a special
   case of "resource-specific" entity properties, where the specific
   resource is the property map itself.  This means that "self-defined"
   properties are defined within the scope of the property map.

9.3.  Impact on Other Properties

   In the present extension, properties can now be defined on sets of
   entity addresses, rather than just individual endpoint addresses as
   is is the case in RFC7285.  This might change the semantics of a
   property.  These sets can be for example hierachical IP address
   blocks.  For instance, a property such as fictitious "geo-location",
   defined on a set of IP addresses would have a value corresponding to
   the barycenter of this set of addresses.

10.  Examples

10.1.  Network Map

   The examples in this section use a very simple default network map:

                  defaultpid:  ipv4:0.0.0.0/0  ipv6:::0/0
                  pid1:        ipv4:192.0.2.0/25
                  pid2:        ipv4:192.0.2.0/27
                  pid3:        ipv4:192.0.3.0/28
                  pid4:        ipv4:192.0.3.16/28

                   Figure 3: Example Default Network Map

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   And another simple alternative network map:

                  defaultpid:  ipv4:0.0.0.0/0  ipv6:::0/0
                  pid1:        ipv4:192.0.2.0/27
                  pid2:        ipv4:192.0.3.0/27

                 Figure 4: Example Alternative Network Map

10.2.  Property Definitions

   Beyond "pid", the examples in this section use four additional
   properties for Internet address domains, "ISP", "ASN", "country" and
   "state", with the following values:

                                   ISP    ASN   country   state
           ipv4:192.0.2.0/23:    BitsRus   -      us       -
           ipv4:192.0.2.0/28:       -    12345    -        NJ
           ipv4:192.0.2.16/28:      -    12345    -        CT
           ipv4:192.0.2.1:          -      -      -        PA
           ipv4:192.0.3.0/28:       -    12346    -        TX
           ipv4:192.0.3.16/28:      -    12346    -        MN

       Figure 5: Example Property Values for Internet Address Domains

   And the examples in this section use the property "region" for the
   PID domain of the default network map with the following values:

                                         region
                      pid:defaultpid:     -
                      pid:pid1:           us-west
                      pid:pid2:           us-east
                      pid:pid3:           us-south
                      pid:pid4:           us-north

      Figure 6: Example Property Values for Default Network Map's PID
                                   Domain

   Note that "-" means the value of the property for the entity is
   "undefined".  So the entity would inherit a value for this property
   by the inheritance rule if possible.  For example, the value of the
   "ISP" property for "ipv4:192.0.2.1" is "BitsRus" because of
   "ipv4:192.0.2.0/24".  But the "region" property for "pid:defaultpid"
   has no value because no entity from which it can inherit.

   Similar to the PID domain of the default network map, the examples in
   this section use the property "ASN" for the PID domain of the
   alternative network map with the following values:

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                                             ASN
                          pid:defaultpid:     -
                          pid:pid1:         12345
                          pid:pid2:         12346

      Figure 7: Example Property Values for Alternative Network Map's
                                 PID Domain

10.3.  Information Resource Directory (IRD)

   The following IRD defines ALTO Server information resources that are
   relevant to the Entity Property Service.  It provides two property
   maps: one for the "ISP" and "ASN" properties, and another one for the
   "country" and "state" properties.  The server could have provided a
   single property map for all four properties, but does not, presumably
   because the organization that runs the ALTO server believes that a
   client is not necessarily interested in getting all four properties.

   The server provides several filtered property maps.  The first
   returns all four properties, and the second returns only the "pid"
   property for the default network map.

   The filtered property maps for the "ISP", "ASN", "country" and
   "state" properties do not depend on the default network map (it does
   not have a "uses" capability), because the definitions of those
   properties do not depend on the default network map.  The Filtered
   Property Map providing the "pid" property does have a "uses"
   capability for the default network map, because the default network
   map defines the values of the "pid" property.

   Note that for legacy clients, the ALTO server provides an Endpoint
   Property Service for the "pid" property defined on the endpoints of
   the default network map.

   The server provides another filtered Property map resource, named
   "ane-dc-property-map", that returns a fictitious properties named
   "storage-capacity", "ram" and "cpu" for ANEs that have a persistent
   identifier.  The entity domain to which the ANEs belong is "self-
   defined" and valid only within the property map.

    GET /directory HTTP/1.1
    Host: alto.example.com
    Accept: application/alto-directory+json,application/alto-error+json

    HTTP/1.1 200 OK
    Content-Length: 2827
    Content-Type: application/alto-directory+json

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    {
      "meta" : {
        "default-alto-network-map" : "default-network-map"
      },
      "resources" : {
        "default-network-map" : {
          "uri" : "http://alto.example.com/networkmap/default",
          "media-type" : "application/alto-networkmap+json"
        },
        "alt-network-map" : {
          "uri" : "http://alto.example.com/networkmap/alt",
          "media-type" : "application/alto-networkmap+json"
        },
        "ia-property-map" : {
          "uri" : "http://alto.example.com/propmap/full/inet-ia",
          "media-type" : "application/alto-propmap+json",
          "uses": [ "default-network-map", "alt-network-map" ],
          "capabilities" : {
            "mappings": {
              "ipv4": [ ".ISP", ".ASN" ],
              "ipv6": [ ".ISP", ".ASN" ]
            }
          }
        },
        "iacs-property-map" : {
          "uri" : "http://alto.example.com/propmap/lookup/inet-iacs",
          "media-type" : "application/alto-propmap+json",
          "accepts": "application/alto-propmapparams+json",
          "uses": [ "default-network-map", "alt-network-map" ],
          "capabilities" : {
            "mappings": {
              "ipv4": [ ".ISP", ".ASN", ".country", ".state" ],
              "ipv6": [ ".ISP", ".ASN", ".country", ".state" ]
            }
          }
        },
        "region-property-map": {
          "uri": "http://alto.example.com/propmap/lookup/region",
          "media-type": "application/alto-propmap+json",
          "accepts": "application/alto-propmapparams+json",
          "uses" : [ "default-network-map", "alt-network-map" ],
          "capabilities": {
            "mappings": {
              "default-network-map.pid": [ ".region" ],
              "alt-network-map.pid": [ ".ASN" ]
            }
          }
        },

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        "ip-pid-property-map" : {
          "uri" : "http://alto.example.com/propmap/lookup/pid",
          "media-type" : "application/alto-propmap+json",
          "accepts" : "application/alto-propmapparams+json",
          "uses" : [ "default-network-map", "alt-network-map" ],
          "capabilities" : {
            "mappings": {
              "ipv4": [ "default-network-map.pid",
                        "alt-network-map.pid" ],
              "ipv6": [ "default-network-map.pid",
                        "alt-network-map.pid" ]
            }
          }
        },
        "legacy-endpoint-property" : {
          "uri" : "http://alto.example.com/legacy/eps-pid",
          "media-type" : "application/alto-endpointprop+json",
          "accepts" : "application/alto-endpointpropparams+json",
          "capabilities" : {
            "properties" : [ "default-network-map.pid",
                             "alt-network-map.pid" ]
          }
        },
        "ane-dc-property-map": {
          "uri" : "http://alto.example.com/propmap/lookup/ane-dc",
          "media-type" : "application/alto-propmap+json",
          "accepts": "application/alto-propmapparams+json",
          "capabilities": {
            "mappings": {
              ".ane" : [ "storage-capacity", "ram", "cpu" ]
            }
          }
        }
      }
    }

                           Figure 8: Example IRD

10.4.  Full Property Map Example

   The following example uses the properties and IRD defined above in
   Section 10.3 to retrieve a Property Map for entities with the "ISP"
   and "ASN" properties.

   Note that, to be compact, the response does not include the entity
   "ipv4:192.0.2.0", because values of all those properties for this
   entity are inherited from other entities.

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   Also note that the entities "ipv4:192.0.2.0/28" and
   "ipv4:192.0.2.16/28" are merged into "ipv4:192.0.2.0/27", because
   they have the same value of the "ASN" property.  The same rule
   applies to the entities "ipv4:192.0.3.0/28" and "ipv4:192.0.3.0/28".
   Both of "ipv4:192.0.2.0/27" and "ipv4:192.0.3.0/27" omit the value
   for the "ISP" property, because it is inherited from
   "ipv4:192.0.2.0/23".

   GET /propmap/full/inet-ia HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json

   HTTP/1.1 200 OK
   Content-Length: 418
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {"resource-id": "default-network-map",
          "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
         {"resource-id": "alt-network-map",
          "tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
       ]
     },
     "property-map": {
       "ipv4:192.0.2.0/23":   {".ISP": "BitsRus"},
       "ipv4:192.0.2.0/27":   {".ASN": "12345"},
       "ipv4:192.0.3.0/27":   {".ASN": "12346"}
     }
   }

10.5.  Filtered Property Map Example #1

   The following example uses the filtered property map resource to
   request the "ISP", "ASN" and "state" properties for several IPv4
   addresses.

   Note that the value of "state" for "ipv4:192.0.2.0" is the only
   explicitly defined property; the other values are all derived by the
   inheritance rules for Internet address entities.

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   POST /propmap/lookup/inet-iacs HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: 158
   Content-Type: application/alto-propmapparams+json

   {
     "entities" : [ "ipv4:192.0.2.0",
                    "ipv4:192.0.2.1",
                    "ipv4:192.0.2.17" ],
     "properties" : [ ".ISP", ".ASN", ".state" ]
   }

   HTTP/1.1 200 OK
   Content-Length: 540
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {"resource-id": "default-network-map",
          "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
         {"resource-id": "alt-network-map",
          "tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
       ]
     },
     "property-map": {
       "ipv4:192.0.2.0":
              {".ISP": "BitsRus", ".ASN": "12345", ".state": "PA"},
       "ipv4:192.0.2.1":
              {".ISP": "BitsRus", ".ASN": "12345", ".state": "NJ"},
       "ipv4:192.0.2.17":
              {".ISP": "BitsRus", ".ASN": "12345", ".state": "CT"}
     }
   }

10.6.  Filtered Property Map Example #2

   The following example uses the filtered property map resource to
   request the "ASN", "country" and "state" properties for several IPv4
   prefixes.

   Note that the property values for both entities "ipv4:192.0.2.0/26"
   and "ipv4:192.0.3.0/26" are not explicitly defined.  They are
   inherited from the entity "ipv4:192.0.2.0/23".

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   Also note that some entities like "ipv4:192.0.2.0/28" and
   "ipv4:192.0.2.16/28" in the response are not explicitly listed in the
   request.  The response includes them because they are refinements of
   the requested entities and have different values for the requested
   properties.

   The entity "ipv4:192.0.4.0/26" is not included in the response,
   because there are neither entities which it is inherited from, nor
   entities inherited from it.

   POST /propmap/lookup/inet-iacs HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: 170
   Content-Type: application/alto-propmapparams+json

   {
     "entities" : [ "ipv4:192.0.2.0/26",
                    "ipv4:192.0.3.0/26",
                    "ipv4:192.0.4.0/26" ],
     "properties" : [ ".ASN", ".country", ".state" ]
   }

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   HTTP/1.1 200 OK
   Content-Length: 766
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {"resource-id": "default-network-map",
          "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
         {"resource-id": "alt-network-map",
          "tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
       ]
     },
     "property-map": {
       "ipv4:192.0.2.0/26":  {".country": "us"},
       "ipv4:192.0.2.0/28":  {".ASN": "12345",
                              ".state": "NJ"},
       "ipv4:192.0.2.16/28": {".ASN": "12345",
                              ".state": "CT"},
       "ipv4:192.0.2.0":     {".state": "PA"},
       "ipv4:192.0.3.0/26":  {".country": "us"},
       "ipv4:192.0.3.0/28":  {".ASN": "12345",
                              ".state": "TX"},
       "ipv4:192.0.3.16/28": {".ASN": "12345",
                              ".state": "MN"}
     }
   }

10.7.  Filtered Property Map Example #3

   The following example uses the filtered property map resource to
   request the "default-network-map.pid" property and the "alt-network-
   map.pid" property for a set of IPv4 addresses and prefixes.

   Note that the entity "ipv4:192.0.3.0/27" is decomposed into two
   entities "ipv4:192.0.3.0/28" and "ipv4:192.0.3.16/28", as they have
   different "default-network-map.pid" property values.

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   POST /propmap/lookup/pid HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: 221
   Content-Type: application/alto-propmapparams+json

   {
     "entities" : [
                   "ipv4:192.0.2.128",
                   "ipv4:192.0.2.0/27",
                   "ipv4:192.0.3.0/27" ],
     "properties" : [ "default-network-map.pid",
                      "alt-network-map.pid ]
   }

   HTTP/1.1 200 OK
   Content-Length: 774
   Content-Type: application/alto-propmap+json

   {
     "meta": {
       "dependent-vtags": [
         {"resource-id": "default-network-map",
          "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
         {"resource-id": "alt-network-map",
          "tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
       ]
     },
     "property-map": {
       "ipv4:192.0.2.128":   {"default-network-map.pid": "defaultpid",
                              "alt-network-map.pid": "defaultpid"},
       "ipv4:192.0.2.0/27":  {"default-network-map.pid": "pid2",
                              "alt-network-map.pid": "pid1"},
       "ipv4:192.0.3.0/28":  {"default-network-map.pid": "pid3",
                              "alt-network-map.pid": "pid2"},
       "ipv4:192.0.3.16/28": {"default-network-map.pid": "pid4",
                              "alt-network-map.pid": "pid2"}
     }
   }

10.8.  Filtered Property Map Example #4

   Here is an example of using the filtered property map to query the
   regions for several PIDs in "default-network-map".  The "region"
   property is specified as a "self-defined" property, i.e., the values
   of this property are defined by this property map resource.

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   POST /propmap/lookup/region HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: 132
   Content-Type: application/alto-propmapparams+json

   {
     "entities" : ["default-network-map.pid:pid1",
                   "default-network-map.pid:pid2"],
     "properties" : [ ".region" ]
   }

   HTTP/1.1 200 OK
   Content-Length: 326
   Content-Type: application/alto-propmap+json

   {
     "meta" : {
       "dependent-vtags" : [
          {"resource-id": "default-network-map",
           "tag": "7915dc0290c2705481c491a2b4ffbec482b3cf62"}
       ]
     },
     "property-map": {
       "default-network-map.pid:pid1": {
         ".region": "us-west"
       },
       "default-network-map.pid:pid2": {
         ".region": "us-east"
       }
     }
   }

10.9.  Filtered Property Map for ANEs Example #5

   The following example uses the filtered property map resource "ane-
   dc-property-map" to request properties "storage-capacity" and "cpu"
   on several ANEs defined in this property map.

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   POST /propmap/lookup/ane-dc HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: 155
   Content-Type: application/alto-propmapparams+json

   {
     "entities" : [".ane:dc21",
                   ".ane:dc45.srv9",
                   ".ane:dc6.srv-cluster8"],
     "properties" : [ "storage-capacity", "cpu"]
   }

   HTTP/1.1 200 OK
   Content-Length: 295
   Content-Type: application/alto-propmap+json

   {
     "meta" : {
     },
     "property-map": {
       ".ane:dc21":
         {"storage-capacity" : 40000 Gbytes, "cpu" : 500 Cores},
       ".ane:dc45.srv9":
         {"storage-capacity" : 100 Gbytes, "cpu" : 20 Cores},
       ".ane:dc6.srv-cluster8":
         {"storage-capacity" : 6000 Gbytes, "cpu" : 100 Cores}
     }
   }

11.  Security Considerations

   Both Property Map and Filtered Property Map defined in this document
   fit into the architecture of the ALTO base protocol, and hence the
   Security Considerations (Section 15 of [RFC7285]) of the base
   protocol fully apply: authenticity and integrity of ALTO information
   (i.e., authenticity and integrity of Property Maps), potential
   undesirable guidance from authenticated ALTO information (e.g.,
   potentially imprecise or even wrong value of a property such as geo-
   location), confidentiality of ALTO information (e.g., exposure of a
   potentially sensitive entity property such as geo-location), privacy
   for ALTO users, and availability of ALTO services should all be
   considered.

   ALTO clients using this extension should in addition be aware that
   the entity properties they require may convey more details than the
   endpoint properties conveyed by using [RFC7285].  Client requests may
   reveal details on their activity or plans thereof, that a malicious

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   usage may monetize or use for attacks or undesired surveillance.
   Likewise, ALTO Servers expose entities and properties related to
   specific parts of the infrastructure that reveal details on
   capabilities, locations, or resource availability.  These details may
   be maliciously used for competition purposes, or to cause resources
   shortage or undesired publication.

   To address these concerns, the Property Maps provided by this
   extension require additional attention on two security considerations
   discussed in [RFC7285]: "potential undesirable guidance from
   authenticated ALTO information" (Section 15.2 of [RFC7285]) and
   "confidentiality of ALTO information" (Section 15.3 of [RFC7285]).
   Threats to the availability of the ALTO Service caused by highly
   demanding queries should be addressed as specified in Section 15.5 of
   [RFC7285].

   *  Potential undesirable guidance from authenticated ALTO
      information: it can be caused by Property values that change over
      time and thus lead to performance degradation or system rejection
      of application requests.

      To avoid these consequences, a more robust ALTO client should
      adopt and extend protection strategies specified in Section 15.2
      of [RFC7285].  For example, to be notified immediately when a
      particular ALTO value that the Client depends on changes, it is
      RECOMMENDED that both the ALTO Client and ALTO Server using this
      extension implement "Application-Layer Traffic Optimization (ALTO)
      Incremental Updates Using Server-Sent Events (SSE)" [RFC8895].

   *  Confidentiality of ALTO information: as discussed in Section 15 of
      [RFC7285], properties may have sensitive customer-specific
      information.  If this is the case, an ALTO Server may limit access
      to those properties by providing several different property maps.
      For non-sensitive properties, the ALTO Server would provide a URI
      which accepts requests from any client.  Sensitive properties, on
      the other hand, would only be available via a secure URI which
      would require client authentication.  Another way is to expose
      highly abstracted coarse-grained property values to all Clients
      while restricting access to URIs exposing more fine-grained values
      to authorized Clients.  Restricted access URIs may be gathered in
      delegate IRDs as specified in Section 9.2.4 of [RFC7285].

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      Also, while technically this document does not introduce any
      security risks not inherent in the Endpoint Property Service
      defined by [RFC7285], the GET-mode property map resource defined
      in this document does make it easier for a client to download
      large numbers of property values.  Accordingly, an ALTO Server
      should limit GET-mode property maps to properties that do not
      contain sensitive data.

      Section 12 on IANA considerations of this document specifies that
      the ALTO service provider MUST be aware of the potential
      sensitiveness of exposed entity domains and properties.
      Section 12.2.2.  (ALTO Entity Domain Type Registration Process) of
      this document specifies that when the registration of an entity
      domain type is requested at the IANA, the request MUST include
      security considerations that show awareness of how the exposed
      entity addresses may be related to private information about an
      ALTO client or an infrastructure service provider.  Likewise,
      Section 12.3.  (ALTO Entity Property Type Registry) of this
      document specifies that when the registration of a property type
      is requested at the IANA, the request MUST include security
      considerations that explain why this property type is required for
      ALTO-based operations.

      The risk of ALTO information being leaked to malicious Clients or
      third parties is addressed similarly to in Section 7 of [RFC8896].
      ALTO Clients and Servers SHOULD support both TLS 1.3 [RFC8446] and
      TLS 1.2 [RFC5246] and MAY support and use newer versions of TLS as
      long as the negotiation process succeeds.

12.  IANA Considerations

   This document defines additional application/alto-* media types.  It
   defines an ALTO Entity Domain Type Registry that extends the ALTO
   Address Type Registry defined in [RFC7285].  It also defines an ALTO
   Entity Property Type Registry that extends the ALTO endpoint property
   registry defined in [RFC7285].

12.1.  application/alto-* Media Types

   This document registers two additional ALTO media types, listed in
   Table 1.

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         +=============+=========================+===============+
         | Type        | Subtype                 | Specification |
         +=============+=========================+===============+
         | application | alto-propmap+json       | Section 7.1   |
         +-------------+-------------------------+---------------+
         | application | alto-propmapparams+json | Section 8.3   |
         +-------------+-------------------------+---------------+

                   Table 1: Additional ALTO Media Types.

   Type name:
      application

   Subtype name:
      This document registers multiple subtypes, as listed in Table 1.

   Required parameters:
      n/a

   Optional parameters:
      n/a

   Encoding considerations:
      Encoding considerations are identical to those specified for the
      "application/json" media type.  See [RFC8259].

   Security considerations:
      Security considerations related to the generation and consumption
      of ALTO Protocol messages are discussed in Section 15 of
      [RFC7285].

   Interoperability considerations:
      This document specifies formats of conforming messages and the
      interpretation thereof.

   Published specification:
      This document is the specification for these media types; see
      Table 1 for the section documenting each media type.

   Applications that use this media type:
      ALTO servers and ALTO clients either stand alone or are embedded
      within other applications.

   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.

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      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:
      Internet Engineering Task Force (mailto:iesg@ietf.org).

12.2.  ALTO Entity Domain Type Registry

   This document requests IANA to create and maintain the "ALTO Entity
   Domain Type Registry", listed in Table 2.

     +============+============+=============+======================+
     | Identifier | Entity     | Hierarchy & | Media Type of        |
     |            | Identifier | Inheritance | Defining Resource    |
     |            | Encoding   |             |                      |
     +============+============+=============+======================+
     | ipv4       | See        | See Section | application/alto-    |
     |            | Section    | 6.1.3       | networkmap+json      |
     |            | 6.1.1      |             |                      |
     +------------+------------+-------------+----------------------+
     | ipv6       | See        | See Section | application/alto-    |
     |            | Section    | 6.1.3       | networkmap+json      |
     |            | 6.1.2      |             |                      |
     +------------+------------+-------------+----------------------+
     | pid        | See        | None        | application/alto-    |
     |            | Section    |             | networkmap+json      |
     |            | 6.2        |             |                      |
     +------------+------------+-------------+----------------------+

                    Table 2: ALTO Entity Domain Types

   This registry serves two purposes.  First, it ensures uniqueness of
   identifiers referring to ALTO entity domain types.  Second, it states
   the requirements for allocated entity domain types.

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12.2.1.  Consistency Procedure between ALTO Address Type Registry and
         ALTO Entity Domain Type Registry

   One potential issue of introducing the "ALTO Entity Domain Type
   Registry" is its relationship with the "ALTO Address Types Registry"
   already defined in Section 14.4 of [RFC7285].  In particular, the
   entity identifier of a type of an entity domain registered in the
   "ALTO Entity Domain Type Registry" MAY match an address type defined
   in "ALTO Address Type Registry".  It is necessary to precisely define
   and guarantee the consistency between "ALTO Address Type Registry"
   and "ALTO Entity Domain Registry".

   We define that the ALTO Entity Domain Type Registry is consistent
   with ALTO Address Type Registry if two conditions are satisfied:

   *  When an address type is already or able to be registered in the
      ALTO Address Type Registry [RFC7285], the same identifier MUST be
      used when a corresponding entity domain type is registered in the
      ALTO Entity Domain Type Registry.

   *  If an ALTO entity domain type has the same identifier as an ALTO
      address type, their addresses encoding MUST be compatible.

   To achieve this consistency, the following items MUST be checked
   before registering a new ALTO entity domain type in a future
   document:

   *  Whether the ALTO Address Type Registry contains an address type
      that can be used as an identifier for the candidate entity domain
      type identifier.  This has been done for the identifiers "ipv4"
      and "ipv6" of Table 2.

   *  Whether the candidate entity domain type identifier can
      potentially be an endpoint address type, as defined in Sections
      2.1 and 2.2 of [RFC7285].

   When a new ALTO entity domain type is registered, the consistency
   with the ALTO Address Type Registry MUST be ensured by the following
   procedure:

   *  Test: Do corresponding entity domain type identifiers match a
      known "network" address type?

      -  If yes (e.g., cell, MAC or socket addresses):

         o  Test: Is such an address type present in the ALTO Address
            Type Registry?

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            +  If yes: Set the new ALTO entity domain type identifier to
               be the found ALTO address type identifier.

            +  If no: Define a new ALTO entity domain type identifier
               and use it to register a new address type in the ALTO
               Address Type Registry following Section 14.4 of
               [RFC7285].

         o  Use the new ALTO entity domain type identifier to register a
            new ALTO entity domain type in the ALTO Entity Domain Type
            Registry following Section 12.2.2 of this document.

      -  If no (e.g., pid name, ane name or country code): Proceed with
         the ALTO Entity Domain Type registration as described in
         Section 12.2.2.

12.2.2.  ALTO Entity Domain Type Registration Process

   New ALTO entity domain types are assigned after IETF Review [RFC8126]
   to ensure that proper documentation regarding the new ALTO entity
   domain types and their security considerations has been provided.
   RFCs defining new entity domain types SHOULD indicate how an entity
   in a registered type of domain is encoded as an EntityID, and, if
   applicable, the rules defining the entity hierarchy and property
   inheritance.  Updates and deletions of ALTO entity domains types
   follow the same procedure.

   Registered ALTO entity domain type identifiers MUST conform to the
   syntactical requirements specified in Section 5.1.2.  Identifiers are
   to be recorded and displayed as strings.

   Requests to the IANA to add a new value to the Entity Domain Type
   registry MUST include the following information:

   *  Identifier: The name of the desired ALTO entity domain type.

   *  Entity Identifier Encoding: The procedure for encoding the
      identifier of an entity of the registered domain type as an
      EntityID (see Section 5.1.3).  If corresponding entity identifiers
      of an entity domain type match a known "network" address type, the
      Entity Identifier Encoding of this domain identifier MUST include
      both Address Encoding and Prefix Encoding of the same identifier
      registered in the ALTO Address Type Registry [RFC7285].  To define
      properties, an individual entity identifier and the corresponding
      full-length prefix MUST be considered aliases for the same entity.

   *  Hierarchy: If the entities form a hierarchy, the procedure for
      determining that hierarchy.

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   *  Inheritance: If entities can inherit property values from other
      entities, the procedure for determining that inheritance.

   *  Media type of defining information resource: Some entity domain
      types allow an entity domain name to be combined with an
      information resource name to define a resource-specific entity
      domain.  Such an information resource is called "defining
      information resource".  In this case, the authorized media type of
      the defining information resources MUST be unique and MUST be
      specified in the document defining the entity domain type.  When
      an entity domain type allows combinations with defining resources,
      this MUST be indicated here, together with the authorized media
      type for the defining resources.  The defining information
      resource for a resource-specific entity domain is the one that:

      -  has an entry in the IRD,

      -  defines these entities,

      -  does not use another information resource that defines these
         entities,

      -  defines and exposes entity identifiers that are all persistent.

      -  has a unique media type equal to the one specified in the
         document defining the entity domain type.

   *  Knowing the media type of the defining information resource is
      useful when Servers indicate resource specific entity domains in
      the property map capabilities.  Clients need to know if the
      combination of information resource type and entity domain type is
      allowed.  See also, Section 4.6 and Section 5.1 for more
      information.

   *  Mapping to ALTO Address Type: A boolean value to indicate if the
      entity domain type can be mapped to the ALTO address type with the
      same identifier.

   *  Security Considerations: In some usage scenarios, entity
      identifiers carried in ALTO Protocol messages may reveal
      information about an ALTO client or an ALTO service provider.
      Applications and ALTO service providers using addresses of the
      registered type should be cognizant of how (or if) the addressing
      scheme relates to private information and network proximity.

   This specification requests registration of the identifiers "ipv4",
   "ipv6" and "pid", as shown in Table 2.

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12.3.  ALTO Entity Property Type Registry

   This document requests IANA to create and maintain the "ALTO Entity
   Property Type Registry", listed in Table 3.

   This registry extends the "ALTO Endpoint Property Type Registry",
   defined in [RFC7285], in that a property type is defined on one or
   more entity domains, rather than just on IPv4 and IPv6 Internet
   address domains.  An entry in this registry is an ALTO entity
   property type defined in Section 5.2.1.  Thus, a registered ALTO
   entity property type identifier MUST conform to the syntactical
   requirements specified in that section.

   +============+====================+=================================+
   | Identifier | Intended Semantics | Media Type of                   |
   |            |                    | Defining Resource               |
   +============+====================+=================================+
   | pid        | See Section 7.1.1  | application/alto-               |
   |            | of [RFC7285]       | networkmap+json                 |
   +------------+--------------------+---------------------------------+

                    Table 3: ALTO Entity Property Types.

   Requests to the IANA to add a new value to the registry MUST include
   the following information:

   *  Identifier: The unique id for the desired ALTO entity property
      type.  The format MUST be as defined in Section 5.2.1 of this
      document.  It includes the information of the applied ALTO entity
      domain and the property name.

   *  Intended Semantics: ALTO entity properties carry with them
      semantics to guide their usage by ALTO clients.  Hence, a document
      defining a new type SHOULD provide guidance to both ALTO service
      providers and applications utilizing ALTO clients as to how values
      of the registered ALTO entity property should be interpreted.

   *  Media type of defining information resource: when the property
      type allows values to be defined relatively to a given information
      resource, the latter is referred to as the "defining information
      resource", see also description in Section 4.7.  The media type of
      the possibly used defining information resource MUST be unique and
      MUST be specified here, as well as in the document that defines
      the property type.

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   *  Security Considerations: ALTO entity properties expose information
      to ALTO clients.  ALTO service providers should be cognizant of
      the security ramifications related to the exposure of an entity
      property.

   In security considerations, the request should also discuss the
   sensitivity of the information, and why it is required for ALTO-based
   operations.  Regarding this discussion, the request SHOULD follow the
   recommendations of Section 14.3.  ALTO Endpoint Property Type
   Registry in [RFC7285].

   This document requests registration of the identifier "pid", listed
   in Table 3.  Semantics for this property are documented in
   Section 7.1.1 of [RFC7285].  No security issues related to the
   exposure of a "pid" identifier are considered, as it is exposed with
   the Network Map Service defined and mandated in [RFC7285].

13.  Acknowledgments

   The authors would like to thank Dawn Chen (Tongji University), and
   Shenshen Chen (Tongji/Yale University) for their contributions to
   earlier drafts.  Thank you also to Qiao Xiang (Yale University),
   Shawn Lin, Xin Wang and Vijay Gurbani (Vail systems) for fruitful
   discussions.  Last, big thanks to Danny Perez (University of
   Campinas) and Luis Contreras (Telefonica) for their substantial
   review feedback and suggestions to improve this document.

14.  References

14.1.  Normative References

   [ISO3166-1]
              ISO (International Organization for Standardization), .,
              "ISO 3166-1: Codes for the representation of names of
              countries and their subdivisions -- Part 1: Country
              codes", 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

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   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
              2006, <https://www.rfc-editor.org/info/rfc4632>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <https://www.rfc-editor.org/info/rfc5952>.

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

14.2.  Informative References

   [I-D.gao-alto-fcs]
              Zhang, J., Gao, K., Wang, J., and Y. Yang, "ALTO
              Extension: Flow-based Cost Query", Work in Progress,
              Internet-Draft, draft-gao-alto-fcs-07, 16 March 2020,
              <http://www.ietf.org/internet-drafts/draft-gao-alto-fcs-
              07.txt>.

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   [I-D.ietf-alto-cdni-request-routing-alto]
              Seedorf, J., Yang, Y., Ma, K., Peterson, J., and J. Zhang,
              "Content Delivery Network Interconnection (CDNI) Request
              Routing: CDNI Footprint and Capabilities Advertisement
              using ALTO", Work in Progress, Internet-Draft, draft-ietf-
              alto-cdni-request-routing-alto-16, 12 January 2021,
              <http://www.ietf.org/internet-drafts/draft-ietf-alto-cdni-
              request-routing-alto-16.txt>.

   [I-D.ietf-alto-path-vector]
              Gao, K., Lee, Y., Randriamasy, S., Yang, Y., and J. Zhang,
              "ALTO Extension: Path Vector", Work in Progress, Internet-
              Draft, draft-ietf-alto-path-vector-13, 20 November 2020,
              <http://www.ietf.org/internet-drafts/draft-ietf-alto-path-
              vector-13.txt>.

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,
              <https://www.rfc-editor.org/info/rfc7011>.

   [RFC7921]  Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
              <https://www.rfc-editor.org/info/rfc7921>.

   [RFC8895]  Roome, W. and Y. Yang, "Application-Layer Traffic
              Optimization (ALTO) Incremental Updates Using Server-Sent
              Events (SSE)", RFC 8895, DOI 10.17487/RFC8895, November
              2020, <https://www.rfc-editor.org/info/rfc8895>.

   [RFC8896]  Randriamasy, S., Yang, R., Wu, Q., Deng, L., and N.
              Schwan, "Application-Layer Traffic Optimization (ALTO)
              Cost Calendar", RFC 8896, DOI 10.17487/RFC8896, November
              2020, <https://www.rfc-editor.org/info/rfc8896>.

Appendix A.  Features introduced with the Entity Property Maps extension

   The Entity Property Maps extension described in this document
   introduces a number of features that are summarized in table below.
   The first column provides the name of the feature.  The second column
   provides the section number of this document that gives a high level
   description of the feature.  The third column provides the section
   number of this document that gives a normative description relating
   to the feature, when applicable.

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   +======================+=============+==============================+
   | Feature              | High-level  | Related normative            |
   |                      | description | description                  |
   +======================+=============+==============================+
   | Entity               | Section 3.1 | Section 5.1.3                |
   +----------------------+-------------+------------------------------+
   | Entity domain        | Section 3.2 |                              |
   | (ED)                 |             |                              |
   +----------------------+-------------+------------------------------+
   | Entity domain        | Section     | Section 5.1.1                |
   | type                 | 3.2.1       |                              |
   +----------------------+-------------+------------------------------+
   | Entity domain        | Section     | Section 5.1.2                |
   | name                 | 3.2.2       |                              |
   +----------------------+-------------+------------------------------+
   | Entity property      | Section 3.3 | Section 5.2, Section 5.2.1,  |
   | (EP) type            |             | Section 5.2.2, Section 5.2.3 |
   +----------------------+-------------+------------------------------+
   | Entity property      | Section 3.4 | Section 7, Section 8         |
   | map                  |             |                              |
   +----------------------+-------------+------------------------------+
   | Resource-specific    | Section 4.2 | Section 5.1.2,               |
   | ED name              |             | Section 5.1.2.1              |
   +----------------------+-------------+------------------------------+
   | Resource-specific    | Section 4.3 | Section 5.2.3                |
   | EP value             |             |                              |
   +----------------------+-------------+------------------------------+
   | Entity Hierarchy     | Section 4.4 | Section 5.1.4                |
   | and property         |             |                              |
   | inheritance          |             |                              |
   +----------------------+-------------+------------------------------+
   | Defining             | Section     | Section 12.2.2, Section 12.3 |
   | information          | 4.6,        |                              |
   | resource             | Section 4.7 |                              |
   +----------------------+-------------+------------------------------+

        Table 4: Features introduced with ALTO Entity Property Maps

Authors' Addresses

   Wendy Roome
   Nokia Bell Labs (Retired)
   124 Burlington Rd
   Murray Hill, NJ 07974
   United States of America

   Phone: +1-908-464-6975
   Email: wendy@wdroome.com

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   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   91460 NOZAY
   France

   Email: Sabine.Randriamasy@nokia-bell-labs.com

   Y. Richard Yang
   Yale University
   51 Prospect Street
   New Haven,  CT 06511
   United States of America

   Phone: +1-203-432-6400
   Email: yry@cs.yale.edu

   Jingxuan Jensen Zhang
   Tongji University
   4800 Cao'An Hwy
   Shanghai
   201804
   China

   Email: jingxuan.n.zhang@gmail.com

   Kai Gao
   Sichuan University
   No.24 South Section 1, Yihuan Road
   Chengdu
   610000
   China

   Email: kaigao@scu.edu.cn

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