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ALTO WG                                                         W. Roome
Internet-Draft                                            S. Randriamasy
Intended status: Standards Track                         Nokia Bell Labs
Expires: January 9, 2020                                         Y. Yang
                                                         Yale University
                                                                J. Zhang
                                                       Tongji University
                                                            July 8, 2019


                Unified Properties for the ALTO Protocol
                  draft-ietf-alto-unified-props-new-08

Abstract

   This document extends the Application-Layer Traffic Optimization
   (ALTO) Protocol [RFC7285] by generalizing the concept of "endpoint
   properties" to domains of other entities, and by presenting those
   properties as maps, similar to the network and cost maps in
   [RFC7285].

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted 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 January 9, 2020.








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Copyright Notice

   Copyright (c) 2019 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
   2.  Overview: Basic Concepts  . . . . . . . . . . . . . . . . . .   5
     2.1.  Entity  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Entity Property . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Property Map  . . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Information Resource  . . . . . . . . . . . . . . . . . .   6
     2.5.  Entity Domain . . . . . . . . . . . . . . . . . . . . . .   7
       2.5.1.  Resource-Specific Entity Domain . . . . . . . . . . .   7
       2.5.2.  Relationship between Entity and Entity Domain . . . .   7
       2.5.3.  Aggregated Entity Domain  . . . . . . . . . . . . . .   7
       2.5.4.  Resource-Specific Entity Property . . . . . . . . . .   8
     2.6.  Scope of Property Map . . . . . . . . . . . . . . . . . .   8
     2.7.  Entity Hierarchy and Property Inheritance . . . . . . . .   9
   3.  Protocol Specification: Basic Data Type . . . . . . . . . . .  10
     3.1.  Entity Domain . . . . . . . . . . . . . . . . . . . . . .  10
       3.1.1.  Entity Domain Type  . . . . . . . . . . . . . . . . .  10
       3.1.2.  Entity Domain Name  . . . . . . . . . . . . . . . . .  10
       3.1.3.  Entity Identifier . . . . . . . . . . . . . . . . . .  11
       3.1.4.  Hierarchy and Inheritance . . . . . . . . . . . . . .  12
     3.2.  Entity Property . . . . . . . . . . . . . . . . . . . . .  12
       3.2.1.  Entity Property Type  . . . . . . . . . . . . . . . .  12
       3.2.2.  Entity Property Name  . . . . . . . . . . . . . . . .  13
     3.3.  Information Resource Export . . . . . . . . . . . . . . .  13
       3.3.1.  Resource-Specific Entity Domain Export  . . . . . . .  13
       3.3.2.  Entity Property Mapping Export  . . . . . . . . . . .  14
   4.  Entity Domain Types . . . . . . . . . . . . . . . . . . . . .  14
     4.1.  Internet Address Domain Types . . . . . . . . . . . . . .  14
       4.1.1.  IPv4 Domain . . . . . . . . . . . . . . . . . . . . .  14
       4.1.2.  IPv6 Domain . . . . . . . . . . . . . . . . . . . . .  15
       4.1.3.  Hierarchy and Inheritance of Internet Address Domains  15
     4.2.  PID Domain  . . . . . . . . . . . . . . . . . . . . . . .  16



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       4.2.1.  Entity Domain Type  . . . . . . . . . . . . . . . . .  16
       4.2.2.  Domain-Specific Entity Identifiers  . . . . . . . . .  16
       4.2.3.  Hierarchy and Inheritance . . . . . . . . . . . . . .  17
       4.2.4.  Relationship To Internet Addresses Domains  . . . . .  17
     4.3.  Internet Address Properties vs. PID Properties  . . . . .  17
   5.  Entity Domains and Property Mappings in Information Resources  17
     5.1.  Network Map Resource  . . . . . . . . . . . . . . . . . .  17
       5.1.1.  Resource-Specific Entity Domain . . . . . . . . . . .  18
       5.1.2.  Entity Property Mapping . . . . . . . . . . . . . . .  18
     5.2.  Endpoint Property Resource  . . . . . . . . . . . . . . .  18
       5.2.1.  Resource-Specific Entity Domain . . . . . . . . . . .  18
       5.2.2.  Entity Property Mapping . . . . . . . . . . . . . . .  19
     5.3.  Property Map Resource . . . . . . . . . . . . . . . . . .  19
   6.  Property Map  . . . . . . . . . . . . . . . . . . . . . . . .  19
     6.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  19
     6.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  19
     6.3.  Accept Input Parameters . . . . . . . . . . . . . . . . .  19
     6.4.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  19
     6.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . .  20
     6.6.  Response  . . . . . . . . . . . . . . . . . . . . . . . .  20
   7.  Filtered Property Map . . . . . . . . . . . . . . . . . . . .  21
     7.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  21
     7.2.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  21
     7.3.  Accept Input Parameters . . . . . . . . . . . . . . . . .  21
     7.4.  Capabilities  . . . . . . . . . . . . . . . . . . . . . .  22
     7.5.  Uses  . . . . . . . . . . . . . . . . . . . . . . . . . .  22
     7.6.  Response  . . . . . . . . . . . . . . . . . . . . . . . .  22
   8.  Impact on Legacy ALTO Servers and ALTO Clients  . . . . . . .  24
     8.1.  Impact on Endpoint Property Service . . . . . . . . . . .  24
     8.2.  Impact on Resource-Specific Properties  . . . . . . . . .  24
     8.3.  Impact on the pid Property  . . . . . . . . . . . . . . .  25
     8.4.  Impact on Other Properties  . . . . . . . . . . . . . . .  25
   9.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  Network Map . . . . . . . . . . . . . . . . . . . . . . .  25
     9.2.  Property Definitions  . . . . . . . . . . . . . . . . . .  26
     9.3.  Information Resource Directory (IRD)  . . . . . . . . . .  27
     9.4.  Property Map Example  . . . . . . . . . . . . . . . . . .  29
     9.5.  Filtered Property Map Example #1  . . . . . . . . . . . .  30
     9.6.  Filtered Property Map Example #2  . . . . . . . . . . . .  31
     9.7.  Filtered Property Map Example #3  . . . . . . . . . . . .  32
     9.8.  Filtered Property Map Example #4  . . . . . . . . . . . .  33
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  34
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
     11.1.  application/alto-* Media Types . . . . . . . . . . . . .  35
     11.2.  ALTO Entity Domain Type Registry . . . . . . . . . . . .  36
       11.2.1.  Consistency Procedure between ALTO Address Type
                Registry and ALTO Entity Domain Registry . . . . . .  37
       11.2.2.  ALTO Entity Domain Registration Process  . . . . . .  38



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     11.3.  ALTO Entity Property Type Registry . . . . . . . . . . .  39
     11.4.  ALTO Resource-Specific Entity Domain Registries  . . . .  40
       11.4.1.  Network Map  . . . . . . . . . . . . . . . . . . . .  40
       11.4.2.  Endpoint Property  . . . . . . . . . . . . . . . . .  40
     11.5.  ALTO Resource Entity Property Mapping Registries . . . .  40
       11.5.1.  Network Map  . . . . . . . . . . . . . . . . . . . .  40
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  41
   13. Normative References  . . . . . . . . . . . . . . . . . . . .  41
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

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 two
   limitations.

   First, it allows properties to be associated with only a particular
   domain of entities, namely individual IP addresses.  It is reasonable
   to think that collections of endpoints, as defined by CIDRs [RFC4632]
   or PIDs, may also have properties.  Since the EPS cannot be extended
   to new entity domains, new services, with new request and response
   messages, would have to be defined for new entity domains.

   Second, 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 processes costs lookups without querying the ALTO
   server.  [RFC7285] does not define an equivalent 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.  But 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.

   This document specifies a new approach for defining and retrieving
   ALTO properties to address the two limitations.  Specifically, this
   document addresses the first limitation by introducing a generic
   concept called ALTO Entity Domains, where an entity is a
   generalization of an endpoint to also represent, a PID, a network



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   element, or a cell in a cellular network, etc.  As a consequence,
   ALTO Entity Domains defined in this document are a super-set of ALTO
   Address Types defined in [RFC7285].  Their exact relationship is
   specified in Section 11.2.1.

   Entity domains and property names are extensible.  New entity domains
   can be defined without revising the messages defined in this
   document, in the same way that new cost metrics and new endpoint
   properties can be defined without revising the messages defined in
   [RFC7285].

   Additional, this document addresses the second limitation by defining
   two new types of resources, namely Property Map (see Section 6) and
   Filtered Property Map (see Section 7).  The former is a GET-mode
   resource which returns the property values for all entities in a
   domain, and is analogous to a network map or a cost map in [RFC7285].
   The latter is a POST-mode resource which returns the values for a set
   of properties and entities requested by the client, and is analogous
   to a filtered network map or a filtered cost map.

   This document subsumes the Endpoint Property Service defined in
   [RFC7285], although that service may be retained for legacy clients
   (see Section 8).

2.  Overview: Basic Concepts

   Before we define the specification of unified properties, there are
   several basic concepts which we need to introduce.

2.1.  Entity

   The entity concept generalizes the concept of the endpoint defined in
   Section 2.1 of [RFC7285].  An entity is an object that can be an
   endpoint and is identified 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 is even not related to any network address.

   Examples of eligible entities are:

   o  a PID, defined in [RFC7285], that has a provider defined human
      readable abstract identifier defined by a ALTO network map, which
      maps a PID to a set of ipv4 and ipv6 addresses;

   o  an autonomous system (AS), that has an AS number (ASN) as its
      identifier and maps to a set of ipv4 and ipv6 addresses;

   o  a region representing a country, that is identified by its country
      code defined by ISO 3166 and maps to a set of cellular addresses;



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   o  a TCP/IP network flow, that has a server defined identifier
      consisting of the defining TCP/IP 5-Tuple, , which is an example
      that all endpoints are entities while not all entities are
      endpoints;

   o  a routing element, that is specified in [RFC7921] and includes
      routing capability information;

   o  an abstract network element, that has a server defined identifier
      and represents a network node, link or their aggregation.

2.2.  Entity Property

   An entity property defines a property of an entity.  It is similar to
   the endpoint property defined by Section 7.1 of [RFC7285], but can be
   general besides network-aware.

   For example,

   o  an "ipv4" entity may have a property whose value is an Autonomous
      System (AS) number indicating the AS which this IPv4 address is
      owned by;

   o  a "pid" entity may have a property which indicates the central
      geographical location of endpoints included by it.

2.3.  Property Map

   An ALTO property map provides a set of properties for a set of
   entities.  These entities may be in different types.  For example, an
   ALTO property map may define the ASN property for both "ipv4" and
   "ipv6" entities.

2.4.  Information Resource

   This document uses the same definition of the information resource as
   defined by [RFC7285].  Each information resource usually has a JSON
   format representation following a specific schema defined by its
   media type.

   For example, an ALTO network map resource is represented by a JSON
   objectof type InfoResourceNetworkMap defined by the media type
   "application/alto-networkmap+json".








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2.5.  Entity Domain

   An entity domain defines a set of entities in the same type.  This
   type is also called the type of this entity domain.

   Using entity domains, an ALTO property map can indicate which
   entities the ALTO client can query to get their properties.

2.5.1.  Resource-Specific Entity Domain

   To define an entity domain, one naive solution is to enumerate all
   entities in this entity domain.  But it is inefficient when the size
   of the entity domain is large.

   To avoid enumerating all entities, this document introduces an
   approach called "Resource-Specific Entity Domain" to define entity
   domains:

   Each information resource may define several types of entity domains.
   And for each type of entity domain, an information resource can
   define at most one entity domain.  For example, an ALTO netowrk map
   resource can define an IPv4 domain, an IPv6 domain and a pid domain.
   In this document, these entity domains are called resource-specific
   entity domains.  An ALTO property map only need to indicate which
   types of entity domain defined by which information resources can be
   queried, the ALTO client will know which entities are effective to be
   queried.

2.5.2.  Relationship between Entity and Entity Domain

   In this document, an entity is owned by exact one entity domain.  It
   requires that when an ALTO client or server references an entity, it
   must indicate its entity domain explicitly.  Even two entities in two
   different entity domains may reflect to the same physical or logical
   object, we treat them as different entities.

   Because of this rule, although the resource-specific entity domain
   approach has no ambiguity, it may introduce redundancy.

2.5.3.  Aggregated Entity Domain

   Two entities in two different resource-specific entity domains may
   reflect to the same physical or logical object.  For example, the
   IPv4 entity "192.0.2.34" in the IPv4 domain of the network map
   "netmap1" and the IPv4 entity "192.0.2.34" in the IPv4 domain of the
   network map "netmap2" should indicate the same Internet endpoint
   addressed by the IPv4 address "192.0.2.34".




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   Each entity in each resource-specific entity domain may only have
   part of properties of its associated physical or logical object.  For
   example, the IPv4 entity in the IPv4 domain of the network map
   "netmap1" only has the PID property defined by "netmap1"; same to the
   IPv4 entity in the IPv4 domain of the network map "netmap2".  If the
   ALTO client wants to get the complete properties, using the resource-
   specific entity domain, the ALTO client has to query the IPv4 entity
   "192.0.2.34" twice.

   To simplify the query process of the ALTO client, this document
   introduces the concept "Aggregated Entity Domain".  An aggregated
   entity domain defines an aggregated set of entities coming from
   multiple resource-specific entity domains in the same type.  An
   entity in the aggregated entity domain includes all properties
   defined for the associated entity in each associated resource-
   specific entity domains.  For example, the IPv4 entity "192.0.2.34"
   in the aggregated entity domain between the IPv4 domain of "netmap1"
   and the IPv4 domain of "netmap2" has PID properties defined by both
   "netmap1" and "netmap2".

2.5.4.  Resource-Specific Entity Property

   According to the example of the aggregated entity domain, an entity
   may have multiple properties in the same type but associated to
   different information resources.  To distinguish them, this document
   uses the same approach proposed by Section 10.8.1 of [RFC7285], which
   is called "Resource-Specific Entity Property".

2.6.  Scope of Property Map

   Using entity domains to organize entities, an ALTO property map
   resource actually provides a set of properties for some entity
   domains.  If we ignore the syntax sugar of the aggregated entity
   domain, we can consider an ALTO property map resource just provides a
   set of (ri, di) => (ro, po) mappings, where (ri, di) means a
   resource-specific entity domain of type di defined by the information
   resource ri, and (ro, po) means a resource-specific entity property
   po defined by the information resource ro.

   For each (ri, di) => (ro, po) mapping, the scope of an ALTO property
   map resource must be one of cases in the following diagram:










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                       domain.resource   domain.resource
                       (ri) = r          (ri) = this
                     +-----------------|-----------------+
       prop.resource | Export          | Non-exist       |
       (ro) = r      |                 |                 |
                     +-----------------|-----------------+
       prop.resource | Extend          | Define          |
       (ro) = this   |                 |                 |
                     +-----------------|-----------------+

   where "this" points to the resulting property map resource, "r"
   presents an existing ALTO information resource other the resulting
   property map resource.

   o  ri = ro = r ("export" mode): the property map resource just
      transforms the property mapping di => po defined by r into the
      unified representation format and exports it.  For example: r =
      "netmap1", di = "ipv4", po = "pid".  The property map resource
      exports the "ipv4 => pid" mapping defined by "netmap1".

   o  ri = r, ro = this ("extend" mode): the property map extends
      properties of entities in the entity domain (r, di) and defines a
      new property po on them.  For example: the property map resource
      ("this") defines a "geolocation" property on domain "netmap1.pid".

   o  ri = ro = this ("define" mode): the property map defines a new
      intrinsic entity domain and defines property po for each entities
      in this domain.  For example: the property map resource ("this")
      defines a new entity domain "asn" and defines a property
      "ipprefixes" on this domain.

   o  ri = this, ro = r: in the scope of a property map resource, it
      does not make sense that another existing ALTO information
      resource defines a property for this property map resource.

2.7.  Entity Hierarchy and Property Inheritance

   Enumerating all individual effective entities are inefficient.  Some
   types of entities have the hierarchy format, e.g., cidr, which stand
   for sets of individual entities.  Many entities in the same
   hierarchical format entity sets may have the same proprety values.
   To reduce the size of the property map representation, this document
   introduces an approach called "Property Inheritance".  Individual
   entities can inherit the property from its hierarchical format entity
   set.






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3.  Protocol Specification: Basic Data Type

3.1.  Entity Domain

3.1.1.  Entity Domain Type

   An entity domain has a type, which is defined 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), hyphen ("-", U+002D), and low line ("_", U+005F).
   For example, the strings "ipv4", "ipv6", and "pid" are valid entity
   domain types.

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

   An entity domain type defines the semantics of a type of entity
   domains.  Each entity domain type MUST be registered with the IANA.
   The format of the entity identifiers (see Section 3.1.3) in that type
   of entity domains, as well as any hierarchical or inheritance rules
   (see Section 3.1.4) for those entities, MUST be specified at the same
   time.

3.1.2.  Entity Domain Name

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

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

   This document distinguish three types of entity domains: resource-
   specific entity domains, self-defined entity domain and aggregated
   entity domains.  Their entity domain names are derived as follows.

   Each ALTO information resource MAY define a resource-specific entity
   domain (which could be empty) in a given entity domain type.  A
   resource-specific entity domain is identified by an entity domain
   name derived as follows.  It MUST start with a resource ID using the
   ResourceID type defined in [RFC7285], followed by the "." separator
   (U+002E), followed by an EntityDomainType typed string.  For example,
   if an ALTO server provides two network maps "netmap-1" and "netmap-
   2", they can define two different "pid" domains identified by
   "netmap-1.pid" and "netmap-2.pid" respectively.  To be simplified, in
   the scope of a specific information resource, the resource-specific
   entity domain defined by itself can be identified by the "."
   EntityDomainTyep without the ResourceID.





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   When the associated information resource of a resource-specific
   entity domain is the current information resource itself, this
   resource-specific entity domain is a self-defined entity domain, and
   its ResourceID SHOULD be ignored from its entity domain name.

   Given a set of ALTO information resources, there MAY be an aggregated
   entity domain in a given entity domain type amongst them.  An
   aggregated entity domain is simply identified by its entity domain
   type.  For example, given two network maps "net-map-1" and "net-map-
   2", "ipv4" and "ipv6" identify two aggregated Internet address entity
   domains (see Section 4.1) between them.

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

3.1.3.  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 registering a new
   entity domain type.  Identifiers MAY be hierarchical, and properties
   MAY be inherited based on that hierarchy.  Again, 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 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.








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3.1.4.  Hierarchy and Inheritance

   To make the representation efficient, some types of entity domains
   MAY allow the ALTO client/server to use a hierarchical format entity
   identifier to represent a block of individual entities. e.g., In an
   IPv4 domain "net1.ipv4", a cidr "net1.ipv4:192.0.2.0/26" represents
   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.

3.2.  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 be
   identified.  One entity MAY have multiple properties in the same
   type.

3.2.1.  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).

   Each entity property type MUST be registered with the IANA.  The
   intended semantics of the entity property type MUST be specified at
   the same time.

   To distinguish with the endpoint property type, the entity property
   type has the following features.

   o  Some entity property types may be applicable to entities in only
      particular types of entity domains, not all.  For example, the
      "pid" property is not applicable to entities in a "pid" typed
      entity domain, but is applicable to entities in the "ipv4" or
      "ipv6" domains.

   o  The intended semantics of the value of a entity property may also
      depend on the the entity domain type of this entity.  For example,
      suppose that the "geo-location" property is defined as the
      coordinates of a point, encoded as (say) "latitude longitude
      [altitude]."  When applied to an entity that represents a specific
      host computer, identified by an address in the "ipv4" or "ipv6"
      entity domain, the property defines the host's location.  However,
      when applied to an entity in a "pid" domain, the property would




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      indicate the location of the center of all hosts in this "pid"
      entity.

3.2.2.  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.

   When the associated information resource of the entity property is
   the current information resource itself, the ResourceID in the
   property name SHOULD be ignored.  For example, the ".asn" property of
   an "ipv4" entity indicates the AS number of the AS which this IPv4
   address is owned by.

3.3.  Information Resource Export

   Each information resource MAY export a set of entity domains and
   entity property mappings.

3.3.1.  Resource-Specific Entity Domain Export

   Each type of information resource MAY export several types of entity
   domains.  For example, a network map resource defines a "pid" domain,
   a "ipv4" domain and a "ipv6" domain (which may be empty).

   When a new ALTO information resource type is registered, if this type
   of information resource can export an existing type of entity domain,
   the corresponding document MUST define how to export such type of
   entity domain from such type of information resource.

   When a new entity domain type is defined, if an existing type of
   information resource can export an entity domain in this entity
   domain type, the corresponding document MUST define how to export
   such type of entity domain from such type of information resource.



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3.3.2.  Entity Property Mapping Export

   For each entity domain which could be exported by an information
   resource, this information resource MAY also export some mapping from
   this entity domain to some entity property.  For example, a network
   map resource can map an "ipv4" entity to its "pid" property.

   When a new ALTO information resource type is registered, if this type
   of information resource can export an entity domain in an existing
   entity domain type, and map entities in this entity domain to an
   existing type of entity property, the corresponding document MUST
   define how to export such type of an entity property.

   When a new ALTO entity domain type or a new entity property type is
   defined, if an existing type of resource can export an entity domain
   in this entity domain type, and map entities in this entity domain to
   this type of entity property, the corresponding document MUST define
   how to export such type of an entity property.

4.  Entity Domain Types

   This document defines three entity domain types.  The definition of
   each entity domain type below includes the following: (1) entity
   domain type name, (2) entity domain-specific entity identifiers, and
   (3) hierarchy and inheritance semantics.  Since a global entity
   domain type defines a single global entity domain, we say entity
   domain instead of entity domain type.

4.1.  Internet Address Domain Types

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

4.1.1.  IPv4 Domain

4.1.1.1.  Entity Domain Type

   ipv4

4.1.1.2.  Domain-Specific Entity Identifiers

   Individual addresses are strings as specified by the IPv4Addresses
   rule of Section 3.2.2 of [RFC3986]; blocks of addresses are prefix-
   match strings as specified in Section 3.1 of [RFC4632].  For the
   purpose of defining properties, an individual Internet address and



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   the corresponding full-length prefix are considered aliases for the
   same entity.  Thus "ipv4:192.0.2.0" and "ipv4:192.0.2.0/32" are
   equivalent.

4.1.2.  IPv6 Domain

4.1.2.1.  Entity Domain Type

   ipv6

4.1.2.2.  Domain-Specific Entity Identifiers

   Individual addresses are strings as specified by Section 4 of
   [RFC5952]; blocks of addresses are prefix-match strings as specified
   in Section 7 of [RFC5952].  For the purpose of defining 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.

4.1.3.  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 some block C which prefix-matches I,
   then the address I inherits the value of P defined for block C.  If
   more than one such block defines a value for P, I inherits the value
   of P in the block with the longest prefix.  It is important to notice
   that this longest prefix rule will ensure no multiple inheritance,
   and hence no ambiguity.

   Address blocks can also inherit properties: if a property P is not
   defined for a block C, but is defined for some block C' which covers
   all IP addresses in C, and C' has a shorter mask than C, then block C
   inherits the property from C'.  If there are several such blocks C',
   C inherits from the block with the longest prefix.

   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:



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                         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.

   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:

   o  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."

   o  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.

4.2.  PID Domain

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

4.2.1.  Entity Domain Type

   pid

4.2.2.  Domain-Specific Entity Identifiers

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




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4.2.3.  Hierarchy and Inheritance

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

4.2.4.  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 some or all properties
   of a PID to the prefixes in that PID.

   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".

4.3.  Internet Address Properties vs. PID Properties

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

   The PID domain 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 the Internet address domain.  On the other hand, a
   property that explains why a PID was formed, or how it relates a
   provider's network, would best be associated with the PID domain.

5.  Entity Domains and Property Mappings in Information Resources

5.1.  Network Map Resource

   The ALTO network map resource defined by the media type "application/
   alto-networkmap+json" exports the following types of entity domains
   and entity property mappings.







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5.1.1.  Resource-Specific Entity Domain

   An ALTO network map resource defines a "pid" domain, an "ipv4" domain
   and an "ipv6" domain by follows:

   o  The defined "pid" domain includes all PIDs in keys of the
      "network-map" object.

   o  The defined "ipv4" domain includes all IPv4 addresses appearing in
      the "ipv4" field of the endpoint address group of each PID.

   o  The defined "ipv6" domain includes all IPv6 addresses appearing in
      the "ipv6" field of the endpoint address group of each PID.

5.1.2.  Entity Property Mapping

   For each of the preceding entity domains, an ALTO network map
   resource provides the properties mapping as follows:

   ipv4 -> pid:  An "networkmap" typed resource can map an "ipv4" entity
      to a "pid" property whose value is a PID defined by this
      "networkmap" resource and including the IPv4 address of this
      entity.

   ipv6 -> pid:  An "networkmap" typed resource can map an "ipv6" entity
      to a "pid" property whose value is a PID defined by this
      "networkmap" resource and including the IPv6 address of this
      entity.

5.2.  Endpoint Property Resource

   The ALTO endpoint property resource defined by the media type
   "application/alto-endpointprop+json" exports the following types of
   entity domains and entity property mappings.

5.2.1.  Resource-Specific Entity Domain

   An ALTO endpoint property resource defined an "ipv4" domain and an
   "ipv6" domain by follows:

   o  The defined "ipv4" domain includes all IPv4 addresses appearing in
      keys of the "endpoint-properties" object.

   o  The defined "ipv6" domain includes all IPv6 addresses appearing in
      keys of the "endpoint-properties" object.






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5.2.2.  Entity Property Mapping

   For each of the preceding entity domains, an ALTO endpoint property
   resource exports the properties mapping from it to each supported
   global endpoint property.  The property value is the corresponding
   global endpoint property value in the "endpiont-properties" object.

5.3.  Property Map Resource

   To avoid the nested reference and its potential complexity, this
   document does not specify the export rule of resource-specific entity
   domain and entity property mapping for the ALTO property map resource
   defined by the media type "application/alto-propmap+json" (see
   Section 6.1).

6.  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 9.4 gives an example of a property map request and its
   response.

6.1.  Media Type

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

6.2.  HTTP Method

   The property map is requested using the HTTP GET method.

6.3.  Accept Input Parameters

   None.

6.4.  Capabilities

   The capabilities are defined by an object of type
   PropertyMapCapabilities:










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       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.

6.5.  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).

6.6.  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



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   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:

   o  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.

   o  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.

   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.

7.  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 9.5, Section 9.6, Section 9.7 and Section 9.8 give examples
   of filtered property map requests and responses.

7.1.  Media Type

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

7.2.  HTTP Method

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

7.3.  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



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   "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 7.4).

   properties:  List of properties to be returned for each entity.  Each
      specified property MUST be included in the list of properties in
      this resource's "capabilities" field (see Section 7.4).  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.

7.4.  Capabilities

   The capabilities are defined by an object of type
   PropertyMapCapabilities, as defined in Section 6.4.

7.5.  Uses

   Same to the "uses" field of the Property Map resource (see
   Section 6.5).

7.6.  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 as
   follows:

   o  An entity identifier in "entities" in the request is invalid if:

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



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      *  The entity identifier is an invalid identifier in the entity
         domain.

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

      If an entity identifier in "entities" in 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 this entity identifier.

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

      It is not an error that a filtered property map resource does not
      define a requested property's value for a particular entity.  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 6.6), except that:

   o  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.

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

   o  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., an "ipv4" or "ipv6" address block),
      the response MUST cover properties for all identifiers in this
      hierarchical identifier.

   It is important that the filtered property map response MUST include
   all inherited property values for the requested entities and all the




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   entities which are able to inherit property values from them.  To
   achieve this goal, the ALTO server MAY follow three rules:

   o  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.

   o  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
      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.

   o  If an entity in the response is already covered by some other
      entities in the same response, it SHOULD be removed from the
      response for compactness.  For example, 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.  Impact on Legacy ALTO Servers and ALTO Clients

8.1.  Impact on Endpoint Property Service

   Since the property map and the filtered property map defined in this
   document provide the functionality of the Endpoint Property Service
   (EPS) defined in Section 11.4 of [RFC7285], it is RECOMMENDED that
   the EPS be deprecated in favor of Property Map and Filtered Property
   Map.  However, ALTO servers MAY provide an EPS for the benefit of
   legacy clients.

8.2.  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
   upon, while global property names have no such prefix.  The property
   map and the filtered property map defined in this document do not
   distinguish between those two types of properties.  Instead, if there



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   is a dependency, it is indicated by the "uses" capability of a
   property map, and is shared by all properties and entity domains in
   that map.  Accordingly, it is RECOMMENDED that resource-specific
   endpoint properties be deprecated, and no new resource-specific
   endpoint properties be defined.

8.3.  Impact on the pid Property

   Section 7.1.1 of [RFC7285] defines the resource-specific endpoint
   property name "pid", whose value is the name of the PID containing
   that endpoint.  For compatibility with legacy clients, an ALTO server
   which provides the "pid" property via the EPS MUST use that
   definition, and that syntax.

   However, when used with property maps, this document amends the
   definition of the "pid" property as follows.

   First, the name of the property is simply "pid"; the name is not
   prefixed with the resource ID of a network map.  The "uses"
   capability of the property map indicates the associated network map.
   This implies that a property map can only return the "pid" property
   for one network map; if an ALTO server provides several network maps,
   it MUST provide a Property Map for each of the network maps.

   Second, a client MAY request the "pid" property for a block of
   Internet addresses.  An ALTO server determines the value of "pid" for
   an address block C as the rules defined in Section 7.6.

   Note that although an ALTO server MAY provide a GET-mode property map
   which returns the entire map for the "pid" property, there is no need
   to do so, because that map is simply the inverse of the network map.

8.4.  Impact on Other Properties

   In general, there should be little or no impact on other previously
   defined properties.  The only consideration is that properties can
   now be defined on blocks of identifiers, rather than just individual
   identifiers, which might change the semantics of a property.

9.  Examples

9.1.  Network Map

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







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            defaultpid:  ipv4:0.0.0.0/0  ipv6:::0/0
            pid1:        ipv4:192.0.2.0/25
            pid2:        ipv4:192.0.2.0/28  ipv4:192.0.2.16/28
            pid3:        ipv4:192.0.3.0/28
            pid4:        ipv4:192.0.3.16/28

                   Figure 3: Example Default Network Map

   And another simple alternative network map:

            defaultpid:  ipv4:0.0.0.0/0  ipv6:::0/0
            pid1:        ipv4:192.0.2.0/28  ipv4:192.0.2.16/28
            pid2:        ipv4:192.0.3.0/28  ipv4:192.0.3.16/28

                 Figure 4: Example Alternative Network Map

9.2.  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
           ipv4:192.0.2.0:          -      -      -        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



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   "ISP" property for "ipv4:192.0.2.0" 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:

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

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

9.3.  Information Resource Directory (IRD)

   The following IRD defines the relevant resources of the ALTO server.
   It provides two property maps, one for the "ISP" and "ASN"
   properties, and another for the "country" and "state" properties.
   The server could have provided a single property map for all four
   properties, but did not, presumably because the organization that
   runs the ALTO server believes any given client is not interested in
   all four properties.

   The server provides two filtered property maps.  The first returns
   all four properties, and the second just returns 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 for the "pid" property does have a "uses" capability for
   the default network map, because that defines the values of the "pid"
   property.

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

        "meta" : {
          ...
          "default-alto-network-map" : "default-network-map"
        },
        "resources" : {
          "default-network-map" : {
            "uri" : "http://alto.example.com/networkmap/default",



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            "media-type" : "application/alto-networkmap+json"
          },
          "alt-network-map" : {
            "uri" : "http://alto.example.com/networkmap/alt",
            "media-type" : "application/alto-networkmap+json"
          },
          .... property map resources ....
          "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/full/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.exmaple.com/propmap/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" ],
              }
            }
          },
          "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" : {



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              "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" ]
             }
          }
        }

                           Figure 8: Example IRD

9.4.  Property Map Example

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

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

   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









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   HTTP/1.1 200 OK
   Content-Length: ###
   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"}
     }
   }

9.5.  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.

   POST /propmap/lookup/inet-iacs HTTP/1.1
   Host: alto.example.com
   Accept: application/alto-propmap+json,application/alto-error+json
   Content-Length: ###
   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" ]
   }









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   HTTP/1.1 200 OK
   Content-Length: ###
   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"}
     }
   }

9.6.  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".

   Also note that some entities like "ipv4:192.0.2.0/28" and
   "ipv4:192.0.2.16/28" in the response are not listed in the request
   explicitly.  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.









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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: ###
   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" ]
   }

   HTTP/1.1 200 OK
   Content-Length: ###
   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"}
    }
   }

9.7.  Filtered Property Map Example #3

   The following example uses the filtered property map resource to
   request the "pid" property for several IPv4 addresses and prefixes.

   Note that the entity "ipv4:192.0.3.0/27" is redundant in the
   response.  Although it can inherit a value of "defaultpid" for the



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   "pid" property from the entity "ipv4:0.0.0.0/0", none of addresses in
   it is in "defaultpid".  Because blocks "ipv4:192.0.3.0/28" and
   "ipv4:192.0.3.16/28" have already cover all addresses in that block.
   So an ALTO server who wants a compact response can omit this entity.

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

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

   HTTP/1.1 200 OK
   Content-Length: ###
   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"},
       "ipv4:192.0.2.0/27":  {"default-network-map.pid": "defaultpid"},
       "ipv4:192.0.3.0/28":  {"default-network-map.pid": "pid3"},
       "ipv4:192.0.3.16/28": {"default-network-map.pid": "pid4"}
     }
   }

9.8.  Filtered Property Map Example #4

   The following example uses the filtered property map resource to
   request the "region" property for several PIDs defined in "default-
   network-map".  The value of the "region" property for each PID is not
   defined by "default-network-map", but the reason why the PID is
   defined by the network operator.





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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: ###
   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: ###
   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.  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.





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   A particular fundamental security consideration when an ALTO server
   provides a Property Map is to define precisely the policies on who
   can access what properties for which entities.  Security mechanisms
   such as authentication and confidentiality mechanisms then should be
   applied to enforce the policy.  For example, a policy can be that a
   property P can be accessed only by its owner (e.g., the customer who
   is allocated a given IP address).  Then, the ALTO server will need to
   deploy corresponding mechanisms to realize the policy.  The policy
   may allow non-owners to access a coarse-grained value of the property
   P.  In such a case, the ALTO server may provide a different URI to
   provide the information.

11.  IANA Considerations

   This document defines additional application/alto-* media types, and
   extends the ALTO endpoint property registry.

11.1.  application/alto-* Media Types

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

   +--------------+--------------------------+------------------------+
   | Type         | Subtype                  | Specification          |
   +--------------+--------------------------+------------------------+
   | application  | alto-propmap+json        | Section 6.1            |
   | application  | alto-propmapparams+json  | Section 7.3            |
   +--------------+--------------------------+------------------------+

                   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
      [RFC7159].

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




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   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.

      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).

11.2.  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 Identifier         | Hierarchy & Inheritance |
   |             | Encoding                  |                         |
   +-------------+---------------------------+-------------------------+
   | ipv4        | See Section 4.1.1         | See Section 4.1.3       |
   | ipv6        | See Section 4.1.2         | See Section 4.1.3       |
   | pid         | See Section 4.2           | None                    |
   +-------------+---------------------------+-------------------------+

                       Table 2: ALTO Entity Domains.





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

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

   One potential issue of introducing the "ALTO Entity Domain Registry"
   is its relationship with the "ALTO Address Types Registry" already
   defined in Section 14.4 of [RFC7285].  In particular, the entity
   identifier of an entity domain registered in the "ALTO Entity Domain
   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 Registry is consistent with
   ALTO Address Type Registry if two conditions are satisfied:

   o  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 is registered in the ALTO
      Entity Domain Registry.

   o  If an ALTO entity domain 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 in a future document:

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

   o  Whether the candidate entity identifier of the entity domain is
      able to be an endpoint address, as defined in Sections 2.1 and 2.2
      of [RFC7285].

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

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

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




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

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

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

         +  Use the new ALTO entity domain identifier to register a new
            ALTO entity domain in the ALTO Entity Domain Registry
            following Section 11.2.2 of this document.

      *  If no (e.g., pid name, ane name or country code): Proceed with
         the ALTO Entity Domain registration as described in
         Section 11.2.2.

11.2.2.  ALTO Entity Domain Registration Process

   New ALTO entity domains are assigned after IETF Review [RFC5226] to
   ensure that proper documentation regarding the new ALTO entity
   domains and their security considerations has been provided.  RFCs
   defining new entity domains SHOULD indicate how an entity in a
   registered 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 follow the same
   procedure.

   Registered ALTO entity domain identifiers MUST conform to the
   syntactical requirements specified in Section 3.1.2.  Identifiers are
   to be recorded and displayed as strings.

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

   o  Identifier: The name of the desired ALTO entity domain.

   o  Entity Identifier Encoding: The procedure for encoding the
      identifier of an entity of the registered type as an EntityId (see
      Section 3.1.3).  If corresponding entity identifiers of an entity
      domain 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].  For the purpose of
      defining properties, an individual entity identifier and the
      corresponding full-length prefix MUST be considered aliases for
      the same entity.



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

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

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

   o  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 made aware 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.

11.3.  ALTO Entity Property Type Registry

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

   To distinguish with the "ALTO Endpoint Property Type Registry", each
   entry in this registry is an ALTO entity property type defined in
   Section 3.2.1.  Thus, registered ALTO entity property type identifier
   MUST conform to the syntactical requirements specified in that
   section.

   The initial registered ALTO entity property types are listed in
   Table 3.

             +-------------+---------------------------------+
             | Identifier  | Intended Semantics              |
             +-------------+---------------------------------+
             | pid         | See Section 7.1.1 of [RFC7285]  |
             +-------------+---------------------------------+

                   Table 3: ALTO Entity Property Types.

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

   o  Identifier: The unique id for the desired ALTO entity property
      type.  The format MUST be as defined in Section 3.2.1 of this




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      document.  It includes the information of the applied ALTO entity
      domain and the property name.

   o  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.

   This document requests registration of the identifier "pid", as shown
   in Table 3.

11.4.  ALTO Resource-Specific Entity Domain Registries

11.4.1.  Network Map

   Media-type: application/alto-networkmap+json

               +---------------------+---------------------+
               | Entity Domain Type  | Intended Semantics  |
               +---------------------+---------------------+
               | ipv4                | See Section 5.1.1   |
               | ipv6                | See Section 5.1.1   |
               | pid                 | See Section 5.1.1   |
               +---------------------+---------------------+

        Table 4: ALTO Network Map Resource-Specific Entity Domain.

11.4.2.  Endpoint Property

   Media-type: application/alto-endpointprop+json

               +---------------------+---------------------+
               | Entity Domain Type  | Intended Semantics  |
               +---------------------+---------------------+
               | ipv4                | See Section 5.2.1   |
               | ipv6                | See Section 5.2.1   |
               +---------------------+---------------------+

     Table 5: ALTO Endpoint Property Resource-Specific Entity Domain.

11.5.  ALTO Resource Entity Property Mapping Registries

11.5.1.  Network Map

   Media-type: application/alto-networkmap+json





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   +----------------+-----------------+-------------+------------------+
   | Mapping        | Entity Domain   | Property    | Intended         |
   | Descriptor     | Type            | Type        | Semantics        |
   +----------------+-----------------+-------------+------------------+
   | ipv4 -> pid    | ipv4            | pid         | See              |
   |                |                 |             | Section 5.1.2    |
   | ipv6 -> pid    | ipv6            | pid         | See              |
   |                |                 |             | Section 5.1.2    |
   +----------------+-----------------+-------------+------------------+

            Table 6: ALTO Network Map Entity Property Mapping.

12.  Acknowledgments

   The authors would like to thank discussions with Kai Gao, Qiao Xiang,
   Shawn Lin, Xin Wang, Danny Perez, and Vijay Gurbani.  The authors
   thank Dawn Chen (Tongji University), and Shenshen Chen (Tongji/Yale
   University) for their contributions to earlier drafts.

13.  Normative References

   [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>.

   [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>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [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>.






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   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [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>.

   [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>.

Authors' Addresses

   Wendy Roome
   Nokia Bell Labs (Retired)
   124 Burlington Rd
   Murray Hill, NJ  07974
   USA

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


   Sabine Randriamasy
   Nokia Bell Labs
   Route de Villejust
   NOZAY  91460
   FRANCE

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


   Y. Richard Yang
   Yale University
   51 Prospect Street
   New Haven, CT  06511
   USA

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







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   Jingxuan Jensen Zhang
   Tongji University
   4800 Caoan Road
   Shanghai  201804
   China

   Email: jingxuan.n.zhang@gmail.com












































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