Update to the ipn URI scheme
draft-ietf-dtn-ipn-update-04

Delay/Disruption Tolerant Networking                           R. Taylor
Internet-Draft                                            Ori Industries
Updates: [9171, 7116] (if approved)                           E. Birrane
Intended status: Standards Track                                 JHU/APL
Expires: 13 November 2023                                    12 May 2023

                      Update to the ipn URI scheme
                      draft-ietf-dtn-ipn-update-04

Abstract

   This document updates both the specification of the ipn URI scheme
   previously defined in [RFC7116] and the rules for encoding of these
   URIs when used as an Endpoint Identifier (EID) in Bundle Protocol
   Version 7 (BPv7) as defined in [RFC9171].  These updates update and
   clarify the structure and behavior of the ipn URI scheme, define
   encodings of ipn scheme URIs, and establish the registries necessary
   to manage this scheme.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at
   https://ricktaylor.github.io/ipn2/draft-taylor-dtn-ipn-update.html.
   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-dtn-ipn-update/.

   Discussion of this document takes place on the Delay/Disruption
   Tolerant Networking Working Group mailing list (mailto:dtn@ietf.org),
   which is archived at https://mailarchive.ietf.org/arch/browse/dtn/.
   Subscribe at https://www.ietf.org/mailman/listinfo/dtn/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ricktaylor/ipn2.

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/.

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   Internet-Drafts are draft documents valid for a maximum of six months
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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  Core Concepts . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  The Null ipn URI  . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Allocator Identifiers . . . . . . . . . . . . . . . . . .   6
       3.2.1.  Allocator Identifier Ranges . . . . . . . . . . . . .   6
       3.2.2.  The Default Allocator . . . . . . . . . . . . . . . .   8
     3.3.  Node Numbers  . . . . . . . . . . . . . . . . . . . . . .   9
       3.3.1.  Fully-qualified Node Numbers  . . . . . . . . . . . .   9
     3.4.  Special Node Numbers  . . . . . . . . . . . . . . . . . .   9
       3.4.1.  The Zero Node Number  . . . . . . . . . . . . . . . .  10
       3.4.2.  LocalNode ipn URIs  . . . . . . . . . . . . . . . . .  10
       3.4.3.  Private Use Node Numbers  . . . . . . . . . . . . . .  10
     3.5.  Service Numbers . . . . . . . . . . . . . . . . . . . . .  10
   4.  Textual Encoding of ipn URIs  . . . . . . . . . . . . . . . .  11
   5.  Usage of ipn URIs with BPv7 . . . . . . . . . . . . . . . . .  11
     5.1.  Uniqueness Constraints  . . . . . . . . . . . . . . . . .  12
     5.2.  The Null Endpoint . . . . . . . . . . . . . . . . . . . .  12
     5.3.  BPv7 Node ID  . . . . . . . . . . . . . . . . . . . . . .  12
     5.4.  LocalNode ipn EIDs  . . . . . . . . . . . . . . . . . . .  12
     5.5.  Private Use Endpoints . . . . . . . . . . . . . . . . . .  13
     5.6.  Administrative Endpoints  . . . . . . . . . . . . . . . .  13
   6.  Encoding ipn URIs with BPv7 . . . . . . . . . . . . . . . . .  13
     6.1.  ipn EID CBOR Encoding . . . . . . . . . . . . . . . . . .  13
       6.1.1.  Two-Element Scheme-Specific Encoding  . . . . . . . .  14

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       6.1.2.  Three-Element Scheme-Specific Encoding  . . . . . . .  15
     6.2.  ipn EID CBOR Decoding . . . . . . . . . . . . . . . . . .  15
     6.3.  ipn EID Matching  . . . . . . . . . . . . . . . . . . . .  16
   7.  Special Considerations  . . . . . . . . . . . . . . . . . . .  16
     7.1.  Scheme Compatibility  . . . . . . . . . . . . . . . . . .  17
     7.2.  Late Binding  . . . . . . . . . . . . . . . . . . . . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
     8.1.  Reliability and consistency . . . . . . . . . . . . . . .  18
     8.2.  Malicious construction  . . . . . . . . . . . . . . . . .  18
     8.3.  Back-end transcoding  . . . . . . . . . . . . . . . . . .  18
     8.4.  Rare IP address formats . . . . . . . . . . . . . . . . .  18
     8.5.  Sensitive information . . . . . . . . . . . . . . . . . .  18
     8.6.  Semantic attacks  . . . . . . . . . . . . . . . . . . . .  19
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  'ipn' Scheme URI Allocator Identifiers registry . . . . .  19
       9.1.1.  Guidance for Designated Experts . . . . . . . . . . .  20
     9.2.  'ipn' Scheme URI Default Allocator Node Numbers
           registry  . . . . . . . . . . . . . . . . . . . . . . . .  20
     9.3.  'ipn' Scheme URI Service Numbers registry . . . . . . . .  21
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     10.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  ipn URI Scheme Text Syntax . . . . . . . . . . . . .  24
   Appendix B.  ipn URI Scheme Text Representation Examples  . . . .  24
     B.1.  Using the Default Allocator . . . . . . . . . . . . . . .  24
     B.2.  Using a non-default Allocator . . . . . . . . . . . . . .  25
     B.3.  The Null ipn URI  . . . . . . . . . . . . . . . . . . . .  25
     B.4.  A LocalNode ipn URI . . . . . . . . . . . . . . . . . . .  25
   Appendix C.  ipn URI Scheme CBOR Encoding . . . . . . . . . . . .  25
   Appendix D.  ipn URI Scheme CBOR Encoding Examples  . . . . . . .  26
     D.1.  Using the Default Allocator . . . . . . . . . . . . . . .  26
     D.2.  Using a non-default Allocator . . . . . . . . . . . . . .  27
     D.3.  The 'null' Endpoint . . . . . . . . . . . . . . . . . . .  27
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction

   The ipn URI scheme was originally defined in [RFC7116] as a way to
   identify network nodes and node services using concisely-encoded
   integers that can be processed faster and with fewer resources than
   other verbose identifier schemes.  The scheme was designed for use
   with the experimental Bundle Protocol version 6 (BPv6, [RFC5050]) and
   IPN was defined as an acronym for the term "InterPlanetary Network"
   in reference to its intended use for deep-space networking.  Since
   then, the efficiency benefit of integer identifiers makes ipn scheme
   URIs useful for any networks operating with limited power, bandwidth,
   and/or compute budget.  Therefore the term IPN is now used as a non-

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   acronymous name.

   Similar to the experimental BPv6, the standardized Bundle Protocol
   version 7 (BPv7, [RFC9171]) codifies support for the use of the ipn
   URI scheme for the specification of bundle Endpoint Identifiers
   (EIDs).  The publication of BPv7 has resulted in operational
   deployments of BPv7 nodes for both terrestrial and non-terrestrial
   use cases.  This includes BPv7 networks operating over the
   terrestrial Internet and BPv7 networks operating in self-contained
   environments behind a shared administrative domain.  The growth in
   the number and scale of deployments of BPv7 DTNs has been accompanied
   by a growth in the usage of the ipn URI scheme which has highlighted
   areas to improve the structure, moderation, and management of this
   scheme.

   This document updates the specification of the ipn URI scheme, in a
   backwards-compatible way, to provide needed improvements both in the
   scheme itself and its usage to specify EIDs with BPv7.  Specifically,
   this document introduces a hierarchical structure for the assignment
   of ipn scheme URIs, clarifies the behavior and interpretation of ipn
   scheme URIs, defines efficient encodings of ipn scheme URIs, and
   updates/defines the registries associated for this scheme.

   Although originally developed by the deep space community for use
   with Bundle Protocol, the ipn URI scheme is sufficiently generic to
   be used in other environments where a concise unique representation
   of a resource on a particular node is required.

   It is important to remember that like most other URI schemes, the ipn
   URI scheme defines a unique identifier of a resource, and does not
   include any topological information describing how to route messages
   to that resource.

2.  Conventions and Definitions

   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.

   For the remainder of this document the term "ipn URI" is used to
   refer to a URI that uses the ipn scheme.

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3.  Core Concepts

   All ipn URIs, no matter the textual representation or binary
   encoding, MUST be considered as a tuple of the following three
   components:

   *  The Allocator Identifier

   *  The Node Number

   *  The Service Number

   The Allocator Identifier indicates the entity responsible for
   assigning Node Numbers to individual resource nodes, maintaining
   uniqueness whilst avoiding the need for a single registry for all
   assigned Node Numbers.  See Allocator Identifiers (Section 3.2).

   The Node Number is a shared identifier assigned to all ipn URIs for
   resources co-located on a single node.  See Node Numbers
   (Section 3.3).

   The Service Number identifies the particular type of service of a
   resource.  See Service Numbers (Section 3.5).

   The combination of these three components guarantees that every
   correctly constructed ipn URI uniquely identifies a single resource.
   Additionally, the combination of the Allocator identifier and the
   Node Number provides a mechanism to uniquely identify the node on
   which a particular resource is expected to exist.  See
   Fully-qualified Node Number (Section 3.3.1).

   When considered from the perspective of BPv7, a Node Number is shared
   by all endpoints co-located on a single bundle processing node, and a
   Service Number identifies a certain type of bundle processing
   service.

3.1.  The Null ipn URI

   It has been found that there is value in defining a unique 'null' ipn
   URI to indicate "nowhere".  This ipn URI is termed the "Null ipn
   URI", and has all three components: Allocator Identifier, Node
   Number, and Service Number, set to the value zero (0).  No resource
   identified by Null ipn URI exists, and is therefore by definition
   unreachable.

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3.2.  Allocator Identifiers

   An Allocator is any organization that wishes to assign Node Numbers
   for use with the ipn URI scheme, and has the facilities and
   governance to manage a public registry of assigned Node Numbers.  The
   authorization to assign these numbers is provided through the
   assignment of an Allocator Identifier by IANA.  Regardless of other
   attributes of an Allocator, such as a name, point of contact, or
   other identifying information, Allocators are identified by Allocator
   Identifiers: a unique, unsigned integer.

   The Allocator Identifier MUST be the sole mechanism used to identify
   the Allocator that has assigned the Node Number in an ipn URI.  An
   Allocator may have multiple assigned Allocator Identifiers, but a
   given Allocator Identifier MUST only be associated with a single
   Allocator.

   A new IANA "'ipn' Scheme URI Allocator Identifiers" registry is
   defined for the registration of Allocator Identifiers, see 'ipn'
   Scheme URI Allocator Identifiers registry (Section 9.1).  Although
   the uniqueness of Allocator identifiers is required to enforce
   uniqueness of ipn URIs, some identifiers are explicitly reserved for
   experimentation or future use.

   Each Allocator assigns Node Numbers according to its own policies,
   without risk of creating an identical ipn URI, as permitted by the
   rules in the Node Numbers (Section 3.3) section of this document.
   Other than ensuring that any Node Numbers it allocates are unique
   amongst all Node Numbers it assigns, an Allocator does not need to
   coordinate its allocations with other Allocators.

   If a system does not require interoperable deployment of ipn scheme
   URIs, then the Private Use Node Number range, reserved by the Default
   Allocator (Section 3.2.2) for this purpose SHOULD be used.

3.2.1.  Allocator Identifier Ranges

   Some organizations with internal hierarchies may wish to delegate the
   allocation of Node Numbers to one or more of their sub-organizations.
   Rather than assigning unique Allocator Identifiers to each sub-
   organization on a first-come first-served basis, there are
   operational benefits in assigning Allocator Identifiers to such an
   organization in a structured way so that an external observer can
   detect that a group of Allocator Identifiers are organizationally
   associated.

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   An Allocator Identifier range is a set of consecutive Allocator
   Identifiers associated with the same Allocator.  Each individual
   Allocator Identifier in a given range SHOULD be assigned to a
   distinct sub-organization of the Allocator.  Assigning identifiers in
   this way allows external observers to both associate individual
   Allocator Identifiers with a single organization and to usefully
   differentiate amongst sub-organizations.

   The practice of associating a consecutive range of numbers with a
   single organization is inspired by the Classless Inter-domain Routing
   assignment of Internet Addresses described in [RFC4632].  In that
   assignment scheme, an organization (such as an Internet Service
   Provider) is assigned a network prefix such that all addresses
   sharing that same prefix are considered to be associated with that
   organization.

   Each Allocator Identifier range is identified by the first Allocator
   Identifier in the range and the number of consecutive identifiers in
   the range.

   Allocator Identifier ranges differ from CIDR addresses in two
   important ways.

   1.  Allocator Identifiers are used to identify organizations and are
       not, themselves, addresses.

   2.  Allocator Identifiers may be less than 32 bits in length.

   In order to differentiate between Allocator Identifier ranges using
   efficient bitwise operations, all ranges MUST be of a length that is
   a power of 2, and for given range of length N bits, the least-
   significant N bits of the first Allocator Identifier MUST be all 0.

   An example of the use of Allocator Identifier ranges for four
   organizations (A, B, C, and D) is as follows:

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   +==============+=============+=============+=====================+
   | Organization | Range (dec) | Range (hex) | Range Length (Bits) |
   +==============+=============+=============+=====================+
   | Org A        |  974848 ..  |  0xEE000 .. |        7 bits       |
   |              |    974975   |   0xEE07F   |                     |
   +--------------+-------------+-------------+---------------------+
   | Org B        |  974976 ..  |  0xEE080 .. |        4 bits       |
   |              |    974991   |   0xEE08F   |                     |
   +--------------+-------------+-------------+---------------------+
   | Org C        |  974992 ..  |  0xEE090 .. |        1 bit        |
   |              |    974993   |   0xEE091   |                     |
   +--------------+-------------+-------------+---------------------+
   | Org D        |    974994   |   0xEE092   |        0 bits       |
   +--------------+-------------+-------------+---------------------+

         Table 1: Allocator Identifier Range Assignment Example

   With these assignments, any Allocator Identifier whose most-
   significant 25 bits match 0xEE000 belong to organization A.
   Similarly, any Allocator Identifier whose most-significant 28 bits
   match 0xEE080 belong to organization B and any Allocator Identifier
   whose most-significant 31 bits are 0xEE090 belong to organization C.
   Organisation D has a single Allocator Identifier, and hence a range
   of bit-length 0.

3.2.2.  The Default Allocator

   As of the publication of [RFC7116], the only organization permitted
   to assign Node Numbers was the Internet Assigned Numbers Authority
   (IANA) which assigned Node Numbers via the IANA "CBHE Node Numbers"
   registry.  This means that all ipn URIs created prior to the addition
   of Allocator Identifiers are assumed to have Node Number allocations
   that comply with the IANA "CBHE Node Numbers" registry.

   The presumption that, unless otherwise specified, Node Numbers are
   allocated by IANA from a specific registry is formalized in this
   update to the ipn URI scheme by designating IANA as the "Default
   Allocator", and assigned the Allocator identifier zero (0) in the
   'ipn' Scheme URI Allocator Identifiers registry (Section 9.1).  In
   any case where an encoded ipn URI does not explicitly include an
   Allocator Identifier, an implementation MUST assume that the Node
   Number has been allocated by the Default Allocator.

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   A new IANA "'ipn' Scheme URI Default Allocator Node Numbers" registry
   is defined to control the allocation of Node Numbers values by the
   Default Allocator.  This new registry inherits behaviours and
   existing assignments from the IANA "CBHE Node Numbers" registry, and
   reserves some other values as defined in the Special Node Numbers
   (Section 3.4) section below.

3.3.  Node Numbers

   A Node Number identifies a node that hosts a resource in the context
   of an Allocator.  A Node Number is an unsigned integer.  A single
   Node Number assigned by a single Allocator MUST refer to a single
   node.

   All Node Number assignments, by all Allocators, MUST be in the range
   0 to 2^32-1.

   It is RECOMMENDED that Node Number zero (0) not be assigned by an
   Allocator to avoid confusion with the Null ipn URI (Section 3.1).

3.3.1.  Fully-qualified Node Numbers

   One of the advantages of ipn URis is the ability to easily split the
   identity of a particular service from the node upon which the service
   exists.  For example a message received from one particular ipn URI
   may require a response to be sent to a different service on the same
   node that sent the original message.  Historically the identifier of
   the sending node has been colloquially referred to as the "node
   number" or "node identifier".

   To avoid future confusion, when referring to the identifier of a
   particular node the term "Fully-qualified Node Number" (FQNN) MUST be
   used to refer to the combination of the Node Number component and
   Allocator Identifier component of an ipn URI that uniquely identifies
   a particular node.  In other words, an FQNN is the unique identifier
   of a particular node that supports services identified by ipn URIs.

   In examples in this document, FQNNs are written as (Allocator
   Identifier, Node Number), e.g. (977000,100) is the FQNN for a node
   assigned Node Number 100 by an Allocator with Allocator Identifier
   977000.

3.4.  Special Node Numbers

   Some special-case Node Numbers are defined by the Default Allocator,
   see 'ipn' Scheme URI Default Allocator Node Numbers registry
   (Section 9.2).

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3.4.1.  The Zero Node Number

   The Default Allocator assigns the use of Node Number zero (0) solely
   for identifying the Null ipn URI (Section 3.1).

   This means that any ipn URI with a zero (0) Allocator Identifier and
   a zero (0) Node Number, but a non-zero Service Number component is
   invalid.  Such ipn URIs MUST NOT be composed, and processors of such
   ipn URIs MUST consider them as the Null ipn URI.

3.4.2.  LocalNode ipn URIs

   The Default Allocator reserves Node Number 2^32-1 (0xFFFFFFFFF) to
   specify resources on the local node, rather than on any specific
   individual node.

   This means that any ipn URI with a zero (0) Allocator Identifier and
   a Node Number of 2^32-1 refers to a service on the local bundle node.
   ipn URIs of this form are termed "LocalNode ipn URIs".

3.4.3.  Private Use Node Numbers

   The Default Allocator provides a range of Node Numbers that are
   reserved for "Private Use", as defined in [RFC8126].

   Any ipn URI with a zero (0) Allocator Identifier and a Node Number
   reserved for "Private Use" is not guaranteed to be unique beyond a
   single administrative domain.  An administrative domain, as used
   here, is defined as the set of nodes that share a unique allocation
   of FQNNs from the "Private Use" range.  They can be considered to be
   equivalent to "Private Address Space" IPv4 addresses, as defined in
   [RFC1918].

3.5.  Service Numbers

   A Service Number identifies a particular service operating on a node.
   The purpose of the Service Number is to provide well-known numeric
   identifiers for types of service in a network.  A Service Number is
   an unsigned integer.

   A new IANA "'ipn' Scheme URI Service Numbers" registry is defined for
   the registration of Service Numbers, see 'ipn' Scheme URI Service
   Numbers registry (Section 9.3).  This registry defines standardized
   Service Numbers for services such as an administrative or well-known
   protocol service endpoints.  This registry also defines ranges
   explicitly reserved for both experimentation and ad-hoc service
   identification.

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4.  Textual Encoding of ipn URIs

   All ipn scheme URIs comply with [RFC3986], and are therefore
   represented by scheme identifier, and a scheme-specific part.  The
   scheme identifier is: ipn, and the scheme-specific parts are
   represented as a sequence of numeric components separated with the .
   character.  It is formally defined in Appendix A (Appendix A), and
   can be informally considered as:

   ipn:[<allocator-identifier>.]<node-number>.<service-number>

   To keep the text representation concise, the follow rules apply:

   1.  All leading 0 characters MUST be omitted.  A single 0 is valid.

   2.  If the Allocator Identifier is zero (0), then the <allocator-
       identifier> and . MUST be omitted.

   3.  If the Allocator Identifier is zero (0), and the Node Number is
       2^32-1, i.e. the URI is an ipn LocalNode URI (Section 3.4.2),
       then the character ! MAY be used instead of the digits
       4294967295, although both forms are valid encodings.

   Examples of the textual representation of ipn URIs can be found in
   Appendix B (Appendix B).

5.  Usage of ipn URIs with BPv7

   From the earliest days of experimentation with the Bundle Protocol
   there has been a need to identify the source and destination of a
   bundle.  The IRTF standardisation of the experimental BPv6 termed the
   logical source or destination of a bundle as an "Endpoint" identified
   by an "Endpoint Identifier" (EID).  BPv6 EIDs are formatted as URIs.
   This definition and representation of EIDs was carried from the IRTF
   BPv6 specification to the IETF BPv7 specification.  BPv7 additionally
   defined an IANA registry called the "Bundle Protocol URI Scheme
   Types" registry which identifies those URI schemes than might be used
   to represent EIDs.  The ipn URI scheme is one such URI scheme.

   This section identifies the behavior and interpretation of ipn URI
   schemes that MUST be followed when using this URI scheme to represent
   EIDs in BPv7.  An ipn URI used as a BPv7 or BPv6 EID is termed an
   "ipn EID".

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5.1.  Uniqueness Constraints

   An ipn EID MUST identify a singleton endpoint.  The bundle processing
   node that is the sole member of that endpoint MUST be the node
   identified by the Fully-qualified Node Number (Section 3.3.1) of the
   node.

   A single bundle processing node MAY have multiple ipn EIDs associated
   with it.  However, every ipn EID that shares a FQNN MUST refer to the
   same bundle processing node.

   For example, ipn:977000.100.1, ipn:977000.100.2, and ipn:977000.100.3
   MUST all refer to services registered on the bundle processing node
   identified with FQNN (977000,100).  None of these EIDs could be
   registered on any other bundle processing node.

5.2.  The Null Endpoint

   Section 3.2 of [RFC9171] defines the concept of the 'null' endpoint,
   which is an endpoint that has no members and which is identified by a
   special 'null' EID.

   Within the ipn URI scheme, the 'null' EID is represented by the Null
   ipn URI (Section 3.1).  This means that the URIs dtn:none
   (Section 4.2.5.1.1 of [RFC9171]) and ipn:0.0 both refer to the BPv7
   'null' endpoint.

5.3.  BPv7 Node ID

   Section 4.2.5.2 of [RFC9171] introduces the concept of a "Node ID"
   that has the same format as an EID and that uniquely identifies a
   bundle processing node.

   Any ipn EID can serve as a "Node ID" for the bundle processing node
   identified by its Fully-qualified Node Number (Section 3.3.1).  For
   example, any ipn EID of the form ipn:A.B.C may be used as the Source
   Node ID of any bundle created by the bundle processing node
   identified by the FQNN (A,B).

5.4.  LocalNode ipn EIDs

   When a LocalNode ipn URI (Section 3.4.2) is used as a BPv7 or BPv6
   EID it is termed a "LocalNode ipn EID".

   Because a LocalNode ipn EID only has meaning on the local bundle
   node, any such EID MUST be considered 'non-routeable'.  This means
   that any bundle using a LocalNode ipn EID as a bundle source or
   bundle destination MUST NOT be allowed to leave the local node.

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   Similarly, LocalNode ipn EIDs SHOULD NOT be present in any other part
   of a bundle that is transmitted off of the local node.  For example,
   a LocalNode ipn EID SHOULD NOT be used as a Bundle Protocol Security
   [RFC9172] security source EID for a bundle transmitted from the local
   bundle node, because such a source EID would have no meaning at a
   downstream bundle node.

5.5.  Private Use Endpoints

   Bundles destined for EIDs that use an ipn URI with an Fully-qualified
   Node Number (Section 3.3.1) that is within the "Private Use" range of
   the Default Allocator MUST be considered 'non-routeable'.

   This means that they MUST NOT be permitted to exit a single
   administrative domain, see Private Use (Section 3.4.3).

5.6.  Administrative Endpoints

   The service type identified by a Service Number of zero (0) MUST be
   interpreted as the administrative endpoint of the node, as defined in
   Section 3.2 of [RFC9171].

   Non-zero Service Numbers MUST NOT be used to identify the
   administrative endpoint of a bundle node in an ipn EID.

6.  Encoding ipn URIs with BPv7

   Section 4.2.5.1 of [RFC9171] requires that any URI scheme used to
   represent BPv7 EIDs MUST define how the scheme-specific part of the
   URI scheme is CBOR encoded.  To meet this requirement, this section
   describes the CBOR encoding and decoding approach for ipn EIDs.  The
   formal definition of these encodings is presented in Appendix C
   (Appendix C).

   While there is a single, canonical, textual representation of an ipn
   URI, there may exist multiple encodings for that URI.  For example,
   Section 2.1 of [RFC3986] defines a percent-encoding mechanism for a
   URI text string.  Alternatively, Section 3.4.5.3 of [RFC8949] allows
   for the encoding of URIs as CBOR text strings identified with a CBOR
   tag value of 32.

6.1.  ipn EID CBOR Encoding

   Generic URI approaches to encoding ipn EIDs are unlikely to be
   efficient because they do not consider the underlying structure of
   the ipn URI scheme.  Since the creation of the ipn URI scheme was
   motivated by the need for concise identification and rapid
   processing, the encoding of ipn EIDs maintains these properties.

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   Fundamentally, [RFC9171] ipn EIDs are represented as a sequence of
   identifiers.  In the text syntax, the numbers are separated with the
   . delimiter; in CBOR, this ordered series of numbers can be
   represented by an array.  Therefore, when encoding ipn EIDs for use
   with BPv7, the scheme-specific part of an ipn URI MUST be represented
   as a CBOR array of either two (2) or three (3) elements.  Each
   element of the array MUST be encoded as a single CBOR unsigned
   integer.

   The structure and mechanisms of the two-element and three-element
   encodings are described below, and examples of the different
   encodings are provided in Appendix D (Appendix D).

6.1.1.  Two-Element Scheme-Specific Encoding

   In the two-element scheme-specific encoding of an ipn EID, the first
   element of the array is an encoding of the Fully-qualified Node
   Number (Section 3.3.1) and the second element of the array is the ipn
   EID Service Number.

   The FQNN encoding MUST be a 64 bit unsigned integer constructed in
   the following way:

   1.  The least significant 32 bits MUST represent the Node Number
       associated with the ipn EID.

   2.  The most significant 32 bits MUST represent the Allocator
       Identifier associated with the ipn EID.

   For example the ipn EID of ipn:977000.100.1 has an FQNN of
   (977000,100) which would be encoded as 0xEE86800000064.  The
   resulting two-element array [0xEE86800000064, 0x01] would be encoded
   in CBOR as the 11 octet value 0x821B000EE8680000006401.

   The two-element scheme-specific encoding provides for backwards
   compatibility with the encoding provided in Section 4.2.5.1.2 of
   [RFC9171].  When used in this way, the encoding of the FQNN replaces
   the use of the "Node Number" that was specified in RFC9171.  When the
   Node Number is allocated by the Default Allocator, then the encoding
   of the FQNN and the RFC9171 encoding of the "Node Number" are
   identical.

   This encoding scheme MUST be implemented by any BPv7 bundle
   processing node that supports ipn URIs for the specification of BPv7
   EIDs.

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6.1.2.  Three-Element Scheme-Specific Encoding

   In the three-element scheme-specific encoding of an ipn EID, the
   first element of the array is the Allocator Identifier, the second
   element of the array is Node Number, and the third element of the
   array is the Service Number.

   For example, the ipn EID of ipn:977000.100.1 would result in the
   three-element array of [977000,100,1] which would be encoded in CBOR
   as the 9 octet value 0x831A000EE868186401.

   The three-element scheme-specific encoding allows for a more
   efficient representation of ipn EIDs using smaller Allocator
   Identifiers.

   When encoding an ipn EID using the Default Allocator with this
   encoding scheme, the first element of the array MUST be the value
   zero (0).  In this case using the two-element encoding will result in
   a more concise CBOR representation, and it is RECOMMENDED that
   implementations do so.

6.2.  ipn EID CBOR Decoding

   The presence of different scheme-specific encodings does not
   introduce any decoding ambiguity.

   An ipn EID CBOR decoder can reconstruct an ipn EID using the
   following logic.  In this description, the term enc_eid refers to the
   CBOR encoded ipn EID, and the term ipn_eid refers to the decoded ipn
   EID.

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   if enc_eid.len() == 3
   {
     ipn_eid.allocator_identifier := enc_eid[0];
     ipn_eid.node_number := enc_eid[1];
     ipn_eid.service_number := enc_eid[2];
   }
   else if enc_eid.len() == 2
   {
     let N := enc_eid[0];
     ipn_eid.service_number := enc_eid[1];

     if N >= 2^32
     {
       ipn_eid.allocator_identifier := N >> 32;
       ipn_eid.node_number := N & (2^32-1);
     }
     else
     {
       ipn_eid.allocator_identifier := 0;
       ipn_eid.node_number := N;
     }
   }

6.3.  ipn EID Matching

   Regardless of whether the two-element or three-element scheme-
   specific encoding is used, ipn EID matching MUST be performed on the
   decoded EID information itself.  Different encodings of the same ipn
   EID MUST be treated as equivalent when performing EID-specific
   functions.

   For example, the ipn EID of ipn:977000.100.1 can be represented as
   either the two-element encoding of 0x821B000EE8680000006401 or the
   three-element encoding of 0x831A000EE868186401.  While message
   integrity and other syntax-based checks may treat these values
   differently, any EID-based comparisons MUST treat these values the
   same - as representing the ipn EID ipn:977000.100.1.

7.  Special Considerations

   The ipn URI scheme provides a compact and hierarchical mechanism for
   identifying services on network nodes.  There is a significant amount
   of utility in the ipn URI scheme approach to identification.
   However, implementers should take into consideration the following
   observations on the use of the ipn URI scheme.

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7.1.  Scheme Compatibility

   The ipn scheme update that has been presented in this document
   preserves backwards compatibility with any ipn URI scheme going back
   to the provisional definition of the ipn scheme in the experimental
   Compressed Bundle Header Encoding [RFC6260] in 2011.  This means that
   any ipn URI that was valid prior to the publication of this update
   remains a valid ipn URI.

   Similarly, the two-element scheme-specific encoding (Section 6.1.1)
   is also backwards compatible with the encoding of ipn URIs provided
   in [RFC9171].  Any existing BPv7-compliant implementation will
   produce an ipn URI encoding in compliance with this specification.

   The introduction of optional non-default Allocator Identifiers and a
   three-element scheme-specific encoding make this ipn URI scheme
   update not forwards compatible.  Existing software MUST be updated to
   be able to process non-default Allocator Identifiers and three-
   element scheme-specific encodings.  It is RECOMMENDED that BP
   implementations upgrade to process these new features to benefit from
   the scalability provided by Allocator Identifiers and the encoding
   efficiencies provided by the three-element encoding.

7.2.  Late Binding

   [RFC9171] mandates the concept of "late binding" of an EID, where-by
   the address of the destination of a bundle is resolved from its
   identifier hop by hop as it transits a DTN.  This per-hop binding of
   identifiers to addresses underlines the fact that EIDs are purely
   names, and should not carry any implicit or explicit information
   concerning the current location or reachability of an identified node
   and service.  This removes the need to rename a node as its location
   changes.

   The concept of "late binding" is preserved in this ipn URI scheme.
   Elements of an ipn URI SHOULD NOT be regarded as carrying information
   relating to location, reachability, or other addressing/routing
   concern.

   An example of incorrect behaviour would be to assume that a given
   Allocator assigns Node Numbers derived from link-layer addresses and
   to interpret the Node Number component of an ipn URI directly as a
   link-layer address.  No matter the mechanism an Allocator uses for
   the assignment of Node Numbers, they remain just numbers, without
   additional meaning.

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8.  Security Considerations

   This section updates the security considerations from
   Section 4.2.5.1.2 of [RFC9171] to account for the inclusion of
   Allocator Identifiers in the ipn URI scheme.

8.1.  Reliability and consistency

   None of the BP endpoints identified by ipn EIDs are guaranteed to be
   reachable at any time, and the identity of the processing entities
   operating on those endpoints is never guaranteed by the Bundle
   Protocol itself.  Verification of the signature provided by the Block
   Integrity Block targeting the bundle's primary block, as defined by
   Bundle Protocol Security [RFC9172], is required for this purpose.

8.2.  Malicious construction

   Malicious construction of a conformant ipn URI is limited to the
   malicious selection of Allocator Identifiers, Node Numbers, and
   Service Numbers.  That is, a maliciously constructed ipn EID could be
   used to direct a bundle to an endpoint that might be damaged by the
   arrival of that bundle or, alternatively, to declare a false source
   for a bundle and thereby cause incorrect processing at a node that
   receives the bundle.  In both cases (and indeed in all bundle
   processing), the node that receives a bundle should verify its
   authenticity and validity before operating on it in any way.

8.3.  Back-end transcoding

   The limited expressiveness of URIs of the ipn scheme effectively
   eliminates the possibility of threat due to errors in back-end
   transcoding.

8.4.  Rare IP address formats

   Not relevant, as IP addresses do not appear anywhere in conformant
   ipn URIs.

8.5.  Sensitive information

   Because ipn URIs are used only to represent the numeric identities of
   resources, the risk of disclosure of sensitive information due to
   interception of these URIs is minimal.  Examination of ipn EIDs could
   be used to support traffic analysis; where traffic analysis is a
   plausible danger, bundles should be conveyed by secure convergence-
   layer protocols that do not expose endpoint IDs.

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8.6.  Semantic attacks

   The simplicity of ipn URI scheme syntax minimizes the possibility of
   misinterpretation of a URI by a human user.

9.  IANA Considerations

   The following sections detail requests to IANA for the creation of a
   new registry, and the renaming of two existing registries.

9.1.  'ipn' Scheme URI Allocator Identifiers registry

   IANA is requested to create a new registry entitled "'ipn' Scheme URI
   Allocator Identifiers".  The registration policy for this registry
   is:

   +================+==================================================+
   |     Range      | Registration Policy                              |
   +================+==================================================+
   |  0 .. 2^16-1   | Expert Review, Single Allocator Identifiers only |
   +----------------+--------------------------------------------------+
   |    2^16 ..     | Expert Review                                    |
   |     2^30-1     |                                                  |
   +----------------+--------------------------------------------------+
   |    2^30 ..     | Experimentation                                  |
   |     2^31-1     |                                                  |
   +----------------+--------------------------------------------------+
   |    2^31 ..     | Reserved, Future Expansion                       |
   |     2^32-1     |                                                  |
   +----------------+--------------------------------------------------+
   |    >= 2^32     | Reserved                                         |
   +----------------+--------------------------------------------------+

         Table 2: 'ipn' Scheme URI Numbering Allocator Identifiers
                           registration policies

   Each entry in this registry associates one or more Allocator
   Identifiers with a single organization.  Within the registry, the
   organization is identified using the "Name" and "Point of Contact"
   fields.  It is expected that each identified organization publishes
   some listing of allocated node numbers - the pointer to which is
   listed in the "Reference" field of the registry.

   The initial values for the registry are:

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   +==============+======+=========+======+===========+==============+
   | Organization |Range |  Range  |Range | Reference |   Point of   |
   |              |(dec) |  (hex)  |Length|           |   Contact    |
   |              |      |         |(Bits)|           |              |
   +==============+======+=========+======+===========+==============+
   | Default      |  0   |   0x0   |  0   |    This   |     IANA     |
   | Allocator    |      |         |      |  document |              |
   +--------------+------+---------+------+-----------+--------------+
   | CCSDS        |  1   |   0x1   |  0   |    TBD    | www.sana.org |
   +--------------+------+---------+------+-----------+--------------+
   | Example      |974848| 0xEE000 |  12  |    This   |     IANA     |
   | Range        |  ..  |    ..   | bits |  document |              |
   |              |978943| 0xEEFFF |      |           |              |
   +--------------+------+---------+------+-----------+--------------+

      Table 3: 'ipn' Scheme URI Allocator Identifiers initial values

   The "Example Range" is assigned for use in examples in documentation.

9.1.1.  Guidance for Designated Experts

   TDB
   // The working group is satisfied with the technical specification in
   // this document, but there are reservations amongst the WG around
   // the governance of the assignment of Allocator Identifiers, and is
   // engaging with the IESG/IANA to ensure best practice is followed.
   // The intent is to use mechanism similar to those in place for IP
   // addresses (RFC1881, RFC3513, RFC1466,...), AS numbers and domains
   // (RFC1591).

9.2.  'ipn' Scheme URI Default Allocator Node Numbers registry

   IANA is requested to rename the "CBHE Node Numbers" registry defined
   in Section 3.2.1 of [RFC7116] to the "'ipn' Scheme URI Default
   Allocator Node Numbers" registry.

   The registration policy for this registry is updated to be:

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   +================+=================================================+
   |     Range      | Registration Policy                             |
   +================+=================================================+
   |       0        | Reserved for the Null ipn URI (Section 3.1)     |
   +----------------+-------------------------------------------------+
   |  1 .. 2^14-1   | Private Use                                     |
   +----------------+-------------------------------------------------+
   | 2^14 .. 2^32-2 | Expert Review                                   |
   +----------------+-------------------------------------------------+
   |     2^32-1     | Reserved for LocalNode ipn URIs (Section 3.4.2) |
   +----------------+-------------------------------------------------+
   |    >= 2^32     | Invalid                                         |
   +----------------+-------------------------------------------------+

         Table 4: 'ipn' Scheme URI Default Allocator Node Numbers
                          registration policies

   As IANA is requested to rename the registry, all existing
   registrations will remain.

9.3.  'ipn' Scheme URI Service Numbers registry

   IANA is requested to rename the "CBHE Service Numbers" registry
   defined in Section 3.2.2 of [RFC7116] to the "'ipn' Scheme URI
   Service Numbers" registry.

   The registration policy for this registry is updated to be:

   +================+========================+
   |     Range      | Registration Policy    |
   +================+========================+
   |    0 .. 23     | RFC Required           |
   +----------------+------------------------+
   |  24 .. 2^15-1  | Specification Required |
   +----------------+------------------------+
   | 2^15 .. 2^31-1 | Private Use            |
   +----------------+------------------------+
   |    >= 2^31     | Reserved               |
   +----------------+------------------------+

        Table 5: 'ipn' Scheme URI Service
          Numbers registration policies

   The current values for the registry remain, and are rewritten as:

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   +=======+=========+================================+============+
   | Value | Version | Description                    | Reference  |
   +=======+=========+================================+============+
   |   0   |  BPv6,  | The Administrative Endpoint    | [RFC7116], |
   |       |   BPv7  |                                | This       |
   |       |         |                                | document   |
   +-------+---------+--------------------------------+------------+
   |   1   |   BPv6  | CCSDS File Delivery Service    | [CFDP]     |
   +-------+---------+--------------------------------+------------+
   |   1   |   BPv7  | Unassigned                     |            |
   +-------+---------+--------------------------------+------------+
   |   2   |   BPv6  | Reserved                       | [RFC7116]  |
   +-------+---------+--------------------------------+------------+
   |   2   |   BPv7  | Unassigned                     |            |
   +-------+---------+--------------------------------+------------+
   |  3 .. |  BPv6,  | Unassigned                     |            |
   |   63  |   BPv7  |                                |            |
   +-------+---------+--------------------------------+------------+
   | 64 .. |   BPv6  | Allocated to the Space         | [RFC7116]  |
   |  1023 |         | Assigned Numbers Authority     |            |
   |       |         | (SANA) for use by Consultative |            |
   |       |         | Committee for Space Data       |            |
   |       |         | Systems (CCSDS) missions       |            |
   +-------+---------+--------------------------------+------------+
   | 64 .. |   BPv7  | Unassigned                     |            |
   |  1023 |         |                                |            |
   +-------+---------+--------------------------------+------------+

        Table 6: 'ipn' Scheme URI Service Numbers initial values

10.  References

10.1.  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/rfc/rfc2119>.

   [RFC5050]  Scott, K. and S. Burleigh, "Bundle Protocol
              Specification", RFC 5050, DOI 10.17487/RFC5050, November
              2007, <https://www.rfc-editor.org/rfc/rfc5050>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/rfc/rfc5234>.

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   [RFC7116]  Scott, K. and M. Blanchet, "Licklider Transmission
              Protocol (LTP), Compressed Bundle Header Encoding (CBHE),
              and Bundle Protocol IANA Registries", RFC 7116,
              DOI 10.17487/RFC7116, February 2014,
              <https://www.rfc-editor.org/rfc/rfc7116>.

   [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/rfc/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/rfc/rfc8174>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/rfc/rfc8949>.

   [RFC9171]  Burleigh, S., Fall, K., Birrane, E., and III., "Bundle
              Protocol Version 7", RFC 9171, DOI 10.17487/RFC9171,
              January 2022, <https://www.rfc-editor.org/rfc/rfc9171>.

10.2.  Informative References

   [CFDP]     The Consultative Committee for Space Data Systems, "CCSDS
              FILE DELIVERY PROTOCOL (CFDP)", January 2007,
              <https://public.ccsds.org/Pubs/727x0b4s.pdf>.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
              J., and E. Lear, "Address Allocation for Private
              Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
              February 1996, <https://www.rfc-editor.org/rfc/rfc1918>.

   [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/rfc/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/rfc/rfc4632>.

   [RFC6260]  Burleigh, S., "Compressed Bundle Header Encoding (CBHE)",
              RFC 6260, DOI 10.17487/RFC6260, May 2011,
              <https://www.rfc-editor.org/rfc/rfc6260>.

   [RFC9172]  Birrane, E., III., and K. McKeever, "Bundle Protocol
              Security (BPSec)", RFC 9172, DOI 10.17487/RFC9172, January
              2022, <https://www.rfc-editor.org/rfc/rfc9172>.

Appendix A.  ipn URI Scheme Text Syntax

   The text syntax of an ipn URI MUST comply with the following ABNF
   [RFC5234] syntax, including the core ABNF syntax rule for DIGIT
   defined by that specification:

   ipn-uri = "ipn:" ipn-hier-part

   ipn-hier-part = fqnn "." service-number

   fqnn = "!" / allocator-part

   allocator-part = (allocator-identifier ".")? node-number

   allocator-identifier = non-zero-number

   node-number = number

   service-number = number

   number = "0" \ non-zero-number

   non-zero-number = (%x31-39 *DIGIT)

Appendix B.  ipn URI Scheme Text Representation Examples

   This section provides some example ipn URIs in their textual
   representation.

B.1.  Using the Default Allocator

   Consider the ipn URI identifying Service Number 2 on Node Number 1
   allocated by the Default Allocator (0).

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   The complete seven character representation of this URI would be as
   follows:

   ipn:1.2

B.2.  Using a non-default Allocator

   Consider the ipn URI identifying Service Number 1 on Node Number 1
   allocated by Allocator 977000.

   The complete 14 character representation of this URI would be as
   follows:

   ipn:977000.1.2

B.3.  The Null ipn URI

   The Null ipn URI (Section 3.1) is represented as:

   ipn:0.0

B.4.  A LocalNode ipn URI

   Consider the ipn URI identifying Service Number 7 on the local node.

   The complete seven character representation of this URI would be as
   follows:

   ipn:!.7

Appendix C.  ipn URI Scheme CBOR Encoding

   A BPv7 endpoint identified by an ipn URI, when encoded in Concise
   Binary Object Representation (CBOR) [RFC8949], MUST comply with the
   following Concise Data Definition Language (CDDL) [RFC8610]
   specification:

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   eid = $eid .within eid-structure

   eid-structure = [
     uri-code: uint,
     SSP: any
   ]

   ; ... Syntax for other uri-code values defined in RFC9171 ...

   $eid /= [
     uri-code: 2,
     SSP: ipn-ssp2 / ipn-ssp3
   ]
   ipn-ssp2 = [
     fqnn: uint,  ; packed value
     service-number: uint
   ]
   ipn-ssp3 = [
     authority-number: uint .lt 4294967296,
     node-number: uint .lt 4294967296,
     service-number: uint
   ]

   Note: The node-number component will be the numeric representation of
   the concatenation of the Allocator Identifier and Node Number when
   the 2-element encoding scheme has been used.

Appendix D.  ipn URI Scheme CBOR Encoding Examples

   This section provides some example CBOR encodings of ipn EIDs.

D.1.  Using the Default Allocator

   Consider the ipn EID ipn:1.1.  This textual representation of an ipn
   EID identifies Service Number 1 on Node Number 1 allocated by the
   Default Allocator (0).

   The complete five octet encoding of this EID using the two-element
   scheme-specific encoding would be as follows:

   82       # 2-Element Endpoint Encoding
      02    # uri-code: 2 (IPN URI scheme)
      82    # 2 Element ipn EID scheme-specific encoding
         01 # Node Number
         01 # Service Number

   The complete six octet encoding of this EID using the three-element
   scheme-specific encoding would be as follows:

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   82       # 2-Element Endpoint Encoding
      02    # uri-code: 2 (IPN URI scheme)
      83    # 3 Element ipn EID scheme-specific encoding
         00 # Default Allocator
         01 # Node Number
         01 # Service Number

D.2.  Using a non-default Allocator

   Consider the ipn EID ipn:977000.1.1.  This textual representation of
   an ipn EID identifies Service Number 1 on Node Number 1 allocated by
   Allocator 977000.

   The complete thirteen octet encoding of this EID using the two-
   element scheme-specific encoding would be as follows:

  82                        # 2-Element Endpoint Encoding
     02                     # uri-code: 2 (IPN URI scheme)
     82                     # 2 Element ipn EID scheme-specific encoding
        1B 000EE86800000001 # Fully-qualified Node Number
        01                  # Service Number

   The complete ten octet encoding of this EID using the three-element
   scheme-specific encoding would be as follows:

   82                # 2-Element Endpoint Encoding
      02             # uri-code: 2 (IPN URI scheme)
      83             # 3 Element ipn EID scheme-specific encoding
         1A 000EE868 # Allocator Identifier
         01          # Node Number
         01          # Service Number

D.3.  The 'null' Endpoint

   The 'null' EID of ipn:0.0 can be encoded in the following ways:

   The complete five octet encoding of the 'null' ipn EID using the two-
   element scheme-specific encoding would be as follows:

   82       # 2-Element Endpoint Encoding
      02    # uri-code: 2 (IPN URI scheme)
      82    # 2 Element ipn EID scheme-specific encoding
         00 # Node Number
         00 # Service Number

   The complete six octet encoding of the 'null'' ipn EID using the
   three-element scheme-specific encoding would be as follows:

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   82       # 2-Element Endpoint Encoding
      02    # uri-code: 2 (IPN URI scheme)
      83    # 3 Element ipn EID scheme-specific encoding
         00 # Default Allocator
         00 # Node Number
         00 # Service Number

Acknowledgments

   The following DTNWG participants contributed technical material, use
   cases, and critical technical review for this URI scheme update:
   Scott Burleigh of the IPNGROUP, Keith Scott, Brian Sipos of the Johns
   Hopkins University Applied Physics Laboratory, and Jorge Amodio of
   LJCV Electronics.

   Additionally, the authors wish to thank members of the CCSDS SIS-DTN
   working group at large who provided useful review and commentary on
   this document and its implications for the future of networked space
   exploration.

Authors' Addresses

   Rick Taylor
   Ori Industries
   Email: rick.taylor@ori.co

   Ed Birrane
   JHU/APL
   Email: Edward.Birrane@jhuapl.edu

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