]> Ori Industries

rick.taylor@ori.co

JHU/APL

Edward.Birrane@jhuapl.edu

Transport Delay/Disruption Tolerant Networking DTN ipn BPv7 CBHE Bundle Protocol The Delay Tolerant Networking 'ipn' Endpoint Identifier scheme was first defined as Compressed Bundle Header Encoding (CBHE) for use with the Bundle Protocol version 6 (BPv6) . updated and requested IANA registries associated with the ipn scheme when used with BPv6. The Bundle Protocol version 7 (BPv7) specification also defines an ipn scheme (for use with BPv7) by reusing the format from . The evolution and specification of the ipn scheme has led to confusion over its use and format between BPv6 and BPv7. This document defines the ipn scheme as it is to be used with BPv7 and also updates to make it clear that IANA CBHE registries are only to be used for BPv6. This document also updates the format of the BPv7 ipn scheme to include Numbering Authorities and requests the formation of BPv7 ipn scheme IANA registries. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Delay/Disruption Tolerant Networking Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction From the earliest days of experimentation with "store and forward" data transfer with the Bundle Protocol, the desire has existed for a simple way to enumerate the nodes and services in a Delay Tolerant Network (DTN). With the IRTF standardisation of the experimental Bundle Protocol version 6 (BPv6) , an associated specification for numeric node identifiers and numeric service identifiers was described in . Further, also defined the 'ipn' Endpoint Identifier (EID) naming scheme which identifies a DTN endpoint using node and service identifiers. The acronym IPN was originally an expansion of the term "InterPlanetary Network" as the original aim of this scheme was to provide a compact namespace for an interoperable space-based DTN architecture. Beyond space-based applications, terrestrial nodes might also operate with limited power, bandwidth, and/or compute budget. The adoption of DTN in the IETF, resulting in the publication of the Bundle Protocol version 7 (BPv7) , will result 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. In all cases, concisely encoded numeric identifiers for both nodes and services provides processing advantages over more verbose naming schemes. Therefore additional focus has been placed on the capabilities of the 'ipn' scheme for use beyond its historical purpose for space-based DTN architectures. This expanded use of the 'ipn' scheme for BPv7 networks requires both some updates to the 'ipn' scheme itself and a clearer distinction between the uses of 'ipn' schemes in BPv6 and BPv7 networks. This document updates the definition of the 'ipn' scheme (in ways that are backwards compatible for existing 'ipn' uses) to include adding an optional naming authority to distinguish node namespaces. This document also defines new IANA registries associated with both the updated IPN scheme and the use of node and service identifiers for use specifically with BPv7.

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 when, and only when, they appear in all capitals, as shown here.

The Legacy 'ipn' Scheme in RFC9171 This section describes the specification of the 'ipn' EID scheme as defined in and is included as convenient reference for the rest of this document.

Encoding specifies the 'ipn' EID scheme for BPv7, with an identical format to the specification of the 'ipn' EID scheme for BPv6 in , namely as a sequence of two unsigned integers. The first number representing the identifier of the node (node-nbr), and the second being the identifier of a particular service expected at that node (service-nbr).

Text Encoding As specified in , the textual encoding of an 'ipn' scheme EID must comply with the following ABNF syntax, including the core ABNF syntax rule for DIGIT defined by that specification:

CBOR Encoding As specified in , when encoded in Concise Binary Object Representation (CBOR) , an 'ipn' scheme EID must comply with the following Concise Data Definition Language (CDDL) specification: Because the encoding of node-nbr and service-nbr (specified in the CDDL as nodenum and servicenum) are defined as CBOR uint types, both values are restricted by this encoding to a range of [0 .. 2^64-1].

Uniqueness Constraints As described in , the identifier of a node (Node ID) must be a singleton endpoint, see . allocates the service-nbr 0 to the 'Bundle Protocol Administrative Record' for the 'ipn' EID scheme for BPv6, and derives from this earlier specification, and more loosely states that the service-nbr zero (0) MAY identify the 'administrative endpoint' of a node, and in combination with a valid node-nbr, it can be used as a BPv7 Node ID. From this we can deduce the following rules:

1. An 'ipn' scheme EID, perhaps with service-nbr 0, MAY be a valid unique Node ID when used with BPv7.
2. Because the node-nbr component of 'ipn' scheme EIDs of all services on a node must be identical, when used with BPv7, the node-nbr component MUST be unique to each node within a given network.

Because the ipn scheme encodes the Node Id, every 'ipn' scheme EID is a singleton EID. This means the following: 1. Only a single node can ever be registered in a given 'ipn' scheme EID at a given time. 1. Every 'ipn' scheme EID to which a node is registered must share the same node-nbr.

Global Flat Namespace Since the legacy ipn scheme encodes the Node ID as the node number, and the Node ID must be a globally unique identifier, this means that the legacy ipn scheme node-nbrs must, themselves, be globally unique. The legacy ipn scheme node-nbr exists in a single, global, flat namespace. The reliance on such a namespace is not problematic when deploying a private, self-contained network: If there are few nodes that can ever intercommunicate, then those nodes can have node-nbrs allocated by the administrator of that network and there will be no problem with uniqueness coming from a serialized, central authority. However, as the number of nodes and number of administrative authorities in a network scale, the administrative burden of assigning node-nbrs increases.

Allocation Ranges A potential solution to this, as described in , is to assign ranges of node-nbrs to different authorities, from which they can independently allocate node-nbrs. The use of a global, flat namespace (in general) and the use of predefined allocations (in particular) present two practical problems relating to encoding efficiency and namespace exhaustion. This division of the number space is an adequate solution for the uniqueness problem, but it introduces a new issue: The encoding-length of each node-nbr is no longer minimal, as the offset to the start of the range assigned to the allocating authority is included in the node-nbr. For example: allocates the range [2^14 .. 2^21-1] for node-nbrs for use with BPv6, and if CCSDS choses to continue to use this number range for BPv7, the CBOR encoding of every Node ID will be at least 7 octets (including 2 octets for the outer array with uri-code), even when interoperability is not required: Another side-effect of assigning ranges of the number space to different sub-allocating authorities is to reduce the total availability of node-nbrs. Although the current allocation strategy defined in leaves approximately 2^42 numbers unallocated, the recommendation to IANA is that these numbers should be allocated in blocks of 2^14. The history of IPv4 address allocation, see , demonstrates that exhaustion of a 2^32 bit number space happens surprisingly quickly.

Updates to RFC7116 and RFC9171 This section updates the use of 'ipn' scheme EIDs when used with BPv7 as specified in to address some of the limitations described above, and renames two of the registries defined in to clarify their usage with BPv6 only.

BPv7 'ipn' Scheme Node Numbers The following rules update or clarify the specification of node-nbr in :

1. The node-nbr component of an 'ipn' scheme EID MUST be an unsigned integer >= 0.
2. The 'ipn' scheme EID "ipn:0.0" is assigned to the 'null' endpoint, see .
3. If the node-nbr component of an 'ipn' scheme EID is zero (0), then the service-nbr component MUST be zero (0).
4. Non-zero 'ipn' EID scheme node-nbrs are explicitly 'Private Use', see . Therefore they MUST NOT be regarded as unique beyond the administrative domain defined by the allocating authority, and interoperability with other administrative domains MUST NOT be assumed.
5. Values >= 2^64 for the node-nbr component of an 'ipn' scheme EID are 'Reserved', see , to allow concise unsigned integer (type 0) CBOR encoding.

To support this update, a new IANA "Bundle Protocol Version 7 'ipn' Scheme Node Numbers" registry is defined for the node-nbr component of an 'ipn' scheme EID when used with BPv7.

BPv6 'ipn' Scheme Node Numbers The "CBHE Node Numbers" registry specified in is renamed without change to the "Bundle Protocol Version 6 'ipn' Scheme Node Numbers" registry, to clarify that it is for use solely with BPv6, see IANA Considerations.

BPv7 'ipn' Scheme Service Numbers The following rules update or clarify the specification of service-nbr in , deriving from the definitions in :

1. The service-nbr component of an 'ipn' scheme EID MUST be an unsigned integer >= 0.
2. The administrative endpoint as defined in of an 'ipn' scheme EID MUST be service-nbr zero (0).
3. Values >= 2^64 for the service-nbr component of an 'ipn' scheme EID are 'Reserved', see , to allow concise unsigned integer (type 0) CBOR encoding.

To support this update, a new IANA "Bundle Protocol Version 7 'ipn' Scheme Service Numbers" registry is defined for the service-nbr component of an 'ipn' scheme EID when used with BPv7.

BPv6 'ipn' Scheme Service Numbers The "CBHE Service Numbers" registry specified in is renamed without change to the "Bundle Protocol Version 6 'ipn' Scheme Service Numbers" registry, to clarify that it is for use solely with BPv6, see IANA Considerations.

The Interoperable BPv7 'ipn' Scheme The consequence of the updates to the 'ipn' EID scheme described above is to remove any capability to send bundles between nodes with 'ipn' scheme EIDs enumerated by two different allocating authorities, as there is no explicit indication of which authority allocated which corresponding node-nbr, resulting in a violation of the uniqueness constraints. This situation is obviously untenable when building DTNs beyond a fairly small scale.

Numbering Authorities Underlying the BPv6 'ipn' scheme node-nbr range assignment if is the desire to reduce the administrative burden on a single allocation authority for all node-nbrs by delegating the authority to assign numbers to a pre-agreed set of numbering authorities. Although the range-based mechanism of delegating this authority has been criticised above, the desire for delegation of numbering to a group of independent authorities in an interoperable way is still valid. To address this, this document introduces the concept of Numbering Authorities. A Numbering Authority has a unique numeric identifier, but has the authority to allocate any node-nbr in the full 2^64 unsigned integer range according to its own rules. In order to ensure interoperability between Numbering Authorities, a new IANA "Bundle Protocol Version 7 'ipn' Scheme Authority Numbers" registry is defined for the registration of Authority Numbers, see IANA Considerations. Although the uniqueness of Numbering Authority identifiers is required for interoperable DTN operations, identifier ranges are explicitly reserved for experimentation and private use for when interoperability is not required. The only number allocation constraint placed upon a Numbering Authority is that the node-nbr zero (0) MUST not be allocated.

Numbering Sub-authorities Some organisations that register as Numbering Authorities may be sufficiently large that acting as a single allocating authority for their desired number range becomes administratively untenable, for example government agencies. In this case, the ability to delegate number allocation to sub-authorities is desired. To address this, this specification permits the addition of a Numbering Sub-authority numeric identifier, when required, from a registry controlled by the Numbering Authority to the Interoperable BPv7 'ipn' scheme EID. In order to avoid unbounded sequences of sub-sub-authorities, making processing in constrained devices overly onerous, only a single Numbering Sub-authority is permitted in an Interoperable BPv7 'ipn' scheme EID.

The Local Numbering Authority The numeric identifier zero (0) is allocated in the "Bundle Protocol Version 7 'ipn' Scheme Authority Numbers" registry for the Local Numbering Authority. When a bundle processing agent processes a bundle containing EIDs using the Interoperable BPv7 'ipn' scheme, with a Numbering Authority identifier of zero (0), the Numbering Authority identifier of such EIDs MUST considered to be the same as the Numbering Authority of the 'ipn' scheme NodeId of the bundle processing agent. The Local Numbering Authority does not support Numbering Sub-authorities, and therefore any Numbering Sub-authority identifier MUST NOT be included when composing Interoperable BPv7 'ipn' scheme EIDs. When a bundle processing agent encounters an Interoperable BPv7 'ipn' scheme EID with Number Authority identifier zero (0) and a Numbering Sub-authority identifier, then the Numbering Sub-authority identifier MUST be ignored.

Backwards Compatibility Although the Interoperable BPv7 'ipn' EID scheme introduces the ability to include Numbering Authority identifiers, it does not preclude the use of BPv7 'ipn' scheme EIDs without such an identifier. To allow for backwards compatibility, when a bundle processing agent processes a BPv7 bundle containing 'ipn' scheme EIDs without a Numbering Authority identifier, unless the EID is the 'null' endpoint (ipn:0.0), the Numbering Authority identifier MUST considered to be zero (0), and therefore treated in the the same manner as the Local Numbering Authority.

Prefix Encoding Fundamentally, 'ipn' scheme EIDs are represented as a sequence of unsigned integers: In the text encoding, the numbers are separated with the '.' delimiter; in CBOR, encoded as an array of unsigned integers. Adding the numeric identifier of the numbering authority, possibly with sub-authorities, that allocated the subsequent node-nbr as a prefix to EIDs allows for a concise encoding of a suitable discriminator, without reducing the total availability of node-nbrs. In the text encoding, this is as simple as pre-pending numeric identifiers for the numbering authorities, separated with the '.' delimiter, to the text. For the CBOR encoding, this is achieved by increasing the dimension of the array of unsigned integers to include the relevant numbering authority identifiers. For example, the EID "ipn:2.1.0" uniquely identifies the administrative endpoint of the node allocated the node-nbr 1 by the numbering authority with identifier 2. This EID can be concisely encoded in CBOR as 6 octets, including 2 octets for the outer array with uri-code: This prefixing method is be extended to allow numbering authorities to delegate allocation of numbers to sub-authorities as they see fit, by appending further sub-authority identifiers to the prefix.

Text Encoding The textual encoding of an 'ipn' scheme EID MUST comply with the following ABNF syntax, including the core ABNF syntax rule for DIGIT defined by that specification:

CBOR Encoding When encoded in Concise Binary Object Representation (CBOR) , an 'ipn' scheme EID MUST comply with the following Concise Data Definition Language (CDDL) specification: Because the encoding of auth-nbr, sub-auth-nbr, node-nbr, and service-nbr are defined as CBOR uint types, all values are restricted by this encoding to a range of [0 .. 2^64-1].

Recommendations 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 may 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. Because of this late binding concept, the authority components of an interoperable 'ipn' scheme EID SHOULD NOT be regarded as some kind of "type field", and used to derive additional information from the other components of the EID. An example of incorrect behaviour would be: "I know authority X allocates node-nbrs derived from the MAC address of some link-layer device on each node, and so I can just send packets directly to that MAC address". No matter the authority that controls the allocation of node-nbrs, they remain just numbers, without additional meaning.

Security Considerations TODO

IANA Considerations The following sections detail requests to IANA for new registries, and the renaming of existing registries.

Bundle Protocol Version 7 'ipn' Scheme Local Node Numbers registry IANA is requested to create a new registry entitled "Bundle Protocol Version 7 'ipn' Scheme Local Node Numbers" with the following assignments: Bundle Protocol Version 7 'ipn' Scheme Local Node Numbers

Value	Description	Reference
0	The null endpoint	This document
1 .. 2^64-1	Private Use	This document
>= 2^64	Reserved	This document

All possible values are assigned.

Bundle Protocol Version 7 'ipn' Scheme Service Numbers registry IANA is requested to create a new registry entitled "Bundle Protocol Version 7 'ipn' Scheme Service Numbers" The registration policy for this registry is: Bundle Protocol Version 7 'ipn' Scheme Service Numbers registration policies

Range	Registration Policy
0 .. 23	RFC Required
24 .. 4095	Specification Required
4096 .. 2^32-1	Private Use
2^32 .. 2^64-1	Experimental Use
>= 2^64	Reserved

The initial values for the registry are: Bundle Protocol Version 7 'ipn' Scheme Service Numbers initial values

Value	Description	Reference
0	The administrative endpoint	This document

Bundle Protocol Version 7 'ipn' Scheme Authority Numbers registry IANA is requested to create a new registry entitled "Bundle Protocol Version 7 'ipn' Scheme Authority Numbers" The registration policy for this registry is: Bundle Protocol Version 7 'ipn' Scheme Authority Numbers registration policies

Range	Registration Policy
0 .. 2^16-1	First Come First Served
2^16 .. 2^32-1	Private Use
2^32 .. 2^64-1	Experimental Use
>= 2^64	Reserved

The initial values for the registry are: Bundle Protocol Version 7 'ipn' Scheme Authority Numbers initial values

Value	Description	Reference
0	The Local Numbering Authority	This document

CBHE Node Numbers registry IANA is request to rename the "CBHE Node Numbers" registry defined in to the "Bundle Protocol Version 6 'ipn' Scheme Node Numbers", with no change to its allocation rules or current allocations.

CBHE Service Numbers registry IANA is requested to rename the "CBHE Service Numbers" registry defined in to the "Bundle Protocol Version 6 'ipn' Scheme Service Numbers", with no change to its allocation rules or current allocations.

References Normative References Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. The DTNRG Research Group has defined the experimental Licklider Transmission Protocol (LTP) and the Compressed Bundle Header Encoding (CBHE) mechanism for the InterPlanetary Network ('ipn' URI scheme). Moreover, RFC 5050 defines values for the Bundle Protocol administrative record type. All of these fields are subject to a registry. For the purpose of its research work, the group has created ad hoc registries. As the specifications are stable and have multiple interoperable implementations, the group would like to hand off the registries to IANA for official management. This document describes the necessary IANA actions. This document presents a specification for the Bundle Protocol, adapted from the experimental Bundle Protocol specification developed by the Delay-Tolerant Networking Research Group of the Internet Research Task Force and documented in RFC 5050. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. Informative References This informational RFC discusses important directions for possible future evolution of the Internet architecture, and suggests steps towards the desired goals. This memo provides information for the Internet community. It does not specify an Internet standard. This document describes a convention by which Delay-Tolerant Networking (DTN) Bundle Protocol (BP) "convergence-layer" adapters may represent endpoint identifiers in a compressed form within the primary blocks of bundles, provided those endpoint identifiers conform to the structure prescribed by this convention. Compressed Bundle Header Encoding (CBHE) compression is a convergence-layer adaptation. It is opaque to bundle processing. Therefore, it has no impact on the interoperability of different Bundle Protocol implementations, but instead affects only the interoperability of different convergence-layer adaptation implementations. This document is a product of the Delay-Tolerant Networking Research Group and has been reviewed by that group. No objections to its publication as an RFC were raised. This document defines an Experimental Protocol for the Internet community. This document describes the end-to-end protocol, block formats, and abstract service description for the exchange of messages (bundles) in Delay Tolerant Networking (DTN). This document was produced within the IRTF's Delay Tolerant Networking Research Group (DTNRG) and represents the consensus of all of the active contributors to this group. See http://www.dtnrg.org for more information. This memo defines an Experimental Protocol for the Internet community.

Discussion Points (This whole section is to be removed prior to publication)

Why define all of the RFC9171 'ipn' scheme node-nbrs as 'Private Use'? Because there is currently no BPv7 standard specifying that they are not, and current implementations already assume that they can just use node-nbrs as they like. The de-facto standard, at of time of writing, is that DTNs using the 'ipn' EID scheme are not interoperable, or have pre-agreed an allocation scheme between communities participating in a joint DTN. This pre-agreement is just a shared administrative domain, probably with range-based sub-allocation scheme which results in inefficient encoding, and is still not universally interoperable, but this update does not break those implementations. Even with this update, when ipn EIDs are used without an auth-nbr, there is no guarantee of interoperability, and they are therefore "Private Use".

Why not just sub-divide the BPv7 'ipn' node-nbr space like BPv6? See Allocation Ranges.

Why not a new 'ipn3' EID scheme? Is there really any difference in outcome between the following cases?:

1. An existing parser receives a bundle with an EID with a 3-ary ipn EID
2. An existing parser receives a bundle with an EID with an unrecognised scheme identifier

In the former case, the parser will recognised the scheme as 'ipn' but then fail as the dimension of the subsequent array is not 2. In the latter case the parser will fail one octet earlier when the scheme is not recognised. In both cases, the EID will not be recognised as valid, forwarding will be "contraindicated", and the process described in Step 2 of should be followed. It is believed that introducing a new EID scheme will just result in fragmentation of support. 'ipn' is popular because it is simple; let's not introduce another 'simple' EID scheme to compete with it, but rather add just enough support for universal interoperability. 'ipn' as defined in RFC9171 needs clarification, so why not just add the tweaks necessary as long as we don't break back-compatibility?

Why not use just the 'dtn' scheme for interoperability? Because the 'dtn' scheme definition in RFC9171 is intentionally left wide open for further work. That work has yet to happen and is a considered a much more complex task than a simple update to the 'ipn' scheme.

Won't these changes break BPv6 compatibility? Because of the difference in encoding between BPv6 and BPv7, there is no on-the-wire compatibility between the versions. Any 'dual-stack' gateway BPA is going to have to encapsulate BPv6 in BPv7 (or vice-versa), so the EID of the decapsulating endpoint will have to be used in the 'envelope' bundle. There is no way a BPv7 node can send a bundle to a BPv6 node directly using BPv7, so backwards compatibility of EIDs between protocol versions is not needed.

Why not have an unbounded number of sub-authorities? It's possible to encode, and has been considered by the authors, but the conclusion was: ipn:it.is.really.not.a.great.idea.to.have.unbounded.sequences.of.identifiers.when.it.comes.to.processing.EIDs.in.constrained.environments.0 An optional, single sub-authority seemed like a sensible idea, but feel free to argue on the list for more.

Acknowledgments TODO acknowledge.