| Internet-Draft | ipn-update | September 2022 |
| Taylor & Birrane | Expires 19 March 2023 | [Page] |
The Delay Tolerant Networking 'ipn' Endpoint Identifier scheme was first defined as Compressed Bundle Header Encoding (CBHE) [RFC6260] for use with the Bundle Protocol version 6 (BPv6) [RFC5050]. [RFC7116] updated [RFC6260] and requested IANA registries associated with the ipn scheme when used with BPv6. The Bundle Protocol version 7 (BPv7) specification [RFC9171] also defines an ipn scheme (for use with BPv7) by reusing the format from [RFC6260]. 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 [RFC7116] 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.¶
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-taylor-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.¶
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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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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) [RFC5050], an associated specification for numeric node identifiers and numeric service identifiers was described in Section 2.1 of [RFC6260]. Further, [RFC6260] 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) [RFC9171], 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.¶
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.¶
This section describes the specification of the 'ipn' EID scheme as defined in [RFC9171] and is included as convenient reference for the rest of this document.¶
Section 4.2.5.1.2 of [RFC9171] specifies the 'ipn' EID scheme for BPv7, with an identical format to the specification of the 'ipn' EID scheme for BPv6 in Section 2.1 of [RFC6260], 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).¶
As specified in [RFC9171], the textual encoding of an 'ipn' scheme EID 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 = node-nbr nbr-delim service-nbr node-nbr = 1*DIGIT nbr-delim = "." service-nbr = 1*DIGIT¶
As specified in [RFC9171], when encoded in Concise Binary Object Representation (CBOR) [RFC8949], an 'ipn' scheme EID must comply with the following Concise Data Definition Language (CDDL) [RFC8610] specification:¶
eid = $eid .within eid-structure
eid-structure = [
uri-code: uint,
SSP: any
]
; ... Syntax for uri-code 1 (dtn scheme) omitted ...
$eid /= [
uri-code: 2,
SSP: [
nodenum: uint,
servicenum: uint
]
]
¶
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].¶
As described in Section 4.2.5.2 of [RFC9171], the identifier of a node (Node ID) must be a singleton endpoint, see Section 3.1 of [RFC9171]. Section 3.2.2 of [RFC7116] allocates the service-nbr 0 to the 'Bundle Protocol Administrative Record' for the 'ipn' EID scheme for BPv6, and Section 4.2.5.1.2 of [RFC9171] 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:¶
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.¶
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.¶
A potential solution to this, as described in Section 3.2.1 of [RFC7116], 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: Section 3.2.1 of [RFC7116] allocates [CCSDS] 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:¶
82 # array(2)
02 # uri-code: 2
82 # array(2)
19 4000 # node-nbr: 16384
00 # service-nbr: 0
¶
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 [RFC7116] 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 Section 2.1 of [RFC1287], demonstrates that exhaustion of a 2^32 bit number space happens surprisingly quickly.¶
This section updates the use of 'ipn' scheme EIDs when used with BPv7 as specified in [RFC9171] to address some of the limitations described above, and renames two of the registries defined in [RFC7116] to clarify their usage with BPv6 only.¶
The following rules update or clarify the specification of node-nbr in Section 4.2.5.1.2 of [RFC9171]:¶
The "CBHE Node Numbers" registry specified in Section 3.2.1 of [RFC7116] 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 (Section 7).¶
The following rules update or clarify the specification of service-nbr in Section 4.2.5.1.2 of [RFC9171], deriving from the definitions in Section 3.2.2 of [RFC7116]:¶
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.¶
The "CBHE Service Numbers" registry specified in Section 3.2.2 of [RFC7116] 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 (Section 7).¶
The consequence of the updates to the 'ipn' EID scheme described above (Section 4) 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.¶
Fundamentally, [RFC9171] '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:¶
82 # array(2)
02 # uri-code: 2
83 # array(3)
02 # auth-nbr: 2
01 # node-nbr: 1
00 # service-nbr: 0
¶
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.¶
The textual encoding of an 'ipn' scheme EID 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 = auth-part? node-nbr nbr-delim service-nbr auth-part = auth-nbr nbr-delim sub-auth-part? sub-auth-part = sub-auth-nbr nbr-delim auth-nbr = 1*DIGIT sub-auth-nbr = 1*DIGIT node-nbr = 1*DIGIT service-nbr = 1*DIGIT nbr-delim = "."¶
When encoded in Concise Binary Object Representation (CBOR) [RFC8949], an 'ipn' scheme EID MUST comply with the following Concise Data Definition Language (CDDL) [RFC8610] specification:¶
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: [
? authority,
node-nbr: uint,
service-nbr: uint
]
authority = (
auth-nbr: uint,
? sub-auth-nbr: uint
)
]
¶
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].¶
[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 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.¶
The following sections detail requests to IANA for new registries, and the renaming of existing registries.¶
IANA is requested to create a new registry entitled "Bundle Protocol Version 7 'ipn' Scheme Service Numbers"¶
The registration policy for this registry is:¶
| 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:¶
| Value | Description | Reference |
|---|---|---|
| 0 | The administrative endpoint | This document |
IANA is request to rename the "CBHE Node Numbers" registry defined in Section 3.2.1 of [RFC7116] to the "Bundle Protocol Version 6 'ipn' Scheme Node Numbers", with no change to its allocation rules or current allocations.¶
IANA is requested to rename the "CBHE Service Numbers" registry defined in Section 3.2.2 of [RFC7116] to the "Bundle Protocol Version 6 'ipn' Scheme Service Numbers", with no change to its allocation rules or current allocations.¶
(This whole section is to be removed prior to publication)¶
See Allocation Ranges (Section 3.3.1).¶
Is there really any difference in outcome between the following cases?:¶
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 Section 5.4 of [RFC9171] 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?¶
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.¶
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.¶
TODO acknowledge.¶