Network Working Group                                          D. Thaler
Internet-Draft                                                 Microsoft
Updates: 2863 (if approved)                                 D. Romascanu
Intended status: Standards Track                             Independent
Expires: September 30, 2019                               March 29, 2019

       Guidelines and Registration Procedures for Interface Types


   The registration and use of interface types ("ifType" values)
   predated the use of IANA Considerations sections and YANG modules,
   and so confusion has arisen about the interface type allocation
   process.  This document provides updated guidelines for the
   definition of new interface types, for consideration by those who are
   defining, registering, or evaluating those definitions.

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
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   This Internet-Draft will expire on September 30, 2019.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   ( in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Problems  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Interface Sub-Layers and Sub-Types  . . . . . . . . . . . . .   3
   5.  Registration  . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Media-specific OID-subtree assignments  . . . . . . . . .   6
     5.3.  Registration Template . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The IANA IfType-MIB was originally defined in [RFC1573] as a separate
   MIB module together with the Interfaces Group MIB (IF-MIB) module.
   The IF-MIB module has since been updated and is currently specified
   in [RFC2863], but this latest IF-MIB RFC no longer contains the IANA
   IfType-MIB.  Instead, the IANA IfType-MIB is now maintained as a
   separate module.  Similarly, [RFC7224] created an initial IANA
   Interface Type YANG Module, and the current version is maintained by

   The current IANA IfType registries are in [iana-if-type],
   [IANAifType-MIB], and [ifType].

   Although the ifType registry was originally defined in a MIB module,
   the assignment and use of interface type values are not tied to MIB
   modules or any other management mechanism.  Interface type values can
   be used as values of data model objects (MIB objects, YANG objects,
   etc.), as parts of a unique identifier of a data model for a given
   interface type (e.g., in an OID), or simply as values exposed by
   local APIs or UI on a device.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP

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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Problems

   This document addresses the following issues:

   1.  As noted in Section 1, the former guidance was written with
       wording specific to MIB modules, and accordingly some confusion
       has resulted when using YANG modules.  This document clarifies
       that ifTypes are independent from the type of, or even existence
       of, a data model.

   2.  The use of, and requirements around, sub-layers and sub-types are
       not well understood even though good examples of both exist.
       This is discussed in Section 4.

   3.  The registry is kept in the format of MIB and YANG modules, but
       there was no process guidance written to check that updates were
       syntactically correct, which led to the registry having syntax
       errors that broke tools.  Section 5.1 adds a validation step to
       the documented assignment procedure.

   4.  Transmission values [ifType] have often been allocated as part of
       ifType allocation, but no guidance exists about whether a
       requester must ask for it or not, and the request form has no
       such required field.  As a result, IANA has asked the Designated
       Expert to decide for each allocation, but no relevant guidance
       for the Designated Expert has been documented.  This is discussed
       in Section 5.2.

   5.  Various documents and registries say to submit requests via
       email, but a web form exists for submitting requests, which has
       caused some confusion around which is to be used.  This is
       discussed in Section 6.

4.  Interface Sub-Layers and Sub-Types

   When multiple sub-layers exist below the network layer, each sub-
   layer can be represented by its own row in the ifTable with its own
   ifType, with the ifStackTable being used to identify the upward and
   downward multiplexing relationships between rows.  Section 3.1.1 of
   [RFC2863] provides more discussion, and Section 3.1.2 of that RFC
   provides guidance for defining interface sub-layers.  More recent
   experience shows that these guidelines are phrased in a way that is
   now too restrictive, since at the time [RFC2863] was written, MIB
   modules were the dominant data model.

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   This document clarifies that such guidance also applies to YANG

   Some ifTypes may define sub-types.  For example, the tunnel(131)
   ifType defines sub-types, where each IANAtunnelType can have its own
   MIB and/or YANG module with protocol-specific information, but there
   is enough in common that some information is exposed in a generic IP
   Tunnel MIB corresponding to the tunnel(131) ifType.

   For requests that involve multiple sub-layers below the network
   layer, requests MUST include (or reference) a discussion of the
   multiplexing relationships between sub-layers, ideally with a
   diagram.  Various well-written examples exist of such definitions,
   including [RFC3637] section 3.4.1, [RFC4087] section 3.1.1, and
   [RFC5066] section 3.1.1.

   Definers of sub-layers and sub-types should consider which model is
   more appropriate for their needs.  A sub-layer is generally used
   whenever either a dynamic relationship exists (i.e., which instances
   layer over which other instances can change over time) or a
   multiplexing relationship exists with another sub-layer.  A sub-type
   can be used when neither of these are true, but where one interface
   type is conceptually a subclass of another interface type, as far as
   a management data model is concerned.

   PROPOSED CLARIFICATION/ELABORATION: In general, the intent of an
   interface type or sub-type is that its definition should be
   sufficient to identify an interoperable protocol.  In some cases,
   however, a protocol might be defined in a way that is not sufficient
   to provide interoperability with other compliant implementations of
   that protocol.  In such a case, an ifType definition should discuss
   whether specific instantiations (or profiles) of behavior should use
   a sub-layer model (e.g., each vendor might layer the protocol over
   its own sub-layer that provides the missing details), or a sub-type
   model (i.e., each vendor might subclass the protocol without any
   layering relationship).  If a sub-type model is more appropriate,
   then the data model for the protocol might include a sub-type
   identifier so that management software can discover objects specific
   to the subtype.  In either case, such discussion is important to
   guide definers of a data model for the more specific information
   (i.e., a lower sub-layer or a subtype), as well as the Designated
   Expert that must review requests for any such ifTypes or sub-types.

5.  Registration

   The IANA policy (using terms defined in [RFC8126]) for registration
   is Expert Review.  The role of the Designated Expert in the procedure
   is to raise possible concerns about wider implications of proposals

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   for use and deployment of interface types.  While it is recommended
   that the responsible Area Director and the IESG take into
   consideration the Designated Expert opinions, nothing in the
   procedure empowers the Designated Expert to override properly
   arrived-at IETF or working group consensus.

5.1.  Procedures

   Someone wishing to register a new ifType value MUST:

   1.  Check the IANA registry to see whether there is already an entry
       that could easily satisfy the modeling and functional
       requirements for the requested entry.  If there is already such
       an entry, use it or update the existing specification.  Text in
       an Internet-Draft, or part of some other permanently available,
       stable specification may be written to clarify the usage of an
       existing entry or entries for the desired purpose.

   2.  Check the IANA registry to see whether there is already some
       other entry with the desired name.  If there is already an
       unrelated entry under the name, choose a different name.

   3.  Prepare a registration request using the template specified in
       Section 5.3.  The registration request can be contained in an
       Internet-Draft, submitted alone, or as part of some other
       permanently available, stable, specification.  The registration
       request can also be submitted in some other form (as part of
       another document or as a stand-alone document), but the
       registration request will be treated as an "IETF Contribution"
       under the guidelines of [RFC5378].

   4.  Submit the registration request (or pointer to document
       containing it) to IANA at or via the web form at .

   Upon receipt of a registration request, the following steps MUST be

   1.  IANA checks the submission for completeness; if required
       information is missing or any citations are not correct, IANA
       will reject the registration request.  A registrant can resubmit
       a corrected request if desired.

   2.  IANA requests Expert Review of the registration request against
       the corresponding guidelines from this document.

   3.  The Designated Expert will evaluate the request against the

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   4.  Once the Designated Expert approves registration, IANA updates
       [ifType], [IANAifType-MIB], and [iana-if-type] to show the
       registration.  When adding values to the IANAifType-MIB, IANA
       should verify that the updated MIB module is syntactically
       correct before publishing the update.  There are various existing
       tools or web sites that can be used to do this verification.

   5.  If instead the Designated Expert does not approve registration
       (e.g., for any of the reasons in [RFC8126] section 3), a
       registrant can resubmit a corrected request if desired, or the
       IESG can override the Designated Expert and approve it per the
       process in Section 5.3 of [RFC8126].

5.2.  Media-specific OID-subtree assignments

   The current IANAifType-MIB notes:

      The relationship between the assignment of ifType values and of
      OIDs to particular media-specific MIBs is solely the purview of
      IANA and is subject to change without notice.  Quite often, a
      media-specific MIB's OID-subtree assignment within MIB-II's
      'transmission' subtree will be the same as its ifType value.
      However, in some circumstances this will not be the case, and
      implementors must not pre-assume any specific relationship between
      ifType values and transmission subtree OIDs.

   The following change is proposed:

   CURRENT: For every ifType registration, the corresponding
   transmission number value should be registered or marked "Reserved."

   PROPOSED: For future ifType assignments, an OID-subtree assignment
   MIB-II's 'transmission' subtree will be made with the same value.

   RATIONALE: (1) This saves effort in the future since if a
   transmission number is later needed, no IANA request is needed that
   would then require another Expert Review. (2) The transmision
   numbering space is not scarce, so there seems little need to reserve
   the number for a different purpose than what the ifType is for. (3)
   The Designated Expert need not review whether a transmission number
   value should be registered when processing each ifType request, thus
   reducing the possibility of delaying assignment of ifType values. (4)
   There is no case on record where allocating the same value could have
   caused any problem.

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5.3.  Registration Template

   This template describes the fields that MUST be supplied in a
   registration request suitable for adding to the registry:

   Label for IANA ifType requested:  As explained in Section 7.1.1 of
      [RFC2578], a label for a named-number enumeration must consist of
      one or more letters or digits, up to a maximum of 64 characters,
      and the initial character must be a lower-case letter.  (However,
      labels longer than 32 characters are not recommended.)  Note that
      hyphens are not allowed.

   Name of IANA ifType requested:  A short description (e.g., a protocol
      name), suitable to appear in a comment in the registry.

   Description of the proposed use of the IANA ifType:  Requesters MUST
      include answers, either directly or via a link to some document
      with the answers, to the following questions in the explanation of
      the proposed use of the IANA IfType:

      o  How would IP run over your ifType?

      o  Would there be another interface sublayer between your ifType
         and IP?

      o  Would your ifType be vendor-specific or proprietary?  (If so,
         the label MUST start with a string that shows that.  For
         example, if your company's name or acronym is xxx, then the
         ifType label would be something like xxxSomeIfTypeLabel.)

      o  (ADDED) Would your ifType require or allow vendor-specific
         extensions?  If so, would the vendor use their own ifType in
         sub-layer below the requested ifType, or a sub-type of the
         ifType, or some other mechanism?

   Reference, Internet-Draft, or Specification:  A link to some document
      is required.

   Additional information or comments:  Optionally any additional
      comments for IANA or the Designated Expert.

6.  IANA Considerations

   This entire document is about IANA considerations.

   CURRENT: The registries say to use email, but a web form exists
   (, which is an apparent
   contradiction.  Should IANA require using the form?

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   Or require using email?  Or accept submisions either way?

   PROPOSED: In addition, IANA is requested to make the following

   1.  [IANAifType-MIB] currently says: "Requests for new values should
       be made to IANA via email (iana&"  This should be
       updated to instead say: "Requests for new values should be made
       at or by email (iana&"

   2.  [iana-if-type] currently says: "Requests for new values should be
       made to IANA via email (iana&"  This should be updated
       to instead say: "Requests for new values should be made at or by email (iana&"

7.  Security Considerations

   Since this document does not introduce any technology or protocol,
   there are no security issues to be considered for this document

8.  References

8.1.  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-

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578,
              DOI 10.17487/RFC2578, April 1999, <https://www.rfc-

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,

   [RFC5378]  Bradner, S., Ed. and J. Contreras, Ed., "Rights
              Contributors Provide to the IETF Trust", BCP 78, RFC 5378,
              DOI 10.17487/RFC5378, November 2008, <https://www.rfc-

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   [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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

8.2.  Informative References

              IANA, "iana-if-type YANG Module", February 2019,

              IANA, "IANAifType-MIB", February 2019,

   [ifType]   IANA, "ifType definitions", February 2019,

   [RFC1573]  McCloghrie, K. and F. Kastenholz, "Evolution of the
              Interfaces Group of MIB-II", RFC 1573,
              DOI 10.17487/RFC1573, January 1994, <https://www.rfc-

   [RFC3637]  Heard, C., Ed., "Definitions of Managed Objects for the
              Ethernet WAN Interface Sublayer", RFC 3637,
              DOI 10.17487/RFC3637, September 2003, <https://www.rfc-

   [RFC4087]  Thaler, D., "IP Tunnel MIB", RFC 4087,
              DOI 10.17487/RFC4087, June 2005, <https://www.rfc-

   [RFC5066]  Beili, E., "Ethernet in the First Mile Copper (EFMCu)
              Interfaces MIB", RFC 5066, DOI 10.17487/RFC5066, November
              2007, <>.

   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,

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Authors' Addresses

   David Thaler


   Dan Romascanu


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