Guidelines and Registration Procedures for Interface Types and Tunnel Types
draft-thaler-iftype-reg-04

Network Working Group                                          D. Thaler
Internet-Draft                                                 Microsoft
Updates: 2863 (if approved)                                 D. Romascanu
Intended status: Standards Track                             Independent
Expires: January 8, 2020                                   July 07, 2019

 Guidelines and Registration Procedures for Interface Types and Tunnel
                                 Types
                       draft-thaler-iftype-reg-04

Abstract

   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.  Tunnel types were then added later, with the same
   requirements and allocation policy as interface types.  This document
   provides updated guidelines for the definition of new interface types
   and tunnel 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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 8, 2020.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problems  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Interface Sub-Layers and Sub-Types  . . . . . . . . . . . . .   4
     4.1.  Alternate Values  . . . . . . . . . . . . . . . . . . . .   5
   5.  Available Formats . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Registration  . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  Media-specific OID-subtree assignments  . . . . . . . . .   8
     6.3.  Registration Template . . . . . . . . . . . . . . . . . .   9
       6.3.1.  ifType  . . . . . . . . . . . . . . . . . . . . . . .   9
       6.3.2.  tunnelType  . . . . . . . . . . . . . . . . . . . . .  10
   7.  Submitting Requests . . . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

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
   IANA.

   The current IANA IfType registry is at [ifType-registry], with the
   same values also appearing in [yang-if-type], and the IANAifType
   textual convention at [IANAifType-MIB].

   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

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   interface type (e.g., in an OID), or simply as values exposed by
   local APIs or UI on a device.

   The TUNNEL-MIB was then defined in [RFC2667] (now obsoleted by
   [RFC4087]) which created a tunnelType registry ([tunnelType-registry]
   and the IANAtunnelType textual convention at [IANAifType-MIB]) and
   defined the assignment policy for tunnelType values to always be
   identical to the policy for assigning ifType values.

2.  Terminology

   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.

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 and tunnelTypes 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.  Since the ifType and tunnelType registries were originally
       defined, and are still retrievable, in the format of MIB modules
       (in addition to other formats), confusion arose when adding YANG
       modules as another format, as to whether each format is a
       separate registry.  This is discussed in Section 5.

   4.  The registries are retrievable in the format of MIB and YANG
       modules, but there was no process guidance written to check that
       those formats were syntactically correct as updates were made,
       which led to the registry having syntax errors that broke tools.
       Section 6.1 adds a validation step to the documented assignment
       procedure.

   5.  Transmission values [transmission-registry] 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

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       Designated Expert to decide for each allocation, but no relevant
       guidance for the Designated Expert has been documented.  This is
       remedied in Section 6.2.

   6.  Various documents and registries said to submit requests via
       email, but a web form exists for submitting requests, which
       caused some confusion around which is to be used.  This is
       discussed in Section 7.

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.

   This document clarifies that such guidance also applies to YANG
   modules.

   Some ifTypes may define sub-types.  For example, the tunnel(131)
   ifType defines sub-types, where each tunnelType 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.

   NEW CLARIFICATION/ELABORATION: In general, the intent of an interface
   type or sub-type is that its definition should be sufficient to

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   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.

4.1.  Alternate Values

   Another design decision is whether to reuse an existing ifType or
   tunnelType value, possibly using a sub-type or sub-layer model for
   refinements, or to use a different value for a new mechanism.

   If there is already an entry that could easily satisfy the modeling
   and functional requirements for the requested entry, it should be
   reused so that applications and tools that use the existing value can
   be used without changes.  If however, the modeling and functional
   requirements are significantly different enough such that having
   existing applications and tools use the existing value would be seen
   as a problem, a new value should be used.

   For example, originally multiple ifType values were used for
   different flavors of Ethernet (ethernetCsmacd(6), iso88023Csmacd(7),
   fastEther(62), etc.), typically because they were registered by
   multiple vendors.  [RFC3635] then deprecated all but
   ethernetCsmacd(6), since using different values was seen as
   problematic since all were functionally similar.

   As another example, the Teredo tunnel protocol [RFC4380] encapsulates
   packets over UDP, and a udp(8) tunnelType value was defined in
   [RFC2667], with the description "The value UDP indicates that the
   payload packet is encapsulated within a normal UDP packet (e.g., RFC
   1234)."  However, the protocol model is quite different between
   [RFC1234] and Teredo.  For example, [RFC1234] supports encapsulation
   of multicast/broadcast traffic whereas Teredo does not.  As such, it
   would be more confusing to applications and tools to represent them
   using the same tunnel type, and so [RFC4087] defined a new value for
   Teredo.

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   In summary, definers of new interface or tunnel mechanisms should use
   a new ifType or tunnelType value rather than reusing an existing
   value when key aspects such as the header format or the link model
   (point-to-point, non-broadcast multi-access, broadcast capable multi-
   access, unidirectional broadcast, etc.) are significantly different
   from existing values, but reuse the same value when the differences
   can be expressed in terms of differing values of existing objects,
   other than ifType/tunnelType, in the standard YANG or MIB module.

5.  Available Formats

   Many registries are available in multiple formats.  For example, XML,
   HTML, CSV, and Plain text are common formats in which many registries
   are available.  This document clarifies that the [IANAifType-MIB],
   [yang-if-type], and [yang-tunnel-type] MIB and YANG modules are
   merely additional formats in which the ifType and tunnelType
   registries are available.  The MIB and YANG modules are not separate
   registries, and the same values are always present in all formats of
   the same registry.

   CURRENT: The confusion stems in part due to the fact that the IANA
   "Protocol Registries" [protocol-registries] lists the YANG and MIB
   module formats separately, as if they were separate registries.
   However, the entries for the yang-if-type and iana-tunnel-type YANG
   modules say "See ifType definitions registry." and "See tunnelType
   registry (mib-2.interface.ifTable.ifEntry.ifType.tunnelType)."
   respectively, although the entry for the IANAifType-MIB has no such
   note.

   PROPOSED: It is proposed to clarify the relationship for the ifType
   and tunnelType registries as follows:

   1.  Add the following note to the entry for the IANAifType-MIB at
       [protocol-registries]: "This is one of the available formats of
       the ifType and tunnelType registries."

   2.  Change the note on the entry for the iana-if-type YANG module at
       [protocol-registries] to read: "This is one of the available
       formats of the ifType registry."

   3.  Change the note on the entry for the iana-tunnel-type YANG module
       at [protocol-registries] to read: "This is one of the available
       formats of the tunnelType registry."

   4.  Create a section for "Interface Parameters" at
       [protocol-registries], with entries for "Interface Types
       (ifType)" [ifType-registry], "Tunnel Types (tunnelType)"

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       [tunnelType-registry], and "Transmission Values"
       [transmission-registry].

   5.  Update the ifType definitions registry [ifType-registry] to list
       MIB [IANAifType-MIB] and YANG [yang-if-type] as Available
       Formats.

   6.  Update the tunnelType definitions registry [tunnelType-registry]
       to list MIB [IANAifType-MIB] and YANG [yang-tunnel-type] as
       Available Formats, and change the title to "tunnelType
       Definitions" for consistency with the [ifType-registry] title.

   7.  Replace the [yang-if-type] page with the YANG module content,
       rather than having a page that itself claims to have multiple
       Available Formats.

   8.  Replace the [yang-tunnel-type] page with the YANG module content,
       rather than having a page that itself claims to have multiple
       Available Formats.

6.  Registration

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

6.1.  Procedures

   Someone wishing to register a new ifType or tunnelType 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.

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   3.  Prepare a registration request using the template specified in
       Section 6.3.  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 iana@iana.org or (if requesting an
       ifType) via the web form at https://www.iana.org/form/iftype .

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

   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
       criteria.

   4.  Once the Designated Expert approves registration, IANA updates
       [ifType-registry], [IANAifType-MIB], and [yang-if-type] to show
       the registration for an Interface Type, or [tunnelType-registry],
       [IANAifType-MIB], and [yang-tunnel-type] to show the registration
       for a Tunnel Type.  When adding values, IANA should verify that
       the updated MIB module and YANG module formats are 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].

6.2.  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

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      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 to be made:

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

   NEW: 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.

6.3.  Registration Template

6.3.1.  ifType

   The following template describes the fields that MUST be supplied in
   a registration request suitable for adding to the ifType 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:

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      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  (NEW) Would your ifType require or allow vendor-specific
         extensions?  If so, would the vendor use their own ifType in a
         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.

6.3.2.  tunnelType

   CURRENT: No form exists for tunnelType, and it is not enforced that
   new requests have to use the ifType form.

   PROPOSED: The following template describes the fields that MUST be
   supplied in a registration request suitable for adding to the
   tunnelType registry:

   Label for IANA tunnelType 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 tunnelType 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 tunnelType:  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 tunnelType:

      o  How would IP run over your tunnelType?

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

      o  Would your tunnelType 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
         tunnelType label would be something like xxxSomeIfTypeLabel.)

      o  Would your tunnelType require or allow vendor-specific
         extensions?  If so, would the vendor use their own tunnelType
         in a sub-layer below the requested tunnelType, or some sort of
         sub-type of the tunnelType, 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.

7.  Submitting Requests

   [IANAifType-MIB] currently says: "Requests for new values should be
   made to IANA via email (iana&iana.org)."  However, a web form exists
   (https://www.iana.org/form/iftype), which is an apparent
   contradiction, but submissions either way are accepted.

   IANA is requested to update the MIB module to instead say: "Interface
   types must not be directly added to the IANAifType-MIB MIB module.
   They must instead be added to the "ifType definitions" registry at
   [ifType-registry]."

   (Note that [yang-if-type] was previously updated with this language.)

8.  IANA Considerations

   This entire document is about IANA considerations.

9.  Security Considerations

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

10.  References

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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/info/rfc2119>.

   [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-
              editor.org/info/rfc2578>.

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
              <https://www.rfc-editor.org/info/rfc2863>.

   [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-
              editor.org/info/rfc5378>.

   [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/info/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/info/rfc8174>.

10.2.  Informative References

   [IANAifType-MIB]
              IANA, "IANAifType-MIB", February 2019,
              <http://www.iana.org/assignments/ianaiftype-mib>.

   [ifType-registry]
              IANA, "ifType definitions", June 2019,
              <https://www.iana.org/assignments/smi-numbers/smi-
              numbers.xhtml#smi-numbers-5>.

   [protocol-registries]
              IANA, "Protocol Registries", June 2019,
              <https://www.iana.org/protocols>.

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   [RFC1234]  Provan, D., "Tunneling IPX traffic through IP networks",
              RFC 1234, DOI 10.17487/RFC1234, June 1991,
              <https://www.rfc-editor.org/info/rfc1234>.

   [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-
              editor.org/info/rfc1573>.

   [RFC2667]  Thaler, D., "IP Tunnel MIB", RFC 2667,
              DOI 10.17487/RFC2667, August 1999, <https://www.rfc-
              editor.org/info/rfc2667>.

   [RFC3635]  Flick, J., "Definitions of Managed Objects for the
              Ethernet-like Interface Types", RFC 3635,
              DOI 10.17487/RFC3635, September 2003, <https://www.rfc-
              editor.org/info/rfc3635>.

   [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-
              editor.org/info/rfc3637>.

   [RFC4087]  Thaler, D., "IP Tunnel MIB", RFC 4087,
              DOI 10.17487/RFC4087, June 2005, <https://www.rfc-
              editor.org/info/rfc4087>.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              DOI 10.17487/RFC4380, February 2006, <https://www.rfc-
              editor.org/info/rfc4380>.

   [RFC5066]  Beili, E., "Ethernet in the First Mile Copper (EFMCu)
              Interfaces MIB", RFC 5066, DOI 10.17487/RFC5066, November
              2007, <https://www.rfc-editor.org/info/rfc5066>.

   [RFC7224]  Bjorklund, M., "IANA Interface Type YANG Module",
              RFC 7224, DOI 10.17487/RFC7224, May 2014,
              <https://www.rfc-editor.org/info/rfc7224>.

   [transmission-registry]
              IANA, "transmission definitions", June 2019,
              <https://www.iana.org/assignments/smi-numbers/smi-
              numbers.xhtml#smi-numbers-7>.

Thaler & Romascanu       Expires January 8, 2020               [Page 13]
Internet-Draft              ifType Guidelines                  July 2019

   [tunnelType-registry]
              IANA, "Internet-standard MIB - mib-
              2.interface.ifTable.ifEntry.ifType.tunnelType", June 2019,
              <https://www.iana.org/assignments/smi-numbers/smi-
              numbers.xhtml#smi-numbers-6>.

   [yang-if-type]
              IANA, "iana-if-type YANG Module", February 2019,
              <http://www.iana.org/assignments/iana-if-type>.

   [yang-tunnel-type]
              IANA, "iana-tunnel-type YANG Module", June 2019,
              <https://www.iana.org/assignments/iana-tunnel-type>.

Authors' Addresses

   Dave Thaler
   Microsoft

   EMail: dthaler@microsoft.com

   Dan Romascanu
   Independent

   EMail: dromasca@gmail.com

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