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RFC 8892ifType GuidelinesAugust 2020
Thaler & RomascanuStandards Track[Page]
Stream:
Internet Engineering Task Force (IETF)
RFC:
8892
Updates:
2863
Category:
Standards Track
Published:
ISSN:
2070-1721
Authors:
D. Thaler
Microsoft
D. Romascanu
Independent

RFC 8892

Guidelines and Registration Procedures for Interface Types and Tunnel Types

Abstract

This document provides guidelines and procedures for those who are defining, registering, or evaluating definitions of new interface types ("ifType" values) and tunnel types.The original definition of the IANA interface type registry predatedthe use of IANA Considerations sections and YANG modules, so some confusion aroseover time. Tunnel types were added later, with the same requirements and allocation policy asinterface types. This document updates RFC 2863 and provides updated guidance forthese registries.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8892.

Copyright Notice

Copyright (c) 2020 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must 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.

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Table of Contents

1.Introduction

The IANA IfType-MIB, which contains the list of interface type (ifType) values,was originally defined in[RFC1573] as a separate MIBmodule together with the Interfaces Group MIB (IF-MIB) module. The IF-MIB module wassubsequently updated and is currently specified in[RFC2863], but the latest IF-MIBRFC no longer contains the IANA IfType-MIB. Instead, the IANA IfType-MIB ismaintained by IANA as a separate module. Similarly,[RFC7224] created an initialIANA 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 alsoappearing in both[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 modulesor any other management mechanism. An interface type value can be usedas the value of a data model object (MIB object, YANG object, etc.),as part of a unique identifier of a data model for a giveninterface type (e.g., in an OID), or simply as a value exposed by localAPIs or UIs on a device.

The TUNNEL-MIB was defined in[RFC2667] (now obsoleted by[RFC4087]),which created a tunnelType registry ([tunnelType-registry] and the IANAtunnelType textualconvention at[IANAifType-MIB]), and itdefined 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 describedin BCP 14[RFC2119][RFC8174] when, and only when, they appearin all capitals, as shown here.

3.Problems

This document addresses the following issues:

  1. As noted inSection 1, the original guidance was written with wordingspecific to MIB modules; accordingly, some confusion has resultedwhen using YANG modules. This document clarifies that ifTypes and tunnelTypes areindependent from the type of, or even existence of, a data model.
  2. The use of and requirements around sub-layers and sub-typeswere not well understood, but good examples of both now exist.This is discussed inSection 4.
  3. Since the "Interface Types (ifType)" and "Tunnel Types (tunnelType)" registries were originally defined, and arestill retrievable, in the format of MIB modules (in addition to other formats),confusion arose when adding YANG modules as another format as to whethereach is a separate registry. This is discussed inSection 5.
  4. The registries are retrievable in the format of MIB and YANG modules, butthere was previously no process guidance written to check that those formats weresyntactically correct as updates were made, which led to the registry having syntax errorsthat broke tools.Section 6.1 adds a validation step to thedocumented assignment procedure.
  5. Various documents and registries previously said to submit requests via email,but a web form exists for submitting requests, which causedsome confusion around which was to be used. This is addressedinSection 6.1.
  6. Transmission values[transmission-registry] have generally been allocated as partof ifType allocation, but no guidance existed as to whether a requestermust ask for it or not, and the request form had no such required field.As a result, IANA has asked the designated expert to decide for eachallocation, but no relevant guidance for the designated expert has beendocumented. This is remedied inSection 6.2.

4.Interface Sub-layers and Sub-types

When multiple sub-layers exist below the network layer,each sub-layer can be represented by its ownrow in the ifTable with its own ifType, with the ifStackTable being used to identify theupward and downward multiplexing relationships between rows.Section 3.1.1 of [RFC2863] provides morediscussion, and3.1.2 provides guidance for defining interfacesub-layers. More recent experience shows that those guidelines werephrased 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 the same guidance also applies to YANG modules.

Some ifTypes may define sub-types. For example, the tunnel(131) ifType defines sub-types known as "tunnelTypes", where each tunnelType can have its own MIB and/or YANGmodule with protocol-specific information, but there is enough in commonthat some information is exposed in a generic IP Tunnel MIB correspondingto the tunnel(131) ifType.

For requests that involve multiple sub-layers below the network layer,requestsMUST include (or reference) a discussion of the multiplexing relationshipsbetween sub-layers, ideally with a diagram. Various well-written examples exist ofsuch definitions, includingSection 3.4.1 of [RFC3637],Section 3.1.1 of [RFC4087],andSection 3.1.1 of [RFC5066].

Definers of sub-layers and sub-types should consider which model is moreappropriate for their needs. A sub-layer is generally used whenever either adynamic relationship exists (i.e., when the set of instances above or below agiven instance can change over time) or a multiplexing relationship existswith another sub-layer. A sub-type can be used when neither of these is truebut where one interface type is conceptually a subclass of another interface type, as faras a management data model is concerned.

In general, the intent of an interface type or sub-type is that its definition shouldbe sufficient to identify an interoperable protocol. In some cases, however,a protocol might be defined in a way that is not sufficient to provideinteroperability with other compliant implementations of that protocol.In such a case, an ifType definition should discuss whether specificinstantiations (or profiles) of behavior should use a sub-layer model(e.g., each vendor might layer the protocol over its own sub-layerthat provides the missing details) or a sub-type model (i.e., eachvendor might subclass the protocol without any layering relationship).If a sub-type model is more appropriate, then the data model for theprotocol might include a sub-type identifier so that management softwarecan discover objects specific to the sub-type. In either case, suchdiscussion is important to guide definers of a data model for the morespecific information (i.e., a lower sub-layer or a sub-type), as wellas the designated expert, who must review requests for any suchifTypes or sub-types.

4.1.Alternate Values

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

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

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

As another example, 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)." The Teredo tunnelprotocol[RFC4380] was later defined and encapsulates packets over UDP, but theprotocol model is quite different between[RFC1234] and Teredo. Forexample,[RFC1234] supports encapsulation of multicast/broadcast traffic,whereas Teredo does not. As such, it would be more confusing to applicationsand tools to represent them using the same tunnel type, and so[RFC4087]defined a new value for Teredo.

In summary, definers of new interface or tunnel mechanisms should use a new ifType ortunnelType value rather than reuse an existing value when key aspects suchas 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 they should reuse the same value when the differencescan 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 registriesare available. This document clarifies that the[IANAifType-MIB],[yang-if-type], and[yang-tunnel-type] MIB and YANG modulesare merely additional formats in which the "Interface Types (ifType)" and "Tunnel Types (tunnelType)"registries are available. The MIB and YANG modules are not separate registries, and the samevalues are always present in all formats of the same registry.

The confusion stemmed in part from the fact that the IANA "Protocol Registries"[protocol-registries] listed the YANG and MIB module formats separately,as if they were separate registries. However, the entries for theyang-if-type and iana-tunnel-type YANG modules said "See ifType definitions registry"and "See tunnelType registry (mib-2.interface.ifTable.ifEntry.ifType.tunnelType)"respectively, although the entry for the IANAifType-MIB had no such note.Section 7.1 addresses this.

6.Registration

The IANA policy (using terms defined in[RFC8126]) for registration isExpert Review for both interface types and tunnel types. The role of the designated expert in the procedure is toraise possible concerns about wider implications of proposals for use anddeployment of interface types. While it is recommended that the responsibleArea Director and the IESG take into consideration the designatedexpert opinions, nothing in the procedure empowers thedesignated expert to override properly arrived-at IETF or working groupconsensus.

6.1.Procedures

Someone wishing to register a new ifType or tunnelType valueMUST:

  1. Check the IANA registry to see whether there is already an entry that couldeasily 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 permanentlyavailable, stable specification may be written to clarify the usage of anexisting entry or entries for the desired purpose.
  2. Check the IANA registry to see whether there is already some other entry withthe desired name. If there is already an unrelated entry under the desired name, choosea different name.
  3. Prepare a registration request using the template specified inSection 6.3.The registration request can be contained in an Internet-Draft, submittedalone, or submitted as part of some permanently available, stable specification. The registration request can also be submitted in someother 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 a document containing it)to IANA at iana@iana.org or (if requesting an ifType) via the web format<https://www.iana.org/form/iftype>.

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

  1. IANA checks the submission for completeness; if required information ismissing or any citations are not correct, IANA will reject the registrationrequest. A registrant can resubmit a corrected request if desired.
  2. IANA requests Expert Review of the registration request against thecorresponding guidelines from this document.
  3. The designated expert will evaluate the request against the criteria.
  4. Once the designated expert approves a 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 registrationfor a tunnel type.When adding values, IANA should verify that the updatedMIB module and YANG module formats are syntactically correct before publishing the update. There arevarious existing tools or websites that can be used to do this verification.
  5. If instead the designated expertdoes not approve registration (e.g., for any of the reasons in[RFC8126],Section 5), a registrant can resubmit a corrected requestif desired, or the IESG can override the designated expert and approveit per the process inSection 3.3 of [RFC8126].

6.2.Media-Specific OID-Subtree Assignments

[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 advice above remains unchanged, but this document changes the allocation procedureto streamline the process, so that an ifType value and a transmission number valuewith the same value will be assigned at the same time.

Rationale:

(1)
This saves future effort if atransmission number is later deemed necessary, since no IANA request isneeded that would then require another Expert Review.
(2)
The transmission numbering space is not scarce, so there seems to be little need to reserve the number for a different purpose than what the ifTypeis for.
(3)
The designated expert need not review whether a transmissionnumber value should be registered when processing each ifType request, thusreducing the possibility of delaying assignment of ifType values.
(4)
There is no case on record where allocating the same value could havecaused any problems.

6.3.Registration Template

6.3.1.ifType

The following template describes the fields thatMUST be supplied in a registration requestsuitable for adding to the "Interface Types (ifType)" registry:

Label for IANA ifType requested:
As explained inSection 7.1.1 of [RFC2578], a label for a named-number enumerationmust consist of one or more letters or digits, up to a maximum of 64 characters, and the initial character must be a lowercase 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:

RequestersMUST include answers, either directly or via a link to a documentwith the answers, to the following questions in the explanationof the proposed use of the IANA IfType:

  • How would IP run over your ifType?
  • Would there be another interface sub-layer between your ifType and IP?
  • Would your ifType be vendor specific / proprietary? (If so, the labelMUST start with a string that shows that. For example, if your company'sname or acronym is xxx, then the ifType label would be something likexxxSomeIfTypeLabel.)
  • 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,a sub-type of the ifType, or some other mechanism?
Reference, Internet-Draft, or Specification:
A link to a document is required.
Additional information or comments:
Optional; any additional comments for IANA or the designated expert.

6.3.2.tunnelType

Prior to this document, no form existed for tunnelType (and new tunnelType requests did notneed to use the ifType form that did exist). This document therefore specifies a tunnelTypeform.

The following template describes the fields thatMUST be supplied in a registration request suitable for adding to the "Tunnel Types (tunnelType)" registry:

Label for IANA tunnelType requested:
As explained inSection 7.1.1 of [RFC2578], a label for a named-number enumerationmust consist of one or more letters or digits, up to a maximum of 64 characters, andthe initial character must be a lowercase letter. (However, labels longer than 32characters 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:

RequestersMUST include answers, either directly or via a link to a documentwith the answers, to the following questions in the explanationof the proposed use of the IANA tunnelType:

  • How would IP run over your tunnelType?
  • Would there be another interface sub-layer between your tunnelType and IP?
  • Would your tunnelType be vendor-specific or proprietary? (If so, the labelMUST start with a string that shows that. For example, if your company'sname or acronym is xxx, then the tunnelType label would be something likexxxSomeTunnelTypeLabel.)
  • 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 a document is required.
Additional information or comments:
Optionally any additional comments for IANA or the designated expert.

7.IANA Considerations

This entire document is about IANA considerations, but this section discusses actions taken by and to be taken by IANA. There are three registries affected:

  1. Interface Types (ifType)[ifType-registry]: The registration process is updated inSection 6.1, and the template is updated inSection 6.3.1.
  2. Tunnel Types (tunnelType)[tunnelType-registry]: The registration process is updated inSection 6.1, and the template is updated inSection 6.3.2.
  3. Transmission Number Values[transmission-registry]: The assignment process is updated inSection 6.2.

At the time of publication of this document, IANA is unable toperform some of the actions requested below due to limitations of their currentplatform and toolset. In such cases, IANA is requested to perform these actionsas and when the migration to a new platform that would enable these actions is complete.

7.1.MIB and YANG Modules

IANA is to complete the following to clarify the relationship between MIB modules, YANG modules, and the relevant registries.

  1. The following note has been added to the IANAifType-MIB at[protocol-registries]: "This is one of the available formats of the Interface Types (ifType) and Tunnel Types (tunnelType) registries."

  2. The note for the iana-if-type YANG module at[protocol-registries] has been updated to read: "This is one of the available formats of the Interface Types (ifType) registry."

  3. The note for the iana-tunnel-type YANG module at[protocol-registries] has been updated to read: "This is one of the available formats of the Tunnel Types (tunnelType) registry."

  4. The new "Interface Parameters" category at[protocol-registries] includes entries for "Interface Types (ifType)"[ifType-registry], "Tunnel Types (tunnelType)"[tunnelType-registry], and "Transmission Number Values"[transmission-registry].
  5. Update the "Interface Types (ifType)" registry[ifType-registry] to list MIB[IANAifType-MIB] and YANG[yang-if-type] as Available Formats.
  6. Update the "Tunnel Types (tunnelType)" registry[tunnelType-registry] to list MIB[IANAifType-MIB] and YANG[yang-tunnel-type] as Available Formats.
  7. Replace the[yang-if-type] page with the YANG module content rather than having a page that claims to have multiple Available Formats.
  8. Replace the[yang-tunnel-type] page with the YANG module content rather than having a page that claims to have multiple Available Formats.

  9. In addition,[IANAifType-MIB] is to be updated as follows:

    OLD:

    Requests for new values should be made to IANA via email (iana@iana.org).

    NEW:

    Interface types must not be directly added to the IANAifType-MIB MIB module.They must instead be added to the "Interface Types (ifType)" registry at[ifType-registry].

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

  10. IANA has added this document as a reference in the "Interface Types (ifType)", "Tunnel Types (tunnelType)", and "Transmission Number Values" registries, as well as the iana-if-type YANG Module, iana-tunnel-type YANG Module, and IANAifType-MIB.

7.2.Transmission Number Assignments

Per the discussion inSection 6.2,[ifType-registry] has been updated as follows:

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.

Similarly, the following change has been made to[transmission-registry]:

OLD:

For every transmission number registration, the correspondingifType value should be registered or marked "Reserved".

NEW:

For future transmission number assignments, an 'ifType' will be made with the same value.

8.Security Considerations

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

For security considerations related to MIB and YANG modules thatexpose these values, seeSection 9 of [RFC2863],Section 6 of [RFC4087], andSection 3 of [RFC8675].

9.References

9.1.Normative References

[RFC2119]
Bradner, S.,"Key words for use in RFCs to Indicate Requirement Levels",BCP 14,RFC 2119,DOI 10.17487/RFC2119,,<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,,<https://www.rfc-editor.org/info/rfc2578>.
[RFC2863]
McCloghrie, K. and F. Kastenholz,"The Interfaces Group MIB",RFC 2863,DOI 10.17487/RFC2863,,<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,,<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,,<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,,<https://www.rfc-editor.org/info/rfc8174>.

9.2.Informative References

[IANAifType-MIB]
IANA,"IANAifType-MIB Definitions",<http://www.iana.org/assignments/ianaiftype-mib>.
[ifType-registry]
IANA,"Interface Types (ifType)",<https://www.iana.org/assignments/smi-numbers>.
[protocol-registries]
IANA,"Protocol Registries",<https://www.iana.org/protocols>.
[RFC1234]
Provan, D.,"Tunneling IPX traffic through IP networks",RFC 1234,DOI 10.17487/RFC1234,,<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,,<https://www.rfc-editor.org/info/rfc1573>.
[RFC2667]
Thaler, D.,"IP Tunnel MIB",RFC 2667,DOI 10.17487/RFC2667,,<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,,<https://www.rfc-editor.org/info/rfc3635>.
[RFC3637]
Heard, C.M., Ed.,"Definitions of Managed Objects for the Ethernet WAN Interface Sublayer",RFC 3637,DOI 10.17487/RFC3637,,<https://www.rfc-editor.org/info/rfc3637>.
[RFC4087]
Thaler, D.,"IP Tunnel MIB",RFC 4087,DOI 10.17487/RFC4087,,<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,,<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,,<https://www.rfc-editor.org/info/rfc5066>.
[RFC7224]
Bjorklund, M.,"IANA Interface Type YANG Module",RFC 7224,DOI 10.17487/RFC7224,,<https://www.rfc-editor.org/info/rfc7224>.
[RFC8675]
Boucadair, M., Farrer, I., and R. Asati,"A YANG Data Model for Tunnel Interface Types",RFC 8675,DOI 10.17487/RFC8675,,<https://www.rfc-editor.org/info/rfc8675>.
[transmission-registry]
IANA,"Transmission Number Values",<https://www.iana.org/assignments/smi-numbers>.
[tunnelType-registry]
IANA,"Tunnel Types (tunnelType)",<https://www.iana.org/assignments/smi-numbers>.
[yang-if-type]
IANA,"iana-if-type YANG Module",<http://www.iana.org/assignments/iana-if-type>.
[yang-tunnel-type]
IANA,"iana-tunnel-type YANG Module",<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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