YANG Types for DNS Classes and Resource Record Types

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This Internet-Draft will expire on 25 November 2021.¶

Copyright Notice

Copyright (c) 2021 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.¶

Table of Contents

1. Introduction

YANG [RFC7950] has become a de facto standard as a language for modeling configuration and state data, as well as specifying management operations and asynchronous notifications. It is reasonable to expect that the approach based on utilizing such data models along with standard management protocols such as NETCONF and RESTCONF can be effectively used in DNS operations, too. In fact, several efforts are currently underway that attempt to use NETCONF or RESTCONF for configuring and managing¶

• authoritative servers¶
• resolvers¶
• zone data.¶

While it is possible to use the management protocols mentioned above with ad hoc or proprietary data models, their real potential can be realized only if there is a (completely or partly) unified data model supported by multiple DNS software implementations. Operators can then, for instance, run several different DNS server implementations in parallel, and use a common configuration and management interface and data for all of them. Also, it becomes considerably easier to migrate to another implementation.¶

Based on the previous experience from the IETF Routing Area, it is to be expected that the development of unified data models for DNS will be a lengthy and complicated process that will require active cooperation and compromises from the vendors and developers of major DNS server platforms. Nevertheless, it is likely that any DNS-related data modeling effort will need to use various DNS parameters and enumerations that are specified in several IANA registries. For use with YANG, these parameters and enumerations have to be translated into corresponding YANG types or other structures. Such translations should be straightforward and relatively uncontroversial.¶

This document provides a translation of two fundamental DNS-related IANA registries to YANG. It contains the initial revision of the YANG module "iana-dns-class-rr-type" that defines derived types for the common parameters of DNS resource records (RR): class and type. These YANG types, "dns-class" and "rr-type", reflect the IANA registries "DNS CLASSes" and "Resource Record (RR) TYPEs" [IANA-DNS-PARAMETERS].¶

Appendix A contains an XSLT 1.0 stylesheet that is intended to be used by IANA for generating the initial revision of the "iana-dns-class-rr-type" YANG module. Subsequently, whenever a new class or RR type is added to the above registries, IANA will also update the "iana-dns-class-rr-type" YANG module, following the instructions in Section 4 below.¶

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.¶

The terminology for describing YANG data models is found in [RFC7950].¶

3. YANG Design Considerations

The IANA document "Domain Name System (DNS) Parameters" [IANA-DNS-PARAMETERS] contains altogether thirteen registries. The YANG module "iana-dns-class-rr-type" defines derived types corresponding to only two of the registries that are essential for data models involving zone data, namely "DNS CLASSes" and "Resource Record (RR) TYPEs". It is expected that the remaining registries in [IANA-DNS-PARAMETERS], as well as other DNS-related IANA registries, will be analogically reflected in future YANG modules as necessary. This way, an appropriate combination of YANG modules can be chosen depending on which YANG types are needed for a given data modeling purpose.¶

The registries "DNS CLASSes" and "Resource Record (RR) TYPEs" are transformed into YANG enumeration types "dns-class-name" and "rr-type-name", respectively. This is the initial fragment of the former:¶

  typedef dns-class-name {
    type enumeration {
      enum IN {
        value 1;
        description
          "Internet (IN)";
        reference
          "RFC 1035";
      }
      ...
    }
    ...
  }

The other derived type, "rr-type-name", is defined analogically.¶

[RFC3597] introduced the option of specifying a class or RR type via its assigned decimal number, as an alternative to the mnemonic name. For example, the "IN" class can be equivalently written as "CLASS1", and "AAAA" type can be written as "TYPE28".¶

Accordingly, the derived types "dns-class" and "rr-type" are defined in the YANG module as a union of two member types:¶

• 16-bit decimal integer ("uint16")¶
• mnemonic name belonging to the enumerations "dns-class-name" and "rr-type-name", respectively.¶

For instance, the "rr-type" type is defined as follows:¶

  typedef rr-type {
    type union {
      type uint16;
      type rr-type-name;
    }
    description
      "This type allows for referring to a DNS resource record type
       using either the assigned mnemonic name or numeric value.";
  }

As unassigned and reserved class and RR type values are not included in the mnemonic name enumerations, they can only be specified using their decimal values.¶

4. IANA Considerations

RFC Editor: In this section, replace all occurrences of "XXXX" with the actual RFC number (and remove this note).¶

This section deals with actions and processes necessary for IANA to undertake to maintain the "iana-dns-class-rr-type" YANG module. This YANG module is intended to reflect the "DNS CLASSes" and "Resource Record (RR) TYPEs" registries in [IANA-DNS-PARAMETERS]. The most recent revision of the YANG module is available from the "YANG Parameters" registry [IANA-YANG-PARAMETERS].¶

Upon publication of this document, the initial revision of the "iana-dns-class-rr-type" YANG module SHALL be created by applying the XSLT stylesheet from Appendix A to the XML version of [IANA-DNS-PARAMETERS].¶

IANA SHALL add this note to the "iana-dns-class-rr-type" item of the "YANG Module Names" registry [IANA-YANG-PARAMETERS]:¶

Classes and types of DNS resource records must not be directly added to the "iana-dns-class-rr-type" YANG module. They must instead be added to the "DNS CLASSes" and "Resource Record (RR) TYPEs" registries, respectively.¶

When a new DNS class or RR type is added to the "DNS CLASSes" or "Resource Record (RR) TYPEs" registry, a new "enum" statement SHALL be added to the "dns-class-name" or "rr-type-name" type, respectively. The assigned name defined by the "enum" statement SHALL be the same as the mnemonic name of the new class or type. The following substatements to the "enum" statement SHALL be defined:¶

"value":

Use the decimal value from the registry.¶

"status":

Include only if a class or type registration has been deprecated or obsoleted. In both cases, use the value "obsolete" as the argument of the "status" statement.¶

"description":

Replicate the corresponding information from the registry, namely the full name of the new DNS class, or the meaning of the new RR type, if any.¶

"reference":

Replicate the reference(s) from the registry.¶

Unassigned or reserved values SHALL NOT be included in the "dns-class-name" and "rr-type-name" enumeration types.¶

Each time the "iana-dns-class-rr-type" YANG module is updated, a new "revision" statement SHALL be added before the existing "revision" statements.¶

IANA SHALL add this new note to the "DNS CLASSes" and "Resource Record (RR) TYPEs" registries:¶

When this registry is modified, the YANG module "iana-dns-class-rr-type" must be updated as defined in RFC XXXX.¶

The "Reference" text in the "DNS CLASSes" registry SHALL be updated as follows:¶

OLD:
  [RFC6895]

NEW:
  [RFC6895][RFCXXXX]

¶

The "Reference" text in the "Resource Record (RR) TYPEs" registry SHALL be updated as follows:¶

OLD:
  [RFC6895][RFC1035]

NEW:
  [RFC6895][RFC1035][RFCXXXX]

¶

5. Security Considerations

This documents translates two IANA registries into YANG data types and otherwise introduces no technology or protocol. Consequently, there are no security issues to be considered for this document.¶

Appendix A. XSLT Stylesheet

RFC Editor: In this section, replace all occurrences of "XXXX" with the actual RFC number (and remove this note).¶

This appendix contains an XSLT 1.0 stylesheet [W3C.REC-xslt-19991116] that is intended to be used for generating the initial revision of the "iana-dns-class-rr-type" YANG module. This is achieved by applying the stylesheet to the XML version of the IANA registry "Domain Name System (DNS) Parameters" [IANA-DNS-PARAMETERS] that was current at the time when this document was published.¶

Using the ubiquitous xsltproc tool, the YANG module text can be generated with this command:¶

    $ xsltproc iana-dns-class-rr-type.xsl dns-parameters.xml

<CODE BEGINS> file "iana-dns-class-rr-type.xsl"

<?xml version="1.0" standalone="yes"?>
<stylesheet xmlns="http://www.w3.org/1999/XSL/Transform"
            xmlns:iana="http://www.iana.org/assignments"
            version="1.0">
  <output method="text"/>
  <strip-space elements="*"/>

  <variable name="dq">"</variable>
  <variable name="sq">'</variable>
  <variable name="lf">&#xA;</variable>

  <variable name="module-intro">
    <text>module iana-dns-class-rr-type {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:iana-dns-class-rr-type";
  prefix dnsct;

  organization
    "Internet Assigned Numbers Authority (IANA)";

  contact
    "        Internet Assigned Numbers Authority

     Postal: ICANN
             4676 Admiralty Way, Suite 330
             Marina del Rey, CA 90292

     Tel:    +1 310 823 9358

     &lt;mailto:iana@iana.org&gt;";

  description
    "This YANG module translates IANA registries 'DNS CLASSes' and
     'Resource Record (RR) TYPEs' to YANG derived types.

     Copyright (c) 2020 IETF Trust and the persons identified as
     authors of the code. All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject to
     the license terms contained in, the Simplified BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This initial version of this YANG module was generated from
     the corresponding IANA registries using a XSLT stylesheet
     from Appendix A of RFC XXXX
     (https://tools.ietf.org/html/rfcXXXX); see the RFC itself for
     full legal notices.";

  reference
    "IANA 'Domain Name System (DNS) Parameters' registry
     https://www.iana.org/assignments/dns-parameters";</text>
     <text>&#xA;&#xA;</text>
  </variable>

  <template name="enum">
    <param name="id"/>
    <value-of select="concat('      enum ', $id)"/>
    <text> {&#xA;        value </text>
    <value-of select="concat(iana:value, ';&#xA;')"/>
    <if test="contains(iana:description, 'OBSOLETE')">
      <text>        status obsolete;&#xA;</text>
    </if>
    <apply-templates select="iana:description"/>
    <variable name="xrefs" select="iana:xref[@type!='note']"/>
    <if test="$xrefs">
      <text>        reference&#xA;          "</text>
      <if test="count($xrefs)&gt;1">- </if>
      <apply-templates select="iana:xref[@type!='note']"/>
    </if>
    <text>      }&#xA;</text>
  </template>

  <template match="/">
    <value-of select="$module-intro"/>
    <apply-templates select="iana:registry[@id='dns-parameters']"/>
    <text>}&#xA;</text>
  </template>

  <template match="iana:registry[@id='dns-parameters']">
    <apply-templates select="iana:updated"/>
    <apply-templates
        select="iana:registry[@id='dns-parameters-2']"/>
    <apply-templates
        select="iana:registry[@id='dns-parameters-4']"/>
  </template>

  <template match="iana:updated">
    <value-of select="concat('  revision ', ., ' {')"/>
    <text>
    description
      "Initial revision.";
    reference
      "RFC XXXX: YANG Types for DNS Classes and Resource Record
       Types";
  }

  /* Typedefs */&#xA;&#xA;</text>
  </template>

  <template match="iana:registry[@id='dns-parameters-2']">
    <text>  typedef dns-class-name {&#xA;</text>
    <text>    type enumeration {&#xA;</text>
    <apply-templates
        select="iana:record[not(iana:description='Unassigned' or
                starts-with(iana:description,'Reserved'))]"
        mode="class"/>
    <text>    }
    description
      "This enumeration type defines mnemonic names and corresponding
       numeric values of DNS classes.";
    reference
      "RFC 6895: Domain Name System (DNS) IANA Considerations";
  }

  typedef dns-class {
    type union {
      type uint16;
      type dns-class-name;
    }
    description
      "This type allows for referring to a DNS class using either the
       assigned mnemonic name or numeric value.";
  }&#xA;&#xA;</text>
  </template>

  <template match="iana:registry[@id='dns-parameters-4']">
    <text>  typedef rr-type-name {&#xA;</text>
    <text>    type enumeration {&#xA;</text>
    <apply-templates
        select="iana:record[iana:type!='Unassigned' and
                iana:type!='Private use' and iana:type!='Reserved']"
        mode="rr-type"/>
    <text>    }
    description
      "This enumeration type defines mnemonic names and corresponding
       numeric values of DNS resource record types.";
    reference
      "- RFC 6895: Domain Name System (DNS) IANA Considerations

       - RFC 1035: Domain Names - Implementation and Specification";
  }

  typedef rr-type {
    type union {
      type uint16;
      type rr-type-name;
    }
    description
      "This type allows for referring to a DNS resource record type
       using either the assigned mnemonic name or numeric value.";
  }&#xA;</text>
  </template>

  <template match="iana:record" mode="class">
    <call-template name="enum">
      <with-param name="id">
        <choose>
          <when test="contains(iana:description,'(')">
            <value-of select="substring-before(substring-after(
                              iana:description, '('), ')')"/>
          </when>
          <otherwise>
            <value-of
                select="substring-after(iana:description, ' ')"/>
          </otherwise>
        </choose>
      </with-param>
    </call-template>
  </template>

  <template match="iana:record" mode="rr-type">
    <call-template name="enum">
      <with-param name="id" select="iana:type"/>
    </call-template>
  </template>

  <template match="iana:description">
    <text>        description&#xA;          </text>
    <value-of select="concat($dq, ., $dq, ';&#xA;')"/>
  </template>

  <template match="iana:xref">
    <choose>
      <when test="@type='rfc'">
        <value-of
            select="concat('RFC ', substring-after(@data, 'rfc'))"/>
      </when>
      <when test="@type='person'">
        <apply-templates
            select="/iana:registry/iana:people/iana:person[
                    @id=current()/@data]"/>
      </when>
      <when test="@type='text'">
        <value-of select="translate(., $dq, $sq)"/>
      </when>
      <otherwise>
        <value-of select="@data"/>
      </otherwise>
    </choose>
    <choose>
      <when test="position()=last()">
        <text>";&#xA;</text>
      </when>
      <otherwise>
        <text>&#xA;           - </text>
      </otherwise>
    </choose>
  </template>

  <template match="iana:person">
    <value-of select="concat(iana:name, ' &lt;', iana:uri, '&gt;')"/>
  </template>

</stylesheet>


<CODE ENDS>

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