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+Internet Engineering Task Force (IETF)                         L. Lhotka
+Request for Comments: 9108                                        CZ.NIC
+Category: Standards Track                                      P. Špaček
+ISSN: 2070-1721                              Internet Systems Consortium
+                                                          September 2021
+
+
+          YANG Types for DNS Classes and Resource Record Types
+
+Abstract
+
+   This document introduces the YANG module "iana-dns-class-rr-type",
+   which contains derived types reflecting two IANA registries: DNS
+   CLASSes and Resource Record (RR) TYPEs.  These YANG types are
+   intended as the minimum basis for future data modeling work.
+
+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 at
+   https://www.rfc-editor.org/info/rfc9108.
+
+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
+   2.  Terminology
+   3.  YANG Design Considerations
+   4.  IANA Considerations
+     4.1.  URI Registrations
+     4.2.  YANG Module Registrations
+   5.  Security Considerations
+   6.  References
+     6.1.  Normative References
+     6.2.  Informative References
+   Appendix A.  XSLT Stylesheet
+   Authors' Addresses
+
+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 [RFC6241] and RESTCONF [RFC8040] 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, and
+
+   *  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 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 compromise 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 version of the YANG
+   module "iana-dns-class-rr-type", which 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 version 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 can be found in
+   [RFC7950].  DNS terminology used in this document can be found in
+   [RFC1035] and [RFC8499].
+
+3.  YANG Design Considerations
+
+   At the time of writing, the "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 analogously 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 similarly.
+
+   [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 reference 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
+
+   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 version of the YANG module is available from the "YANG
+   Parameters" registry [IANA-YANG-PARAMETERS].
+
+   With the publication of this document, IANA has created and posted
+   the initial version of the "iana-dns-class-rr-type" YANG module by
+   applying the XSLT stylesheet from Appendix A to the XML version of
+   [IANA-DNS-PARAMETERS].
+
+   IANA has added 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.  IANA "deprecated" maps to
+                   YANG status "deprecated", and IANA "obsolete" maps to
+                   YANG status "obsolete".
+
+   "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 has added this 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 [RFC9108].
+
+   The "Reference" text in the "DNS CLASSes" registry has been updated
+   as follows:
+
+   OLD:
+
+   |  [RFC6895]
+
+   NEW:
+
+   |  [RFC6895][RFC9108]
+
+   The "Reference" text in the "Resource Record (RR) TYPEs" registry has
+   been updated as follows:
+
+   OLD:
+
+   |  [RFC6895][RFC1035]
+
+   NEW:
+
+   |  [RFC6895][RFC1035][RFC9108]
+
+4.1.  URI Registrations
+
+   This document registers a URI in the "IETF XML Registry" [RFC3688].
+   The following registration has been made:
+
+   URI:  urn:ietf:params:xml:ns:yang:iana-dns-class-rr-type
+   Registrant Contact:  The IESG.
+   XML:  N/A; the requested URI is an XML namespace.
+
+4.2.  YANG Module Registrations
+
+   This document registers a YANG module in the "YANG Module Names"
+   registry [RFC6020].  The following registration has been made:
+
+   Name:  iana-dns-class-rr-type
+   Namespace:  urn:ietf:params:xml:ns:yang:iana-dns-class-rr-type
+   Prefix:  dnsct
+   Reference:  RFC 9108
+
+5.  Security Considerations
+
+   This document translates two IANA registries into YANG data types and
+   otherwise introduces no technology or protocol.  The definitions
+   themselves have no security impact on the Internet, but their use in
+   concrete YANG modules might have.  The security considerations
+   spelled out in the YANG specification [RFC7950] apply to this
+   document as well.
+
+6.  References
+
+6.1.  Normative References
+
+   [IANA-DNS-PARAMETERS]
+              IANA, "Domain Name System (DNS) Parameters",
+              <https://www.iana.org/assignments/dns-parameters>.
+
+   [IANA-YANG-PARAMETERS]
+              IANA, "YANG Parameters",
+              <https://www.iana.org/assignments/yang-parameters>.
+
+   [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>.
+
+   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
+              DOI 10.17487/RFC3688, January 2004,
+              <https://www.rfc-editor.org/info/rfc3688>.
+
+   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
+              the Network Configuration Protocol (NETCONF)", RFC 6020,
+              DOI 10.17487/RFC6020, October 2010,
+              <https://www.rfc-editor.org/info/rfc6020>.
+
+   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
+              RFC 7950, DOI 10.17487/RFC7950, August 2016,
+              <https://www.rfc-editor.org/info/rfc7950>.
+
+   [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>.
+
+   [W3C.REC-xslt-19991116]
+              Clark, J., "XSL Transformations (XSLT) Version 1.0", W3C
+              Recommendation REC-xslt-19991116, November 1999,
+              <https://www.w3.org/TR/1999/REC-xslt-19991116>.
+
+6.2.  Informative References
+
+   [RFC1035]  Mockapetris, P., "Domain names - implementation and
+              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
+              November 1987, <https://www.rfc-editor.org/info/rfc1035>.
+
+   [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record
+              (RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
+              2003, <https://www.rfc-editor.org/info/rfc3597>.
+
+   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
+              and A. Bierman, Ed., "Network Configuration Protocol
+              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
+              <https://www.rfc-editor.org/info/rfc6241>.
+
+   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
+              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
+              <https://www.rfc-editor.org/info/rfc8040>.
+
+   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
+              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
+              January 2019, <https://www.rfc-editor.org/info/rfc8499>.
+
+Appendix A.  XSLT Stylesheet
+
+   This appendix contains an XSLT 1.0 stylesheet [W3C.REC-xslt-19991116]
+   that is to be used to generate 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 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="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
+                12025 Waterfront Drive, Suite 300
+                Los Angeles, CA 90094
+
+        Tel:    +1 424 254 5300
+
+        &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) 2021 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 version of this YANG module was generated from
+        the corresponding IANA registries using an XSLT stylesheet
+        from Appendix A of RFC 9108
+        (https://www.rfc-editor.org/info/rfc9108); 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 9108: 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 reference 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 reference 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>
+
+Authors' Addresses
+
+   Ladislav Lhotka
+   CZ.NIC
+   Czech Republic
+
+   Email: ladislav.lhotka@nic.cz
+
+
+   Petr Špaček
+   Internet Systems Consortium
+   Czech Republic
+
+   Email: pspacek@isc.org