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Versions: 00 01 02 03 04 05 06 RFC 5935

Network Working Group                                          B. Natale
Internet-Draft                                                     MITRE
Intended status: Standards Track                          March 27, 2009
Expires: September 27, 2009


    Expressing SNMP SMI Datatypes in XML Schema Definition Language
             draft-ietf-opsawg-smi-datatypes-in-xsd-05.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on September 27, 2009.

Copyright Notice

   Copyright (c) 2009 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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   Please review these documents carefully, as they describe your rights
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Abstract

   This memo defines the IETF standard expression of Structure of
   Management Information (SMI) base datatypes in Extensible Markup
   Language (XML) Schema Definition (XSD) language.  The primary
   objective of this memo is to enable the production of XML documents
   that are as faithful to the SMI as possible, using XSD as the
   validation mechanism.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  XSD for SMI Base Datatypes . . . . . . . . . . . . . . . . . .  7
   5.  Rationale  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Numeric Datatypes  . . . . . . . . . . . . . . . . . . . . 10
     5.2.  OctetString  . . . . . . . . . . . . . . . . . . . . . . . 10
     5.3.  Opaque . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.4.  IpAddress  . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.5.  ObjectIdentifier . . . . . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  SMI Base Datatypes Namespace Registration  . . . . . . . . 14
     7.2.  SMI Base Datatypes Schema Registration . . . . . . . . . . 14
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     9.2.  Informational References . . . . . . . . . . . . . . . . . 16
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17




















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1.  Introduction

   Numerous uses exist -- both within and outside the traditional IETF
   network management community -- for the expression of management
   information described in and accessible via SMI Management
   Information Base (MIB) modules as XML documents [XML].  For example,
   XML-based management applications which want to incorporate MIB
   modules as data models and/or to access MIB module instrumentation
   via gateways to SNMP agents will benefit from an IETF standard
   mapping of SMI datatypes to XML documents via XSD.

   MIB data models are described using SMIv2 [RFC2578] and, for legacy
   MIBs, SMIv1 [RFC1155].  MIB data is conveyed in variable bindings
   ("varbinds") within protocol data units (PDUs) within SNMP messages
   using the base/primitive datatypes defined in the SMI.

   The SMI allows for creation of derivative datatypes, termed "textual
   conventions" ("TCs"), each of which has a unique name, a syntax which
   is or refines a primitive SMI datatype, and relatively precise
   application-level semantics.  TCs are used principally to facilitate
   correct application-level handling of MIB data and for the
   convenience of humans reading MIB modules and appropriately rendered
   MIB data output.  Values in varbinds corresponding to MIB objects
   with TC syntaxes are always encoded as the primitive SMI datatype
   underlying the TC syntax.  Thus, the XSD mappings defined in this
   memo will support MIB objects with TC syntax as well as those with
   base SMI syntax.

   Various independent schemes have been devised for expressing the SMI
   datatypes in XSD [XMLSchema].  These schemes have exhibited a degree
   of commonality (especially concerning the numeric SMI datatypes), but
   also sufficient differences (especially concerning the non-numeric
   SMI datatypes) to preclude uniformity and general interoperability.

   The primary purpose of this memo is to define a standard expression
   of SMI base datatypes in XSD to ensure fidelity, consistency, and
   general interoperability in this respect.  Internet operators,
   management tool developers, and users will benefit from the wider
   selection of management tools and the greater degree of unified
   management -- with attendant improvements in timeliness and accuracy
   of management information -- which such a standard facilitates.

   On its own, this memo specifies the IETF standard way to render SMI
   data values carried in SNMP messages as XML in a faithful,
   consistent, and interoperable way.

   Certain XML-based applications will find this specification
   sufficient for their purposes.  Other XML applications may need to



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   make more complete reuse of existing MIB modules, requiring standard
   XSDs for TCs [RFC2579] and MIB structure [RFC2578].  Documents
   supporting those requirements are planned, but have not been produced
   at the time of this writing.

   The objective of this memo, and of any future related specifications
   that might be produced, is to define the XSD equivalent
   [XSDDatatypes] of SMIv2 (STD58) to encourage XML-based protocols to
   carry, and XML-based applications to use, the information modeled in
   SMIv2-compliant MIB modules.

   Having such a standard mapping of SMIv2 to XML via XSD validation
   will enable and promote efficient reuse of existing (including
   future) MIB modules and instrumentation by XML-based management
   protocols and applications.

   The goal of fidelity to the SMIv2 standard (STD58), as specified in
   the "Requirements" section below, is crucial to this effort to
   leverage the established "rough consensus" for the precise data
   modeling used in MIB modules, and to leverage existing "running code"
   for implemented SMIv2 data models.  This effort does not include
   redesign of SMIv2 datatypes or data structures or textual conventions
   to overcome known limitations -- that work can be pursued in other
   efforts.



























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2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].














































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3.  Requirements

   The following set of requirements is intended to produce XML
   documents which can be validated via the XSD defined in this
   specification to faithfully represent values carried "on-the-wire" in
   SNMP PDUs as defined by the SMI:

   R1.  All SMI base datatypes MUST have a corresponding XSD datatype.

   R2.  SMIv2 is the normative SMI for this document -- SMIv1 modules,
        if encountered, MUST be converted (at least logically) in
        accordance with Section 2.1, inclusive, of the "Coexistence" RFC
        [RFC3584].

   R3.  The XSD datatype specified for a given SMI datatype MUST be able
        to represent all valid values for that SMI datatype.

   R4.  The XSD datatype specified for a given SMI datatype MUST
        represent any special encoding rules associated with that SMI
        datatype.

   R5.  The XSD datatype specified for a given SMI datatype MUST include
        any restrictions on values associated with the SMI datatype.

   R6.  The XSD datatype specified for a given SMI datatype MUST be the
        most direct XSD datatype, with the most parsimonious
        restrictions, which matches the foregoing requirements.

   R7.  The XML output produced as a result of meeting the foregoing
        requirements SHOULD be the most direct (i.e., avoiding
        superfluous "decoration") from the perspective of readability by
        humans.



















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4.  XSD for SMI Base Datatypes

   This document provides XSD datatype mappings for the SMIv2 base
   datatypes only -- i.e., the eleven "ObjectSyntax" datatypes defined
   in RFC 2578.  These datatypes -- via tag values defined in the SMIv2
   to identify them in varbinds -- constrain values carried "on-the-
   wire" in SNMP PDUs between SNMP management applications and SNMP
   agents:

   o  INTEGER, Integer32

   o  Unsigned32, Gauge32

   o  Counter32

   o  TimeTicks

   o  Counter64

   o  OCTET STRING

   o  Opaque

   o  IpAddress

   o  OBJECT IDENTIFIER

   The "BITS" pseudo-type (also referred to as a "construct" in RFC
   2578) is treated as a Textual Convention, not a base datatype, for
   the purpose of this document.





















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   BEGIN

   <?xml version="1.0" encoding="utf-8"?>
   <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:opsawg:smi:base:1.0"
   targetNamespace="urn:ietf:params:xml:ns:opsawg:smi:base:1.0"
   elementFormDefault="qualified"
   attributeFormDefault="unqualified"
   xml:lang="en">

     <xs:annotation>
       <xs:documentation>
           Mapping of SMIv2 base datatypes from RFC 2578

           Contact:      Bob Natale
           Organization: MITRE
           Address:      7515 Colshire Drive
                         McLean VA 22102
                         USA
           Telephone:    +1 703-983-2505
           E-Mail:       rnatale@mitre.org
           Last Updated: 200903090000Z
       </xs:documentation>
     </xs:annotation>

     <xs:simpleType name="INTEGER">
       <xs:restriction base="xs:int"/>
     </xs:simpleType>

     <xs:simpleType name="Integer32">
       <xs:restriction base="xs:int"/>
     </xs:simpleType>

     <xs:simpleType name="Unsigned32">
       <xs:restriction base="xs:unsignedInt"/>
     </xs:simpleType>

     <xs:simpleType name="Gauge32">
       <xs:restriction base="xs:unsignedInt"/>
     </xs:simpleType>

     <xs:simpleType name="Counter32">
       <xs:restriction base="xs:unsignedInt"/>
     </xs:simpleType>

     <xs:simpleType name="TimeTicks">
       <xs:restriction base="xs:unsignedInt"/>
     </xs:simpleType>



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     <xs:simpleType name="Counter64">
       <xs:restriction base="xs:unsignedLong"/>
     </xs:simpleType>

     <xs:simpleType name="OctetString">
       <xs:restriction base="xs:hexBinary">
         <xs:maxLength value="65535"/>
       </xs:restriction>
     </xs:simpleType>

     <xs:simpleType name="Opaque">
       <xs:restriction base="xs:hexBinary"/>
     </xs:simpleType>

     <xs:simpleType name="IpAddress">
       <xs:restriction base="xs:string">
         <xs:pattern value=
         "((0|(1[0-9]{0,2})|
           (2(([0-4][0-9]?)|(5[0-5]?)|([6-9]?)))|
           ([3-9][0-9]?))\.){3}
           (0|(1[0-9]{0,2})|
           (2(([0-4][0-9]?)|(5[0-5]?)|([6-9]?)))|
           ([3-9][0-9]?))"/>
       </xs:restriction>
     </xs:simpleType>

     <xs:simpleType name="ObjectIdentifier">
       <xs:restriction base="xs:string">
         <xs:pattern value=
         "(([0-1](\.[1-3]?[0-9]))|
           (2\.(0|([1-9]\d*))))
           (\.(0|([1-9]\d*))){0,126}"/>
       </xs:restriction>
     </xs:simpleType>

   </xs:schema>
   END














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5.  Rationale

   The XSD datatypes, including any specified restrictions, were chosen
   based on fit with the requirements specified earlier in this
   document, and with attention to simplicity while maintaining fidelity
   to the SMI.  Also, the "canonical representations" (i.e., refinements
   of the "lexical representations") documented in the W3C XSD
   specifications are assumed.

5.1.  Numeric Datatypes

   All of the numeric XSD datatypes specified in the previous section --
   INTEGER, Integer32, Unsigned32, Gauge32, Counter32, TimeTicks, and
   Counter64 -- comply with the relevant requirements

   o  They cover all valid values for the corresponding SMI datatypes.

   o  They comply with the standard encoding rules associated with the
      corresponding SMI datatypes.

   o  They inherently match the range restrictions associated with the
      corresponding SMI datatypes.

   o  They are the most direct XSD datatypes which exhibit the foregoing
      characteristics relative to the corresponding SMI datatypes (which
      is why no "restriction" statements -- other than the "base" XSD
      type -- are required in the XSD).

   o  The XML output produced from the canonical representation of these
      XSD datatypes is also the most direct from the perspective of
      readability by humans (i.e., no leading "+" sign and no leading
      zeros).

   Special note to application developers: Compliance with this schema
   in an otherwise correct translation from raw ("on-the-wire"
   representation) SNMP MIB data produces values that are faithful to
   the original.  However, the Gauge32, Counter32, Counter64, and
   TimeTicks datatypes have special application semantics that must be
   considered when using their raw values for anything other than
   display, printing, storage, or transmission of the literal value.
   RFC 2578 provides the necessary details.

5.2.  OctetString

   This XSD datatype corresponds to the SMI "OCTET STRING" datatype.

   Several independent schemes for mapping SMI datatypes to XSD have
   used the XSD "string" type to represent "OCTET STRING", but this



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   mapping does not conform to the requirements specified in this
   document.  Most notably, "string" cannot faithfully represent all
   valid values (0 thru 255) that each octet in an "OCTET STRING" can
   have -- or at least cannot do so in a way that provides for easy
   human readability of the resulting XML output.

   Consequently, the XSD datatype "hexBinary" is specified as the
   standard mapping of the SMI "OCTET STRING" datatype.  In hexBinary,
   each octet is encoded as two hexadecimal digits; the canonical
   representation limits the set of allowed hexadecimal digits to 0-9
   and uppercase A-F.

   The hexBinary representation of "OCTET STRING" complies with the
   relevant requirements:

   o  It covers all valid values for the corresponding SMI datatype.

   o  It complies with the standard encoding rules associated with the
      corresponding SMI datatype.

   o  With the "maxLength" restriction to 65535 octets, the XSD datatype
      specification matches the restrictions associated with the
      corresponding SMI datatype.

   o  It is the most direct XSD datatype which exhibits the foregoing
      characteristics relative to the corresponding SMI datatype (which
      must allow for any valid binary octet value).

   o  The XML output produced from the canonical representation of this
      XSD datatype is not optimal with respect to readability by humans;
      however, that is a consequence of the SMI datatype itself.  Where
      human readability is more of a concern, it is likely that the
      actual MIB objects in question will be represented by textual
      conventions which limit the set of values that will be included in
      the OctetStrings and will, thus, bypass the hexBinary typing.

5.3.  Opaque

   The "hexBinary" XSD datatype is specified as the representation of
   the SMI "Opaque" datatype generally for the same reasons as
   "hexBinary" is specified for the "OctetString" datatype:

   o  It covers all valid values for the corresponding SMI datatype.

   o  It complies with the standard encoding rules associated with the
      corresponding SMI datatype.





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   o  There are no restriction issues associated with using "hexBinary"
      for "Opaque".

   o  It is the most direct XSD datatype which exhibits the foregoing
      characteristics relative to the corresponding SMI datatype (which
      must allow for any valid binary octet value).

   o  The XML output produced from the canonical representation of this
      XSD datatype is not optimal with respect to readability by humans;
      however, that is a consequence of the SMI datatype itself.
      Unmediated "Opaque" data is intended for consumption by
      applications, not humans.

5.4.  IpAddress

   The XSD "string" datatype is the natural choice to represent an
   IpAddress as XML output.  The "pattern" restriction applied in this
   case results in a dotted-decimal string of four values between "0"
   and "255" separated by a period (".") character.  This pattern also
   precludes leading zeros.

5.5.  ObjectIdentifier

   This XSD datatype corresponds to the SMI "OBJECT IDENTIFIER"
   datatype.

   The XSD "string" datatype is also the natural choice to represent an
   ObjectIdentifier as XML output, for the same reasons as for the
   IpAddress choice.  The "pattern" restriction applied in this case
   results in a dotted-decimal string of up to 128 elements (referred to
   as "sub-ids"), each holding an "Unsigned32" integer value.

   Note that, while not mentioned in Sec. 7.1.3 of RFC 2578, due to the
   use of Abstract Syntax Notation One (ASN.1) Basic Encoding Rules
   (BER) the first two components of an "OBJECT IDENTIFIER" have limited
   value ranges and are encoded into a single sub-id value [Steedman].
   The ASN.1/BER standards specify that the numerical value of the first
   sub-identifier is derived from the values of the first two "OBJECT
   IDENTIFIER" components in the value being encoded, using the formula:
   (X*40) + Y, where X is the value of the first component and Y is the
   value of the second component.  This packing of the first two
   components recognizes that only three values are allocated from the
   root node, and at most 39 subsequent values from nodes reached by X =
   0 and X = 1.  The minimum length of an "OBJECT IDENTIFIER" is two
   sub-ids (with a zero-valued "OBJECT IDENTIFIER" represented as
   "0.0").  No explicit "minLength" restriction (which would be "3" to
   allow for the minimum of two sub-ids and a single separating dot) is
   required, since the pattern itself enforces this restriction.



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6.  Security Considerations

   Security considerations for any given SMI MIB module are likely to be
   relevant to any XSD/XML mapping of that MIB module; however, the
   mapping defined in this document does not itself introduce any new
   security considerations.

   If and when proxies or gateways are developed to convey SNMP
   management information from SNMP agents to XML-based management
   applications via XSD/XML mapping of MIB modules based on this
   specification and its planned siblings, special care will need to be
   taken to ensure that all applicable SNMP security mechanisms are
   supported in an appropriate manner yet to be determined.






































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7.  IANA Considerations

   In accordance with RFC 3688 [RFC3688], we request the following
   namespace and schema registrations associated with this document in
   the IANA XML Registry:

   o  urn:ietf:params:xml:ns:opsawg:smi:base:[version_id]

   o  urn:ietf:params:xml:schema:opsawg:smi:base:[version_id]

7.1.  SMI Base Datatypes Namespace Registration

   This document registers a URI for the SMI Base Datatypes XML
   namespace in the IETF XML registry.  Following the format in RFC
   3688, IANA has made the following registration:

   URI: urn:ietf:params:xml:ns:opsawg:smi:base:1.0

   Registration Contact: The IESG.

   XML: N/A, the requested URI is an XML namespace.

7.2.  SMI Base Datatypes Schema Registration

   This document registers a URI for the SMI Base Datatypes XML schema
   in the IETF XML registry.  Following the format in RFC 3688, IANA has
   made the following registration:

   URI: urn:ietf:params:xml:schema:opsawg:smi:base:1.0

   Registration Contact: The IESG.

   XML: Section 4 of this document.


















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8.  Acknowledgements

   Dave Harrington provided strategic and technical leadership to the
   team which developed this particular specification.  Yan Li did much
   of the research into existing approaches that was used as a baseline
   for the recommendations in this particular specification.

   This document owes much to draft-romascanu-netconf-datatypes-xx and
   to many other sources (including libsmi and group discussions on the
   NETCONF mailing lists) developed by those who have researched and
   published candidate mappings of SMI datatypes to XSD.

   Individuals who participated in various discussions of this topic at
   IETF meetings and on IETF mailing lists include: Ray Atarashi,
   Yoshifumi Atarashi, Andy Bierman, Sharon Chisholm, Avri Doria, Mark
   Ellison, Rob Ennes, Mehmet Ersue, David Harrington, Alfred Hines,
   Eliot Lear, Chris Lonvick, Faye Ly, Randy Presuhn, Juergen
   Schoenwaelder, Andre Westerinen, and Bert Wijnen.

































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9.  References

9.1.  Normative References

   [RFC1155]  Rose, M. and K. McCloghrie, "Structure and identification
              of management information for TCP/IP-based internets",
              STD 16, RFC 1155, May 1990.

   [RFC2119]  Bradner, s., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC3584]  Frye, R., Levi, D., Routhier, S., and B. Wijnen,
              "Coexistence between Version 1, Version 2, and Version 3
              of the Internet-standard Network Management Framework",
              BCP 74, RFC 3584, August 2003.

9.2.  Informational References

   [RFC2579]  McCloghrie, K., Perkins, D., and J. Schoenwaelder,
              "Textual Conventions for SMIv2", STD 58, RFC 2579,
              April 1999.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [Steedman]
              Steedman, D., "ASN.1: The Tutorial and Reference".

   [XML]      World Wide Web Consortium, "Extensible Markup Language
              (XML) 1.0", W3C XML, February 1998,
              <http://www.w3.org/TR/1998/REC-xml-19980210>.

   [XMLSchema]
              World Wide Web Consortium, "XML Schema Part 1: Structures
              Second Edition", W3C XML Schema, October 2004,
              <http://www.w3.org/TR/xmlschema-1/>.

   [XSDDatatypes]
              World Wide Web Consortium, "XML Schema Part 2: Datatypes
              Second Edition", W3C XML Schema, October 2004,
              <http://www.w3.org/TR/xmlschema-2/>.






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Author's Address

   Bob Natale
   MITRE
   7515 Colshire Dr
   MS H405
   McLean, VA  22102
   USA

   Phone: +1 703-983-2505
   Email: rnatale@mitre.org








































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