Network Working Group B. Natale, Ed.
Internet-Draft MITRE
Intended status: Standards Track Y. Li, Ed.
Expires: January 15, 2009 Huawei Technologies
July 14, 2008
Expressing SNMP SMI Datatypes in XML Schema Definition Language
draft-ietf-opsawg-smi-datatypes-in-xsd-02.txt
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Abstract
This memo (when approved as a standards-track RFC) 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
Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . . 17
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 20
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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 [ref.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 and structures to XML documents via
XSD.
MIB data models are described using SMIv2 [RFC2578] and, for legacy
MIBs, SMIv1 [RFC1155]. MIB data is conveyed via SNMP using the base
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 based on a core 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.
Various independent schemes have been devised for expressing the SMI
datatypes and TCs in XSD [ref.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 general
interoperability.
The primary purpose of this memo is to define a standard expression
of SMI base datatypes in XSD to ensure uniformity 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 will facilitate.
This memo is the first in a set of three related and (logically)
ordered specifications:
1. SMI Base Datatypes [RFC2578] in XSD
2. SMI MIB Structure [RFC2578] in XSD
3. SNMP Textual Conventions [RFC2579] in XSD
As a set, these documents define the XSD equivalent of SMIv2 to
encourage XML-based protocols to carry, and XML-based applications to
use, the information modeled in SMIv2-compliant MIB modules.
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This work defines XSD equivalents of the datatypes and data
structures [RFC2578] and the textual conventions [RFC2579] defined in
the SMIv2 standard (STD58) to encourage 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
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 concerns only the SMI base datatypes -- i.e., the ten
"ObjectSyntax" datatypes defined in RFC2578. These datatypes -- via
tag values defined in the SMI 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 OctetString
o Opague
o IpAddress
o ObjectIdentifier
The "BITS" pseudo-type (also referred to as a "construct" in RFC2578)
is treated as a Textual Convention for the purpose of this document
and, therefore, will be defined in the "SNMP Textual Conventions in
XSD" document.
The following should be considered a "notional" XSD file for now,
pending agreement on the actual datatype specifications. An
appropriate (official) targetNamespace must be designated (and
approved) and agreement must be reached on whether any additional XSD
content must be included (e.g., whether non-default values for
elementFormDefault or attributeFormDefault or schemaLocation, etc.,
need to be specified).
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.
</xs:documentation>
</xs:annotation>
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<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>
<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">
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<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 datatype 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 and Counter32 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. This is particularly important
for Counter32 values. 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
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 ready
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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 "Opague" 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.
o There are no restriction issues associated with using "hexBinary"
for "Opague".
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 "Opague" data is intended for consumption by
applications, not humans.
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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"), holding "Unsigned32" integer values.
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
subidentifier is derived from the values of the first two object
identifier components in the object identifier value being encoded,
using the formula: (X*40) + Y, where X is the value of the first
object identifier component and Y is the value of the second object
identifier component. This packing of the first two object
identifier 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, we will register namespaces and schemas
for all three documents in this set with the IANA XML Registry.
These entries -- corresponding to this base datatypes document and
the future textual conventions and MIB structure documents -- will be
as follows:
o urn:ietf:params:xml:ns:opsawg:smi:base:[version_id]
o urn:ietf:params:xml:schema:opsawg:smi:base:[version_id]
o urn:ietf:params:xml:ns:opsawg:smi:tc:[version_id]
o urn:ietf:params:xml:schema:opsawg:smi:tc:[version_id]
o urn:ietf:params:xml:ns:opsawg:smi:structure:[version_id]
o urn:ietf:params:xml:schema:opsawg:smi:structure:[version_id]
The following sub-sections refer to the present document only.
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 and textual conventions
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, David Harrington, Eliot Lear, Chris Lonvick, Faye
Ly, Randy Presuhn, Juergen Schoenwaelder, Andre Westerinen, and Bert
Wijnen. (Others who have been inadvertently omitted from this list
should notify the editors.)
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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.
[RFC2579] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Textual Conventions for SMIv2", STD 58, RFC 2579,
April 1999.
9.2. Informational References
[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.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[Steedman]
Steedman, D., "ASN.1: The Tutorial and Reference".
[ref.XML] World Wide Web Consortium, "Extensible Markup Language
(XML) 1.0", W3C XML, February 1998,
<http://www.w3.org/TR/1998/REC-xml-19980210>.
[ref.XMLSchema]
World Wide Web Consortium, "XML Schema Part 1: Structures
Second Edition", W3C XML Schema, October 2004,
<http://www.w3.org/TR/xmlschema-1/>.
[ref.XSDDatatype]
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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Appendix A. Open Issues
o Confirm IANA XML registration values and process.
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Appendix B. Change Log
o -00 Initial version
o -01 version:
o
* Incorporated mailing list comments on -00 version from Juergen
Schoenwaelder
* Incorporated mailing list comments on -00 version from David
Harrington
o -02 version:
o
* Fixed ObjectIdentifier pattern per correction from Juergen
Schoenwaelder, and text in sec. 5.5 adjusted accordingly.
* Moved non-normative references to Informational section per
David Harrington
* Tightened wording in to "XSD for SMI Datatypes" section per
Mark Ellison
* Added a note about Gauge32 and Counter32 application semantics
to the "Rationale" section per Mark Ellison
* Security section wording tightened per David Harrington
* The IANA Considerations section completed--will need
adjustment.
* Acknowledgments entries expanded and alphabetized
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Authors' Addresses
Bob Natale (editor)
MITRE
7515 Colshire Dr
MS H405
McLean, VA 22102
USA
Phone: +1 703-983-2505
Email: rnatale@mitre.org
Yan Li (editor)
Huawei Technologies
No.3 Xinxi Road, Shangdi Information Industry Base
Beijing, HaiDian District 100085
P.R.China
Phone: +86 10 8288 2008
Email: liyan_77@huawei.com
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