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
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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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