GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc2926

Network Working Group J. Kempf Request for Comments: 2926 Sun Microsystems, Inc. Category: Informational R. Moats

                                                          Coreon, Inc.
                                                         P. St. Pierre
                                                Sun Microsystems, Inc.
                                                        September 2000
        Conversion of LDAP Schemas to and from SLP Templates

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This document describes a procedure for mapping between Service
 Location Protocol (SLP) service advertisements and lightweight
 directory access protocol (LDAP) descriptions of services.  The
 document covers two aspects of the mapping.  One aspect is mapping
 between SLP service type templates and LDAP directory schema.
 Because the SLP service type template grammar is relatively simple,
 mapping from service type templates to LDAP types is straightforward.
 Mapping in the other direction is straightforward if the attributes
 are restricted to use just a few of the syntaxes defined in RFC 2252.
 If arbitrary ASN.1 types occur in the schema, then the mapping is
 more complex and may even be impossible.  The second aspect is
 representation of service information in an LDAP directory.  The
 recommended representation simplifies interoperability with SLP by
 allowing SLP directory agents to backend into LDAP directory servers.
 The resulting system allows service advertisements to propagate
 easily between SLP and LDAP.

Kempf, et al. Informational [Page 1] RFC 2926 Conversion of LDAP Schemas September 2000

Table of Contents

 1.0 Introduction ................................................  2
 2.0 Mapping SLP Templates to LDAP Schema ........................  3
   2.1 Mapping from SLP Attribute Types to LDAP Attribute Types ..  8
     2.1.1 Integer ...............................................  8
     2.1.2 String ................................................  8
     2.1.3 Boolean ...............................................  9
     2.1.4 Opaque ................................................  9
   2.2 Keyword Attributes ........................................  9
   2.3 Template Flags ............................................  9
     2.3.1 Multi-valued ..........................................  9
     2.3.2 Optional .............................................. 10
     2.3.3 Literal ............................................... 10
     2.3.4 Explicit Matching ..................................... 10
   2.4 Default and Allowed Value Lists ........................... 10
   2.5 Descriptive Text .......................................... 11
   2.6 Generating LDAP Attribute OIDs ............................ 11
   2.7 Example ................................................... 11
 3.0 Attribute Name Conflicts .................................... 15
 4.0 Mapping from Schema to Templates ............................ 15
   4.1 Mapping LDAP Attribute Types to SLP Attribute Types ....... 16
   4.2 Mapping ASN.1 Types to SLP Types .......................... 17
     4.2.1 Integer ............................................... 18
     4.2.2 Boolean ............................................... 18
     4.2.3 Enumerated ............................................ 18
     4.2.4 Object Identifier ..................................... 19
     4.2.5 Octet String .......................................... 19
     4.2.6 Real .................................................. 19
   4.3 Example ASN.1 Schema ...................................... 19
 5.0 Representing SLP Service Advertisements in an LDAP DIT ...... 22
 6.0 Internationalization Considerations ......................... 24
 7.0 Security Considerations ..................................... 24
 8.0 References .................................................. 25
 9.0 Authors' Addresses .......................................... 26
 10.0 Full Copyright Statement ................................... 27

1.0 Introduction

 SLP templates [1] are intended to create a simple encoding of the
 syntactic and semantic conventions for individual service types,
 their attributes, and conventions.  They can easily be generated,
 transmitted, read by humans and parsed by programs, as it is a string
 based syntax with required comments.  Directory schemas serve to
 formalize directory entry structures for use with LDAP [2] These
 directories serve to store information about many types of entities.
 Network services are an example of one such entity.

Kempf, et al. Informational [Page 2] RFC 2926 Conversion of LDAP Schemas September 2000

 Interoperability between SLP and LDAP is important so clients using
 one protocol derive benefit from services registered through the
 other. In addition, LDAP directory servers can serve as the backend
 for SLP directory agents (DAs) if interoperability is possible In
 order to facilitate interoperability, this document creates mappings
 between the SLP template grammar and LDAP directory schema, and
 establishes some conventions for representing service advertisements
 in LDAP directories. The goal of the translation is to allow SLPv2
 queries (which are syntactically and semantically equivalent to
 LDAPv3 string queries [7]) to be submitted to an LDAP directory
 server by an SLP DA backended into LDAP without extensive processing
 by the DA.
 The simple notation and syntactic/semantic attribute capabilities of
 SLP templates map easily into directory schemas, and are easily
 converted into directory schemas, even by automated means.  The
 reverse may not be true. If the LDAP schema contains attributes with
 unrecognized or complex syntaxes, the translation may be difficult or
 impossible.  If, however, the LDAP schema only uses a few of the
 common syntaxes defined in RFC 2252 [8], then the translation is more
 straightforward. In addition, to foster complete bidirectionality,
 the mapping must follow a very specific representation in its DESC
 attributes.
 This document outlines the correct mappings for SLP templates into
 the syntactic representation specified for LDAP directory schema by
 RFC 2252 [8]. This syntax is a subset of the ASN.1/BER described in
 the X.209 specification [9], and is used by the LDAPv3 [2] directory
 schema.  Likewise, rules and guidelines are proposed to facilitate
 consistent mapping of ASN.1 based schemas to be translated in the SLP
 template grammar. Finally, a proposal for a representation of service
 advertisements in LDAP directory services is made that facilitates
 SLP interoperability.
 Except when used as elements in the definition of LDAP schemas, 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 [16].

2.0 Mapping SLP Templates to LDAP Schema

 We define the following abstract object class as the parent class for
 all services.  Any specific service type is a subclass of this, with
 its own attributes:

Kempf, et al. Informational [Page 3] RFC 2926 Conversion of LDAP Schemas September 2000

    ( 1.3.6.1.4.1.6252.2.27.6.2.1
      NAME 'slpService'
      DESC 'parent superclass for SLP services'
      ABSTRACT
      SUP top
      MUST  ( template-major-version-number $
              template-minor-version-number $
              description $
              template-url-syntax $
              service-advert-service-type $
              service-advert-scopes )
      MAY   ( service-advert-url-authenticator $
              service-advert-attribute-authenticator ) )
 The attributes correspond to various parts of the SLP service
 template and SLP service advertisement.
 SLP service type templates begin with four definitions that set the
 context of the template:
    template-type - This defines the service type of the template. The
    service type can be a simple service type, like "service:ftp", an
    abstract service type, like "service:printer" or a concrete
    service type, like "service:printer:lpr". The type name can
    additionally include a naming authority, for example
    "service:printer.sun:local".  The name that appears in this field
    omits the "service:" prefix.
    template-version - A string containing a major and minor version
    number, separated by a period.
    template-description - A block of human readable text describing
    what the service type does.
    template-url-syntax - An ABNF [6] grammar describing the service
    type specific part of the service URL.
 The SLP template-type definition is used as the name of the LDAP
 object class for the template, a subclass of the "slpService" class,
 together with the "service" prefix to indicate that the name is for a
 service. In the translating service type name, colons and the period
 separating the naming authority are converted into hyphens. If the
 template defines an SLP concrete type, the concrete type name is
 used; the abstract type name is never used.  For example, the
 template for "service:printer:lpr" is translated into an LDAP object
 class called "service-printer-lpr". Furthermore, if the type name
 contains a naming authority, the naming authority name must be

Kempf, et al. Informational [Page 4] RFC 2926 Conversion of LDAP Schemas September 2000

 included. For example, the service type name
 "service:printer.sun:local" becomes "service-printer-sun-local".  The
 LDAP object class is always "STRUCTURAL".
 The template-version definition is partitioned into two attributes,
 template-major-version-number and template-minor-version-number. The
 LDAP definition for these attributes is:
    ( 1.3.6.1.4.1.6252.2.27.6.1.1
      NAME 'template-major-version-number'
      DESC 'The major version number of the service type template'
      EQUALITY integerMatch
      SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
      SINGLE-VALUE
    )
    ( 1.3.6.1.4.1.6252.2.27.6.1.2
      NAME 'template-minor-version-number'
      DESC 'The minor version number of the service type template'
      EQUALITY integerMatch
      SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
      SINGLE-VALUE
    )
 The template-url-syntax definition in the SLP template is described
 by the following attribute:
    ( 1.3.6.1.4.1.6252.2.27.6.1.3
      NAME 'template-url-syntax'
      DESC 'An ABNF grammar describing the service type
            specific part of the service URL'
      EQUALITY caseExactIA5Match
      SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
      SINGLE-VALUE
    )
 The template-description attribute is translated into the X.520
 standard attribute "description" [3].
 We further establish the convention that SLP template characteristics
 that can't be translated into LDAP are inserted into the DESC field
 of the object class definition. The items are separated by empty
 lines (consisting of two "LINE FEED" characters), are preceded by a
 LINE FEED character, and are tagged at the  beginning of the line to
 indicate what they represent.   This allows the template to be
 reconstructed from the schema by properly parsing the comments.

Kempf, et al. Informational [Page 5] RFC 2926 Conversion of LDAP Schemas September 2000

 The bulk of an SLP template consists of attribute definitions.  There
 are four items in an SLP template attribute definition that need to
 be mapped into LDAP:
    Attribute Name - Since SLPv2 attribute names are defined to be
    compatible with LDAPv3, SLP attributes map directly into LDAP
    attributes with no change. Similarly, LDAP attributes map directly
    to SLP attributes.
    Attribute Type - The SLP attribute type is mapped into the LDAP
    attribute type.
    Attribute Flags - The SLP attribute flags are mapped into
    characteristics of the LDAP attribute definition, or into the DESC
    field if no equivalent LDAP attribute definition characteristic
    occurs.
    Default and Allowed Values - These must be handled by the client
    or a DA enabled to handle templates, as in SLP. For reference,
    however, they should be included in the DESC field of the LDAP
    attribute definition.
    Descriptive Text - The SLP template descriptive text should be
    mapped into the DESC field.
 We discuss mapping of types, flags, default and allowed values, and
 descriptive text in the subsections below.
 OIDs for SLP template conversion schema elements are standardized
 under the enterprise number of SrvLoc.Org (6252) [18].
 For purposes of representing an SLP entry, we also define two
 standardized LDAP syntaxes and attributes with standardized OIDs.
    ( 1.3.6.1.4.1.6252.2.27.6.2.2
      DESC 'SLP Service Type'
    )
 Defines the syntax for the service type name. The syntax is defined
 in the BNF for the service URL in RFC 2609 Section 2.1 [1].
    ( 1.3.6.1.4.1.6252.2.27.6.2.3
      DESC 'SLP Scope'
    )
 Defines the syntax for the scope name. The syntax is defined in the
 BNF for scope names in RFC 2608 Section 6.4.1 [5].

Kempf, et al. Informational [Page 6] RFC 2926 Conversion of LDAP Schemas September 2000

    ( 1.3.6.1.4.1.6252.2.27.6.1.4
      NAME 'service-advert-service-type'
      DESC 'The service type of the service advertisement, including
            the "service:" prefix.'
      EQUALITY caseExactIA5Match
      SYNTAX 1.3.6.1.4.1.6252.2.27.6.2.2
      SINGLE-VALUE
    )
 Defines an attribute for the service type name.
    ( 1.3.6.1.4.1.6252.2.27.6.1.5
      NAME 'service-advert-scopes'
      DESC 'A list of scopes for a service advertisement.'
      EQUALITY caseExactIA5Match
      SYNTAX 1.3.6.1.4.1.6252.2.27.6.2.3
    )
 Defines a multivalued attribute for the scopes.
 Searches for abstract types can be made with an LDAP query that
 wildcards the concrete type. For example, a search for all service
 advertisements of the printer abstract type can be made with the
 following query:
       (service-advert-service-type=service:printer:*)
 SLP specifies that service URLs and attribute lists can be
 accompanied by a structured authenticator consisting of a digital
 signature and information necessary to verify the signature.  A
 syntax and two standardized SLP attributes are defined for this
 purpose:
    ( 1.3.6.1.4.1.6252.2.27.6.2.3 DESC 'SLP Authenticator')
    The syntax of an SLP authenticator is the bytes of the
    authenticator in network byte order, see RFC 2608, Section 9.2
    [5].
    ( 1.3.6.1.4.1.6252.2.27.6.1.6
      NAME 'service-advert-url-authenticator'
      DESC 'The authenticator for the URL, null if none.'
      SYNTAX 1.3.6.1.4.1.6252.2.27.6.2.3
      SINGLE-VALUE
    )
    This attribute contains the SLP URL authenticator, as defined in
    RFC 2608, Section 9.2 [5].

Kempf, et al. Informational [Page 7] RFC 2926 Conversion of LDAP Schemas September 2000

    ( 1.3.6.1.4.1.6252.2.27.6.1.7
      NAME 'service-advert-attribute-authenticator'
      DESC 'The authenticator for the attribute list, null if none.'
      SYNTAX 1.3.6.1.4.1.6252.2.27.6.2.3
      SINGLE_VALUE
    )
    This attribute contains the SLP attribute authenticator, as
    defined in RFC 2608, Section 9.2 [5].

2.1 Mapping from SLP Attribute Types to LDAP Attribute Types

 We define the mapping from SLP attribute types to LDAP as follows:
    SLP Type    ASN.1 Type               LDAP Type
    ---------------------------------------------------
     Integer     INTEGER              INTEGER
     String      DirectoryString      Directory String
     Boolean     BOOLEAN              Boolean
     Opaque      OCTET STRING         Octet String
     Keyword     (N/A)                IA5 String
 The following subsections discuss further details of the mapping.

2.1.1 Integer

 SLP integers compare as integers when performing a query.  LDAP
 integers behave similarly.  Consequently, the mapping from the SLP
 integer type to LDAP is INTEGER, with the integerMatch matching rule.

2.1.2 String

 SLP strings are encoded as described in the SLP protocol
 specification [5].  All value strings are considered case insensitive
 for matching operations.  SLP strings are not null terminated and are
 encoded in UTF-8.
 SLP strings are mapped to the LDAP Directory String type. The
 Directory String type exactly matches the SLP string type, i.e. it is
 a non-null terminated UTF-8 string. The caseIgnoreMatch equality
 rule, caseIgnoreOrderingMatch ordering rule, and
 caseIgnoreSubstringsMatch substring rule are used for comparing
 string attribute values.

Kempf, et al. Informational [Page 8] RFC 2926 Conversion of LDAP Schemas September 2000

2.1.3 Boolean

 Boolean attributes may have one of two possible values.  In SLP,
 these values are represented as strings, TRUE and FALSE.  In SLP's
 string encoding of a boolean value, case does not matter.
 The SLP Boolean type maps directly into an LDAP BOOLEAN. The
 caseIgnoreMatch rule is used for equality matching.

2.1.4 Opaque

 SLP attribute values of type Opaque are represented as OCTET STRING
 in LDAP, and the octetStringMatch matching rule is used to compare
 them.

2.2 Keyword Attributes

 SLP service type templates allow the definition of keyword
 attributes.  Keyword attributes are attributes whose only
 characteristic is their presence. Keyword attributes have no flag
 information, nor any default or allowed values (since, by definition,
 they have no values).
 ASN.1 has no concept of keyword attributes. Keyword attributes are
 translated into a "May" clause in the ASN.1 class definition for the
 service type. If the keyword attribute is present, then its value is
 of no consequence, but for consistency we make it simply the NUL
 character, "\00".

2.3 Template Flags

 SLP template flags can be handled as described in the following
 subsections.

2.3.1 Multi-valued

 Multi-valued attributes are defined in an SLP template using the one
 value.  All values for a given attribute must be of the same type.
 LDAP attribute definitions require that a single valued attribute
 include the SINGLE-VALUE tag if the attribute is single valued.
 Otherwise, the attribute is assumed to be multivalued by default.

Kempf, et al. Informational [Page 9] RFC 2926 Conversion of LDAP Schemas September 2000

2.3.2 Optional

 SLP uses the 'O' flag to indicate an attribute may or may not be
 present.  These optional attributes are defined using the "May"
 clause in the ASN.1 definition class definition for the service type.
 All other attributes must be defined as a "Must".

2.3.3 Literal

 ASN.1 does not have a mechanism to indicate that the values of an
 attribute may not be translated from one language to another, since
 ASN.1 schema are not typically translated. This flag is dropped when
 translating a template, but presence of the flag should be noted in
 the DESC field. It should be placed on a separate line and tagged
 with "Literal:" so the template can be reconstructed from the schema.

2.3.4 Explicit Matching

 The SLP template syntax uses a flag of 'X' to indicate that an
 attribute must be present in order for the query to be properly
 satisfied.  There is no provision for requiring that particular
 attributes be in a query. Consequently, this flag is dropped when
 translating a template, but presence of the flag should be noted in
 the DESC field. It should be placed on a separate line and tagged
 with "Explicit:" so the template can be reconstructed from the
 schema.

2.4 Default and Allowed Value Lists

 The SLP template grammar provides the capability to define default
 and allowed values for an attribute. The SLP protocol does not
 enforce these restrictions on registered attributes, however.  The
 default and allowed values may be used by client side applications,
 or alternatively it may also be used by DAs to initialize
 registrations having no attributes and to limit attribute values to
 the template allowed values.
 LDAP servers also do not support default and allowed values on
 attributes. Therefore, enforcement of default and allowed values in
 SLP templates is left up to the clients or a DA, if the DA is
 backending into LDAP. The default and allowed values should be
 included in the DESC field. The comments should be placed on separate
 lines and labeled with the "Default:" and "Allowed:" tags to allow
 reconstruction of the template.

Kempf, et al. Informational [Page 10] RFC 2926 Conversion of LDAP Schemas September 2000

2.5 Descriptive Text

 The descriptive text associated with an attribute definition should
 be included in the DESC field. It should start on a separate line and
 begin with the "Description:" tag.

2.6 Generating LDAP Attribute OIDs

 LDAP attributes require an OID. In general, there is no a priori way
 that an algorithm can be defined for generating OIDs, because it will
 depend on the conventions used by the organization developing the
 template. In some cases, an organization's procedure for generating
 OIDs may be regular enough that a template developer can
 algorithmically generate OIDs off of an assigned root. Whatever means
 is used, the template developer should assure that unique OIDs are
 assigned to each SLP attribute that is translated into an LDAP
 attribute.

2.7 Example

 The template included below is a hypothetical abstract printer
 service template, similar to that described in [10].
    template-type = printer
    template-version = 0.0
    template-description =
    The printer service template describes the attributes supported by
    network printing devices.  Devices may be either directly
    connected to a network, or connected to a printer spooler that
    understands the a network queuing protocol such as IPP, lpr or the
    Salutation  Architecture.
    template-url-syntax =
    ;The URL syntax is specific to the printing protocol being
    ;employed
    description = STRING
    # This attribute is a free form string that can contain any
    # site-specific descriptive information about this printer.
    printer-security-mechanisms-supported = STRING L M
    none
    # This attribute indicates the security mechanisms supported
    tls, ssl, http-basic, http-digest, none

Kempf, et al. Informational [Page 11] RFC 2926 Conversion of LDAP Schemas September 2000

    printer-operator = STRING O L M
    # A person, or persons responsible for maintaining a
    # printer on a day-to-day basis, including such tasks
    # as filling empty media trays, emptying full output
    # trays, replacing toner cartridges, clearing simple
    # paper jams, etc.
    printer-location-address = STRING O
    # Physical/Postal address for this device.  Useful for
    # nailing down a group of printers in a very large corporate
    # network.  For example: 960 Main Street, San Jose, CA 95130
    printer-priority-queue = BOOLEAN O
    FALSE
    # TRUE indicates this printer or print queue is a priority
    # queuing device.
    printer-number-up = INTEGER O
    1
    # This job attribute specifies the number of source
    # page-images to impose upon a single side of an instance
    # of a selected medium.
    1, 2, 4
    printer-paper-output = STRING M L O
    standard
    # This attribute describes the mode in which pages output
    # are arranged.
    standard, noncollated sort, collated sort, stack, unknown
 We assume that the concrete type "service:printer:lpr" for printers
 that speak the LPR protocol [4] has the following template
 definition:
    template-type = printer:lpr
    template-version = 0.0
    template-description =
    The printer:lpr service template describes the attributes
    supported by network printing devices that speak the
    LPR protocol. No new attributes are included.
    template-url-syntax = queue
    queue = ;The queue name, see RFC 1179.

Kempf, et al. Informational [Page 12] RFC 2926 Conversion of LDAP Schemas September 2000

 The LDAP class definition for the "service:printer:lpr" concrete
 service type is translated as follows:
 ( ---place the assigned OID here---
   NAME  'service-printer-lpr'
   DESC  'Description: The printer:lpr service template
               describes the attributes supported by network printing
               devices that speak the LPR protocol. No new attributes
               are included.
          URL Syntax: queue
               queue = ;The queue name, see RFC 1179.'
   SUP   slpService
   MUST  ( description $ security-mechanisms-supported $
   labeledURI)
   MAY   ( operator $ location-address $ priority-queue $
           number-up $ paper-output)
 )
 The attribute definitions are translated as follows:
 ( ---place the assigned OID here---
   NAME 'printer-security-mechanisms-supported'
   DESC 'Description: This attribute indicates the security mechanisms
         supported.
         Default: value
         Allowed: tls, ssl, http-basic, http-digest, none
         Literal:'
   EQUALITY caseIgnoreMatch
   ORDERING caseIgnoreOrderingMatch
   SUBSTR caseIgnoreSubstringsMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
 )
 ( ---place the assigned OID here---
   NAME 'printer-operator'
   DESC 'Description: A person, or persons responsible for
         maintaining a printer on a day-to-day basis, including
         such tasks as filling empty media trays, emptying full
         output trays, replacing toner cartridges, clearing simple
         paper jams, etc.

Kempf, et al. Informational [Page 13] RFC 2926 Conversion of LDAP Schemas September 2000

         Literal:'
   EQUALITY caseIgnoreMatch
   ORDERING caseIgnoreOrderingMatch
   SUBSTR caseIgnoreSubstringsMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
 )
 ( --place the assigned OID here---
   NAME 'printer-location-address'
   DESC 'Description Physical/Postal address for this device.
         Useful for nailing down a group of printers in a very
         large corporate network.  For example: 960 Main Street,
         San Jose, CA 95130.'
   EQUALITY caseIgnoreMatch
   ORDERING caseIgnoreOrderingMatch
   SUBSTR caseIgnoreSubstringsMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
   SINGLE-VALUE
 )
 ( ---place the assigned OID here---
   NAME 'printer-priority-queue'
   DESC 'Description: TRUE indicates this printer or print
        queue is a priority queuing device.'
   EQUALITY booleanMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
   SINGLE-VALUE
 )
 ( ---place the assigned OID here---
   NAME 'printer-number-up'
   DESC 'Description: This job attribute specifies the number
         of source page-images to impose upon a single side of
         an instance of a selected medium. This attribute is
         INTEGER.
         Default: 1
         Allowed: 1, 2, 3, 4'
   EQUALITY integerMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
   SINGLE-VALUE
 )

Kempf, et al. Informational [Page 14] RFC 2926 Conversion of LDAP Schemas September 2000

 ( ---place the assigned OID here---
   NAME 'printer-paper-output'
   DESC 'Description: This attribute describes the mode in
         which pages output are arranged. Default value is
         standard.
         Default: standard
         Allowed: standard, noncollated sort, collated sort,
           stack, unknown.
         Literal:'
   EQUALITY caseIgnoreMatch
   ORDERING caseIgnoreOrderingMatch
   SUBSTR caseIgnoreSubstringsMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
 )

3.0 Attribute Name Conflicts

 LDAP has a flat name space, and attribute names and OIDs must be
 unique in a directory server. In order to avoid name conflicts in the
 translation of SLP templates to LDAP schemas, template developers may
 want to consider prepending the name of the service type to the
 attribute. Postprocessing attribute names to make them unique when
 translated is not possible, because it would require the DA to
 rewrite queries before submitting them to the directory server. In
 addition, developers should use standard LDAP attributes when such
 attributes are available.
 In the above example template, the abstract type name "printer" is
 prepended to attributes to avoid conflicts. The standard
 "description" attribute defined by X.520 [3] is used to translate the
 template description attribute.

4.0 Mapping from Schema to Templates

 The reverse mapping from LDAP schema to SLP service type templates
 requires dealing with both LDAP and ASN.1 data types.  RFC 2252
 defines 33 attribute syntaxes that should be supported by LDAP
 directory servers.  These syntaxes are defined using BNF for strings
 or using ASN.1 for binary  valued attributes defined by X.520.
 Mapping of the LDAP data types into SLP template types is fairly
 straightforward, but mapping arbitrary ASN.1 data types is somewhat
 more complicated and requires encoding the ASN.1 data type into a
 string. To a certain extent, this masks the ASN.1 data type because
 it becomes impossible to distinguish between a native string having

Kempf, et al. Informational [Page 15] RFC 2926 Conversion of LDAP Schemas September 2000

 content equivalent to an encoded ASN.1 string. However, inclusion of
 the ASN.1 data type in the comment provides additional information
 should a reverse transformation from SLP to ASN.1 be required.
 The following subsections deal with both LDAP and ASN.1 attribute
 data type mappings.

4.1 Mapping LDAP Attribute Syntaxes to SLP Attribute Types

 The following table contains the mappings for LDAP syntaxes to SLP
 data types:
       LDAP Type                              SLP Type
    --------------------------------------------------------
       ACI Item                                 NA
       Access Point                             NA
       Attribute Type Description               NA
       Audio                                    Opaque
       Binary                                   ASN.1 escape
       Bit String                               String
       Boolean                                  Boolean
       Certificate                              Opaque
       Certificate List                         Opaque
       Certificate Pair                         Opaque
       Country String                           String
       DN                                       String
       Data Quality Syntax                      NA
       Delivery Method                          NA
       Directory String                         String
       DIT Content Rule Description             NA
       DIT Structure Rule Description           NA
       DL Submit Permission                     NA
       DSA Quality Syntax                       NA
       Enhanced Guide                           NA
       Facsimile Telephone Number               String
       Fax                                      Opaque
       Generalized Time                         String
       Guide                                    NA
       IA5 String                               String
       INTEGER                                  Integer
       JPEG                                     Opaque
       LDAP Syntax Description                  NA
       LDAP Schema Definition                   NA
       LDAP Schema Description                  NA
       Master and Shadow Access Points          NA
       Matching Rule Description                NA
       Matching Rule Use Description            NA
       Mail Preference                          NA

Kempf, et al. Informational [Page 16] RFC 2926 Conversion of LDAP Schemas September 2000

       MHS OR Address                           String
       Modify Rights                            NA
       Name and Optional UID                    NA
       Name Form Description                    NA
       Numeric String                           String
       Object Class Description                 NA
       Octet String                             Opaque
       OID                                      String
       Other Mailbox                            String
       Postal Address                           String
       Protocol Information                     NA
       Presentation Address                     String
       Printable String                         String
       Substring Assertion                      NA
       Subtree Specification                    NA
       Supplier Information                     NA
       Supplier or Consumer                     NA
       Supplier And Consumer                    NA
       Supported Algorithm                      NA
       DSE Type                                 NA
       Telephone Number                         String
       Teletex Terminal Identifier              String
       Telex Number                             String
       UTC Time                                 String

4.2 Mapping ASN.1 Types to SLP Types

 ASN.1 employs a much richer set of data types than provided by SLP.
 The table below show the mapping of selected ASN.1 data type to their
 nearest SLP equivalent.  Because of the complexity and flexibility of
 ASN.1, a complete list cannot be provided.
 As sample of some ASN.1 encodings and their mappings to SLP:
    ASN.1 type               SLP type
    -----------------------------------------
    INTEGER                  Integer
    BOOLEAN                  Boolean
    ENUMERATED               String
    OBJECT IDENTIFIER        String
    OCTET STRING             Opaque
    REAL                     String
 Data types that do not map directly to SLP data types should be
 defined as either a String, or as Opaque.  ASN.1 types that may only
 contain valid characters for Strings, as defined in X.680 [9] should
 be encoded as strings.  ASN.1 types such as GraphicString that change
 their character set encoding in part way through a value should not

Kempf, et al. Informational [Page 17] RFC 2926 Conversion of LDAP Schemas September 2000

 be encoded as strings, however, If such types are required, the SLP
 Opaque type should be used. In either case, the first line of the
 help text is used to indicate the original ASN.1 data type.
 The following subsections describe how to convert from the ASN.1 BER
 [9] to the SLP template for the different types in the table above.

4.2.1 Integer

 Both SLP templates and ASN.1 support Integers, so there is a one to
 one mapping between an SLP Integer attribute and an ASN.1 Integer
 attribute.  Details on the encoding of integers is summarized in the
 SLP template to ASN.1 section above.

4.2.2 Boolean

 Boolean values are supported by both SLP and ASN.1, though on wire
 encodings differ.  X.680 [9] specifies zero and non-zero encoding for
 booleans, where SLP encodes booleans using the strings TRUE and
 FALSE.  In general, most LDAP servers will use the LDAP Boolean type
 (which is a string), so again the ASN.1 type should be recorded in
 the comment or it will be lost.

4.2.3 Enumerated

 SLP templates support the concept of enumerations through the listing
 of allowed values in the attribute definition.  These enumerations
 are not strictly binding on clients or DAs, but they are similar to
 the ASN.1 definition of enumerations. BER encodes the ASN.1
 enumeration by passing the number of the element's position in the
 enumeration.  This requires both sides to have knowledge of the
 specific enumeration prior to decoding an enumeration's value. SLP
 provides no specific support for transmitting enumerations. They are
 simply String types. Information on the ASN.1 type and ASN.1 encoding
 of the enumeration values is recorded in the comment.
 Example:
 color-supported = STRING   M
 none
 # ASN.1: Enumeration.
 # ASN.1 Mapping: none = 0, highlight = 1, three color = 2,
 #   four color = 4, monochromatic = 5
 #This attribute specifies whether the Printer supports
 # color and, if so, what type.
 none,highlight,three color,four color,monochromatic

Kempf, et al. Informational [Page 18] RFC 2926 Conversion of LDAP Schemas September 2000

4.2.4 Object Identifier

 Object identifiers(OIDs) are commonly used in the ASN.1 world to
 identify object and attributes.  OIDs are a numerical representation
 of an element's place in the naming hierarchy. Each element at a
 particular level of a hierarchy has a unique number assigned within
 that level of the hierarchy. A sample OID would be the naming tree
 for SNMP MIBs:  iso(1) org(3) dod(6) internet(1) mgmt(2) mib(1) would
 be written as the string "1.3.6.1.2.1".
 Because this representation reduces down to a string of dot separated
 numbers, this maps easily to the SLP String type.  The help text for
 this element should indicate it is an ASN.1 OID
    identifier = STRING
    # ASN.1: OID
    # The object identifier for this SNMP agent.

4.2.5 Octet String

 An ASN.1 octet string should be mapped to an Opaque in an SLP
 template.  An octet string is a sequence of bytes, whereas an Opaque
 is a a string that encodes a sequence of bytes. Again, the ASN.1 type
 is lost unless recorded in the comment.

4.2.6 Real

 There is no direct mapping between floating point numbers and any SLP
 data types.  Attributes having the ASN.1 type of Real are mapped to
 SLP type String.  Comments are added to the attribute help text
 indicating the value was originally an ASN.1 real.  For example:
    weight = STRING
    # ASN.1: Real
    # The objects weight in pounds.

4.3 Example ASN.1 Schema

 The following is an example schema for an exported filesystem.  The
 section presents it as in ASN.1 and the following section shows the
 SLP template translation. The template translation does not capture
 the actual attribute format for the Set type, that would be done in
 the LDAP client software making the translation. Note that even
 though the class definition does not conform with the previously
 defined conventions for SLP classes, the schema can still be
 translated into an SLP template.  The syntax used in this example
 follows

Kempf, et al. Informational [Page 19] RFC 2926 Conversion of LDAP Schemas September 2000

  1. - Abstraction of a fstab entry (a "mount").
  2. - These lookups would likely be performed by an
  3. - an automounter type application.

mount OBJECT-CLASS ::= {

               SUBCLASS OF { top }
               MUST CONTAIN { mountHost |
                              mountDirectory |
                              mountType
                            }
               MAY CONTAIN { mountOption |
                             mountDumpFrequency |
                             mountPassNo
                           }
               ID { <oid1> }
       }
  1. The mount host.

mountHost ATTRIBUTE ::= {

                       WITH SYNTAX caseIgnoreString
                       EQUALITY MATCHING RULE caseIgnoreMatch
                       SINGLE VALUE
                       ID { <oid2> }
       }
  1. The file system to mount.

mountDirectory ATTRIBUTE ::= {

                       WITH SYNTAX caseIgnoreString
                       EQUALITY MATCHING RULE caseIgnoreMatch
                       SINGLE VALUE
                       ID { <oid3> }
       }
  1. The type of file system being mounted.

mountType ATTRIBUTE ::= {

                       WITH SYNTAX INTEGER { ufs(1),
                                             hsfs(2),
                                             nfs(3),
                                             rfs(4)
                                           }
                       EQUALITY MATCHING RULE integerMatch
                       SINGLE VALUE
                       ID { <oid4> }
       }

Kempf, et al. Informational [Page 20] RFC 2926 Conversion of LDAP Schemas September 2000

  1. Options for the mount operation.

mountOption ATTRIBUTE ::= {

                       WITH SYNTAX caseIgnoreString
                       EQUALITY MATCHING RULE caseIgnoreString
                       ID { <oid5> }
       }
  1. How often to dump the file system.

mountDumpFrequency ATTRIBUTE :: = {

                               WITH SYNTAX  INTEGER (0..9)
                               EQUALITY MATCHING RULE integerMatch
                               SINGLE VALUE
                               ID { <oid6> }
       }
  1. Boot time mount pass number.

mountPassNo ATTRIBUTE ::= {

                       WITH SYNTAX INTEGER
                       EQUALITY MATCHING RULE integerMatch
                       SINGLE VALUE
                       ID { <oid7> }
       }
 The translated SLP template is:
    template-type = mount
    template-version = 1.0
    template-description = "Describes a remote filesystem access
    protocol"
    template-url-syntax =
                 filesystem   = 1*[ DIGIT / ALPHA ]
                 urlpath = "/" filesystem
    mountHost = STRING L
    # ASN.1: Case Ignore String, Single Value
    # The mount host
    mountDirectory = STRING L
    # ASN.1: Case Ignore String, Single Value
    # The filesystem to mount

Kempf, et al. Informational [Page 21] RFC 2926 Conversion of LDAP Schemas September 2000

    mountType = STRING L
    ufs
    # ASN.1: Enumeration, Single Value
    # ASN.1 Mapping: ufs = 1, hsfs = 2, nfs = 3, rfs = 4
    # The type of the filesystem being mounted
    ufs, hsfs, nfs, rfs
    mountOption = STRING M O L
    # ASN.1: Case Ignore String
    # mount options for this filesystem
    mountDumpFrequency = INTEGER O
    0
    # ASN.1: Integer Range, Single Value
    # How often to dump this filesystem
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9
    mountPassNo = INTEGER O
    # ASN.1: Integer, Single Value
    # Boot time mount pass number

5.0 Representing SLP Service Advertisements in an LDAP DIT

 In addition to translating between SLP templates and LDAP schema,
 another area requiring compatibility is the representation of SLP
 service advertisements in an LDAP DIT. A standardized representation
 for service information allows SLP DAs to store service
 advertisements in LDAP, and for LDAP clients to query the DIT for
 those services.  Similarly, if LDAP clients represent service
 information in the same form, SLP clients can benefit from
 interoperability.
 A service advertisement contains the service URL in a 'labeledURI'
 attribute [11]. The labeledURI attribute in a service advertisement
 should only contain the service URL for the service, with no
 additional label. It is recommended that the labeledURI be used as
 the RDN for the service object in the DIT.
 Although service advertisements can appear anywhere within the DIT,
 it is recommended that all services be stored under a single common
 point, or root node, to facilitate searching in a domain. This allows
 a  client to search for all of advertisements of a particular service
 type, say, for all printers.  The recommended parent entry is one
 named "ou=service" below the entry which is the representation of the
 domain, as described in RFC 2247.

Kempf, et al. Informational [Page 22] RFC 2926 Conversion of LDAP Schemas September 2000

 For example, a printer service with labeledURI of
 "service:lpr://printsrv/queue1" in the domain foobar.com advertised
 in the LDAP server that holds the entry "dc=foobar,dc=com" tree has
 the following DN:
 "labeledURI=service:lpr://printsrv/queue1, ou=service, dc=foobar,
 dc=com"
 While this leads to a flat space of service storage, since SLP uses
 search filters from LDAP for searches, these filters can be used for
 one-level searches from the root node.
 The following example illustrates how an advertisement having a
 simple service type is represented. The advertisement (in conceptual
 form) for a printer is:
    Service Type: service:lpr://printsrv/queue1
    Scopes: eng,corp
    Attributes:
      description = A general printer for all to use.
      security-mechanisms-supported = none
    Authentication: none
 The RDN of the object is labeledURI=service:lpr://printsrv/queue1,
 and the following LDAP search filter will return this object, along
 with any others of the service type "service:lpr" that match the
 other attributes:
    (&(service-advert-service-type=service:lpr)
      (service-advert-scopes=eng)
      (service-advert-scopes=corp)
      (description=A general printer for all to use.)
      (security-mechanisms-supported=none))
 Service advertisements in SLP also have a lease time associated with
 them. In LDAP servers that support the extensions for dynamic
 directory services [12], the service advertisement entry objectClass
 should be extended with the dynamicObject class. This allows the
 service advertisement to time out within the LDAP directory server.
 If the LDAP directory server does not support the dynamic directory
 services extension, then advertisement lease timeouts must be handled
 by the SLP agent.
 While the service advertisement schema outlined in this section is
 primarily for SLP DAs that use LDAP as a backing store, if LDAP
 agents register services using the same format, complete
 interoperability with SLP is achieved.

Kempf, et al. Informational [Page 23] RFC 2926 Conversion of LDAP Schemas September 2000

6.0 Internationalization Considerations

 SLP specifies that an RFC 1766 [13] language code accompanies every
 service advertisement. Language codes for service advertisements in
 LDAP must be represented according to RFC 2596 [14].
 RFC 2596 prohibits language codes in DNs, and specifies that a
 directory server which does not support language codes must treat an
 attribute with a language code as an unrecognized attributes.
 According to RFC 2596, language codes are appended to attribute names
 with a semicolon (";"). For example, the following attribute/value
 pair is in the German locale:
    (address;lang-de=44 Bahnhofstrasse, 2365 Weibstadt, Deutschland)
 An attribute with a language tag in a specific locale is considered a
 separate attribute from attributes in other locales.
 If the service advertisement is in the default SLP locale ("en", no
 dialect), then the language code need not be appended to the
 attribute name.
 SLP queries in locales other than the default need not be rewritten
 to include language tags before being submitted to the directory
 server.  RFC 2596 specifies that all entries that match are returned,
 including those with language tags, without requiring the language
 tags to be explicitly present in the query. The SLP DA can then
 postprocess the result to select the entries from the required
 locale.

7.0 Security Considerations

 SLP authenticators are stored with the service advertisement in the
 DIT, as discussed in Section~7ef{slpdit}. LDAP clients need to use
 LDAP authentication [15] to assure that they are connecting with a
 secure server. In particular, SLP DAs that use LDAP as a back end
 store and that implement SLP authentication MUST use LDAP
 authentication to assure that the LDAP entries for their service
 registrations are secure.

Acknowledgements

 Many thanks are due to Mark Wahl whose detailed and insightful
 comments were instrumental in helping improve the technical accuracy
 of this document with respect to LDAP.

Kempf, et al. Informational [Page 24] RFC 2926 Conversion of LDAP Schemas September 2000

8.0 References

 [1]  Guttman, E., Perkins, C. and J. Kempf, "Service Templates and
      service: Schemes", RFC 2609, April 1999.
 [2]  Wahl, W., Howes, T. and S. Kille, "Lightweight Directory Access
      Protocol (v3)", RFC 2251, December 1997.
 [3]  International Telecommunications Union. The Directory:Selected
      Attribute Types.  ITU Recommendation X.520. August, 1997.
 [4]  McLaughlin, L., "Line Printer Daemon Protocol, RFC 1179, August
      1990.
 [5]  Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service
      Location Protocol Version 2", RFC 2608, April 1999.
 [6]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, November 1997.
 [7]  Howes, T., "The String Representation of LDAP Search Filters",
      RFC 2254, December 1997.
 [8]  Wahl, W., Coulbeck, A., Howe, T. and S. Kille, "Lightweight
      Directory Access Protocol (v3): Attribute Syntax Definition",
      RFC 2252, December 1997.
 [9]  ITU-T Rec. X.680. Abstract Syntax Notation One (ASN.1) -
      Specification of Basic Notation. 1994.
 [10] Fleming, P., Jones, K., Lewis, H., and McDonald, I., "Internet
      Printing Protocol (IPP): LDAP Schema for Printer Services", Work
      in Progress.
 [11] Smith, M., "Definition of an X.500 Attribute Type and an Object
      Class to Hold Uniform Resource Identifiers (URIs)", RFC 2079,
      January 1997.
 [12] Yaacovi, Y., Wahl, M. and T. Genovese, "Lightweight Directory
      Access Protocol (v3): Extensions for Dynamic Directory
      Services", RFC 2589, May 1999.
 [13] Alvestrand, H., "Tags for the Identification of Languages", RFC
      1766, December 1997.
 [14] Wahl, M. and T. Howes, "Use of Language Codes in LDAP", RFC
      2596, May 1999.

Kempf, et al. Informational [Page 25] RFC 2926 Conversion of LDAP Schemas September 2000

 [15] Wahl, M., Alvestrand, H., Hodges, J. and R. Morgan,
      "Authentication Methods for LDAP", RFC 2829, May 2000.
 [16] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [17] Dubuisson, O. ASN.1: Communication between Heterogeneous
      Systems. OSS Nokalva, 2000.
 [18] http://www.srvloc.org

9.0 Authors' Addresses

 James Kempf
 Sun Microsystems
 901 San Antonio Avenue
 Palo Alto, CA 94303
 USA
 Phone: +1 650 786-5890
 EMail: james.kempf@sun.com
 Ryan Moats
 Coreon, Inc.
 15621 Drexel Circle
 Omaha, NE, 68135
 USA
 EMail: rmoats@coreon.net
 Pete St. Pierre
 Sun Microsystems
 901 San Antonio Avenue
 Palo Alto, CA 94303
 USA
 Phone: +1 415 786-5790
 EMail: Pete.StPierre@Eng.Sun.COM

Kempf, et al. Informational [Page 26] RFC 2926 Conversion of LDAP Schemas September 2000

10. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Kempf, et al. Informational [Page 27]

/data/webs/external/dokuwiki/data/pages/rfc/rfc2926.txt · Last modified: 2000/09/14 16:08 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki