Elep

Network Working Group                                          L. Howard
Internet-Draft                                             PADL Software
Obsoletes: 2307 (if approved)                                H. Chu, Ed.
Intended status: Informational                               Symas Corp.
Expires: February 10, 2010                                August 9, 2009

An Approach for Using LDAP as a Network Information Service
                     draft-howard-rfc2307bis-02.txt

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Abstract

This document describes a mechanism for mapping entities related to
   TCP/IP and the UNIX system [UNIX] into [X.500] entries so that they
   may be resolved with the Lightweight Directory Access Protocol
   [RFC4511].  A set of attribute types and object classes are proposed,
   along with specific guidelines for interpreting them.  The intention
   is to assist the deployment of LDAP as an organizational nameservice.
   No proposed solutions are intended as standards for the Internet.
   Rather, it is hoped that a general consensus will emerge as to the
   appropriate solution to such problems, leading eventually to the
   adoption of standards.  The proposed mechanism has already been
   implemented with some success.

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1.  Background and Motivation

The UNIX (R) operating system, and its derivatives (specifically,
   those which support TCP/IP and conform to the X/Open Single UNIX
   specification [UNIX]) require a means of looking up entities, by
   matching them against search criteria or by enumeration.  (Other
   operating systems that support TCP/IP may provide some means of
   resolving some of these entities.  This schema is applicable to those
   environments also.)

These entities include users, groups, IP services (which map names to
   IP ports and protocols, and vice versa), IP protocols (which map
   names to IP protocol numbers and vice versa), RPCs (which map names
   to ONC Remote Procedure Call [RFC1057] numbers and vice versa), NIS
   netgroups, booting information (boot parameters and MAC address
   mappings), filesystem mounts, IP hosts and networks.

Resolution requests are made through a set of C functions, provided
   in the UNIX system's C library.  For example, the UNIX system utility
   "ls", which enumerates the contents of a filesystem directory, uses
   the C library function getpwuid() in order to map user IDs to login
   names.  Once the request is made, it is resolved using a
   "nameservice" which is supported by the client library.  The
   nameservice may be, at its simplest, a collection of files in the
   local filesystem which are opened and searched by the C library.
   Other common nameservices include the Network Information Service
   (NIS) and the Domain Name System (DNS) [RFC1034].  (The latter is
   typically used for resolving hosts, services and networks.)  Both
   these nameservices have the advantage of being distributed and thus
   permitting a common set of entities to be shared amongst many
   clients.

LDAP is a distributed, hierarchical directory service access protocol
   which is used to access repositories of users and other network-
   related entities.  Because LDAP is often not tightly integrated with
   the host operating system, information such as users may need to be
   kept both in LDAP and in an operating system supported nameservice
   such as NIS.  By using LDAP as the primary means of resolving these
   entities, these redundancy issues are minimized and the scalability
   of LDAP can be exploited.  (By comparison, NIS services based on flat
   files do not have the scalability or extensibility of LDAP or X.500.)

The object classes and attributes defined below are suitable for
   representing the aforementioned entities in a form compatible with
   LDAP and X.500 directory services.

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2.  General Issues

2.1.  Terminology

The key words "MUST", "SHOULD", and "MAY" used in this document are
   to be interpreted as described in [RFC2119].

For the purposes of this document, the term "nameservice" refers to a
   service, such as NIS or flat files, that is used by the operating
   system to resolve entities within a single, local naming context.
   Contrast this with a "directory service" such as LDAP, which supports
   extensible schema and multiple naming contexts.

The term "NIS-related entities" broadly refers to entities which are
   typically resolved using the Network Information Service.  (NIS was
   previously known as YP.)  Deploying LDAP for resolving these entities
   does not imply that NIS be used, as a gateway or otherwise.  In
   particular, the host and network classes are generically applicable,
   and may be implemented on any system that wishes to use LDAP or X.500
   for host and network resolution.

The "DUA" (directory user agent) refers to the LDAP client querying
   these entities, such as an LDAP to NIS gateway or the C library.  The
   "client" refers to the application which ultimately makes use of the
   information returned by the resolution.  It is irrelevant whether the
   DUA and the client reside within the same address space.  The act of
   the DUA making this information to the client is termed
   "republishing".

To avoid confusion, the term "login name" refers to the user's login
   name (being the value of the uid attribute) and the term "user ID"
   refers to the user's integer identification number (being the value
   of the uidNumber attribute).

The phrases "resolving an entity" and "resolution of entities" refer
   respectively to enumerating NIS-related entities of a given type, and
   matching them against a given search criterion.  One or more entities
   are returned as a result of successful "resolutions" (a "match"
   operation will only return one entity).

The use of the term UNIX does not confer upon this schema the
   endorsement of owners of the UNIX trademark.  Where necessary, the
   term "TCP/IP entity" is used to refer to protocols, services, hosts,
   and networks, and the term "UNIX entity" to its complement.  (The
   former category does not mandate the host operating system supporting
   the interfaces required for resolving UNIX entities.)

The OIDs defined below are derived from iso(1) org(3) dod(6)

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internet(1) directory(1) nisSchema(1)

2.2.  Schema

The attributes and classes defined in this document are summarized
   below.

2.2.1.  Attributes

The following attributes are defined in this document:

uidNumber
      gidNumber
      gecos
      homeDirectory
      loginShell
      shadowLastChange
      shadowMin
      shadowMax
      shadowWarning
      shadowInactive
      shadowExpire
      shadowFlag
      memberUid
      memberNisNetgroup
      nisNetgroupTriple
      ipServicePort
      ipServiceProtocol
      ipProtocolNumber
      oncRpcNumber
      ipHostNumber
      ipNetworkNumber
      ipNetmaskNumber
      macAddress
      bootParameter
      bootFile
      nisMapName
      nisMapEntry
      nisPublicKey
      nisSecretKey
      nisDomain
      automountMapName
      automountKey
      automountInformation

Additionally, some of the attributes defined in [RFC4519] and
   [RFC3112] are required.

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2.2.2.  Attribute Option

Centralizing a name service in LDAP allows heterogeneous systems to
   obtain their information from a single place.  However in some cases,
   this information cannot be used uniformly on all of the client
   systems.  These attribute options are defined to allow system-
   specific values to be used where necessary.  The options are defined
   as the following:

host-<hostname>
      hostos-<ostype>

where hostname is a string representing the name of a specific
   machine, and ostype is a string representing a particular operating
   system.

For example, a user named "Babs Jensen" may have a different home
   directory on different machines.  This could be represented as:

homeDirectory: /home/babsj
      homeDirectory;hostos-sunos: /export/home/bjensen
      homeDirectory;host-babshost: /home/root

These attribute options follow sub-typing semantics.  If a DUA
   requests an attribute to be returned in a search operation, and does
   not specify an option, all subtypes of that attribute are returned.

2.2.3.  Object Classes

The following object classes are defined in this document:

posixAccount
      shadowAccount
      posixGroup
      ipService
      ipProtocol
      oncRpc
      ipHost
      ipNetwork
      nisNetgroup
      nisMap
      nisObject
      ieee802Device
      bootableDevice
      nisKeyObject
      nisDomainObject
      automountMap
      automount

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Additionally, some of the attributes defined in [RFC4519] are
   required.

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3.  Attribute Definitions

This section contains attribute definitions to be implemented by DUAs
   supporting this schema:

( 1.3.6.1.1.1.1.0 NAME 'uidNumber'
         DESC 'An integer uniquely identifying a user in an
               administrative domain'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.1 NAME 'gidNumber'
         DESC 'An integer uniquely identifying a group in an
               administrative domain'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.2 NAME 'gecos'
         DESC 'The GECOS field; the common name'
         EQUALITY caseIgnoreMatch
         SUBSTRINGS caseIgnoreSubstringsMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.3 NAME 'homeDirectory'
         DESC 'The absolute path to the home directory'
         EQUALITY caseExactIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.4 NAME 'loginShell'
         DESC 'The path to the login shell'
         EQUALITY caseExactIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
         SINGLE-VALUE )

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( 1.3.6.1.1.1.1.5 NAME 'shadowLastChange'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.6 NAME 'shadowMin'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.7 NAME 'shadowMax'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.8 NAME 'shadowWarning'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.9 NAME 'shadowInactive'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.10 NAME 'shadowExpire'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.11 NAME 'shadowFlag'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

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( 1.3.6.1.1.1.1.12 NAME 'memberUid'
         EQUALITY caseExactMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )

( 1.3.6.1.1.1.1.13 NAME 'memberNisNetgroup'
         EQUALITY caseExactMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )

( 1.3.6.1.1.1.1.14 NAME 'nisNetgroupTriple'
         DESC 'Netgroup triple'
         EQUALITY caseIgnoreMatch
         SUBSTRINGS caseIgnoreSubstringsMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )

( 1.3.6.1.1.1.1.15 NAME 'ipServicePort'
         DESC 'Service port number'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.16 NAME 'ipServiceProtocol'
         DESC 'Service protocol name'
         EQUALITY caseIgnoreMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )

( 1.3.6.1.1.1.1.17 NAME 'ipProtocolNumber'
         DESC 'IP protocol number'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.18 NAME 'oncRpcNumber'
         DESC 'ONC RPC number'
         EQUALITY integerMatch
         ORDERING integerOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

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( 1.3.6.1.1.1.1.19 NAME 'ipHostNumber'
         DESC 'IPv4 addresses as a dotted decimal omitting leading
               zeros or IPv6 addresses as defined in RFC2373'
         EQUALITY caseIgnoreIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

( 1.3.6.1.1.1.1.20 NAME 'ipNetworkNumber'
         DESC 'IP network omitting leading zeros, eg. 192.168'
         EQUALITY caseIgnoreIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.21 NAME 'ipNetmaskNumber'
         DESC 'IP netmask omitting leading zeros, eg. 255.255.255.0'
         EQUALITY caseIgnoreIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.22 NAME 'macAddress'
         DESC 'MAC address in maximal, colon separated hex
               notation, eg. 00:00:92:90:ee:e2'
         EQUALITY caseIgnoreIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

( 1.3.6.1.1.1.1.23 NAME 'bootParameter'
         DESC 'rpc.bootparamd parameter'
         EQUALITY caseExactIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

( 1.3.6.1.1.1.1.24 NAME 'bootFile'
         DESC 'Boot image name'
         EQUALITY caseExactIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

( 1.3.6.1.1.1.1.26 NAME 'nisMapName'
         DESC 'Name of a generic NIS map'
         EQUALITY caseIgnoreMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{64} )

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( 1.3.6.1.1.1.1.27 NAME 'nisMapEntry'
         DESC 'A generic NIS entry'
         EQUALITY caseExactMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{1024}
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.28 NAME 'nisPublicKey'
         DESC 'NIS public key'
         EQUALITY octetStringMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.29 NAME 'nisSecretKey'
         DESC 'NIS secret key'
         EQUALITY octetStringMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.30 NAME 'nisDomain'
         DESC 'NIS domain'
         EQUALITY caseIgnoreIA5Match
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{256} )

( 1.3.6.1.1.1.1.31 NAME 'automountMapName'
         DESC 'automount Map Name'
         EQUALITY caseExactMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.32 NAME 'automountKey'
         DESC 'Automount Key value'
         EQUALITY caseExactMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
         SINGLE-VALUE )

( 1.3.6.1.1.1.1.33 NAME 'automountInformation'
         DESC 'Automount information'
         EQUALITY caseExactMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
         SINGLE-VALUE )

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4.  Class Definitions

This section contains class definitions to be implemented by DUAs
   supporting the schema.

Various schema for mail routing and delivery using LDAP directories
   have been proposed, and as such this document does not consider
   schema for representing mail aliases or distribution lists.

( 1.3.6.1.1.1.2.0 NAME 'posixAccount' SUP top AUXILIARY
         DESC 'Abstraction of an account with POSIX attributes'
         MUST ( cn $ uid $ uidNumber $ gidNumber $ homeDirectory )
         MAY ( authPassword $ userPassword $ loginShell $ gecos $
               description ) )

( 1.3.6.1.1.1.2.1 NAME 'shadowAccount' SUP top AUXILIARY
         DESC 'Additional attributes for shadow passwords'
         MUST uid
         MAY ( authPassword $ userPassword $ description $
               shadowLastChange $ shadowMin $ shadowMax $
               shadowWarning $ shadowInactive $
               shadowExpire $ shadowFlag ) )

( 1.3.6.1.1.1.2.2 NAME 'posixGroup' SUP top AUXILIARY
         DESC 'Abstraction of a group of accounts'
         MUST gidNumber
         MAY ( authPassword $ userPassword $ memberUid $
               description ) )

( 1.3.6.1.1.1.2.3 NAME 'ipService' SUP top STRUCTURAL
         DESC 'Abstraction an Internet Protocol service.
               Maps an IP port and protocol (such as tcp or udp)
               to one or more names; the distinguished value of
               the cn attribute denotes the service's canonical
               name'
         MUST ( cn $ ipServicePort $ ipServiceProtocol )
         MAY description )

( 1.3.6.1.1.1.2.4 NAME 'ipProtocol' SUP top STRUCTURAL
         DESC 'Abstraction of an IP protocol. Maps a protocol number
               to one or more names. The distinguished value of the cn
               attribute denotes the protocol canonical name'
         MUST ( cn $ ipProtocolNumber )
         MAY description )

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( 1.3.6.1.1.1.2.5 NAME 'oncRpc' SUP top STRUCTURAL
         DESC 'Abstraction of an Open Network Computing (ONC)
              [RFC1057] Remote Procedure Call (RPC) binding.
              This class maps an ONC RPC number to a name.
              The distinguished value of the cn attribute denotes
              the RPC service canonical name'
         MUST ( cn $ oncRpcNumber )
         MAY description )

( 1.3.6.1.1.1.2.6 NAME 'ipHost' SUP top AUXILIARY
         DESC 'Abstraction of a host, an IP device. The distinguished
               value of the cn attribute denotes the host's canonical
            name. Device SHOULD be used as a structural class'
         MUST ( cn $ ipHostNumber )
         MAY ( authPassword $ userPassword $ l $ description $
               manager ) )

( 1.3.6.1.1.1.2.7 NAME 'ipNetwork' SUP top STRUCTURAL
         DESC 'Abstraction of a network. The distinguished value of
               the cn attribute denotes the network canonical name'
         MUST ipNetworkNumber
         MAY ( cn $ ipNetmaskNumber $ l $ description $ manager ) )

( 1.3.6.1.1.1.2.8 NAME 'nisNetgroup' SUP top STRUCTURAL
         DESC 'Abstraction of a netgroup. May refer to other
               netgroups'
         MUST cn
         MAY ( nisNetgroupTriple $ memberNisNetgroup $ description ) )

( 1.3.6.1.1.1.2.9 NAME 'nisMap' SUP top STRUCTURAL
         DESC 'A generic abstraction of a NIS map'
         MUST nisMapName
         MAY description )

( 1.3.6.1.1.1.2.10 NAME 'nisObject' SUP top STRUCTURAL
         DESC 'An entry in a NIS map'
         MUST ( cn $ nisMapEntry $ nisMapName )

( 1.3.6.1.1.1.2.11 NAME 'ieee802Device' SUP top AUXILIARY
         DESC 'A device with a MAC address; device SHOULD be
               used as a structural class'
         MAY macAddress )

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( 1.3.6.1.1.1.2.12 NAME 'bootableDevice' SUP top AUXILIARY
         DESC 'A device with boot parameters; device SHOULD be
               used as a structural class'
         MAY ( bootFile $ bootParameter ) )

( 1.3.6.1.1.1.2.14 NAME 'nisKeyObject' SUP top AUXILIARY
         DESC 'An object with a public and secret key'
         MUST ( cn $ nisPublicKey $ nisSecretKey )
         MAY ( uidNumber $ description ) )

( 1.3.6.1.1.1.2.15 NAME 'nisDomainObject' SUP top AUXILIARY
         DESC 'Associates a NIS domain with a naming context'
         MUST nisDomain )

( 1.3.6.1.1.1.2.16 NAME 'automountMap' SUP top STRUCTURAL
         MUST ( automountMapName )
         MAY description )

( 1.3.6.1.1.1.2.17 NAME 'automount' SUP top STRUCTURAL
         DESC 'Automount information'
         MUST ( automountKey $ automountInformation )
         MAY description )

( 1.3.6.1.1.1.2.18 NAME 'groupOfMembers' SUP top STRUCTURAL
         DESC 'A group with members (DNs)'
         MUST cn
         MAY ( businessCategory $ seeAlso $ owner $ ou $ o $
               description $ member ) )

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5.  Implementation Details

5.1.  Suggested Resolution Methods

The preferred means of directing a client application (one using the
   shared services of the C library) to use LDAP as its information
   source for the functions listed in Appendix B is to modify the source
   code to directly query LDAP.  As the source to commercial C libraries
   and applications is rarely available to the end-user, one could
   emulate a supported nameservice (such as NIS).  (This is also an
   appropriate opportunity to perform caching of entries across process
   address spaces.)  In the case of NIS, reference implementations are
   widely available and the RPC interface is well known.

The means by which the operating system is directed to use LDAP is
   implementation dependent.  For example, some operating systems and C
   libraries support end-user extensible resolvers using dynamically
   loadable libraries and a nameservice "switch" (NSS).  The means in
   which the DUA locates LDAP servers is also implementation dependent.

5.2.  Interpreting User and Group Entries

User and group resolution is initiated by the functions prefixed by
   getpw and getgr respectively.  The uid attribute contains the user's
   login name.  The cn attribute, in posixGroup entries, contains the
   group's name.  This document preserves the use of the uid attribute
   even though, being a naming attribute, its syntax is case
   insensitive.  This may cause a problem with existing deployments
   where there exist login names differing only in case.  If DUAs
   support attribute mapping, a different attribute MAY be used to
   represent users' login names.

The account object class provides a convenient structural class for
   posixAccount, and SHOULD be used where additional attributes are not
   required.  Likewise, the groupOfMembers object class SHOULD be used
   for groups.  (The groupOfUniqueNames object class is deprecated and
   SHOULD NOT be used.)

It is suggested that uid and cn are used as the naming attribute for
   posixAccount and posixGroup entries, respectively.  Group members may
   either be login names (values of memberUid) or distinguished names
   (values of member).  In the latter case, the distinguished name must
   be mapped to one or more login names by examining the name's RDN or,
   if it is not distinguished by uid, performing a base search on the DN
   with a filter of "(objectclass=*)".  DUAs MAY wish to cache DN to
   login name mappings.  The DUA MAY traverse nested groups.

An account's GECOS field is preferably determined by a value of the

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gecos attribute.  If no gecos attribute exists, the value of the cn
   attribute MUST be used.  (The existence of the gecos attribute allows
   information embedded in the GECOS field, such as a user's telephone
   number, to be returned to the client without overloading the cn
   attribute.  It also accommodates directories where the common name
   does not contain the user's full name.)

5.2.1.  Using Attribute Options

Some posixAccount attributes may be accompanied by options
   (Section 2.2.2) identifying particular hosts or operating system
   types.  The attribute with a hostos option matching the operating
   system of the DUA SHOULD be used in preference to an attribute
   without any associated options.  The attribute with a host option
   matching the hostname of the DUA SHOULD be used in preference to any
   other attribute.

5.2.2.  Authentication Considerations

5.2.2.1.  Using Password Values

When authenticating using a NIS to LDAP gateway or using NSS, a
   lookup is performed to retrieve the password attribute and the value
   is used in the DUA to authenticate a user.  This approach to
   authentication is deprecated, as it requires that read access to the
   password attribute be granted across a network.

An entry of class posixAccount, posixGroup, or shadowAccount without
   an authPassword or userPassword attribute MUST NOT be used for
   authentication.  In this case the client SHOULD be returned a non-
   matchable password such as "x".

If userPassword is used, its values MUST be represented by the
   following syntax:

passwordvalue   = schemeprefix hashedpasswd
       schemeprefix    = "{" scheme "}"
       scheme          = "crypt" / "md5" / "sha" / "ssha" / altscheme
       altscheme       = "x-" keystring
       hashedpasswd    = hashed password

The hashed password contains a plaintext key hashed using the
   algorithm scheme.  If the schema is "sha", the hashed password is the
   base64 encoding of the SHA-1 digest of the plaintext password.

userPassword values which do not adhere to this syntax MUST NOT be
   used for authentication.  The DUA MUST iterate through the values of
   the attribute until a value matching the above syntax is found.  Only

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if hashedpassword is an empty string does the user have no password.
   DUAs are not required to consider hashing schemes which the client
   will not recognize; in most cases, it may be sufficient to consider
   only "crypt".

DUA MAY use the authPassword attribute instead of userPassword,
   defined in [RFC3112].  The DUA MUST iterate the values of the
   authPassword attribute until a value whose scheme is CRYPT is found.
   The DUA MAY iterate through the values of the userPassword attribute,
   using the syntax defined here, until a value whose scheme is CRYPT is
   found.  If no conforming value is found, the client MUST be returned
   a non-matchable password such as "x".  Authentication using schemes
   other than CRYPT is, although advisable, beyond the scope of this
   document

Below is an example of an authPassword attribute:

authPassword: CRYPT$X5/DBrWPOQQaI

Below is an example of a (deprecated) userPassword attribute:

userPassword: {CRYPT}X5/DBrWPOQQaI

A DUA MAY utilize the attributes in the shadowAccount class to
   provide shadow password service (getspnam() and getspent()).  In such
   cases, the DUA MUST NOT make use of the userPassword attribute for
   getpwnam() et al, and MUST return a non-matchable password (such as
   "x") to the client instead.

5.2.2.2.  Using LDAP Bind

The preferred method for authenticating users with LDAP is to perform
   an LDAP Bind operation with the user's name and password.  In this
   case the method the DSA uses to store and verify the password is
   completely internal to the DSA and not of any concern to the DUA.

Likewise, using the shadowAccount attributes requires the DUA to
   handle password policy enforcement.  However the policies expressed
   in the shadowAccount are limited in scope, and not uniformly
   applicable to all the systems that will be using LDAP.

The preferred method is to leave password policy enforcement to the
   DSA, so that it will be uniformly enforced across all of the various
   systems that rely on the directory.  This enforcement occurs
   implicitly when authenticating using LDAP Bind if the DSA supports
   the LDAP password policy [I-D.behera-ldap-password-policy]
   mechanisms.

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The means in which authentication in the DUA is configured is
   implementation dependent.  Typically it is accomplished using [PAM].
   Further details of authentication are beyond the scope of this
   document.

5.2.3.  Naming Considerations

On UNIX systems, users and groups reside in separate name spaces and
   it is common for the same name to be used by both a user and a group.
   Since they are in separate name spaces there is no ambiguity and no
   conflict.  However, when integrating a name service into LDAP the
   directory may be used with other systems besides UNIX and its
   derivatives.  In particular, the Microsoft Windows operating system
   may also use LDAP for its own name service.  In Windows, users and
   groups reside in a single name space and so one cannot use the same
   name for both a user and a group.

Conflicts in naming conventions may arise in other deployments as
   well, and should be carefully taken into account when migrating from
   other naming services into LDAP.

5.3.  Interpreting Hosts and Networks

The ipHostNumber and ipNetworkNumber attributes are defined in
   preference to dNSRecord (defined in [RFC1279]), in order to simplify
   the DUA's role in interpreting entries in the directory.  A dNSRecord
   expresses a complete resource record, including time to live and
   class data, which is extraneous to this schema.

Additionally, the ipHost and ipNetwork classes permit a host or
   network (respectively) and all its aliases to be represented by a
   single entry in the directory.  This is not necessarily possible if a
   DNS resource record is mapped directly to an LDAP entry.
   Implementations that wish to use LDAP to master DNS zone information
   are not precluded from doing so, and may simply avoid the ipHost and
   ipNetwork classes.

This document redefines, although not exclusively, the ipNetwork
   class defined in [RFC1279], in order to achieve consistent naming
   with ipHost.  The ipNetworkNumber attribute is also used in the
   siteContact object class [ROSE].

The authPassword and userPassword attributes are included in ipHost
   such that hosts MAY be treated as authentication principals.  The
   treatment of these attributes and inherent caveats considered in
   Section 5.2 apply here also.

The trailing zeros in a network address MUST be omitted.  CIDR-style

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network addresses (eg. 192.168.1/24) MAY be used.  Leading zeros MUST
   be removed from all components of an IPv6 address string as defined
   by [RFC2373], section 2.2, item 1.  The IPv6 address string MUST be
   further normalized by following the "::" syntax as defined in
   [RFC2373], section 2.2, item 2.  In addition, "::" MUST be used to
   replace the longest string of zero bits.  If there are two or more
   longest strings of zero bits, then the first string MUST be replaced.
   In addition, the syntax defined by [RFC2373], section 2.2, item 3
   MUST NOT be used.  IPv4 addresses MUST be represented by the IPv4
   dotted decimal string syntax.

For example the following address:

1080:0000:0:0:08:800:200C:417A
       FF01:0:0:0:0:0:01
       0:0:0:0:0:0:0:0001
       0:0:0:0:0:0:0:0

MUST be normalized as:

1080::8:800:200C:417A
       FF01::101
       0::1
       ::

5.4.  Interpreting Other Entities

In general, a one-to-one mapping between entities and LDAP entries is
   proposed, in that each entity has exactly one representation in the
   DIT.  In some cases this is not feasible; for example, a service
   which is represented in more than one protocol domain.  Consider the
   following entry:

dn: cn=domain,ou=services,dc=aja,dc=com
       objectClass: top
       objectClass: ipService
       cn: domain
       cn: nameserver
       ipServicePort: 53
       ipServiceProtocol: tcp
       ipServiceProtocol: udp

This entry MUST map to the following two (2) services entities:

domain  53/tcp  nameserver
       domain  53/udp  nameserver

While the above two entities may be represented as separate LDAP

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entities, with different distinguished names (such as cn=domain+
   ipServiceProtocol=tcp, ... and cn=domain+ipServiceProtocol=udp, ...)
   it is convenient to represent them as a single entry.  If a service
   is represented in multiple protocol domains with different ports,
   then multiple entries are required; multi-valued RDNs MAY be used to
   distinguish them.)

With the exception of authPassword and userPassword values, empty
   values (consisting of a zero length string) are returned by the DUA
   to the client.  The DUA MUST reject any entries which do not conform
   to the schema (missing mandatory attributes).  Non-conforming entries
   SHOULD be ignored while enumerating entries.

The nisDomainObject object class is provided to associate a NIS
   domain with a naming context.  A DUA would retrieve the NIS domain
   name from a configuration file and enumerate the naming contexts
   served by an LDAP server, searching each naming context for
   (nisDomain=%s).  The first matching entry that is found MAY be used
   as a search base for configuration profile information or for entries
   themselves.  For example, the following example shows an association
   between the NIS domain "nis.aja.com" and the naming context
   "dc=aja,dc=com":

dn: dc=aja,dc=com
       objectClass: top
       objectClass: domain
       objectClass: nisDomainObject
       dc: aja
       nisDomain: nis.aja.com

The nisObject object class MAY be used as a generic means of
   representing NIS entities.  Its use is not encouraged; where support
   for entities not described in this schema is desired, an appropriate
   schema should be devised.  Implementers are strongly advised to
   support end-user extensible mappings between NIS entities and object
   classes.  (Where the nisObject class is used, the nisMapName
   attribute MAY be used as a RDN.)  The nisObject class might be used
   to represent automount information.

5.5.  Canonicalizing entries with multi-valued naming attributes

For entities such as hosts, services, networks, protocols, and RPCs,
   where there may be one or more aliases, the respective entry's
   relative distinguished name SHOULD be used to determine the canonical
   name.  Any other values for the same attribute are used as aliases.
   For example, the service described in Section 5.4 has the canonical
   name "domain" and exactly one alias, "nameserver".

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The schema in this document generally only defines one attribute per
   class which is suitable for distinguishing an entity (excluding any
   attributes with integer syntax; it is assumed that entries will be
   distinguished on name).  Usually, this is the common name (cn)
   attribute.  This aids the DUA in determining the canonical name of an
   entity, as it can examine the value of the relative distinguished
   name.  Aliases are thus any values of the distinguishing attribute
   (such as cn) which do not match the canonical name of the entity.

In the event that a different attribute is used to distinguish the
   entry, as may be the case where these object classes are used as
   auxiliary classes, the entry's canonical name may not be present in
   the RDN.  In this case, the DUA MUST choose one of the non-
   distinguished values to represent the entity's canonical name.  As
   the directory server guarantees no ordering of attribute values, it
   may not be possible to distinguish an entry deterministically.  This
   ambiguity SHOULD NOT be resolved by mapping one directory entry into
   multiple entities.

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6.  Implementation Focus

Gateways between NIS and LDAP have been developed by PADL Software
   and Sun Microsystems.  They both support this schema.

An open source implementation of the C library resolution code has
   been written and is available from PADL Software.  It supports C
   libraries on GNU, BSD, AIX, and Solaris operating systems.  PADL have
   also made available a set of scripts for migrating flat files into a
   form suitable for loading into an LDAP server.  Another open source
   implementation of the C library code is available from the OpenLDAP
   Project.

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7.  Security Considerations

The entirety of related security considerations are outside the scope
   of this document.  It is noted that making passwords encrypted with a
   widely understood hash function (such as crypt()) available to non-
   privileged users is dangerous because it exposes them to dictionary
   and brute-force attacks.  This is proposed only for compatibility
   with existing UNIX system implementations.  Sites where security is
   critical SHOULD consider using a strong authentication service for
   user authentication.

Alternatively, the encrypted password could be made available only to
   a subset of privileged DUAs, which would provide "shadow" password
   service to client applications.  This may be difficult to enforce.

Because the schema represents operating system-level entities, access
   to these entities SHOULD be granted on a discretionary basis.  (There
   is little point in restricting access to data which will be
   republished without restriction, however.)  It is particularly
   important that only administrators can modify entries defined in this
   schema, with the exception of allowing a principal to change their
   password (which MAY be done on behalf of the user by a client bound
   as a superior principal, such that password restrictions MAY be
   enforced).  For example, if a user were allowed to change the value
   of their uidNumber attribute, they could subvert security by
   equivalencing their account with the superuser account.

A subtree of the DIT which is to be republished by a DUA (such as a
   NIS gateway) SHOULD be within the same administrative domain that the
   republishing DUA represents.  (For example, principals outside an
   organization, while conceivably part of the DIT, should not be
   considered with the same degree of authority as those within the
   organization.)

Finally, care should be exercised with integer attributes of a
   sensitive nature (particularly the uidNumber and gidNumber
   attributes) which contain zero-length values.  DUAs MAY treat such
   values as corresponding to the "nobody" or "nogroup" user and group,
   respectively.

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8.  Acknowledgements

Thanks to Bob Joslin of the Hewlett Packard Company, and to all those
   that helped with this document's predecessor, RFC 2307.

UNIX is a registered trademark of The Open Group.

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9.  References

[RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

[RFC1057]  Sun Microsystems, Inc., "RPC: Remote Procedure Call
              Protocol specification: Version 2", RFC 1057, June 1988.

[RFC1279]  Hardcastle-Kille, S., "X.500 and Domains", RFC 1279,
              November 1991.

[RFC2373]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 2373, July 1998.

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

[RFC4511]  Sermersheim, J., "Lightweight Directory Access Protocol
              (LDAP): The Protocol", RFC 4511, June 2006.

[RFC4515]  Smith, M. and T. Howes, "Lightweight Directory Access
              Protocol (LDAP): String Representation of Search Filters",
              RFC 4515, June 2006.

[RFC4519]  Sciberras, A., "Lightweight Directory Access Protocol
              (LDAP): Schema for User Applications", RFC 4519,
              June 2006.

[RFC3112]  Zeilenga, K., "LDAP Authentication Password Schema",
              RFC 3112, May 2001.

[I-D.behera-ldap-password-policy]
              Sermersheim, J., Poitou, L., and H. Chu, "Password Policy
              for LDAP Directories",
              draft-behera-ldap-password-policy-10 (work in progress),
              August 2009.

[ROSE]     Rose, M., "The Little Black Book: Mail Bonding with OSI
              Directory Services", ISBN 0-13-683210-5, 2001.

[X.500]    ISO/IEC JTC 1/SC21, "Information Processing Systems - Open
              Systems Interconnection - The Directory: Overview of
              Concepts, Models and Service", 1988.

[UNIX]     Institute of Electrical and Electronics Engineers and The
              Open Group, "IEEE Std 1003.1, 2004 Edition, Single UNIX
              Specification Version 3", IEEE Standard 1003.1, 2004.

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[PAM]      Samar, V. and R. Schemers, "Unified Login with Pluggable
              Authentication Modules (PAM)", OSF RFC 86.0, October 1995.

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Appendix A.  Example Entries

The examples described in this section are provided to illustrate the
   schema described in this draft.  They are not meant to be exhaustive.

The following entry is an example of the posixAccount class:

dn: uid=lester,ou=people,dc=aja,dc=com
       objectClass: top
       objectClass: account
       objectClass: posixAccount
       uid: lester
       cn: Lester the Nightfly
       gecos: Lester
       uidNumber: 10
       gidNumber: 10
       loginShell: /bin/csh
       userPassword: {crypt}$X5/DBrWPOQQaI
       homeDirectory: /home/lester

This corresponds to the UNIX system password file entry:

lester:X5/DBrWPOQQaI:10:10:Lester:/home/lester:/bin/sh

The following entry is an example of the ipHost class:

dn: cn=josie.aja.com,ou=hosts,dc=aja,dc=com
       objectClass: top
       objectClass: device
       objectClass: ipHost
       objectClass: bootableDevice
       objectClass: ieee802Device
       cn: josie.aja.com
       cn: www.aja.com
       ipHostNumber: 10.0.0.1
       macAddress: 00:00:92:90:ee:e2
       bootFile: mach
       bootParameter: root=dan.aja.com:/nfsroot/peg
       bootParameter: swap=dan.aja.com:/nfsswap/peg
       bootParameter: dump=dan.aja.com:/nfsdump/peg

This entry represents the host canonically josie.aja.com, also known
   as www.aja.com.  The Ethernet address and four boot parameters are
   also specified.

An example of the nisNetgroup class:

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dn: cn=nightfly,ou=netgroup,dc=aja,dc=com
       objectClass: top
       objectClass: nisNetgroup
       cn: nightfly
       nisNetgroupTriple: (charlemagne,peg,dunes.aja.com)
       nisNetgroupTriple: (lester,-,)
       memberNisNetgroup: kamakiriad

This entry represents the netgroup nightfly, which contains two
   triples (the user charlemagne, the host peg, and the domain
   dunes.aja.com; and, the user lester, no host, and any domain) and one
   netgroup (kamakiriad).

Finally, an example of the nisObject class:

dn: nisMapName=tracks,dc=dunes,dc=aja,dc=com
       objectClass: top
       objectClass: nisMap
       nisMapName: tracks

dn: cn=Maxine,nisMapName=tracks,dc=dunes,dc=aja,dc=com
       objectClass: top
       objectClass: nisObject
       cn: Maxine
       nisMapName: tracks
       nisMapEntry: Nightfly$4

This represents the NIS map tracks, and a single map entry.

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Appendix B.  Affected Library Functions

The following functions are typically found in the C libraries of
   most UNIX and POSIX compliant systems [UNIX].  An LDAP search filter
   string [RFC4515] which may be used to satisfy the function call is
   included alongside each function name.  Parameters are denoted by %s
   and %d for string and integer arguments, respectively.  Long lines
   are broken:

getpwnam()         (&(objectClass=posixAccount)(uid=%s))
       getpwuid()         (&(objectClass=posixAccount)(uidNumber=%d))
       getpwent()         (objectClass=posixAccount)
       getspnam()         (&(objectClass=shadowAccount)(uid=%s))
       getspent()         (objectClass=shadowAccount)

getgrnam()         (&(objectClass=posixGroup)(cn=%s))
       getgrgid()         (&(objectClass=posixGroup)(gidNumber=%d))
       getgrent()         (objectClass=posixGroup)

getservbyname()    (&(objectClass=ipService)(cn=%s)
                           (ipServiceProtocol=%s))
       getservbyport()    (&(objectClass=ipService)(ipServicePort=%d)
                            (ipServiceProtocol=%s))
       getservent()       (objectClass=ipService)

getrpcbyname()     (&(objectClass=oncRpc)(cn=%s))
       getrpcbynumber()   (&(objectClass=oncRpc)(oncRpcNumber=%d))
       getrpcent()        (objectClass=oncRpc)

getprotobyname()   (&(objectClass=ipProtocol)(cn=%s))
       getprotobynumber() (&(objectClass=ipProtocol)
                             (ipProtocolNumber=%d))
       getprotoent()      (objectClass=ipProtocol)

gethostbyname()    (&(objectClass=ipHost)(cn=%s))
       gethostbyaddr()    (&(objectClass=ipHost)(ipHostNumber=%s))
       gethostent()       (objectClass=ipHost)

getnetbyname()     (&(objectClass=ipNetwork)(cn=%s))
       getnetbyaddr()     (&(objectClass=ipNetwork)(ipNetworkNumber=%s))
       getnetent()        (objectClass=ipNetwork)

setnetgrent()      (&(objectClass=nisNetgroup)(cn=%s))
       getpublickey()     (&(objectClass=nisKeyObject)(...))

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Appendix C.  Suggested DIT structure

The cn attribute is typically used to name entities.  The
   ipHostNumber, ipNetworkNumber, and ipServiceProtocol attributes are
   also naming attributes, such that multi-valued RDNs may be used to
   distinguish between, for example, different interfaces of a
   multihomed host.

The following DIT structure MAY be used for deploying this schema.
   It is not required that DC-naming be used, but it is encouraged:

Naming context                        ObjectClass
       ============================================================
       ou=people,dc=...                      posixAccount
                                             shadowAcount
       ou=group,dc=...                       posixGroup
       ou=services,dc=...                    ipService
       ou=protocols,dc=...                   ipProtocol
       ou=rpc,dc=...                         oncRpc
       ou=hosts,dc=...                       ipHost
       ou=ethers,dc=...                      ieee802Device
                                             bootableDevice
       ou=networks,dc=...                    ipNetwork
       ou=netgroup,dc=...                    nisNetgroup
       nisMapName=...,dc=...                 nisObject
       automountMapName=...,dc=...           automountMap

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Authors' Addresses

Luke Howard
   PADL Software Pty. Ltd.
   PO Box 59
   Central Park, Vic  3145
   AU

Email: lukeh@padl.com

Howard Chu (editor)
   Symas Corp.
   18740 Oxnard Street, Suite 313A
   Tarzana, California  91356
   US

Phone: +1 818 757-7087
   Email: hyc@symas.com

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