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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
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on February 10, 2010.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Howard & Chu Expires February 10, 2010 [Page 1]
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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.
Howard & Chu Expires February 10, 2010 [Page 2]
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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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