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NFSv4 Working Group                                           W. Adamson
Internet-Draft                                                    NetApp
Intended status: Standards Track                              K. Coffman
Expires: April 29, 2010                     CITI, University of Michigan
                                                             N. Williams
                                                        Sun Microsystems
                                                        October 26, 2009


                       NFSv4 Multi-Domain Access
               draft-adamson-nfsv4-multi-domain-access-02

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Abstract

   The Network File System, version 4 (NFSv4) uses a representation of
   identity that allows the use of users and groups from multiple,
   distinct administrative domains, and NFSv4 allows the use of security
   mechanisms that authenticate principals from multiple, distinct
   administrative domains.  This document describes methods by which
   NFSv4 clients and servers can handle principals, users, groups from
   multiple administrative domains.


Table of Contents

   1.      Requirements notation  . . . . . . . . . . . . . . . . . .  3
   2.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
   3.      Background . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.      Terminology  . . . . . . . . . . . . . . . . . . . . . . .  7
   5.      Local Representations of Global Identity . . . . . . . . .  9
   5.1.    Storing Name@Domainname  . . . . . . . . . . . . . . . . .  9
   5.2.    Storing Remote-ID@Domainname . . . . . . . . . . . . . . .  9
   5.2.1.  Storing Remote-ID@Domain-ID  . . . . . . . . . . . . . . .  9
   5.2.2.  ID Mapping . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.3.    Use of Name Services . . . . . . . . . . . . . . . . . . . 10
   5.3.1.  Using LDAP with RFC2307 Schema . . . . . . . . . . . . . . 10
   5.3.2.  Using Active Directory LDAP  . . . . . . . . . . . . . . . 11
   5.3.3.  Resolving Domain Names to Domain IDs . . . . . . . . . . . 11
   5.3.4.  LDAP DIT Construction for a Federated Namespace  . . . . . 11
   6.      GSS-API Principal-to-NFSv4 Authorization Context . . . . . 12
   6.1.    Using GSS-API Naming Extensions  . . . . . . . . . . . . . 12
   6.1.1.  Using a PAC  . . . . . . . . . . . . . . . . . . . . . . . 13
   6.2.    Mapping Principal Names to Usernames . . . . . . . . . . . 13
   6.2.1.  Using a Name Service to Map Principal Names to User
           Accounts . . . . . . . . . . . . . . . . . . . . . . . . . 14
   6.3.    User Group Membership Determination  . . . . . . . . . . . 14
   7.      LDAP Schema Extensions for Multi-Domain NFSv4  . . . . . . 15
   7.1.    LDAP Attribute for Principal Name to Local ID
           Translation  . . . . . . . . . . . . . . . . . . . . . . . 15
   8.      Name Resolution  . . . . . . . . . . . . . . . . . . . . . 16
   8.1.    Using LDAP Caching Proxies . . . . . . . . . . . . . . . . 16
   8.2.    LDAP Schema Extensions for ID Mapping  . . . . . . . . . . 18
   9.      Multi-Domain Access Summary  . . . . . . . . . . . . . . . 19
   10.     Security Considerations  . . . . . . . . . . . . . . . . . 20
   11.     References . . . . . . . . . . . . . . . . . . . . . . . . 21
   11.1.   Normative References . . . . . . . . . . . . . . . . . . . 21
   11.2.   Informative References . . . . . . . . . . . . . . . . . . 22
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 23





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1.  Requirements notation

   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 [RFC2119].














































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2.  Introduction

   The NFS Version 4 [RFC3530] protocol enables the construction of a
   distributed file system which can join NFSv4.0 or NFSv4.1
   [I-D.ietf-nfsv4-minorversion1] servers from multiple administrative
   domains, each potentially using separate name resolution services and
   separate security services, into a common multi-domain name space.

   NFSv4 deals with two kinds of identities: authentication identities
   (referred to here as "principals") and authorization identities
   ("users" and "groups" of users).  NFSv4 supports multiple
   authentication methods, each authenticating an "initiator principal"
   (typically representing a user) to an "acceptor principals" (always
   corresponding to the server).  NFSv4 does not prescribe how to
   represent authorization identities on file systems.  All file access
   decisions constitute "authorization" and are made by servers using
   information about client principals (such as username, group
   memberships, and so on) and file metadata related to authorization,
   such as a file's access control list (ACL).

   Authentication in NFSv4 occurs at the the RPCSEC_GSS [RFC2203] layer
   where GSS-API mechanisms [RFC2743] are used to authenticate users on
   NFSv4 clients to NFSv4 servers, and to provide security services such
   as confidentiality and integrity protection for the protocol's
   messages.  The NFSv4 protocol specifies no particular representation
   for authentication identities as these are entirely mechanism-
   specific

   Authorization for file object access is done at the NFSv4 protocol
   layer (i.e., above the RPCSEC_GSS layer), on the server side, based
   on an authenticated client principal's authorization context and the
   authorization meta-data of the file system objects that the client
   wishes to access.  File authorization meta-data is set and retrieved
   in the NFSv4 RPC [RFC1831] layer, specifically via the object's
   owner, owner_group and acl, dacl and sacl attributes (the last three
   being ACLs).  ACLs are lists of ACL entries (ACEs).  Each ACE has a
   "who" field identifying a subject to whom some permision is granted
   or denied.  The owner and owner_group attributes and the who ACE
   field, all reference users and groups.  On the wire, the protocol
   represents users and groups as strings of characters with this form:
   name@domain, where <name> is a user or group name, and <domain> is a
   the name of an administrative domain, more specifically a DNS
   [RFC1034] domainname.

   NFSv4 server implementations usually do not, and really ought not,
   store authorization identities on disk in the same form as is used on
   the wire.  The reason is that users' and groups' names change all too
   often, while searching for and updating file authorization meta-data



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   after a user/group name change is not trivial, particularly in a
   global namespace spanning multiple administrative domains.

   NFSv4 servers therefore must perform two kinds of mappings: a)
   authentication identity to authorization context (a principal's user
   ID, group memberships, etcetera), and on-the-wire authorization
   identity representation to on-disk authorization identity
   representation.  Many aspects of these mappings are entirely
   implementation-specific, but some require name resolution services,
   and in order to interoperate servers must use such services in
   compatible ways.  Many implementations are limited to being able to
   represent users and groups from a single domain.

   In this document we address both of those kind of mappings,
   describing possible implementation strategies, and specifying a name
   service for interoperation in a global namespace
   [I-D.ietf-nfsv4-federated-fs-reqts].


































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3.  Background

   NFSv4 uses a syntax of the form "name@domain" to represent, on the
   wire, the NFSv4 ACL name for users and groups.  This design provides
   a level of indirection that allows a client and server with different
   internal representations of authorization identity to interoperate
   even when referring to authorization identities from different
   administrative domains.

   Multi-domain capable sites need to meet certain requirements in order
   to ensure that clients and servers can map name@domain to internal
   representations reliably:

   o  name@domain MUST be unique within the DNS domain.

   o  Every local representation of a user and of a group MUST have a
      canonical name@domain, and it must be possible to return the
      canonical name@domain for any identity stored on disk, at least
      when required infrastructure servers (such as name services) are
      online.

   As described in [I-D.ietf-nfsv4-minorversion1] section 2.2.1.1 "RPC
   Security Flavors":

           NFSv4.1 clients and servers MUST implement RPCSEC_GSS.  (This
           requirement to implement is not a requirement to use.)  Other
           flavors, such as AUTH_NONE, and AUTH_SYS, MAY be implemented
           as well.

   The AUTH_NONE security flavor can be useful to the multi-domain NFSv4
   or federated name space to grant universal access to public data
   without any credentials.

   The AUTH_SYS security flavor uses a host-based authentication model
   where the [weakly-authenticated] client asserts the user's
   authorization identities using small integers as user and group
   identity representations.  Because of the small integer authorization
   ID representation, AUTH_SYS can only be used in a name space where
   all clients and servers share a uidNumber and gidNumber translation
   service.  A shared translation service is required because uidNumbers
   and gidNumbers are passed in the RPC credential; there is no
   negotiation of namespace in AUTH_SYS.  Collisions can occur if
   multiple translation services are used.  These and other issues are
   addressed in [I-D.williams-rpcsecgssv3] which describes a new version
   of RPCSEC_GSS that includes a modernized replacement for AUTH_SYS.






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4.  Terminology

      Identity: a way to refer to a user or group.

      Principal: an entity that is authenticated by RPCSEC_GSS (usually,
      but not always, a user; rarely, if ever, a group; sometimes a
      host).

      Authorization context: the set of user and group IDs, privileges,
      labels, and other items relevant to authorization, corresponding
      to a subject (user or principal).

      Domain-local ID: Most installations assign numeric, local
      identifiers to users and groups, using a namespace local to their
      domain.  We call this a domain-local ID.

      Local representation of identity: an item such as a POSIX user
      IDentifier (UID) or group ID (GID), or a Windows Security
      IDentifier (SID), or other such local representation of a user or
      a group of users.

      Global representation of identity: a tuple consisting of a domain
      identifier (possibly the domain's name itself) and a domain-local
      user/group ID.  We do not propose a standard global representation
      of identity, but the concept is useful.

      Domain: a set of users and computers administered by a single
      entity, and identified by a DNS domain name.

      POSIX IDs: small non-negative integers (typically 0..2^31 or
      0..2^32) identifiers.  The namespace of user IDs (UIDs) is
      distinct from the namespace of group IDs (GIDs).

      Windows SIDs: an identifier of security entities, including users
      and groups.  The form of a SID is: S-1-
      <authority><RID_0><RID_1><RID_n> By convention some authority
      numbers denote security entities, identified by RID_n, local to a
      domain identified by RIDs 0..n-1.  Domain RIDs are usually
      generated randomly within a "forest" of domains.

      Name resolution: mapping from {domain, name} to {domain, ID}, and
      vice-versa via lookups.  Can be applied to local or remote
      domains.

      ID mapping: {domain-remote ID } to { domain-local ID } mappings.






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      Logon service: { user ID } -> { groups user is a member of, and
      other authorization context }

















































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5.  Local Representations of Global Identity

   Multi-domain support starts at the fileserver where local ID forms
   need to be able to represent global identities from both, local and
   remote domains.  Local representation of global identity also applies
   to clients, particularly clients with local filesystems.  There's a
   range of local solutions to this multi-domain ID representation
   problem.  In this section we describe several approaches to
   representing a <name>@<local or remote domain> on disk.  None of
   these approaches are REQUIRED; all are INFORMATIVE.  However,
   conventions relating to the use of name services are NORMATIVE.

5.1.  Storing Name@Domainname

   One simple approach to the multiple domain problem is the identity
   function applied to name@domain, with the resultant ID stored on
   disk.

   This approach imposes a severe constraint on the administrators of
   these domains: user and group names must never be reused, as there is
   also no realistic way to keep the name@domain on disk representation
   up to date with user, group or domain renames and removals.  Consider
   a remote domain's NFSv4 servers where real-time employee join/leave
   data may be (typically is!) considered privileged, and remote servers
   may not be sufficiently privileged to access it [elaborate...].

5.2.  Storing Remote-ID@Domainname

   Most installations assign numeric, local identifiers to users and
   groups, using a namespace local to their domain.  We call this a
   domain-local ID.  We can then construct a global identity form
   consisting of a domain ID and a domain-local user/group ID.

   The user or group renaming issue can be addressed by using a global
   identity form where domain-local IDs are required.  I.e., use name
   resolution to lookup name@domain to find the ID local to the domain,
   and join the ID with the result of the identity function applied to
   the domain.  This function still has a renaming problem with respect
   to DNS domain renames, but that is a realistically manageable
   problem.

5.2.1.  Storing Remote-ID@Domain-ID

   The DNS domain renaming issue in the previous section can be
   addressed by assigning and publishing a unique ID to each DNS domain.
   I.e., use name resolution to lookup name@domain to find some ID local
   to the domain, lookup the domain ID and store <remote-ID,domain-ID>.




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5.2.2.  ID Mapping

   Many file systems exported by NFS only store 32-bit user and group
   IDs which limit their ability to utilize the on disk representation
   described in Section 5.2.  Such systems may need to use an additional
   service to map between <remote users, local user IDs> and <remote
   groups, local group IDs>.  We call this an "ID mapping service".

   The use of an ID mapping service is not strictly necessary if the
   system operates on IDs large enough such that <user/group ID, domain
   ID> can be encoded into a native ID.  However, a large class of
   operating systems, those which are Unix or Unix-like operating
   systems, such as Solaris and Linux, use 32-bit UIDs and GIDs in many
   services and therefore need mapping for backwards compatibility
   reasons.

   One example of such a service is to keep a local or distributed
   database for dynamically assigning a local 32 bit ID to every <ID>@
   <domain-ID>, or one could do that only for remote domains, reserving
   only a small part of the local 32-bit ID namespace for remote
   domains' users/groups.

   The remote ID and remote domain are then used as inputs to a name
   resolution service which contacts the remote domain name service to
   resolve the remote name.

5.3.  Use of Name Services

   Such file systems often use a distributed directory service for
   assigning domain local 32 bit IDs to remote users and groups.  The
   Network Information Service [NIS] and the Lightweight Directory
   Access Protocol [RFC4511] are the two broadly used distributed
   directory service protocols used for this purpose.  LDAP is used
   instead of NIS in environments where scale and security are issues.
   Section 7 expands the LDAP protocol to include mappings between
   name@domain and local user and group IDs.

   Support for LDAP [RFC4511] with the RFC2307 schema [RFC2307] is
   REQUIRED.

5.3.1.  Using LDAP with RFC2307 Schema

   Name resolution consists of searches with scope 'sub', a base DN
   corresponding to a domain (more on this below) and a filter of either
   of these forms, with matching on objectClass being optional:






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   o  ((objectClass=posixAccount)(uid="<username>))

   o  ((objectClass=posixGroup)(cn="<groupname>))

   o  ((objectClass=posixAccount)(uidNumber="<UID>))

   o  ((objectClass=posixGroup)(gidNumber="<GID>))

   The base DN should be formatted from a domain's DNS domainname as
   follows.  First format the domainname as a string, then strip the
   trailing dot ('.'), if any, then replace all dots ('.') with ",DC=",
   then prepend "DC=" to the resulting string.  For example,
   foo.bar.example becomes "DC=foo,DC=bar,DC=example".  This convention
   is REQUIRED to be implemented.  Domains with base DNs that do not
   match this convention may be used, but their domainname-to-base-DN
   mappings must be published where NFSv4 clients and servers may find
   them; we provide no conventions for publishing such mappings.
   Implementations MUST support the use of LDAP referrals to find LDAP
   servers authoritative for any given base DN.

   For example, to resolve a user named joe@foo.bar.example to a remote
   ID a system would do an LDAP search with DC=foo,DC=bar,DC=example as
   the base DN, scope='sub' and with a filter of
   ((objectClass=posixAccount)(uid="<username>)) looking for the
   uidNumber attribute.

5.3.2.  Using Active Directory LDAP

   [Add text describing searches by which to resolve name@domain to SIDs
   and vice versa.]

5.3.3.  Resolving Domain Names to Domain IDs

   [Add text on mapping domainnames to domain IDs.]

5.3.4.  LDAP DIT Construction for a Federated Namespace

   [Add text on federated namespace LDAP DIT construction, and caching
   services.












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6.  GSS-API Principal-to-NFSv4 Authorization Context

   In order to authorize user access to files, the NFSv4 server must map
   the RPCSEC_GSS client principal name or the underlying GSS-API
   security context to local security information including a local ID,
   a set of group IDs and other user privileges.  This security
   information is contained in an "authorization context" (also called
   an "access token" in some systems).

   Authorization contexts consist of:

   1.  UserID: This field contains the principal's global ID and/or
       local ID mapping thereof, and the name@domain form thereof.

   2.  PrimarygroupID: This field contains the global ID and/or local ID
       mapping thereof for the principal's primary group, and the
       name@domain form thereof.

   3.  Groups: This field contains an array of group IDs for the groups
       that the user is a member of, in global ID form and/or local ID
       mappings thereof, as well as in name@domain name@domain forms.

   4.  As yet unspecified field(s) for privileges and authorizations
       granted to the principal, if any.

   5.  As yet unspecified field(s) for other privilege information such
       as the multi-level security label range/set of the principal.

   6.  Implementation-specific items relevant to authorization.

   The RPCSEC_GSS client principal authorization context determination
   may be mechanism-specific, and even operating system-specific, but
   from the NFSv4 server's point of view, it is a generic facility.
   Below we describe several methods of authorization context
   determination.

   The NFSv4 authorization context SHOULD be obtained via discrete GSS-
   API name attributes [I-D.ietf-kitten-gssapi-naming-exts]
   corresponding to the above elements of authorization contexts.  URIs
   for those attributes are TBD.  If the named attribute interface is
   not available, or the attributes are not available, other means of
   determining a principal's authorization context SHOULD be used, such
   as those described in Section 6.1 and Section 6.2.

6.1.  Using GSS-API Naming Extensions

   Authorization context information can sometimes be obtained from the
   credentials authenticating a principal; the GSS-API represents such



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   information as attributes of the initiator prinicpal's name.  For
   example: Kerberos 5 [RFC4120] has a method for conveying
   "authorization data", both client-asserted as well as KDC-
   authenticated authorization data, and one KDC implementation uses
   this feature to convey a "privilege attribute certificate" (PAC)
   listing the principal's user and group "security identifiers" (SIDs).
   PKIX [RFC5280] certificates allow for extensions that could be used
   similarly.

6.1.1.  Using a PAC

   The Windows operating system uses something called a "PAC", which
   contains a user Security IDentifier (SID) and a list of group SIDs.
   Some Kerberos Key Distribution Centers (KDCs), notably Windows KDCs,
   issue Kerberos Tickets with PACs as Kerberos authorization data.
   When a client principal is authenticated using such a ticket, the
   server SHOULD extract the PAC from the client's ticket and map, if
   need be, the SIDs in the PAC to local ID representations.

   The authorization context information in a PAC can be considered a
   single, authenticated, discrete GSS-API name attribute, in which case
   the server must parse it into its individual elements.

   [Add references.]

6.2.  Mapping Principal Names to Usernames

   If suitable and sufficient authenticated name attributes for the
   client principal are not available, then the server may try to map
   the client principal name to a local notion of user account, and then
   lookup that user account's authorization context information through
   name service lookups.

   One simple method for Kerberos principal-to-username mapping is to
   first apply an algorithmic or table-based Kerberos client principal
   realm name to domain name mapping, then a client principal name to
   username mapping.  Finally, the server can look up the user's
   authorization context using the user's domain's name services.

   A trivial Kerberos realm-name-to-domainname mapping consists of case-
   folding the realm name to lower-case.  [Add notes about
   internationalization.]  Servers MUST implement this mapping as an
   option, possibly as a default option.

   A trivial Kerberos principal name to username mapping for 1-component
   principal names, is the identity function.  Servers MUST implement
   this mapping as an option, possibly as a default option.




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6.2.1.  Using a Name Service to Map Principal Names to User Accounts

   Name services such as the Solaris gsscred database where the local
   identity is looked up in a database keyed by the GSS exported name
   token, or LDAP with the extension described in Section 7.1, can be
   used to map principal names to user accounts.

6.3.  User Group Membership Determination

   User group membership is easy to determine for users in a system's
   local domain: the operating system will already know how to do that.

   User group membership in remote domain's groups, or for remote users,
   may be determined using LDAP with the RFC2307 schema.  The RFC2307
   schema does not define the values of the 'memberUid' attribute, but
   in practice it seems that those are expected to be the names of users
   as found in the 'uid' attribute of 'posixAccount' entries.  There is
   work in progress to update RFC2307 [I-D.howard-rfc2307bis] to allow
   the use of DNs in the memberUid attribute, as well as group nesting.
   Such use of memberUid should be backwards-compatible, since
   implementations that don't know about that use of memberUid will end
   up ignoring values which are not plain usernames.

   Assuming the ability to store DNs in the memberUid attribute, then,
   group membership determination can be done as follows.  Given a user
   ID whose DN has been resolved:

   1.  Search the user's domain for groups that the user is a member of
       in the user's home domain.  Filter out groups that are not local
       to the user's home domain.

   2.  Search the server's domain for groups that the user is a member
       of in the server's home domain.

   3.  Search the server's domain for groups that the user's group
       memberships determined in step 1 are members of.

   4.  Continue searching for nested group memberships given the list of
       groups from steps 2 and 3.

   However, the above procedure has the same user/group name renaming
   issue.  By skipping step 2 we can get down to just a group renaming
   issue.  To fully address the rename issue we need either a new
   attribute or value type for memberUid, storing user/group IDs in some
   global ID representation.

   [Add text defining such a new attribute/value type.]




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7.  LDAP Schema Extensions for Multi-Domain NFSv4

7.1.  LDAP Attribute for Principal Name to Local ID Translation

   The gSSPrincipal objectclass allows for the use of the gSSAuthName
   attribute described in the following section.

                        objectclass ( 1.3.6.1.4.1.250.10.7
                        NAME 'gSSPrincipal'
                        DESC 'GSS Principal Name'
                        SUP  posixAccount
                        MAY ( gSSAuthName ) )

   Here we present a new LDAP attribute that provides a method for the
   translations between a local ID and (multiple) GSS-API security
   principals, used as described in Section 6.2.

   The gSSAuthName attribute stores a user's GSS-API principal name in
   exported name token form (see [RFC2743]).

                           attributetype ( 1.3.6.1.4.1.250.10.6
                           NAME ( 'gSSAuthName')
                           DESC 'GSS-API exported principal name
                           exported token'
                           EQUALITY bitStringMatch
                           SYNTAX 1.3.6.1.4.1.1466.115.121.1.6)

























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8.  Name Resolution

   As noted in Section 5.2.1, most local representations require a name
   service to perform ID to name translations.  Implementations are
   REQUIRED to support the use of LDAP as a name service, relying on
   LDAP referrals for federated namespace construction.

   Note that in a topographically widely separated set of domains the
   need to do name service lookups in various domains' name services may
   prove brittle, resulting in non-deterministic server behavior (e.g.,
   sometimes a user can access share, sometimes they cannot; sometimes
   they appear to be members of some group, sometimes they do not).  To
   avoid this, site administrators may wish to maintain local caches of
   remote domains' name services such that LDAP searches for users/
   groups in remote domains can be satisfied locally for some set of key
   attributes (such as naming and ID attributes), with referrals used in
   all other cases.

   Domains in a federated namespace may provide each other with LDAP
   LDIF delta feeds by which to maintain cached LDAP contents up to
   date.

8.1.  Using LDAP Caching Proxies

   Many sites use a distributed name service such as Lightweight
   Directory Access Protocol [RFC4511] for distributing system
   configuration data and providing name translation.  RFC2307 [RFC2307]
   defines the LDAP posixAccount object class and an associated set of
   attributes used to resolve account information such as user IDs to
   login names and group IDs to group names.

   The LDAP posixAccount schema can be used to map between the multiple
   domain local ID and the NFSv4 name@domain form by adding remote
   domain DN hierarchies to the local LDAP name service.

   An LDAP service set up in this way is a caching proxy because it
   caches remote domain information.  The DN hierarchy structure has the
   advantage of aiding delta feeds from remote domains because each
   domain's information is in it's own DN subtree.

   An example follows that shows the DN hierarchy for sample.com's LDAP
   service.









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                           dc=com/
                           dc=sample/
                           ou=People/
                           [all the rfc2307 people entries for
                           sample.com]
                           uid=bob

                           dc=edu/
                           dc=university/
                           ou=People/
                           [all the rfc2307 people entries for the
                           remote domain university.edu]
                           uid=alice

   An LDAP hierarchy for two domains, the local sample.com domain and
   the remote university.edu domain.

                                 Figure 1

































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   More detail on two entries from sample.com's LDAP service:

                           dn: uid=bob,ou=People,dc=sample,dc=com
                           objectClass: top
                           objectClass: person
                           objectClass: organizationalPerson
                           objectClass: inetorgperson
                           objectClass: gSSPrincipal
                           cn: Bob B. Bar
                           sn: Bar
                           uidNumber: 5989
                           gidNumber: 100
                           gSSAuthName: <bob@SAMPLE.COM>
                           gSSAuthName: <bob@SAMPLE-ENG.COM>

                           dn: uid=alice,ou=People,dc=university,dc=edu
                           objectClass: top
                           objectClass: person
                           objectClass: organizationalPerson
                           objectClass: inetorgperson
                           objectClass: gSSPrincipal
                           cn: Alice A. Answer
                           sn: Answer
                           uidNumber: 5990
                           gidNumber: 100
                           remoteID: 1234
                           gSSAuthName: <alice@UNIVERSITY.EDU>

                                 Figure 2

   Figure 2 shows two entries in the sample.com LDAP service also shown
   in Figure 1.  One entry is for a local user Bob and one entry for a
   remote user alice.  The mappings of the local uidNumber to an NFSv4
   name@domain are also shown where the NFSv4 name@domain is expressed
   as a concatenation of the posixAccount uid attribute and the DN
   domain.

   Figure 2 also demonstrates the use of the gSSAuthName and remoteID
   attributes.  User bob@sample.com has a principal in both the
   SAMPLE.COM and the SAMPLE_ENG.COM Kerberos realms, and both map to
   his uidNumber.  User alice@university.edu has a principal in the
   UNIVERSITY.EDU Kerberos realm, and a remoteID of 1234 which is her
   uidNumber in the university.edu name service.

8.2.  LDAP Schema Extensions for ID Mapping

   [Add text.]




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9.  Multi-Domain Access Summary

   File systems exported by the NFSv4 file server need to be able to
   represent user and group IDs from multiple domains.

   The RPCSEC_GSS client presents the GSS principal to the NFSv4 server
   which maps the GSS principal into the principal's authorization
   context via methods described in Section 6.  The authorization
   context information is used to determine file access.  Depending on
   the local representation as described in Section 5, ID mapping and/or
   name resolution may be required to translate between IDs and names
   contained in the authorization context.

   An NFSv4 SETATTR or GETATTR with an acl attribute presented to the
   NFSv4 server may also require ID mapping and/or name resolution to
   translate between the name@domain and the local file system ID.



































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10.  Security Considerations

   Yet to be determined
















































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11.  References

11.1.  Normative References

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

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

   [RFC3530]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
              Beame, C., Eisler, M., and D. Noveck, "Network File System
              (NFS) version 4 Protocol", RFC 3530, April 2003.

   [RFC1831]  Srinivasan, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 1831, August 1995.

   [RFC2203]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, September 1997.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              July 2005.

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

   [RFC2307]  Howard, L., "An Approach for Using LDAP as a Network
              Information Service", RFC 2307, March 1998.

   [I-D.howard-rfc2307bis]
              Howard, L. and H. Chu, "An Approach for Using LDAP as a
              Network Information Service", draft-howard-rfc2307bis-02
              (work in progress), August 2009.

   [I-D.ietf-nfsv4-federated-fs-reqts]
              Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M.
              Naik, "Requirements for Federated File Systems",
              draft-ietf-nfsv4-federated-fs-reqts-06 (work in progress),
              October 2009.

   [I-D.ietf-kitten-gssapi-naming-exts]
              Williams, N. and L. Johansson, "GSS-API Naming
              Extensions", draft-ietf-kitten-gssapi-naming-exts-05 (work
              in progress), July 2009.



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   [I-D.ietf-nfsv4-minorversion1]
              Shepler, S., Eisler, M., and D. Noveck, "NFS Version 4
              Minor Version 1", draft-ietf-nfsv4-minorversion1-29 (work
              in progress), December 2008.

11.2.  Informative References

   [I-D.williams-rpcsecgssv3]
              Williams, N., "Remote Procedure Call (RPC) Security
              Version 3", draft-williams-rpcsecgssv3-00 (work in
              progress), January 2009.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [NIS]      Sun Microsystems, "System and Network Administration",
              March 1990.
































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Authors' Addresses

   William A. (Andy) Adamson
   NetApp

   Email: andros@netapp.com


   Kevin Coffman
   CITI, University of Michigan

   Email: kwc@umich.edu


   Nicolas Williams
   Sun Microsystems

   Email: Nicolas.Williams@sun.com

































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