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NFSv4 Working Group                                           W. Adamson
Internet-Draft                                                    NetApp
Intended status: Standards Track                             N. Williams
Expires: July 27, 2015                                      Cryptonector
                                                        January 23, 2015


         Multiple NFSv4 Domain Namespace Deployment Guidelines
                draft-ietf-nfsv4-multi-domain-fs-reqs-01

Abstract

   This document describes administrative constraints to the deployment
   of the NFSv4 protocols required for the construction of an NFSv4 file
   system namespace supporting the use of multiple NFSv4 domains and
   utilizing multi-domain capable file systems.  Also described are
   administrative constraints to name resolution and security services
   appropriate to such a system.  Such a namespace is a suitable way to
   enable a Federated File System supporting the use of multiple NFSv4
   domains.

Requirements Language

   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].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on July 27, 2015.








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Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  NFSv4 Server Identity Mapping . . . . . . . . . . . . . . . .   4
   4.  Stand-alone NFSv4 Domain Deployment Examples  . . . . . . . .   5
   4.1.  AUTH_SYS with Stringified UID/GID . . . . . . . . . . . . .   6
   4.2.  AUTH_SYS with name@domain . . . . . . . . . . . . . . . . .   6
   4.3.  RPCSEC_GSS with name@domain . . . . . . . . . . . . . . . .   7
   5.  Multi-domain Constraints to the NFSv4 Protocol  . . . . . . .   7
   5.1.  Name@domain Constraints . . . . . . . . . . . . . . . . . .   7
   5.1.1.  NFSv4 Domain and DNS Services . . . . . . . . . . . . . .   8
   5.1.2.  NFSv4 Domain, Name Service, and Domain Aware File Systems   9
   5.2.  RPC Security Constraints  . . . . . . . . . . . . . . . . .   9
   5.2.1.  NFSv4 Domain and Security Services  . . . . . . . . . . .  10
   6.  Resolving Multi-domain Authorization Information  . . . . . .  10
   7.  Stand-alone Examples and Multiple NFSv4 Domain Namespaces . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   An NFSv4 domain is defined as a set of users, groups and computers
   running NFSv4.0 [I-D.ietf-nfsv4-rfc3530bis] and NFSv4.1 [RFC5661]
   (hereafter referred to as NFSv4) protocols identified by an NFSv4
   domain name.

   The Federated File System (FedFS) [RFC5716] describes the
   requirements and administrative tools to construct a uniform NFSv4
   file server based namespace that is capable of spanning a whole
   enterprise and that is easy to manage.



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   The FedFS is the standardized method of constructing and
   administrating an enterprise wide NFSv4 filesystem, and so is
   referenced in this document.  The issues with multiple NFSv4 domain
   file systems described in this document apply to all multiple NFSv4
   domain file systems, be they run as a FedFS or not.

   Stand-alone NFSv4 domains can be run in many ways.  While a FedFS can
   be run within all stand-alone NFSv4 domain configurations some of
   these configurations (Section 4) are not compatible with joining a
   multiple NFSv4 domain FedFS namespace.

   Multi NFSv4 domain file systems require support for global identities
   in name services, security services, and in the exporting of on-disk
   local identity representation.  Many of the stand-alone NFSv4 domain
   deployments do not provide full support for global identities.

   This document describes administrative constraints to the deployment
   of the NFSv4 protocols required for the construction of an NFSv4 file
   system namespace supporting the use of multiple NFSv4 domains and
   utilizing multi-domain capable file systems.  Also described are
   administrative constraints to name resolution and security services
   appropriate to such a system.  Such a namespace is a suitable way to
   enable a Federated File System supporting the use of multiple NFSv4
   domains.

2.  Terminology

      Name Service: provides the mapping between {NFSv4 domain, group or
      user name} and {NFSv4 domain, local ID}, as well as the mapping
      between {security principal} and {NFSv4 domain, local ID} via
      lookups.  Can be applied to local or remote domains.  Often
      provided by a Directory Service such as LDAP.

      Domain: This term is used in multiple contexts where it has
      different meanings.  Here we provide specific definitions used in
      this document.

         DNS domain: a set of computers, services, or any internet
         resource identified by an DNS domain name [RFC1034].

         Security realm or domain: a set of configured security
         providers, users, groups, security roles, and security policies
         running a single security protocol and administered by a single
         entity, for example a Kerberos realm.

         NFSv4 domain: a set of users, groups, and computers running
         NFSv4 protocols identified by a unique NFSv4 domain name.  See
         [RFC5661] Section 5.9 "Interpreting owner and owner_group".



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         Multi-domain: In this document this always refers to multiple
         NFSv4 domains.

         FedFS domain: A file namespace that can cross multiple shares
         on multiple file servers using file-access protocols such as
         NFSv4.  A FedFS domain is typically a single administrative
         entity, and has a name that is similar to a DNS domain name.
         Also known as a Federation.

         Administrative domain: a set of users, groups, computers, and
         services administered by a single entity.  Can include multiple
         DNS domains, NFSv4 domains, security domains, and FedFS
         domains.

      Local representation of identity: an object such as a uidNumber
      (UID) or gidNumber (GID) [RFC2307], a Windows Security Identifier
      (SID) [CIFS], or other such representation of a user or a group of
      users on-disk in a file system.

      Global identity: An on-the-wire globally unique form of identity
      that can be mapped to a local representation.  For example, the
      NFSv4 name@domain or the Kerberos principal@REALM.

      Multi-domain capable filesystem: A local filesystem that uses a
      local ID form that can represent identities from both local and
      remote domains.  For example, an SSID based local ID form where
      the SSID contains both a domain and a user or group component.

      Principal: an RPCSEC_GSS authentication identity.  Usually, but
      not always, a user; rarely, if ever, a group; sometimes a host or
      server.

      Authorization Context: A collection of information about a
      principal such as username, userID, group membership, etcetera
      used in authorization decisions.

      Stringified UID or GID: NFSv4 owner and group strings that consist
      of decimal numeric values with no leading zeros, and which do not
      contain an '@' sign.  See Section 5.9 "Interpreting owner and
      owner_group" [RFC5661].

3.  NFSv4 Server Identity Mapping

   NFSv4 servers deal 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 principal" (always



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   corresponding to the NFSv4 server).  NFSv4 does not prescribe how to
   represent authorization identities on file systems.  All file access
   decisions constitute "authorization" and are made by NFSv4 servers
   using authorization context information and file metadata related to
   authorization, such as a file's access control list (ACL).

   NFSv4 servers therefore must perform two kinds of mappings:

   1.  Auth-to-authz: A mapping between the authentication identity and
       the authorization context information.

   2.  Wire-to-disk: A mapping between the on-the-wire authorization
       identity representation and the on-disk authorization identity
       representation.

   A Name Service such as LDAP often provides these mappings.

   Many aspects of these mappings are entirely implementation specific,
   but some require multi-domain capable name resolution and security
   services in order to interoperate in a multiple NFSv4 domain file
   system.

   NFSv4 servers use these mappings for:

   1.  File access: Both the auth-to-authz and the wire-to-disk mappings
       may be required for file access decisions.

   2.  Meta-data setting and listing: The auth-to-authz mapping is
       usually required to service file metadata setting or listing
       requests (such as ACL or unix permission setting or listing) as
       NFSv4 uses the name@domain on-the-wire identity representation
       which usually differs from the exported on-disk identity
       representation.

4.  Stand-alone NFSv4 Domain Deployment Examples

   In order to service as many environments as possible, the NFSv4
   protocol is designed to allow administrators freedom to configure
   their NFSv4 domains as they please.

   Stand-alone NFSv4 domains can be run in many ways.  Here we list some
   stand-alone NFSv4 domain deployment examples focusing on the NFSv4
   server's use of name service mappings (Section 3) and security
   services deployment to demonstrate the need for some multiple NFSv4
   domain constraints to the NFSv4 protocol, name service configuration,
   and security service choices.





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   Because all on-disk identities participating in a stand-alone NFSv4
   domain belong to the same NFSv4 domain, stand-alone NFSv4 domain
   deployments have no requirement for exporting multi-domain capable
   file systems.

   These examples are for a NFSv4 server exporting a 32bit UID/GID based
   file system, a typical deployment.  These examples are listed in the
   order of increasing NFSv4 administrative complexity.

4.1.  AUTH_SYS with Stringified UID/GID

   This example is the closest NFSv4 gets to being run as NFSv3.

   File access: The AUTH_SYS RPC credential provides a UID as the
   authentication identity, and a list of GIDs as authorization context
   information.  File access decisions require no name service
   interaction as the on-the-wire and on-disk representation are the
   same and the auth-to-authz UID and GID authorization context
   information is provided in the RPC credential.

   Meta-data setting and listing: When the NFSv4 clients and servers
   implement a stringified UID/GID scheme, where a stringified UID or
   GID is used for the NFSv4 name@domain on-the-wire identity, then a
   name service is not required for file metadata listing as the UID or
   GID can be constructed from the stringified form on the fly by the
   server.

4.2.  AUTH_SYS with name@domain

   The next level of complexity is to not use a stringified UID/GID
   scheme for file metadata listing.

   File access: This is the same as in Section 4.1.

   Meta-data setting and listing: The NFSv4 server will need to use a
   name service for the wire-to-disk mappings to map between the on-the-
   wire name@domain syntax and the on-disk UID/GID representation.
   Often, the NFSv4 server will use the nsswitch interface for these
   mappings.  A typical use of the nsswitch name service interface uses
   no domain component, just the uid attribute [RFC2307] (or login name)
   as the name component.  This is no issue in a stand-alone NFSv4
   domain deployment as the NFSv4 domain is known to the NFSv4 server
   and can combined with the login name to form the name@domain syntax
   after the return of the name service call.







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4.3.  RPCSEC_GSS with name@domain

   This final example adds the complexity of RPCSEC_GSS with the
   Kerberos 5 GSS security mechanism.

   File Access: The RPCSEC_GSS Kerberos credential provides a
   principal@REALM name as the authentication identity, and (as of this
   writing) no authorization context information.  File access decisions
   therefore require a wire-to-disk mapping of the principal@REALM to a
   UID, and an auth-to-authz mapping to obtain the list of GIDs as the
   authorization context.

   Deployments can use the nsswitch name service interface for the
   principal@REALM to UID mapping by stripping off the REALM portion.
   This requires that the principal portion of the principal@REALM
   matches the uid attribute [RFC2307] (or login name) of the user.

   Meta-data setting and listing: This is the same as in Section 4.2.

5.  Multi-domain Constraints to the NFSv4 Protocol

   Joining NFSv4 domains under a single file namespace imposes slightly
   on the NFSv4 administration freedom.  Here we describe the required
   constraints.

5.1.  Name@domain Constraints

   NFSv4 uses a syntax of the form "name@domain" as the on wire
   representation of the "who" field of an NFSv4 access control entry
   (ACE) for users and groups.  This design provides a level of
   indirection that allows NFSv4 clients and servers with different
   internal representations of authorization identity to interoperate
   even when referring to authorization identities from different NFSv4
   domains.

   Multiple NFSv4 domain capable sites need to meet the following
   requirements in order to ensure that NFSv4 clients and servers can
   map between name@domain and internal representations reliably.  While
   some of these constraints are basic assumptions in NFSv4.0
   [I-D.ietf-nfsv4-rfc3530bis] and NFSv4.1 [RFC5661], they need to be
   clearly stated for the multiple NFSv4 domain case.

   o  The NFSv4 domain portion of name@domain MUST be unique within the
      multiple NFSv4 domain namespace.  See [RFC5661] section 5.9
      "Interpreting owner and owner_group" for a discussion on NFSv4
      domain configuration.





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   o  The name portion of name@domain MUST be unique within the
      specified NFSv4 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.

   Due to UID and GID collisions, stringified UID/GIDs MUST NOT be used
   in a multiple NFSv4 domain file system.

   Note that for stand-alone NFSv4 domains it does not matter if the
   choice of the NFSv4 domain name is replicated by another stand-alone
   NFSv4 domain deployment.  Indeed, if a stringified UID/GID scheme is
   used, or just UNIX mode bits are used (NFSv4 ACLs are not set or
   listed) and the simple nsswitch interface that strips the @domain and
   the @REALM is used, then the domain portion of name@domain can be
   ignored, and even be different for each client and server in the
   domain.

5.1.1.  NFSv4 Domain and DNS Services

   Here we address the relationship between NFSv4 domain name and DNS
   domain name in a multiple NFSv4 domain deployment.

   The definition of an NFSv4 domain name needs clarification to work in
   a multiple NFSv4 domain file system namespace.  Section 5.9 [RFC5661]
   loosely defines the NFSv4 domain name as a DNS domain name.  This
   loose definition for the NFSv4 domain is a good one, as DNS domain
   names are globally unique.  As noted above in Section 5.1, any choice
   of NFSv4 domain name can work within a stand-alone NFSv4 domain
   deployment whereas the NFSv4 domain is required to be unique in a
   multiple NFSv4 domain deployment.

   A typical configuration is that there is a single NFSv4 domain that
   is served by a single DNS domain.  In this case the NFSv4 domain name
   can be the same as the DNS domain name.

   An NFSv4 domain can span multiple DNS domains.  In this case, one of
   the DNS domain names can be chosen as the NFSv4 domain name.

   Multiple NFSv4 domains can also share a DNS domain.  In this case,
   only one of the NFSv4 domains can use the DNS domain name, the other
   NFSv4 domains must choose another unique NFSv4 domain name.






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5.1.2.  NFSv4 Domain, Name Service, and Domain Aware File Systems

   As noted above in Section 5.1, each name@domain is unique across the
   multiple NFSv4 domain namespace, and maps to a local representation
   of ID in each NFSv4 domain.  This means that each NFSv4 domain has a
   single name resolution service exporting the NFSv4 domain local ID
   namespace.

   An NFSv4 domain administrator that wants to give NFSv4 local file
   access to a remote user from a remote NFSv4 domain needs to create a
   local ID for the remote user which can then be assigned on-disk and
   used for local access decisions.  Since the local ID for the remote
   user must be able to be mapped to a name@remote-domain, only multi-
   domain capable file systems can be exported in a multiple NFSv4
   domain namespace.

   We note that many file systems exported by NFSv4 use 32 bit POSIX UID
   and GIDs as a local ID form and as this local ID form has no domain
   component, these file systems are not domain aware and can not
   participate in a multiple NFSv4 domain namespace.  There are ways to
   overcome this deficiency, but these practices are beyond the scope of
   this document.

5.2.  RPC Security Constraints

   As described in [RFC5661] 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 underlying RPCSEC_GSS security mechanism used in a multiple NFSv4
   domain namespace is REQUIRED to employ a method of cross NFSv4 domain
   trust so that a principal from a security service in one NFSv4 domain
   can be authenticated in another NFSv4 domain that uses a security
   service with the same security mechanism.  Kerberos, and PKU2U
   [I-D.zhu-pku2u] are examples of such security services.

   The AUTH_NONE security flavor can be useful in a multiple NFSv4
   domain namespace 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 host (the NFSv4 client) asserts the
   user's authorization identities using small integers, uidNumber, and
   gidNumber [RFC2307], as user and group identity representations.
   Because this authorization ID representation has no domain component,



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   AUTH_SYS can only be used in a namespace where all NFSv4 clients and
   servers share an [RFC2307] name service.  A shared name 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 name services are used, so AUTH_SYS
   MUST NOT be used in a multiple NFSv4 domain file system.

5.2.1.  NFSv4 Domain and Security Services

   As noted above in Section 5.2, caveat AUTH_NULL, multiple NFSv4
   domain security services are RPCSEC_GSS based with the Kerberos 5
   security mechanism being the most commonly (and as of this writing,
   the only) deployed service.

   A single Kerberos 5 security service per NFSv4 domain with the upper
   case NFSv4 domain name as the Kerberos 5 REALM name is a common
   deployment.

   Multiple security services per NFSv4 domain is allowed, and brings
   the issue of mapping multiple Kerberos 5 principal@REALMs to the same
   local ID.  Methods of achieving this are beyond the scope of this
   document.

6.  Resolving Multi-domain Authorization Information

   When an RPCSEC_GSS principal is seeking access to files on an NFSv4
   server, after authenticating the principal, the server must obtain in
   a secure manner the principal's authorization context information
   from an authoritative source such as the name service in the
   principal's NFSv4 domain.

   In the stand-alone NFSv4 domain case where the principal is seeking
   access to files on an NFSv4 server in the principal's home NFSv4
   domain, the server administrator has knowledge of the local policies
   and methods for obtaining the principal's authorization information
   and the mappings to local representation of identity from an
   authoritative source.  E.g., the administrator can configure secure
   access to the local NFSv4 domain name service.

   In the multiple NFSv4 domain case where a principal is seeking access
   to files on an NFSv4 server not in the principal's home NFSv4 domain,
   the server is REQUIRED to obtain in a secure manner the principal's
   authorization context information from an authoritative source.  In
   this case there is no assumption of:

   o  Remote name service configuration knowledge





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   o  The syntax of the remote authorization context information
      presented to the NFSv4 server by the remote name service for
      mapping to a local representation.

   There are several methods the NFSv4 server can use to obtain the
   NFSv4 domain authoritative authorization information for a remote
   principal from an authoritative source.  While any detail is beyond
   the scope of this document, some general methods are listed here.

   1.  A mechanism specific GSS-API authorization payload containing
       credential authorization data such as a "privilege attribute
       certificate" (PAC) [PAC] or a "general PAD" (PAD)
       [I-D.sorce-krbwg-general-pac].  This is the preferred method as
       the payload is delivered as part of GSS-API authentication,
       avoids requiring any knowledge of the remote authoritative
       service configuration, and its syntax is well known.

   2.  When there is a security agreement between the local and remote
       NFSv4 domain name services plus regular update data feeds, the
       NFSv4 server local NFSv4 domain name service can be authoritative
       for principal's in the remote NFSv4 domain.  In this case, the
       NFSv4 server makes a query to it's local NFSv4 domain name
       service just as it does when servicing a local domain principal.
       While this requires detailed knowledge of the remote NFSv4
       domains name service, the authorization context information
       presented to the NFSv4 server is in the same form as a query for
       a local principal.

   3.  An authenticated direct query from the NFSv4 server to the
       principal's NFSv4 domain authoritative name service.  This
       requires the NFSv4 server to have detailed knowledge of the
       remote NFSv4 domain's authoritative name service and detailed
       knowledge of the syntax of the resultant authorization context
       information.

7.  Stand-alone Examples and Multiple NFSv4 Domain Namespaces

   Revisiting the stand-alone (Section 4) NFSv4 domain deployment
   examples, we note that due to the use of AUTH_SYS, neither
   Section 4.1 nor Section 4.2 configurations are suitable for multiple
   NFSv4 domain deployments.

   The Section 4.3 configuration example can participate in a multiple
   NFSv4 domain namespace deployment if:

   o  The NFSv4 domain name is unique across the namespace.

   o  All exported file systems are multi-domain capable.



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   o  A secure method is used to resolve remote NFSv4 domain principals
      authorization information from an authoritative source.

8.  Security Considerations

   There are no security considerations introduced by this document
   beyond those described in NFSv4.0 [I-D.ietf-nfsv4-rfc3530bis] and
   NFSv4.1 [RFC5661].

9.  Normative References

   [CIFS]     Microsoft Corporation, "[MS-CIFS] -- v20130118 Common
              Internet File System (CIFS) Protocol", January 2013.

   [I-D.ietf-nfsv4-rfc3530bis]
              Haynes, T. and D. Noveck, "Network File System (NFS)
              version 4 Protocol", draft-ietf-nfsv4-rfc3530bis-25 (Work
              In Progress), February 2013.

   [I-D.sorce-krbwg-general-pac]
              Sorce, S., Yu, T., and T. Hardjono, "A Generalized PAC for
              Kerberos V5", draft-ietf-krb-wg-general-pac-02 (Work In
              Progress awaiting merge with other document ), June 2011.

   [I-D.zhu-pku2u]
              Zhu, L., Altman, J., and N. Williams, "Public Key
              Cryptography Based User-to-User Authentication - (PKU2U)",
              draft-zhu-pku2u-09 (Work In Progress), November 2008.

   [PAC]      Brezak, J., "Utilizing the Windows 2000 Authorization Data
              in Kerberos Tickets for Access Control to Resources",
              October 2002.

   [RFC1034]  Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",
              RFC 1034, November 1987.

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

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

   [RFC5661]  Shepler, S., Eisler, M., and D. Noveck, "Network File
              System (NFS) Version 4 Minor Version 1 Protocol", RFC
              5661, January 2010.






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   [RFC5716]  Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M.
              Naik, "Requirements for Federated File Systems", RFC 5716,
              January 2010.

Appendix A.  Acknowledgments

   Andy Adamson would like to thank NetApp, Inc. for its funding of his
   time on this project.

   We thank Chuck Lever, Tom Haynes, Brian Reitz, Bruce Fields, and
   David Noveck for their review.

Authors' Addresses

   William A. (Andy) Adamson
   NetApp

   Email: andros@netapp.com


   Nicolas Williams
   Cryptonector

   Email: nico@cryptonector.com



























Adamson & Williams        Expires July 27, 2015                [Page 13]


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