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Versions: (draft-cel-nfsv4-mv0-trunking-update) 00

Network File System Version 4                              C. Lever, Ed.
Internet-Draft                                                    Oracle
Updates: 7530 (if approved)                                    D. Noveck
Intended status: Standards Track                                  NetApp
Expires: July 11, 2018                                   January 7, 2018


                    NFS version 4.0 Trunking Update
                draft-ietf-nfsv4-mv0-trunking-update-00

Abstract

   The location-related attribute in NFS version 4.0, fs_locations, is
   used to support the migration and replication of server file systems.
   This document describes an additional use for this attribute as a
   mechanism for an NFS version 4.0 client to discover an NFS version
   4.0 server's trunking capabilities.  The interaction of trunking with
   migration and replication is also clarified.  This document updates
   RFC 7530.

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 https://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 11, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (https://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



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   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.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Preliminaries . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Document Organization . . . . . . . . . . . . . . . . . .   5
     3.3.  Document Goals  . . . . . . . . . . . . . . . . . . . . .   6
   4.  Overview of changes in RFC7530 Section 8  . . . . . . . . . .   6
   5.  Location Attributes (as updated)  . . . . . . . . . . . . . .   7
   6.  Updates to RFC7530 Section 8.4 (Uses of Location Information)   8
     6.1.  Introduction to uses of Location Information (as updated)   8
     6.2.  Trunking Discovery and Detection (to be added)  . . . . .   9
     6.3.  File System Replication and Trunking (as updated) . . . .  10
     6.4.  File System Migration (as updated)  . . . . . . . . . . .  10
     6.5.  Interaction of Trunking, Migration, and Replication (to
           be added) . . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Location Entries and Server Identity Update (as updated)  . .  12
   8.  Updates to RFC7530 Outside Section Eight  . . . . . . . . . .  13
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     11.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  Section Classification . . . . . . . . . . . . . . .  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   The NFS version 4.0 specification [RFC7530] defines a migration
   feature which enables the transfer of a file system from one server
   to another without disruption of client activity.  There were a
   number of issues with the original definition of this feature, now
   resolved with the publication of [RFC7931].

   After a migration event, a client must determine whether state
   recovery is necessary.  To do this, it needs to determine whether the
   source and destination server addresses represent the same server
   instance, if the client has already established a lease on the
   destination server for other file systems, and if the destination
   server instance has lock state for the migrated file system.





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   As part of addressing this need, [RFC7931] introduces into NFS
   version 4.0 a trunking detection mechanism to enable a client to
   determine whether two distinct network addresses are connected to the
   same NFS version 4.0 server instance; i.e., are trunked.  Even so,
   the NFS version 4.0 specification remains without a complete
   discussion of trunking.

   File system migration, replication, and referrals are distinct
   protocol features.  However, it is not appropriate to treat each of
   these features in isolation.  For example, client migration recovery
   processing needs to deal with the possibility of multiple server
   addresses in a returned fs_locations attribute.  In addition, the
   contents of the fs_locations attribute, which provides both trunking-
   related and replication information, may change over repeated
   retrievals, requiring an integrated description of how clients are to
   deal with such changes.  The issues discussed in the current document
   relate to the interpretation of the fs_locations attribute and to the
   proper client and server handling of changes in fs_locations
   attribute values.

2.  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 BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown
   here.

3.  Preliminaries

3.1.  Terminology

   Most of the terms related to handling the fs_locations attribute are
   appropriately defined in Section 5 below.  However, there are a few
   terms used outside that context that are explained here.

   Regarding network addresses and the handling of trunking we use the
   following terminology:

   o  Each NFSv4 server is assumed to have a set of IP addresses to
      which NFSv4 requests may be sent by clients.  These are referred
      to as the server's network addresses.

   o  Each network address, when combined with a pathname providing the
      location of a file system root directory relative to the
      associated server root file handle, defines a file system network
      access path.




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   o  Two network addresses connected to the same server are said to be
      server-trunkable.

   Particularly important is the distinction between trunking detection
   and trunking discovery.  The definitions we present are applicable to
   all minor versions of NFSv4, but we put particular emphasis on how
   these terms apply to NFS version 4.0.

   o  Trunking detection refers to ways of confirming that two unique
      network addresses are associated with the same NFSv4 server
      instance.  The means available to make this determination depends
      on the protocol version and, in some cases, on the client
      implementation.

      In the case of NFS version 4.0, the means to be used are described
      in [RFC7931] and require use of the Uniform Client String approach
      to be effective.  This is in contrast to later minor versions for
      which the means of trunking detection are described by [RFC5661]
      and are available to every NFS version 4.0 client.

   o  Trunking discovery is a process by which an NFSv4 client,
      accessing one server network address, can obtain other addresses
      that might be associated with the same server instance.  Typically
      a client builds on a trunking detection facility by providing one
      or more methods by which candidate addresses are made available to
      the client, who then uses trunking detection to appropriately
      filter them.

      Trunking discovery is not discussed in [RFC7530] and no
      description of it is provided in [RFC7931].

   Discussion of the term "replica" is complicated for a number of
   reasons.

   Even though the term is used in explaining the issues in [RFC7530]
   that need to be addressed in this document, a full explanation of
   this term requires explanation of related terms connected to the
   fs_locations attribute, which is provided in Section 5 of the current
   document.

   The term is also used in previous documents about NFSv4.0 (i.e.,
   [RFC7530], [RFC7931]) with a meaning different from that in the
   current document.  In these documents each replica is identified by a
   single network access path.  However, in the current document a set
   of network access paths which have server-trunkable network addresses
   and the same root-relative file system pathname are considered to be
   a single replica with multiple network access paths.  Although
   [RFC7931] allowed the client to determine whether two addresses were



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   server-trunkable, it never described these as connected to a single
   replica, leaving in effect the approach established in [RFC7530].

3.2.  Document Organization

   The sections of the current document are divided into four types
   based on how they relate to the eventual updating of the NFS verion
   4.0 specification.  Once this update is published, NFS version 4.0
   will be specified by multiple documents that need to be read
   together, until such time as a consolidated replacement specification
   is produced.

   o  The base specification [RFC7530].

   o  The migration-related update [RFC7931].

   o  An eventual RFC based on the current document.

   The section types are as follows.  See Appendix A for a
   classification of each section of the current document.

   o  An explanatory section does not contain any material that is meant
      to update the specification of NFS version 4.0.  Such sections may
      contain explanation about why and how changes are to be done, but
      do not include any text that is to update [RFC7530] or appear in
      an eventual consolidated document.

   o  A replacement section contains text that is to replace and thus
      supersede text within [RFC7530] and then appear in an eventual
      consolidated document.

   o  An additional section contains text which, although not replacing
      anything in [RFC7530], will be part of the specification of NFS
      version 4.0 and will be expected to be part of an eventual
      consolidated document.

   o  An editing section contains some text that replaces text within
      [RFC7530], although the entire section will not consist of such
      text and will include other text as well.  Such sections make
      relatively minor adjustments in the existing NFS version 4.0
      specification which are expected to be reflected in an eventual
      consolidated document.  Generally such replacement text appears as
      a quotation, possibly taking the form of an indented set of
      paragraphs.







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3.3.  Document Goals

   The goals of this document are as follows:

   o  To provide NFS version 4.0 with a means of trunking discovery,
      compatible with the means of trunking detection introduced by
      [RFC7931].

   o  To describe how NFS version 4.0 clients are to handle the presence
      of multiple network addresses associated to the same server, when
      recovering from a replication and migration event.

   o  To describe how NFS version 4.0 clients are to handle changes in
      the contents of returned fs_locations attributes, including those
      that indicate changes in the responding NFS version 4.0 server's
      trunking configuration.

   The current document pursues these goals by presenting a set of
   updates to [RFC7530] as summarized in Section 4 below.

4.  Overview of changes in RFC7530 Section 8

   With a few small exceptions (see below), all of the updates to
   [RFC7530] to provide support for trunking using the fs_locations
   attribute apply to Section 8 of that document, entitled "Multi-Server
   Namespace".

   o  Section 5 replaces Section 8.1 of [RFC7530], entitled "Location
      Attributes".  This section has been reorganized and extended to
      explicitly allow the use of fs_locations to provide trunking-
      related information that appropriately interacts with the
      migration, replication and referral features of fs_locations.
      Terminology used to describe the interactions is added.

   o  Section 6 updates Section 8.4 of [RFC7530], entitled "Uses of
      Location Information".  This section comprises the bulk of the
      updates.  Each paragraph of Section 8.4 and its sub-sections has
      been reviewed to clarify the provision of trunking-related
      information using the fs_locations attribute.

      *  Section 6.1 replaces the introductory material within
         Section 8.4 of [RFC7530].

      *  Section 6.2 is to be added after the introductory material
         within Section 8.4 of [RFC7530].

      *  Section 6.3 replaces Section 8.4.1 of [RFC7530], entitled "File
         System Replication".



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      *  Section 6.4 replaces Section 8.4.2 of [RFC7530], entitled "File
         System Migration".

      *  Section 6.5 is to be added after the updated Section 8.4.2 of
         [RFC7530].

   o  Section 7 replaces Section 8.5 of [RFC7530], entitled "Location
      Entries and Server Identity".  The last paragraph of the existing
      section has been removed.

   o  A small set of updates outside Section 8 of [RFC7530] are
      presented in Section 8.

   o  Section 9 introduces additional security considerations that are
      to be added to those within Section 19 of [RFC7530], entitled
      "Security Considerations".

5.  Location Attributes (as updated)

   The fs_locations RECOMMENDED attribute allows specification of file
   system locations where the data corresponding to a given file system
   may be accessed.  This attribute represents such file system
   instances as a server address target (as either a DNS host name
   representing one or more network addresses, or a single literal
   network address) together with the path of that file system within
   the associated single-server namespace.  Individual fs_locations
   entries can express trunkable addresses, locations of file system
   replicas on other servers, migration targets, or pure referrals.

   We introduce the following terminology:

   o  Trunking is a situation in which multiple network addresses are
      connected to the same NFS server.  Network addresses connected to
      the same NFS server are said to be server-trunkable.

   o  Trunking detection refers to ways of confirming that two distinct
      network addresses are connected to the same NFSv4 server instance.

   o  Trunking discovery is a process by which a client using one
      network address can obtain other candidate addresses that are
      server-trunkable with it.

   Regarding terminology relating to GETATTR attributes used in trunking
   discovery and other multi-server namespace features:

   o  Location entries (fs_location4, defined in [RFC7530]
      Section 2.2.6) are the individual file system locations in the
      fs_locations attribute (defined in [RFC7530] Section 2.2.7).



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   o  Location elements are derived from location entries.  If a
      location entry specifies a network address there is only a single
      corresponding location element.  When a location entry contains a
      host name, the host name is resolved by the client, producing one
      location element for each of the resulting network addresses.

   o  All location elements consist of a location address, which is the
      network address of an interface to a server, and an fs_name, which
      is the location of the file system within the server's pseudo-fs.

   o  The fs_name is empty if the server has no pseudo-fs and only a
      single exported file system at the root filehandle.

6.  Updates to RFC7530 Section 8.4 (Uses of Location Information)

   The subsections below provide replacement sections for existing
   sections within Section 8.4 of [RFC7530] or new sub-sections to be
   added to that section.

6.1.  Introduction to uses of Location Information (as updated)

   Together with the possibility of absent file systems, the location-
   bearing attribute fs_locations provides a number of important
   facilities that enable reliable, manageable, and scalable data
   access.

   When a file system is present, this attribute can provide alternative
   locations to be used to access the same data in the event of server
   failure, communications problems, or other difficulties that make
   continued access to the current file system impossible or otherwise
   impractical.  Provision of such alternative locations is referred to
   as "replication".

   One type of replication is trunking, where the location entries do
   not in fact represent different servers but are instead distinct
   network paths to the same server.  A client may use location elements
   simultaneously to provide higher-performance access to the target
   file system.  The client utilizes trunking detection and/or
   discovery, further described in Section 6.2 of the current document,
   to determine if location elements are server-trunkable.

   Alternative locations may also represent physical replicas of the
   same file system data or, in the case of various forms of server
   clustering, another server providing access to the same physical file
   system.

   When a file system is present and subsequently becomes absent,
   clients can be given the opportunity to have continued access to



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   their data at an alternative location.  Transfer of the file system
   contents to the new location is referred to as "migration".  The
   client's responsibilities in dealing with this transition depend on
   the specific nature of the new access path as well as how and whether
   data was in fact migrated.  See Section 6.4 and Section 6.5 of the
   current document for details.

   The fs_locations attribute can designate one or more remote locations
   in place of an absent file system.  This is known as a "referral".  A
   particularly important case is that of a "pure referral", in which
   the absent file system has never been present on the NFS server.
   Such a referral is a means by which a file system located on one
   server can redirect clients to file systems located on other servers,
   thus enabling the creation of a multi-server namespace.

   Because client support for the fs_locations attribute is OPTIONAL, a
   server may (but is not required to) take action to hide migration and
   referral events from such clients by acting as a proxy, for example.

6.2.  Trunking Discovery and Detection (to be added)

   Trunking is a situation in which multiple distinct network addresses
   are associated with the same NFS server instance.  As a matter of
   convenience, we say that two network addresses connected to the same
   NFS server instance are server-trunkable.  Section 5.4 of [RFC7931]
   explains why NFSv4 clients need to be aware of NFS server identity to
   manage lease and lock state effectively when multiple connections to
   the same server exist.

   Trunking detection refers to a way for an NFSv4 client to confirm
   that two independently acquired network addresses are connected to
   the same NFSv4 server.  Section 5.8 of [RFC7931] describes an
   OPTIONAL means by which it can be determined if two server network
   addresses correspond to the same NFSv4.0 server instance.  Without
   trunking detection, an NFSv4.0 client has no other way to confirm
   that two network addresses are server-trunkable.

   In the particular context of NFS version 4.0, trunking detection
   requires that the client support the Uniform Client ID String
   approach (UCS), described in Section 5.6 of [RFC7931].  Any NFSv4.0
   client that supports migration or trunking detection needs to present
   a Uniform Client ID String to all NFSv4.0 servers.  If it does not do
   so, it will be unable to perform trunking detection.

   Trunking discovery is the process by which an NFSv4 client using a
   host name or one of an NFSv4 server's network addresses can obtain
   other candidate network addresses that are trunkable with it; i.e., a
   set of addresses that might be connected to the same NFSv4 server



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   instance.  An NFSv4.0 client can discover server-trunkable network
   addresses in a number of ways:

   o  An NFS server's host name is provided either at mount time or in a
      returned location entry.  A DNS query of this host name can return
      more than one network address.  The returned network addresses are
      candidates for trunking.

   o  Location entries returned in an fs_locations attribute can specify
      network addresses.  These network addresses are candidates for
      trunking.

   When there is a means of trunking detection available, an NFSv4.0
   client can confirm that a set of network addresses correspond to the
   same NFSv4.0 server instance and thus any of them can be used to
   access that server.

6.3.  File System Replication and Trunking (as updated)

   On first access to a file system, the client should obtain the value
   of the set of alternative locations by interrogating the fs_locations
   attribute.  Trunking discovery and/or detection can then be applied
   to the location entries to separate the candidate server-trunkable
   addresses from the replica addresses that provide alternative
   locations of the file system.  Server-trunkable addresses may be used
   simultaneously to provide higher performance through the exploitation
   of multiple paths between client and target file system.

   In the event that server failures, communications problems, or other
   difficulties make continued access to the current file system
   impossible or otherwise impractical, the client can use the
   alternative locations as a way to maintain continued access to the
   file system.  See Section 6.5 of the current document for more
   detail.

6.4.  File System Migration (as updated)

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternative location specified by the fs_locations attribute.
   Typically, a client will be accessing the file system in question,
   get an NFS4ERR_MOVED error, and then use the fs_locations attribute
   to determine the new location of the data.  See Section 6.5 of the
   current document for more detail.

   Such migration can be helpful in providing load balancing or general
   resource reallocation.  The protocol does not specify how the file
   system will be moved between servers.  It is anticipated that a



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   number of different server-to-server transfer mechanisms might be
   used, with the choice left to the server implementer.  The NFSv4
   protocol specifies the method used to communicate the migration event
   between client and server.

   When an alternative location is designated as the target for
   migration, it must designate the same data.  Where file systems are
   writable, a change made on the original file system must be visible
   on all migration targets.  Where a file system is not writable but
   represents a read-only copy (possibly periodically updated) of a
   writable file system, similar requirements apply to the propagation
   of updates.  Any change visible in the original file system must
   already be effected on all migration targets, to avoid any
   possibility that a client, in effecting a transition to the migration
   target, will see any reversion in file system state.

6.5.  Interaction of Trunking, Migration, and Replication (to be added)

   When the set of network addresses designated by a location attribute
   changes, NFS4ERR_MOVED might or might not result.  In some of the
   cases in which NFS4ERR_MOVED is returned migration has occurred,
   while in others there is a shift in the network addresses used to
   access a particular file system with no migration.

   1.  When the list of network addresses is a superset of that
       previously in effect, there is no need for migration or any other
       sort of client adjustment.  Nevertheless, the client is free to
       use an additional address in the replacement list if that address
       provides another path to the same server.  Or, the client may
       treat that address as it does a replica, to be used if current
       server addresses become unavailable.

   2.  When the list of network addresses is a subset of that previously
       in effect, immediate action is not needed if an address missing
       in the replacement list is not currently in use by the client.
       The client should avoid using that address in the future, whether
       the address is for a replica or an additional path to the server
       being used.

   3.  When an address being removed is one of a number of paths to the
       current server, the client may continue to use it until
       NFS4ERR_MOVED is received.  This is not considered a migration
       event unless the last available path to the server has become
       unusable.

   When migration does occur, multiple addresses may be in use on the
   server previous to migration and multiple addresses may be available
   for use on the destination server.



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   With regard to the server in use, it may be that return of
   NFS4ERR_MOVED indicates that a particular network address is no
   longer to be used, without implying that migration of the file system
   to a different server is needed.  Clients should not conclude that
   migration has occurred until confirming that all network addresses
   known to be associated with the server are not usable.

   It should be noted that the need to defer this determination is not
   absolute.  If a client is not aware of all network addresses for any
   reason, it may conclude that migration has occurred when it has not
   and treat a switch to a different server address as if it were a
   migration event.  This is harmless since the use of the same server
   via a new address will appear as a successful instance of Transparent
   State Migration.

   While significant harm will not arise from this misapprehension, it
   can give rise to disconcerting situations.  For example, if a lock
   has been revoked during the address shift, it will appear to the
   client as if the lock has been lost during migration, normally
   calling for it to be recoverable via an fs-specific grace period
   associated with the migration event.

   With regard to the destination server, it is desirable for the client
   to be aware of all the valid network addresses that can be used to
   access the destination server.  However, there is no need for this to
   be done immediately.  Implementations can process the additional
   location elements in parallel with normal use of the first valid
   location entry found to access the destination.

   Because a location attribute may include entries relating to the
   current server, the migration destination, and possible replicas to
   use, scanning for available network addresses could potentially be a
   long process.  To keep this process as short as possible, Servers are
   REQUIRED to place location entries that represent addresses usable
   with the current server or a migration target before those associated
   with replicas.  A client can then cease scanning for trunkable
   location entries once it encounters a location element whose fs_name
   differs from the current fs_name, or whose address is not server-
   trunkable with the one it is currently using.

7.  Location Entries and Server Identity Update (as updated)

   As mentioned above, a single location entry may have a server address
   target in the form of a DNS host name that resolves to multiple
   network addresses, while multiple location entries may have their own
   server address targets that reference the same server.





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   When server-trunkable addresses for a server exist, the client may
   assume that for each file system in the namespace of a given server
   network address, there exist file systems at corresponding namespace
   locations for each of the other server network addresses.  It may do
   this even in the absence of explicit listing in fs_locations.  Such
   corresponding file system locations can be used as alternative
   locations, just as those explicitly specified via the fs_locations
   attribute.

8.  Updates to RFC7530 Outside Section Eight

   Since the existing description of NFS4ERR_MOVED in Section 13.1.2.4
   of [RFC7530] does not take proper account of trunking, it needs to be
   modified by replacing the first two sentences of the description with
   the following material:

      The file system that contains the current filehandle object cannot
      be accessed using the current network address.  It may be
      accessible using other network addresses connected to the same
      server, it may have been relocated to another server, or it may
      never have been present.

9.  Security Considerations

   The Security Considerations section of [RFC7530] needs the additions
   below to properly address some aspects of trunking discovery,
   referral, migration, and replication.

      The possibility that requests to determine the set of network
      addresses corresponding to a given server might be interfered with
      or have their responses corrupted needs to be taken into account.

      o  When DNS is used to convert NFS server host names to network
         addresses and DNSSEC [RFC4033] is not available, the validity
         of the network addresses returned cannot be relied upon.
         However, when the client uses RPCSEC_GSS [RFC7861] to access
         NFS servers, it is possible for mutual authentication to detect
         invalid server addresses.  Other forms of transport layer
         security (e.g., [RFC5246]) can also offer strong authentication
         of NFS servers.

      o  Fetching location information SHOULD be performed using
         RPCSEC_GSS with integrity protection, as previously explained
         in the Security Considerations section of [RFC7530].  Making a
         request of this sort without using strong integrity protection
         permits corruption during transit of returned location
         information.  The client implementer needs to recognize that
         using such information to access an NFS server without use of



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         RPCSEC_GSS (e.g., by using AUTH_SYS as defined in [RFC5531])
         can result in the client interacting with an unverified network
         address that is posing as an NFSv4 server.

      o  Despite the fact that it is a REQUIREMENT of [RFC7530] that
         "implementations" provide "support" for the use of RPCSEC_GSS,
         it cannot be assumed that use of RPCSEC_GSS is always possible
         between any particular client-server pair.

      o  Returning only network addresses to a client that has no
         trusted DNS resolution service can hamper its ability to use
         RPCSEC_GSS.

      Therefore an NFSv4 server SHOULD present location entries that
      correspond to file systems on other servers using only host names.
      This enables the client to interrogate the fs_locations on the
      destination server to obtain trunking information (as well as
      replica information) using RPCSEC_GSS with integrity, validating
      the host name provided while assuring that the response has not
      been corrupted.

      When RPCSEC_GSS is not available on an NFS server, returned
      location information is subject to corruption during transit and
      cannot be relied upon.  In the case of a client being directed to
      another server after NFS4ERR_MOVED, this could vitiate the
      authentication provided by the use of RPCSEC_GSS on the
      destination.  Even when RPCSEC_GSS authentication is available on
      the destination, this server might validly represent itself as the
      server to which the client was erroneously directed.  Without a
      way to decide wether the server is a valid one, the client can
      only determine, using RPCSEC_GSS, that the server corresponds to
      the host name provided, with no basis for trusting that server.
      The client should not use such unverified location entries as a
      basis for migration, even though RPCSEC_GSS might be available on
      the destination server.

      When a location attribute is fetched upon connecting with an NFSv4
      server, it SHOULD, as stated above, be done using RPCSEC_GSS with
      integrity protection.

      When location information cannot be protected in transit, the
      client can subject it to additional filtering to prevent the
      client from being inappropriately directed.  For example, if a
      range of network addresses can be determined that assure that the
      servers and clients using AUTH_SYS are subject to appropriate
      constraints (such as physical network isolation and the use of
      administrative controls within the operating systems), then




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      network adresses in this range can be used with others discarded
      or restricted in their use of AUTH_SYS.

      When neither integrity protection nor filtering is possible, it is
      best for the client to ignore trunking and replica information or
      simply not fetch the location information for these purposes.

      To summarize considerations regarding the use of RPCSEC_GSS in
      fetching location information, consider the following
      possibilities for requests to interrogate location information,
      with interrogation approaches on the referring and destination
      servers arrived at separately:

      o  The use of RPCSEC_GSS with integrity protection is RECOMMENDED
         in all cases, since the absence of integrity protection exposes
         the client to the possibility of the results being modified in
         transit.

      o  The use of requests issued without RPCSEC_GSS (e.g., using
         AUTH_SYS), while undesirable, might be unavoidable in some
         cases.  Where the use of returned location information cannot
         be avoided, it should be subject to filtering to eliminate
         untrusted network addresses.  The specifics will vary depending
         on the degree of network isolation and whether the request is
         to the referring or destination servers.

10.  IANA Considerations

   This document does not require actions by IANA.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5531]  Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
              May 2009, <https://www.rfc-editor.org/info/rfc5531>.

   [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <https://www.rfc-editor.org/info/rfc7530>.





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   [RFC7931]  Noveck, D., Ed., Shivam, P., Lever, C., and B. Baker,
              "NFSv4.0 Migration: Specification Update", RFC 7931,
              DOI 10.17487/RFC7931, July 2016,
              <https://www.rfc-editor.org/info/rfc7931>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

11.2.  Informative References

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5661]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
              <https://www.rfc-editor.org/info/rfc5661>.

   [RFC7861]  Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
              Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
              November 2016, <https://www.rfc-editor.org/info/rfc7861>.

Appendix A.  Section Classification

   All sections of this document are considered explanatory with the
   following exceptions.

   o  Sections 5 and 6.1 are replacement sections.

   o  Section 6.2 is an additional section.

   o  Sections 6.3 and 6.4 are replacement sections.

   o  Section 6.5 is an additional section.

   o  Section 7 is a replacement section.

   o  Section 8 is an editing section.

   o  Section 9 is an additional section.



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Acknowledgments

   The authors wish to thank Andy Adamson, who wrote the original
   version of this document.  All the innovation in this document is the
   result of Andy's work, while mistakes are best ascribed to the
   current authors.

   The editor wishes to thank Greg Marsden of Oracle for his support of
   this work, and Rob Thurlow of Oracle for review and suggestions.

   Special thanks go to Transport Area Director Spencer Dawkins, NFSV4
   Working Group Chair Spencer Shepler, and NFSV4 Working Group
   Secretary Thomas Haynes for their support.

Authors' Addresses

   Charles Lever (editor)
   Oracle Corporation
   1015 Granger Avenue
   Ann Arbor, MI  48104
   United States of America

   Phone: +1 248 816 6463
   Email: chuck.lever@oracle.com


   David Noveck
   NetApp
   1601 Trapelo Road
   Waltham, MA  02451
   United States of America

   Phone: +1 781 572 8038
   Email: davenoveck@gmail.com

















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