GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc8587

Internet Engineering Task Force (IETF) C. Lever, Ed. Request for Comments: 8587 Oracle Updates: 7530 D. Noveck Category: Standards Track NetApp ISSN: 2070-1721 May 2019

                  NFS Version 4.0 Trunking Update

Abstract

 In NFS version 4.0, the fs_locations attribute informs clients about
 alternate locations of file systems.  An NFS version 4.0 client can
 use this information to handle migration and replication of server
 file systems.  This document describes how an NFS version 4.0 client
 can also use this information to discover an NFS version 4.0 server's
 trunking capabilities.  This document updates RFC 7530.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8587.

Copyright Notice

 Copyright (c) 2019 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
 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.

Lever & Noveck Standards Track [Page 1] RFC 8587 NFSv4.0 Trunking Update May 2019

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
 3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
 4.  Document Organization . . . . . . . . . . . . . . . . . . . .   6
 5.  Changes within Section 8 of RFC 7530  . . . . . . . . . . . .   7
   5.1.  Updated Section "Location Attributes"
         (Currently Section 8.1) . . . . . . . . . . . . . . . . .   8
   5.2.  Updates to "Uses of Location Information"
         (Currently Section 8.4) . . . . . . . . . . . . . . . . .   9
     5.2.1.  Updates to the Introductory Text of the Current
             Section 8.4 . . . . . . . . . . . . . . . . . . . . .   9
     5.2.2.  New Subsection Titled "Trunking Discovery and
             Detection" (Becomes Section 8.4.1)  . . . . . . . . .  11
     5.2.3.  New Subsection Titled "Location Attributes and
             Selection of Connection Type" (Becomes Section 8.4.2)  12
     5.2.4.  Updated Section "File System Replication" (Becomes
             Section 8.4.3 Retitled "File System Replication and
             Trunking" . . . . . . . . . . . . . . . . . . . . . .  12
     5.2.5.  Updated Section "File System Migration" (Becomes
             Section 8.4.4)  . . . . . . . . . . . . . . . . . . .  13
     5.2.6.  New Subsection Titled "Interaction of Trunking,
             Migration, and Replication" (Becomes Section 8.4.5) .  14
   5.3.  Updated Section "Location Entries and Server Identity"
         (Section 8.5) . . . . . . . . . . . . . . . . . . . . . .  16
 6.  Updates to RFC 7530 outside Section 8 . . . . . . . . . . . .  16
 7.  Updates to the Security Considerations Section of RFC 7530  .  16
 8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
 9.  Updates to the References Section in RFC 7530 . . . . . . . .  19
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  20
   10.2.  Informative References . . . . . . . . . . . . . . . . .  21
 Appendix A.  Section Classification . . . . . . . . . . . . . . .  22
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  22
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

Lever & Noveck Standards Track [Page 2] RFC 8587 NFSv4.0 Trunking Update May 2019

1. Introduction

 The NFS version 4.0 specification [RFC7530] defines a migration
 feature that 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 1)
 the source and destination server addresses represent the same server
 instance, 2) if the client has already established a lease on the
 destination server for other file systems, and 3) if the destination
 server instance has lock state for the migrated file system.
 As part of addressing this need, [RFC7931] introduces trunking into
 NFS version 4.0 along with a trunking detection mechanism.  A
 trunking detection mechanism enables a client to determine whether
 two distinct network addresses are connected to the same NFS version
 4.0 server instance.  Without this knowledge, a client unaware of a
 trunking relationship between paths it is using simultaneously is
 likely to become confused in ways described in [RFC7530].
 NFSv4.1 was defined with an integral means of trunking detection,
 which is described in [RFC5661].  NFSv4.0 initially did not have
 trunking detection; it was added by [RFC7931].  Nevertheless, the use
 of the concept of server-trunkability is the same in both protocol
 versions.
 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, recovery processing of
 client migration needs to deal with the possibility of multiple
 server addresses in a returned fs_locations attribute.  In addition,
 the content 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.

Lever & Noveck Standards Track [Page 3] RFC 8587 NFSv4.0 Trunking Update May 2019

 Therefore, the goals of the current document are as follows:
 o  To provide NFS version 4.0 with a means of finding addresses that
    are trunkable with a given address, i.e., trunking discovery,
    compatible with the means of trunking detection introduced by
    [RFC7931].  For an explanation of trunking detection and
    discovery, see Section 3.
 o  To describe how NFS version 4.0 clients are to handle the presence
    of multiple network addresses associated with 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 Sections 5 and 6.

2. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "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. Terminology

 Most of the terms related to handling the fs_locations attribute are
 appropriately defined in Section 5.1.  However, there are a few
 terminological issues regarding the use of terms outside the context
 of text updating [RFC7530] that are explained in this section.  Note
 that the definitions of trunking-related terms in Section 5.1 apply
 throughout this document, including in explanatory sections that will
 not replace any text in [RFC7530].
 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".  Access to a specific
    server network address might involve the use of multiple network
    ports, since the ports to be used for particular types of
    connections might be required to be different.

Lever & Noveck Standards Track [Page 4] RFC 8587 NFSv4.0 Trunking Update May 2019

 o  Clients may establish connections to NFSv4 servers via one of
    several connection types, supporting the NFSv4 protocol layered on
    top of an RPC stream transport, as described in [RFC5531], or on
    top of RPC-over-RDMA, as described in [RFC8166].  The combination
    of a server network address and a particular connection type is
    referred to as a "server endpoint".
 o  Each network address, when combined with a pathname providing the
    location of a file system root directory relative to the
    associated server root filehandle, defines a file system network
    access path.
 o  Two network addresses connected to the same server are said to be
    server-trunkable.  Unlike subsequent NFSv4 minor versions, NFSv4.0
    recognizes only a single type of trunking relationship between
    addresses.
 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 the current document, a full
 explanation of this term requires explanation of related terms
 connected to the fs_locations attribute, which is provided in
 Section 5.1 of the current document.
 The term is also used in previous documents about NFSv4.0 (i.e.,
 [RFC7530] and [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 that have server-trunkable network
 addresses and the same root-relative file system pathname is
 considered to be a single replica with multiple network access paths.
 Although [RFC7931] enables an NFSv4.0 client to determine whether two
 network addresses are server-trunkable, it never describes the
 addresses as connected to a single replica, in effect leaving the
 approach established in [RFC7530].
 Note that this document, except when explaining problems in
 [RFC7530], always uses the new definition, including in text intended
 to replace existing sections of [RFC7530].

Lever & Noveck Standards Track [Page 5] RFC 8587 NFSv4.0 Trunking Update May 2019

4. 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 version
 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  This document [RFC8587]
 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 an explanation about why and how changes are to be made,
    but they 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.  The titles of the replacement sections
    indicate what section of [RFC7530] is to be replaced.
 o  An additional section contains text that, 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.  The titles of the additional sections
    provide an indication of where the new section would appear when
    consolidated with [RFC7530].
 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.

Lever & Noveck Standards Track [Page 6] RFC 8587 NFSv4.0 Trunking Update May 2019

 Additional and replacement sections sometimes contain references to
 the "current document" by which RFC 8587 is meant.  When those
 sections are incorporated in a consolidated document, those
 references will need to be updated to refer to the appropriate
 sections in that new document.

5. Changes within Section 8 of RFC 7530

 Most of the updates to [RFC7530] that provide support for trunking
 using the fs_locations attribute apply to Section 8 ("Multi-Server
 Namespace") of that document.  In the following list, the replacing
 section refers to its numbering in this document.
 o  Section 5.1 replaces Section 8.1 ("Location Attributes") of
    [RFC7530].  The text in the original 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 5.2 updates Section 8.4 ("Uses of Location Information")
    of [RFC7530].  This section comprises the bulk of the updates.
    Each paragraph of Section 8.4 and its subsections have been
    reviewed to clarify the provision of trunking-related information
    using the fs_locations attribute.
  • Section 5.2.1 replaces the introductory material within

Section 8.4 of [RFC7530], i.e., the material within Section 8.4

       exclusive of subsections.
  • Section 5.2.2 is to be added as a new subsection of Section 8.4

before the updated Section 8.4.1 of [RFC7530]. In a

       consolidated document, it would appear as Section 8.4.1.
  • Section 5.2.3 is to be added as a new subsection of Section 8.4

before the updated Section 8.4.1 of [RFC7530]. In a

       consolidated document, it would appear as Section 8.4.2.
  • Section 5.2.4 replaces Section 8.4.1 ("File System

Replication") of [RFC7530]. In a consolidated document, it

       would appear as Section 8.4.3.
  • Section 5.2.5 replaces Section 8.4.2 ("File System Migration")

of [RFC7530]. In a consolidated document, it would appear as

       Section 8.4.4.

Lever & Noveck Standards Track [Page 7] RFC 8587 NFSv4.0 Trunking Update May 2019

  • Section 5.2.6 is to be added as a new subsection of Section 8.4

before Section 8.4.3 of [RFC7530]. In a consolidated document,

       it would appear as Section 8.4.5, while the existing
       Section 8.3 would appear as Section 8.4.6.
 o  Section 5.3 replaces Section 8.5 ("Location Entries and Server
    Identity") of [RFC7530].  The last paragraph of the existing
    section has been removed.

5.1. Updated Section "Location Attributes" (Currently Section 8.1)

 The fs_locations 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 hostname representing one or
 more network addresses or as 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 instance 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 attributes include only the fs_locations GETATTR
    attribute.
 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).  A
    file system location entry designates a set of network addresses
    to which clients may establish connections.  The entry may
    designate multiple such addresses because the server hostname may
    map to multiple network addresses and because multiple connection

Lever & Noveck Standards Track [Page 8] RFC 8587 NFSv4.0 Trunking Update May 2019

    types may be used to communicate with each specified network
    address.  Such addresses provide multiple ways of connecting to a
    single server.
    Clients use the NFSv4.0 trunking detection mechanism [RFC7931] to
    confirm that such addresses are connected to the same server.  The
    client can ignore non-confirmed trunking relationships and treat
    the corresponding addresses as connected to different servers.
 o  File system location elements are derived from file system
    location entries.  If a file system location entry specifies a
    network address, there is only a single corresponding location
    element.  When a file system location entry contains a hostname,
    the client resolves the hostname, producing one file system
    location element for each of the resulting network addresses.
    Issues regarding the trustworthiness of hostname resolutions are
    further discussed in Section 7 of the current document.
 o  All file system location elements consist of a file system
    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  If the server has no pseudo-fs and only has a single exported file
    system at the root filehandle, the fs_name may be empty.

5.2. Updates to "Uses of Location Information" (Currently Section 8.4)

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

5.2.1. Updates to the Introductory Text of the Current Section 8.4

 Together with the possibility of absent file systems, the
 fs_locations attribute bears file system locations and a number of
 important facilities that enable reliable, manageable, and scalable
 data access.
 When a file system is present on the queried server, this attribute
 can provide a set of alternate locations that clients may use to
 access the file system, when necessary.  Provision of such alternate
 file system locations is referred to as "replication" and is further
 described in Section 5.2.4 of the current document.
 When alternative file system locations are provided, they may
 represent distinct physical copies of the same file system data or
 separate NFS server instances that provide access to the same

Lever & Noveck Standards Track [Page 9] RFC 8587 NFSv4.0 Trunking Update May 2019

 physical file system.  Another possible use of the provision of
 multiple file system location entries is trunking, wherein the file
 system location entries do not, in fact, represent different servers
 but rather are distinct network paths to the same server.
 A client may use file system location elements simultaneously to
 provide higher-performance access to the target file system.  This
 can be done using trunking, although the use of multiple replicas
 simultaneously is possible.  To enable simultaneous access, the
 client utilizes trunking detection and/or discovery, further
 described in Section 5.2.2 of the current document, to determine a
 set of network paths that are server-trunkable with the path
 currently being used to access the file system.  Once this
 determination is made, requests may be routed across multiple paths
 using the existing state management mechanism.
 Multiple replicas may also be used simultaneously, typically when
 accessing read-only datasets.  In this case, each replica requires
 its own state management.  The client performs multiple file opens to
 read the same file content from multiple replicas.
 When a file system is present and subsequently becomes absent,
 clients can be given the opportunity to have continued access to
 their data at an alternative file system location.  Transfer of the
 file system contents to the new file system 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 Sections
 5.2.5 and 5.2.6 of the current document for details.
 The fs_locations attribute can designate one or more remote file
 system 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.

Lever & Noveck Standards Track [Page 10] RFC 8587 NFSv4.0 Trunking Update May 2019

5.2.2. New Subsection Titled "Trunking Discovery and Detection"

      (Becomes Section 8.4.1)
 "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 the NFS
 server identity to manage lease and lock states 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 whether two 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 (UCS)
 approach, 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
 hostname or one of an NFSv4 server's network addresses, can obtain
 other candidate network addresses that are trunkable with the NFSv4
 server's network address, i.e., a set of addresses that might be
 connected to the same NFSv4 server instance.  An NFSv4.0 client can
 discover server-trunkable network addresses in a number of ways:
 o  An NFS server's hostname is provided either at mount time or in a
    returned file system location entry.  A DNS query of this hostname
    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 corresponds to the
 same NFSv4.0 server instance; thus, any of them can be used to access
 that server.

Lever & Noveck Standards Track [Page 11] RFC 8587 NFSv4.0 Trunking Update May 2019

5.2.3. New Subsection Titled "Location Attributes and Selection of

      Connection Type" (Becomes Section 8.4.2)
 NFS version 4.0 may be implemented using a number of different types
 of connections:
    Stream connections may be used to provide RPC service, as
    described in [RFC5531].
    RDMA-capable connections may be used to provide RPC service, as
    described in [RFC8166].
 Because of the need to support multiple connection types, clients
 face the issue of determining the proper connection type to use when
 establishing a connection to a server network address.  The
 fs_locations attribute provides no information to support selection
 of the connection type.  As a result, clients supporting multiple
 connection types need to attempt to establish a connection on various
 connection types, allowing it to determine, via a trial-and-error
 approach, which connection types are supported.
 If a client strongly prefers one connection type, it can perform
 these attempts serially in order of declining preference.  Once there
 is a successful attempt, the established connection can be used.
 Note that with this approach, network partitions can result in a
 sequence of long waits for a successful connection.
 To avoid waiting when there is at least one viable network path
 available, simultaneous attempts to establish multiple connection
 types are possible.  Once a viable connection is established, the
 client discards less-preferred connections.

5.2.4. Updated Section "File System Replication" (Becomes Section 8.4.3

      Retitled "File System Replication and Trunking"
 On first access to a file system, the client should obtain the value
 of the set of alternative file system locations by interrogating the
 fs_locations attribute.  Trunking discovery and/or detection can then
 be applied to the file system 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 the client and
 target file system.
 In the event that server failure, communication problems, or other
 difficulties make continued access to the current file system
 impossible or otherwise impractical, the client can use the

Lever & Noveck Standards Track [Page 12] RFC 8587 NFSv4.0 Trunking Update May 2019

 alternative file system locations as a way to maintain continued
 access to the file system.  See Section 5.2.6 of the current document
 for more detail.

5.2.5. Updated Section "File System Migration" (Becomes Section 8.4.4)

 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 file system 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 5.2.6 of the current document for more detail.
 Such migration can help provide 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 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
 the client and server.
 When the client receives indication of a migration event via an
 NFS4ERR_MOVED error, data propagation to the destination server must
 have already occurred.  Once the client proceeds to access the
 alternate file system location, it must see 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 the file system state.

Lever & Noveck Standards Track [Page 13] RFC 8587 NFSv4.0 Trunking Update May 2019

5.2.6. New Subsection Titled "Interaction of Trunking, Migration, and

      Replication" (Becomes Section 8.4.5)
 When the set of network addresses on a server changes in a way that
 would affect a file system location attribute, there are several
 possible outcomes for clients currently accessing that file system.
 NFS4ERR_MOVED is returned only when the server cannot satisfy a
 request from the client, whether because the file system has been
 migrated to a different server or is only accessible at a different
 trunked address on the same server, or for some other reason.  In
 cases 1 and 2 below, NFS4ERR_MOVED is not returned.
 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.  Alternatively, the
     client may treat that address as it does a replica -- to be used
     if the 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 to access that file
     system 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 prior to migration, and multiple addresses may be available
 for use on the destination server.
 With regard to the server in use, a return of NFS4ERR_MOVED may
 indicate 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 that server are not usable.

Lever & Noveck Standards Track [Page 14] RFC 8587 NFSv4.0 Trunking Update May 2019

 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.
 Although significant harm cannot 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.  When such a
 lock is lost, it is the responsibility of the destination server to
 provide for its recovery via the use of an fs-specific grace period.
 With regard to the destination server, it is desirable for the client
 to be aware of all 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 file
 system location elements in parallel with normal use of the first
 valid file system location entry found to access the destination.
 Because a file system location attribute may include entries relating
 to the current server, the migration destination, and possible
 replicas to use, scanning for available network addresses that might
 be trunkable with addresses the client has already seen could
 potentially be a long process.  To keep this process as short as
 possible, servers that provide information about trunkable network
 paths are REQUIRED to place file system location entries that
 represent addresses usable with the current server or a migration
 target before those associated with replicas.
 This ordering allows a client to cease scanning for trunkable file
 system location entries once it encounters a file system location
 element whose fs_name differs from the current fs_name or whose
 address is not server-trunkable with the address it is currently
 using.  Although the possibility exists that a client might
 prematurely cease scanning for trunkable addresses when receiving a
 location attribute from an older server that does not follow the
 ordering constraint above, the harm is expected to be limited since
 such servers would not be expected to present information about
 trunkable server access paths.

Lever & Noveck Standards Track [Page 15] RFC 8587 NFSv4.0 Trunking Update May 2019

5.3. Updated Section "Location Entries and Server Identity"

    (Section 8.5)
 As mentioned above, a single file system location entry may have a
 server address target in the form of a DNS hostname that resolves to
 multiple network addresses; it is also possible for multiple file
 system location entries to have their own server address targets that
 reference the same server.
 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, file systems at corresponding namespace locations
 exist for each of the other server-trunkable 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.
 If a single file system location entry designates multiple server IP
 addresses, the client should choose a single one to use.  When two
 server addresses are designated by a single file system location
 entry and they correspond to different servers, this normally
 indicates some sort of misconfiguration.  The client should avoid
 using such file system location entries when alternatives are
 available.  When they are not, the client should pick one of the IP
 addresses and use it without using others that are not directed to
 the same server.

6. Updates to RFC 7530 outside Section 8

 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.

7. Updates to the Security Considerations Section of RFC 7530

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

Lever & Noveck Standards Track [Page 16] RFC 8587 NFSv4.0 Trunking Update May 2019

    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 hostnames 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., [RFC8446]) can also offer strong authentication
       of NFS servers.
    o  Fetching file system 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 the transit of returned
       file system location information.  The client implementer needs
       to recognize that using such information to access an NFS
       server without use of 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 [RFC7530] REQUIRES "implementations" to
       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 file system location
    entries that correspond to file systems on other servers using
    only hostnames.  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 hostname provided while ensuring that
    the response has not been corrupted.
    When RPCSEC_GSS is not available on an NFS server, returned file
    system 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

Lever & Noveck Standards Track [Page 17] RFC 8587 NFSv4.0 Trunking Update May 2019

    the destination, this server might validly represent itself as the
    server to which the client was erroneously directed.  Without a
    way to decide whether the server is a valid one, the client can
    only determine, using RPCSEC_GSS, that the server corresponds to
    the hostname provided, with no basis for trusting that server.
    The client should not use such unverified file system location
    entries as a basis for migration, even though RPCSEC_GSS might be
    available on the destination server.
    When a file system location attribute is fetched upon connecting
    with an NFSv4 server, it SHOULD, as stated above, be done using
    RPCSEC_GSS with integrity protection.
    When file system 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
    ensure 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 network addresses 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 file system location information for these
    purposes.
    To summarize considerations regarding the use of RPCSEC_GSS in
    fetching file system location information, consider the following
    recommendations 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 file system 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.

Lever & Noveck Standards Track [Page 18] RFC 8587 NFSv4.0 Trunking Update May 2019

    Privacy considerations relating to uniform client strings (UCS)
    versus non-uniform client strings (non-UCS), discussed in
    Section 5.6 of [RFC7931], are also applicable to their usage for
    trunking detection in NFS version 4.0.

8. IANA Considerations

 This document has no IANA actions.

9. Updates to the References Section in RFC 7530

 The following references should be added to the Normative References
 section of [RFC7530]:
 [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>.
 [RFC8166]  Lever, C., Ed., Simpson, W., and T. Talpey, "Remote
            Direct Memory Access Transport for Remote Procedure
            Call Version 1", RFC 8166, DOI 10.17487/RFC8166,
            June 2017, <https://www.rfc-editor.org/info/rfc8166>.
 The following references should be added to the Informative
 References section of [RFC7530]:
 [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>.
 [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>.
 [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
            Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
            <https://www.rfc-editor.org/info/rfc8446>.

Lever & Noveck Standards Track [Page 19] RFC 8587 NFSv4.0 Trunking Update May 2019

10. References

10.1. 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>.
 [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>.
 [RFC8166]  Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
            Memory Access Transport for Remote Procedure Call Version
            1", RFC 8166, DOI 10.17487/RFC8166, June 2017,
            <https://www.rfc-editor.org/info/rfc8166>.
 [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>.

Lever & Noveck Standards Track [Page 20] RFC 8587 NFSv4.0 Trunking Update May 2019

10.2. 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>.
 [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>.
 [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
            Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
            <https://www.rfc-editor.org/info/rfc8446>.

Lever & Noveck Standards Track [Page 21] RFC 8587 NFSv4.0 Trunking Update May 2019

Appendix A. Section Classification

 All sections of the current document are considered explanatory with
 the following exceptions.
 o  Sections 5.1, 5.2.4, 5.2.5, and 5.3 are replacement sections.
 o  Sections 5.2.2, 5.2.3, and 5.2.6 are additional sections.
 o  Sections 5.2.1, 6, 7, and Section 9 are editing sections.

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 for his support of this work
 and Robert Thurlow for his review and suggestions.
 Special thanks go to Transport Area Director Spencer Dawkins, NFSV4
 Working Group Chairs Spencer Shepler and Brian Pawlowski, and NFSV4
 Working Group Secretary Thomas Haynes for their ongoing support.  We
 are also grateful for the thorough review of this document by
 Benjamin Kaduk and Ben Campbell.

Authors' Addresses

 Charles Lever (editor)
 Oracle Corporation
 United States of America
 Email: chuck.lever@oracle.com
 David Noveck
 NetApp
 United States of America
 Email: davenoveck@gmail.com

Lever & Noveck Standards Track [Page 22]

/data/webs/external/dokuwiki/data/pages/rfc/rfc8587.txt · Last modified: 2019/05/07 18:38 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki