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RFC 3010


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NFS version 4 Protocol

Part 1 of 8, p. 1 to 23
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Obsoleted by:    3530


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Network Working Group                                         S. Shepler
Request for Comments: 3010                                  B. Callaghan
Obsoletes: 1813, 1094                                        D. Robinson
Category: Standards Track                                     R. Thurlow
                                                   Sun Microsystems Inc.
                                                                C. Beame
                                                        Hummingbird Ltd.
                                                               M. Eisler
                                                           Zambeel, Inc.
                                                               D. Noveck
                                                 Network Appliance, Inc.
                                                           December 2000


                         NFS version 4 Protocol

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   NFS (Network File System) version 4 is a distributed file system
   protocol which owes heritage to NFS protocol versions 2 [RFC1094] and
   3 [RFC1813].  Unlike earlier versions, the NFS version 4 protocol
   supports traditional file access while integrating support for file
   locking and the mount protocol.  In addition, support for strong
   security (and its negotiation), compound operations, client caching,
   and internationalization have been added.  Of course, attention has
   been applied to making NFS version 4 operate well in an Internet
   environment.

Key Words

   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 RFC 2119.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   5
   1.1.  Overview of NFS Version 4 Features . . . . . . . . . . . .   6
   1.1.1.  RPC and Security . . . . . . . . . . . . . . . . . . . .   6
   1.1.2.  Procedure and Operation Structure  . . . . . . . . . . .   7
   1.1.3.  File System Model  . . . . . . . . . . . . . . . . . . .   8
   1.1.3.1.  Filehandle Types . . . . . . . . . . . . . . . . . . .   8
   1.1.3.2.  Attribute Types  . . . . . . . . . . . . . . . . . . .   8
   1.1.3.3.  File System Replication and Migration  . . . . . . . .   9
   1.1.4.  OPEN and CLOSE . . . . . . . . . . . . . . . . . . . . .   9
   1.1.5.  File locking . . . . . . . . . . . . . . . . . . . . . .   9
   1.1.6.  Client Caching and Delegation  . . . . . . . . . . . . .  10
   1.2.  General Definitions  . . . . . . . . . . . . . . . . . . .  11
   2.  Protocol Data Types  . . . . . . . . . . . . . . . . . . . .  12
   2.1.  Basic Data Types . . . . . . . . . . . . . . . . . . . . .  12
   2.2.  Structured Data Types  . . . . . . . . . . . . . . . . . .  14
   3.  RPC and Security Flavor  . . . . . . . . . . . . . . . . . .  18
   3.1.  Ports and Transports . . . . . . . . . . . . . . . . . . .  18
   3.2.  Security Flavors . . . . . . . . . . . . . . . . . . . . .  18
   3.2.1.  Security mechanisms for NFS version 4  . . . . . . . . .  19
   3.2.1.1.  Kerberos V5 as security triple . . . . . . . . . . . .  19
   3.2.1.2.  LIPKEY as a security triple  . . . . . . . . . . . . .  19
   3.2.1.3.  SPKM-3 as a security triple  . . . . . . . . . . . . .  20
   3.3.  Security Negotiation . . . . . . . . . . . . . . . . . . .  21
   3.3.1.  Security Error . . . . . . . . . . . . . . . . . . . . .  21
   3.3.2.  SECINFO  . . . . . . . . . . . . . . . . . . . . . . . .  21
   3.4.  Callback RPC Authentication  . . . . . . . . . . . . . . .  22
   4.  Filehandles  . . . . . . . . . . . . . . . . . . . . . . . .  23
   4.1.  Obtaining the First Filehandle . . . . . . . . . . . . . .  24
   4.1.1.  Root Filehandle  . . . . . . . . . . . . . . . . . . . .  24
   4.1.2.  Public Filehandle  . . . . . . . . . . . . . . . . . . .  24
   4.2.  Filehandle Types . . . . . . . . . . . . . . . . . . . . .  25
   4.2.1.  General Properties of a Filehandle . . . . . . . . . . .  25
   4.2.2.  Persistent Filehandle  . . . . . . . . . . . . . . . . .  26
   4.2.3.  Volatile Filehandle  . . . . . . . . . . . . . . . . . .  26
   4.2.4.  One Method of Constructing a Volatile Filehandle . . . .  28
   4.3.  Client Recovery from Filehandle Expiration . . . . . . . .  28
   5.  File Attributes  . . . . . . . . . . . . . . . . . . . . . .  29
   5.1.  Mandatory Attributes . . . . . . . . . . . . . . . . . . .  30
   5.2.  Recommended Attributes . . . . . . . . . . . . . . . . . .  30
   5.3.  Named Attributes . . . . . . . . . . . . . . . . . . . . .  31
   5.4.  Mandatory Attributes - Definitions . . . . . . . . . . . .  31
   5.5.  Recommended Attributes - Definitions . . . . . . . . . . .  33
   5.6.  Interpreting owner and owner_group . . . . . . . . . . . .  38
   5.7.  Character Case Attributes  . . . . . . . . . . . . . . . .  39
   5.8.  Quota Attributes . . . . . . . . . . . . . . . . . . . . .  39
   5.9.  Access Control Lists . . . . . . . . . . . . . . . . . . .  40

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   5.9.1.  ACE type . . . . . . . . . . . . . . . . . . . . . . . .  41
   5.9.2.  ACE flag . . . . . . . . . . . . . . . . . . . . . . . .  41
   5.9.3.  ACE Access Mask  . . . . . . . . . . . . . . . . . . . .  43
   5.9.4.  ACE who  . . . . . . . . . . . . . . . . . . . . . . . .  44
   6.  File System Migration and Replication  . . . . . . . . . . .  44
   6.1.  Replication  . . . . . . . . . . . . . . . . . . . . . . .  45
   6.2.  Migration  . . . . . . . . . . . . . . . . . . . . . . . .  45
   6.3.  Interpretation of the fs_locations Attribute . . . . . . .  46
   6.4.  Filehandle Recovery for Migration or Replication . . . . .  47
   7.  NFS Server Name Space  . . . . . . . . . . . . . . . . . . .  47
   7.1.  Server Exports . . . . . . . . . . . . . . . . . . . . . .  47
   7.2.  Browsing Exports . . . . . . . . . . . . . . . . . . . . .  48
   7.3.  Server Pseudo File System  . . . . . . . . . . . . . . . .  48
   7.4.  Multiple Roots . . . . . . . . . . . . . . . . . . . . . .  49
   7.5.  Filehandle Volatility  . . . . . . . . . . . . . . . . . .  49
   7.6.  Exported Root  . . . . . . . . . . . . . . . . . . . . . .  49
   7.7.  Mount Point Crossing . . . . . . . . . . . . . . . . . . .  49
   7.8.  Security Policy and Name Space Presentation  . . . . . . .  50
   8.  File Locking and Share Reservations  . . . . . . . . . . . .  50
   8.1.  Locking  . . . . . . . . . . . . . . . . . . . . . . . . .  51
   8.1.1.  Client ID  . . . . . . . . . . . . . . . . . . . . . . .  51
   8.1.2.  Server Release of Clientid . . . . . . . . . . . . . . .  53
   8.1.3.  nfs_lockowner and stateid Definition . . . . . . . . . .  54
   8.1.4.  Use of the stateid . . . . . . . . . . . . . . . . . . .  55
   8.1.5.  Sequencing of Lock Requests  . . . . . . . . . . . . . .  56
   8.1.6.  Recovery from Replayed Requests  . . . . . . . . . . . .  56
   8.1.7.  Releasing nfs_lockowner State  . . . . . . . . . . . . .  57
   8.2.  Lock Ranges  . . . . . . . . . . . . . . . . . . . . . . .  57
   8.3.  Blocking Locks . . . . . . . . . . . . . . . . . . . . . .  58
   8.4.  Lease Renewal  . . . . . . . . . . . . . . . . . . . . . .  58
   8.5.  Crash Recovery . . . . . . . . . . . . . . . . . . . . . .  59
   8.5.1.  Client Failure and Recovery  . . . . . . . . . . . . . .  59
   8.5.2.  Server Failure and Recovery  . . . . . . . . . . . . . .  60
   8.5.3.  Network Partitions and Recovery  . . . . . . . . . . . .  62
   8.6.  Recovery from a Lock Request Timeout or Abort  . . . . . .  63
   8.7.  Server Revocation of Locks . . . . . . . . . . . . . . . .  63
   8.8.  Share Reservations . . . . . . . . . . . . . . . . . . . .  65
   8.9.  OPEN/CLOSE Operations  . . . . . . . . . . . . . . . . . .  65
   8.10.  Open Upgrade and Downgrade  . . . . . . . . . . . . . . .  66
   8.11.  Short and Long Leases . . . . . . . . . . . . . . . . . .  66
   8.12.  Clocks and Calculating Lease Expiration . . . . . . . . .  67
   8.13.  Migration, Replication and State  . . . . . . . . . . . .  67
   8.13.1.  Migration and State . . . . . . . . . . . . . . . . . .  67
   8.13.2.  Replication and State . . . . . . . . . . . . . . . . .  68
   8.13.3.  Notification of Migrated Lease  . . . . . . . . . . . .  69
   9.  Client-Side Caching  . . . . . . . . . . . . . . . . . . . .  69
   9.1.  Performance Challenges for Client-Side Caching . . . . . .  70
   9.2.  Delegation and Callbacks . . . . . . . . . . . . . . . . .  71

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   9.2.1.  Delegation Recovery  . . . . . . . . . . . . . . . . . .  72
   9.3.  Data Caching . . . . . . . . . . . . . . . . . . . . . . .  74
   9.3.1.  Data Caching and OPENs . . . . . . . . . . . . . . . . .  74
   9.3.2.  Data Caching and File Locking  . . . . . . . . . . . . .  75
   9.3.3.  Data Caching and Mandatory File Locking  . . . . . . . .  77
   9.3.4.  Data Caching and File Identity . . . . . . . . . . . . .  77
   9.4.  Open Delegation  . . . . . . . . . . . . . . . . . . . . .  78
   9.4.1.  Open Delegation and Data Caching . . . . . . . . . . . .  80
   9.4.2.  Open Delegation and File Locks . . . . . . . . . . . . .  82
   9.4.3.  Recall of Open Delegation  . . . . . . . . . . . . . . .  82
   9.4.4.  Delegation Revocation  . . . . . . . . . . . . . . . . .  84
   9.5.  Data Caching and Revocation  . . . . . . . . . . . . . . .  84
   9.5.1.  Revocation Recovery for Write Open Delegation  . . . . .  85
   9.6.  Attribute Caching  . . . . . . . . . . . . . . . . . . . .  85
   9.7.  Name Caching . . . . . . . . . . . . . . . . . . . . . . .  86
   9.8.  Directory Caching  . . . . . . . . . . . . . . . . . . . .  87
   10.  Minor Versioning  . . . . . . . . . . . . . . . . . . . . .  88
   11.  Internationalization  . . . . . . . . . . . . . . . . . . .  91
   11.1.  Universal Versus Local Character Sets . . . . . . . . . .  91
   11.2.  Overview of Universal Character Set Standards . . . . . .  92
   11.3.  Difficulties with UCS-4, UCS-2, Unicode . . . . . . . . .  93
   11.4.  UTF-8 and its solutions . . . . . . . . . . . . . . . . .  94
   11.5.  Normalization . . . . . . . . . . . . . . . . . . . . . .  94
   12.  Error Definitions . . . . . . . . . . . . . . . . . . . . .  95
   13.  NFS Version 4 Requests  . . . . . . . . . . . . . . . . . .  99
   13.1.  Compound Procedure  . . . . . . . . . . . . . . . . . . . 100
   13.2.  Evaluation of a Compound Request  . . . . . . . . . . . . 100
   13.3.  Synchronous Modifying Operations  . . . . . . . . . . . . 101
   13.4.  Operation Values  . . . . . . . . . . . . . . . . . . . . 102
   14.  NFS Version 4 Procedures  . . . . . . . . . . . . . . . . . 102
   14.1.  Procedure 0: NULL - No Operation  . . . . . . . . . . . . 102
   14.2.  Procedure 1: COMPOUND - Compound Operations . . . . . . . 102
   14.2.1.  Operation 3: ACCESS - Check Access Rights . . . . . . . 105
   14.2.2.  Operation 4: CLOSE - Close File . . . . . . . . . . . . 108
   14.2.3.  Operation 5: COMMIT - Commit Cached Data  . . . . . . . 109
   14.2.4.  Operation 6: CREATE - Create a Non-Regular File Object. 112
   14.2.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery  . . . . . . . . . . . . . . . . . . . . . . . 114
   14.2.6.  Operation 8: DELEGRETURN - Return Delegation  . . . . . 115
   14.2.7.  Operation 9: GETATTR - Get Attributes . . . . . . . . . 115
   14.2.8.  Operation 10: GETFH - Get Current Filehandle  . . . . . 117
   14.2.9.  Operation 11: LINK - Create Link to a File  . . . . . . 118
   14.2.10.  Operation 12: LOCK - Create Lock . . . . . . . . . . . 119
   14.2.11.  Operation 13: LOCKT - Test For Lock  . . . . . . . . . 121
   14.2.12.  Operation 14: LOCKU - Unlock File  . . . . . . . . . . 122
   14.2.13.  Operation 15: LOOKUP - Lookup Filename . . . . . . . . 123
   14.2.14.  Operation 16: LOOKUPP - Lookup Parent Directory  . . . 126

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   14.2.15.  Operation 17: NVERIFY - Verify Difference in
             Attributes . . . . . . . . . . . . . . . . . . . . . . 127
   14.2.16.  Operation 18: OPEN - Open a Regular File . . . . . . . 128
   14.2.17.  Operation 19: OPENATTR - Open Named Attribute
             Directory  . . . . . . . . . . . . . . . . . . . . . . 137
   14.2.18.  Operation 20: OPEN_CONFIRM - Confirm Open  . . . . . . 138
   14.2.19.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access 140
   14.2.20.  Operation 22: PUTFH - Set Current Filehandle . . . . . 141
   14.2.21.  Operation 23: PUTPUBFH - Set Public Filehandle . . . . 142
   14.2.22.  Operation 24: PUTROOTFH - Set Root Filehandle  . . . . 143
   14.2.23.  Operation 25: READ - Read from File  . . . . . . . . . 144
   14.2.24.  Operation 26: READDIR - Read Directory . . . . . . . . 146
   14.2.25.  Operation 27: READLINK - Read Symbolic Link  . . . . . 150
   14.2.26.  Operation 28: REMOVE - Remove Filesystem Object  . . . 151
   14.2.27.  Operation 29: RENAME - Rename Directory Entry  . . . . 153
   14.2.28.  Operation 30: RENEW - Renew a Lease  . . . . . . . . . 155
   14.2.29.  Operation 31: RESTOREFH - Restore Saved Filehandle . . 156
   14.2.30.  Operation 32: SAVEFH - Save Current Filehandle . . . . 157
   14.2.31.  Operation 33: SECINFO - Obtain Available Security  . . 158
   14.2.32.  Operation 34: SETATTR - Set Attributes . . . . . . . . 160
   14.2.33.  Operation 35: SETCLIENTID - Negotiate Clientid . . . . 162
   14.2.34.  Operation 36: SETCLIENTID_CONFIRM - Confirm Clientid . 163
   14.2.35.  Operation 37: VERIFY - Verify Same Attributes  . . . . 164
   14.2.36.  Operation 38: WRITE - Write to File  . . . . . . . . . 166
   15.  NFS Version 4 Callback Procedures . . . . . . . . . . . . . 170
   15.1.  Procedure 0: CB_NULL - No Operation . . . . . . . . . . . 170
   15.2.  Procedure 1: CB_COMPOUND - Compound Operations  . . . . . 171
   15.2.1.  Operation 3: CB_GETATTR - Get Attributes  . . . . . . . 172
   15.2.2.  Operation 4: CB_RECALL - Recall an Open Delegation  . . 173
   16.  Security Considerations . . . . . . . . . . . . . . . . . . 174
   17.  IANA Considerations . . . . . . . . . . . . . . . . . . . . 174
   17.1.  Named Attribute Definition  . . . . . . . . . . . . . . . 174
   18.  RPC definition file . . . . . . . . . . . . . . . . . . . . 175
   19.  Bibliography  . . . . . . . . . . . . . . . . . . . . . . . 206
   20.  Authors . . . . . . . . . . . . . . . . . . . . . . . . . . 210
   20.1.  Editor's Address  . . . . . . . . . . . . . . . . . . . . 210
   20.2.  Authors' Addresses  . . . . . . . . . . . . . . . . . . . 210
   20.3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . 211
   21.  Full Copyright Statement  . . . . . . . . . . . . . . . . . 212

1.  Introduction

   The NFS version 4 protocol is a further revision of the NFS protocol
   defined already by versions 2 [RFC1094] and 3 [RFC1813].  It retains
   the essential characteristics of previous versions: design for easy
   recovery, independent of transport protocols, operating systems and
   filesystems, simplicity, and good performance.  The NFS version 4
   revision has the following goals:

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   o  Improved access and good performance on the Internet.

      The protocol is designed to transit firewalls easily, perform well
      where latency is high and bandwidth is low, and scale to very
      large numbers of clients per server.

   o  Strong security with negotiation built into the protocol.

      The protocol builds on the work of the ONCRPC working group in
      supporting the RPCSEC_GSS protocol.  Additionally, the NFS version
      4 protocol provides a mechanism to allow clients and servers the
      ability to negotiate security and require clients and servers to
      support a minimal set of security schemes.

   o  Good cross-platform interoperability.

      The protocol features a file system model that provides a useful,
      common set of features that does not unduly favor one file system
      or operating system over another.

   o  Designed for protocol extensions.

      The protocol is designed to accept standard extensions that do not
      compromise backward compatibility.

1.1.  Overview of NFS Version 4 Features

   To provide a reasonable context for the reader, the major features of
   NFS version 4 protocol will be reviewed in brief.  This will be done
   to provide an appropriate context for both the reader who is familiar
   with the previous versions of the NFS protocol and the reader that is
   new to the NFS protocols.  For the reader new to the NFS protocols,
   there is still a fundamental knowledge that is expected.  The reader
   should be familiar with the XDR and RPC protocols as described in
   [RFC1831] and [RFC1832].  A basic knowledge of file systems and
   distributed file systems is expected as well.

1.1.1.  RPC and Security

   As with previous versions of NFS, the External Data Representation
   (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFS
   version 4 protocol are those defined in [RFC1831] and [RFC1832].  To
   meet end to end security requirements, the RPCSEC_GSS framework
   [RFC2203] will be used to extend the basic RPC security.  With the
   use of RPCSEC_GSS, various mechanisms can be provided to offer
   authentication, integrity, and privacy to the NFS version 4 protocol.
   Kerberos V5 will be used as described in [RFC1964] to provide one
   security framework.  The LIPKEY GSS-API mechanism described in

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   [RFC2847] will be used to provide for the use of user password and
   server public key by the NFS version 4 protocol.  With the use of
   RPCSEC_GSS, other mechanisms may also be specified and used for NFS
   version 4 security.

   To enable in-band security negotiation, the NFS version 4 protocol
   has added a new operation which provides the client a method of
   querying the server about its policies regarding which security
   mechanisms must be used for access to the server's file system
   resources.  With this, the client can securely match the security
   mechanism that meets the policies specified at both the client and
   server.

1.1.2.  Procedure and Operation Structure

   A significant departure from the previous versions of the NFS
   protocol is the introduction of the COMPOUND procedure.  For the NFS
   version 4 protocol, there are two RPC procedures, NULL and COMPOUND.
   The COMPOUND procedure is defined in terms of operations and these
   operations correspond more closely to the traditional NFS procedures.
   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical file system
   operations.  For example, without previous contact with a server a
   client will be able to read data from a file in one request by
   combining LOOKUP, OPEN, and READ operations in a single COMPOUND RPC.
   With previous versions of the NFS protocol, this type of single
   request was not possible.

   The model used for COMPOUND is very simple.  There is no logical OR
   or ANDing of operations.  The operations combined within a COMPOUND
   request are evaluated in order by the server.  Once an operation
   returns a failing result, the evaluation ends and the results of all
   evaluated operations are returned to the client.

   The NFS version 4 protocol continues to have the client refer to a
   file or directory at the server by a "filehandle".  The COMPOUND
   procedure has a method of passing a filehandle from one operation to
   another within the sequence of operations.  There is a concept of a
   "current filehandle" and "saved filehandle".  Most operations use the
   "current filehandle" as the file system object to operate upon.  The
   "saved filehandle" is used as temporary filehandle storage within a
   COMPOUND procedure as well as an additional operand for certain
   operations.

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1.1.3.  File System Model

   The general file system model used for the NFS version 4 protocol is
   the same as previous versions.  The server file system is
   hierarchical with the regular files contained within being treated as
   opaque byte streams.  In a slight departure, file and directory names
   are encoded with UTF-8 to deal with the basics of
   internationalization.

   The NFS version 4 protocol does not require a separate protocol to
   provide for the initial mapping between path name and filehandle.
   Instead of using the older MOUNT protocol for this mapping, the
   server provides a ROOT filehandle that represents the logical root or
   top of the file system tree provided by the server.  The server
   provides multiple file systems by gluing them together with pseudo
   file systems.  These pseudo file systems provide for potential gaps
   in the path names between real file systems.

1.1.3.1.  Filehandle Types

   In previous versions of the NFS protocol, the filehandle provided by
   the server was guaranteed to be valid or persistent for the lifetime
   of the file system object to which it referred.  For some server
   implementations, this persistence requirement has been difficult to
   meet.  For the NFS version 4 protocol, this requirement has been
   relaxed by introducing another type of filehandle, volatile.  With
   persistent and volatile filehandle types, the server implementation
   can match the abilities of the file system at the server along with
   the operating environment.  The client will have knowledge of the
   type of filehandle being provided by the server and can be prepared
   to deal with the semantics of each.

1.1.3.2.  Attribute Types

   The NFS version 4 protocol introduces three classes of file system or
   file attributes.  Like the additional filehandle type, the
   classification of file attributes has been done to ease server
   implementations along with extending the overall functionality of the
   NFS protocol.  This attribute model is structured to be extensible
   such that new attributes can be introduced in minor revisions of the
   protocol without requiring significant rework.

   The three classifications are: mandatory, recommended and named
   attributes.  This is a significant departure from the previous
   attribute model used in the NFS protocol.  Previously, the attributes
   for the file system and file objects were a fixed set of mainly Unix
   attributes.  If the server or client did not support a particular
   attribute, it would have to simulate the attribute the best it could.

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   Mandatory attributes are the minimal set of file or file system
   attributes that must be provided by the server and must be properly
   represented by the server.  Recommended attributes represent
   different file system types and operating environments.  The
   recommended attributes will allow for better interoperability and the
   inclusion of more operating environments.  The mandatory and
   recommended attribute sets are traditional file or file system
   attributes.  The third type of attribute is the named attribute.  A
   named attribute is an opaque byte stream that is associated with a
   directory or file and referred to by a string name.  Named attributes
   are meant to be used by client applications as a method to associate
   application specific data with a regular file or directory.

   One significant addition to the recommended set of file attributes is
   the Access Control List (ACL) attribute.  This attribute provides for
   directory and file access control beyond the model used in previous
   versions of the NFS protocol.  The ACL definition allows for
   specification of user and group level access control.

1.1.3.3.  File System Replication and Migration

   With the use of a special file attribute, the ability to migrate or
   replicate server file systems is enabled within the protocol.  The
   file system locations attribute provides a method for the client to
   probe the server about the location of a file system.  In the event
   of a migration of a file system, the client will receive an error
   when operating on the file system and it can then query as to the new
   file system location.  Similar steps are used for replication, the
   client is able to query the server for the multiple available
   locations of a particular file system.  From this information, the
   client can use its own policies to access the appropriate file system
   location.

1.1.4.  OPEN and CLOSE

   The NFS version 4 protocol introduces OPEN and CLOSE operations.  The
   OPEN operation provides a single point where file lookup, creation,
   and share semantics can be combined.  The CLOSE operation also
   provides for the release of state accumulated by OPEN.

1.1.5.  File locking

   With the NFS version 4 protocol, the support for byte range file
   locking is part of the NFS protocol.  The file locking support is
   structured so that an RPC callback mechanism is not required.  This
   is a departure from the previous versions of the NFS file locking
   protocol, Network Lock Manager (NLM).  The state associated with file
   locks is maintained at the server under a lease-based model.  The

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   server defines a single lease period for all state held by a NFS
   client.  If the client does not renew its lease within the defined
   period, all state associated with the client's lease may be released
   by the server.  The client may renew its lease with use of the RENEW
   operation or implicitly by use of other operations (primarily READ).

1.1.6.  Client Caching and Delegation

   The file, attribute, and directory caching for the NFS version 4
   protocol is similar to previous versions.  Attributes and directory
   information are cached for a duration determined by the client.  At
   the end of a predefined timeout, the client will query the server to
   see if the related file system object has been updated.

   For file data, the client checks its cache validity when the file is
   opened.  A query is sent to the server to determine if the file has
   been changed.  Based on this information, the client determines if
   the data cache for the file should kept or released.  Also, when the
   file is closed, any modified data is written to the server.

   If an application wants to serialize access to file data, file
   locking of the file data ranges in question should be used.

   The major addition to NFS version 4 in the area of caching is the
   ability of the server to delegate certain responsibilities to the
   client.  When the server grants a delegation for a file to a client,
   the client is guaranteed certain semantics with respect to the
   sharing of that file with other clients.  At OPEN, the server may
   provide the client either a read or write delegation for the file.
   If the client is granted a read delegation, it is assured that no
   other client has the ability to write to the file for the duration of
   the delegation.  If the client is granted a write delegation, the
   client is assured that no other client has read or write access to
   the file.

   Delegations can be recalled by the server.  If another client
   requests access to the file in such a way that the access conflicts
   with the granted delegation, the server is able to notify the initial
   client and recall the delegation.  This requires that a callback path
   exist between the server and client.  If this callback path does not
   exist, then delegations can not be granted.  The essence of a
   delegation is that it allows the client to locally service operations
   such as OPEN, CLOSE, LOCK, LOCKU, READ, WRITE without immediate
   interaction with the server.

Top      ToC       Page 11 
1.2.  General Definitions

   The following definitions are provided for the purpose of providing
   an appropriate context for the reader.

   Client    The "client" is the entity that accesses the NFS server's
             resources.  The client may be an application which contains
             the logic to access the NFS server directly.  The client
             may also be the traditional operating system client remote
             file system services for a set of applications.

             In the case of file locking the client is the entity that
             maintains a set of locks on behalf of one or more
             applications.  This client is responsible for crash or
             failure recovery for those locks it manages.

             Note that multiple clients may share the same transport and
             multiple clients may exist on the same network node.

   Clientid  A 64-bit quantity used as a unique, short-hand reference to
             a client supplied Verifier and ID.  The server is
             responsible for supplying the Clientid.

   Lease     An interval of time defined by the server for which the
             client is irrevocably granted a lock.  At the end of a
             lease period the lock may be revoked if the lease has not
             been extended.  The lock must be revoked if a conflicting
             lock has been granted after the lease interval.

             All leases granted by a server have the same fixed
             interval.  Note that the fixed interval was chosen to
             alleviate the expense a server would have in maintaining
             state about variable length leases across server failures.

   Lock      The term "lock" is used to refer to both record (byte-
             range) locks as well as file (share) locks unless
             specifically stated otherwise.

   Server    The "Server" is the entity responsible for coordinating
             client access to a set of file systems.

   Stable Storage
             NFS version 4 servers must be able to recover without data
             loss from multiple power failures (including cascading
             power failures, that is, several power failures in quick
             succession), operating system failures, and hardware
             failure of components other than the storage medium itself
             (for example, disk, nonvolatile RAM).

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             Some examples of stable storage that are allowable for an
             NFS server include:

             1. Media commit of data, that is, the modified data has
                been successfully written to the disk media, for
                example, the disk platter.

             2. An immediate reply disk drive with battery-backed on-
                drive intermediate storage or uninterruptible power
                system (UPS).

             3. Server commit of data with battery-backed intermediate
                storage and recovery software.

             4. Cache commit with uninterruptible power system (UPS) and
                recovery software.

   Stateid   A 64-bit quantity returned by a server that uniquely
             defines the locking state granted by the server for a
             specific lock owner for a specific file.

             Stateids composed of all bits 0 or all bits 1 have special
             meaning and are reserved values.

   Verifier  A 64-bit quantity generated by the client that the server
             can use to determine if the client has restarted and lost
             all previous lock state.

2.  Protocol Data Types

   The syntax and semantics to describe the data types of the NFS
   version 4 protocol are defined in the XDR [RFC1832] and RPC [RFC1831]
   documents.  The next sections build upon the XDR data types to define
   types and structures specific to this protocol.

2.1.  Basic Data Types

   Data Type     Definition
   _____________________________________________________________________
   int32_t       typedef int             int32_t;

   uint32_t      typedef unsigned int    uint32_t;

   int64_t       typedef hyper           int64_t;

   uint64_t      typedef unsigned hyper  uint64_t;

Top      ToC       Page 13 
   attrlist4     typedef opaque        attrlist4<>;
                 Used for file/directory attributes

   bitmap4       typedef uint32_t        bitmap4<>;
                 Used in attribute array encoding.

   changeid4     typedef       uint64_t        changeid4;
                 Used in definition of change_info

   clientid4     typedef uint64_t        clientid4;
                 Shorthand reference to client identification

   component4    typedef utf8string      component4;
                 Represents path name components

   count4        typedef uint32_t        count4;
                 Various count parameters (READ, WRITE, COMMIT)

   length4       typedef uint64_t        length4;
                 Describes LOCK lengths

   linktext4     typedef utf8string      linktext4;
                 Symbolic link contents

   mode4         typedef uint32_t        mode4;
                 Mode attribute data type

   nfs_cookie4   typedef uint64_t        nfs_cookie4;
                 Opaque cookie value for READDIR

   nfs_fh4       typedef opaque          nfs_fh4<NFS4_FHSIZE>;
                 Filehandle definition; NFS4_FHSIZE is defined as 128

   nfs_ftype4    enum nfs_ftype4;
                 Various defined file types

   nfsstat4      enum nfsstat4;
                 Return value for operations

   offset4       typedef uint64_t        offset4;
                 Various offset designations (READ, WRITE, LOCK, COMMIT)

   pathname4     typedef component4      pathname4<>;
                 Represents path name for LOOKUP, OPEN and others

   qop4          typedef uint32_t        qop4;
                 Quality of protection designation in SECINFO

Top      ToC       Page 14 
   sec_oid4      typedef opaque          sec_oid4<>;
                 Security Object Identifier
                 The sec_oid4 data type is not really opaque.
                 Instead contains an ASN.1 OBJECT IDENTIFIER as used
                 by GSS-API in the mech_type argument to
                 GSS_Init_sec_context.  See [RFC2078] for details.

   seqid4        typedef uint32_t        seqid4;
                 Sequence identifier used for file locking

   stateid4      typedef uint64_t        stateid4;
                 State identifier used for file locking and delegation

   utf8string    typedef opaque          utf8string<>;
                 UTF-8 encoding for strings

   verifier4     typedef opaque        verifier4[NFS4_VERIFIER_SIZE];
                 Verifier used for various operations (COMMIT, CREATE,
                 OPEN, READDIR, SETCLIENTID, WRITE)
                 NFS4_VERIFIER_SIZE is defined as 8

2.2.  Structured Data Types

   nfstime4
                  struct nfstime4 {
                          int64_t seconds;
                          uint32_t nseconds;
                  }

      The nfstime4 structure gives the number of seconds and nanoseconds
      since midnight or 0 hour January 1, 1970 Coordinated Universal
      Time (UTC).  Values greater than zero for the seconds field denote
      dates after the 0 hour January 1, 1970.  Values less than zero for
      the seconds field denote dates before the 0 hour January 1, 1970.
      In both cases, the nseconds field is to be added to the seconds
      field for the final time representation.  For example, if the time
      to be represented is one-half second before 0 hour January 1,
      1970, the seconds field would have a value of negative one (-1)
      and the nseconds fields would have a value of one-half second
      (500000000).  Values greater than 999,999,999 for nseconds are
      considered invalid.

      This data type is used to pass time and date information.  A
      server converts to and from its local representation of time when
      processing time values, preserving as much accuracy as possible.
      If the precision of timestamps stored for a file system object is

Top      ToC       Page 15 
      less than defined, loss of precision can occur.  An adjunct time
      maintenance protocol is recommended to reduce client and server
      time skew.

   time_how4

                  enum time_how4 {
                          SET_TO_SERVER_TIME4 = 0,
                          SET_TO_CLIENT_TIME4 = 1
                  };


   settime4

                  union settime4 switch (time_how4 set_it) {
                   case SET_TO_CLIENT_TIME4:
                           nfstime4       time;
                   default:
                           void;
                  };

        The above definitions are used as the attribute definitions to
        set time values.  If set_it is SET_TO_SERVER_TIME4, then the
        server uses its local representation of time for the time value.


   specdata4

                  struct specdata4 {
                          uint32_t specdata1;
                          uint32_t specdata2;
                  };

        This data type represents additional information for the device
        file types NF4CHR and NF4BLK.


   fsid4

                  struct fsid4 {
                    uint64_t        major;
                    uint64_t        minor;
                  };

        This type is the file system identifier that is used as a
        mandatory attribute.

Top      ToC       Page 16 
   fs_location4

                  struct fs_location4 {
                          utf8string    server<>;
                          pathname4     rootpath;
                  };


   fs_locations4

                  struct fs_locations4 {
                          pathname4     fs_root;
                          fs_location4  locations<>;
                  };

        The fs_location4 and fs_locations4 data types are used for the
        fs_locations recommended attribute which is used for migration
        and replication support.


   fattr4

                  struct fattr4 {
                          bitmap4       attrmask;
                          attrlist4     attr_vals;
                  };

        The fattr4 structure is used to represent file and directory
        attributes.

        The bitmap is a counted array of 32 bit integers used to contain
        bit values.  The position of the integer in the array that
        contains bit n can be computed from the expression (n / 32) and
        its bit within that integer is (n mod 32).

                                      0            1
                    +-----------+-----------+-----------+--
                    |  count    | 31  ..  0 | 63  .. 32 |
                    +-----------+-----------+-----------+--


   change_info4

                  struct change_info4 {
                          bool          atomic;
                          changeid4     before;
                          changeid4     after;
                  };

Top      ToC       Page 17 
        This structure is used with the CREATE, LINK, REMOVE, RENAME
        operations to let the client the know value of the change
        attribute for the directory in which the target file system
        object resides.


   clientaddr4

                  struct clientaddr4 {
                          /* see struct rpcb in RFC 1833 */
                          string r_netid<>;    /* network id */
                          string r_addr<>;     /* universal address */
                  };

        The clientaddr4 structure is used as part of the SETCLIENT
        operation to either specify the address of the client that is
        using a clientid or as part of the call back registration.


   cb_client4

                  struct cb_client4 {
                          unsigned int  cb_program;
                          clientaddr4   cb_location;
                  };

        This structure is used by the client to inform the server of its
        call back address; includes the program number and client
        address.


   nfs_client_id4

                  struct nfs_client_id4 {
                          verifier4     verifier;
                          opaque        id<>;
                  };

        This structure is part of the arguments to the SETCLIENTID
        operation.


   nfs_lockowner4

                  struct nfs_lockowner4 {
                          clientid4     clientid;
                          opaque        owner<>;
                  };

Top      ToC       Page 18 
        This structure is used to identify the owner of a OPEN share or
        file lock.

3.  RPC and Security Flavor

   The NFS version 4 protocol is a Remote Procedure Call (RPC)
   application that uses RPC version 2 and the corresponding eXternal
   Data Representation (XDR) as defined in [RFC1831] and [RFC1832].  The
   RPCSEC_GSS security flavor as defined in [RFC2203] MUST be used as
   the mechanism to deliver stronger security for the NFS version 4
   protocol.

3.1.  Ports and Transports

   Historically, NFS version 2 and version 3 servers have resided on
   port 2049.  The registered port 2049 [RFC1700] for the NFS protocol
   should be the default configuration.  Using the registered port for
   NFS services means the NFS client will not need to use the RPC
   binding protocols as described in [RFC1833]; this will allow NFS to
   transit firewalls.

   The transport used by the RPC service for the NFS version 4 protocol
   MUST provide congestion control comparable to that defined for TCP in
   [RFC2581].  If the operating environment implements TCP, the NFS
   version 4 protocol SHOULD be supported over TCP.  The NFS client and
   server may use other transports if they support congestion control as
   defined above and in those cases a mechanism may be provided to
   override TCP usage in favor of another transport.

   If TCP is used as the transport, the client and server SHOULD use
   persistent connections.  This will prevent the weakening of TCP's
   congestion control via short lived connections and will improve
   performance for the WAN environment by eliminating the need for SYN
   handshakes.

   Note that for various timers, the client and server should avoid
   inadvertent synchronization of those timers.  For further discussion
   of the general issue refer to [Floyd].

3.2.  Security Flavors

   Traditional RPC implementations have included AUTH_NONE, AUTH_SYS,
   AUTH_DH, and AUTH_KRB4 as security flavors.  With [RFC2203] an
   additional security flavor of RPCSEC_GSS has been introduced which
   uses the functionality of GSS-API [RFC2078].  This allows for the use
   of varying security mechanisms by the RPC layer without the
   additional implementation overhead of adding RPC security flavors.
   For NFS version 4, the RPCSEC_GSS security flavor MUST be used to

Top      ToC       Page 19 
   enable the mandatory security mechanism.  Other flavors, such as,
   AUTH_NONE, AUTH_SYS, and AUTH_DH MAY be implemented as well.

3.2.1.  Security mechanisms for NFS version 4

   The use of RPCSEC_GSS requires selection of: mechanism, quality of
   protection, and service (authentication, integrity, privacy).  The
   remainder of this document will refer to these three parameters of
   the RPCSEC_GSS security as the security triple.

3.2.1.1.  Kerberos V5 as security triple

   The Kerberos V5 GSS-API mechanism as described in [RFC1964] MUST be
   implemented and provide the following security triples.

   column descriptions:

   1 == number of pseudo flavor
   2 == name of pseudo flavor
   3 == mechanism's OID
   4 == mechanism's algorithm(s)
   5 == RPCSEC_GSS service

1      2     3                    4              5
-----------------------------------------------------------------------
390003 krb5  1.2.840.113554.1.2.2 DES MAC MD5    rpc_gss_svc_none
390004 krb5i 1.2.840.113554.1.2.2 DES MAC MD5    rpc_gss_svc_integrity
390005 krb5p 1.2.840.113554.1.2.2 DES MAC MD5    rpc_gss_svc_privacy
                                  for integrity,
                                  and 56 bit DES
                                  for privacy.

   Note that the pseudo flavor is presented here as a mapping aid to the
   implementor.  Because this NFS protocol includes a method to
   negotiate security and it understands the GSS-API mechanism, the
   pseudo flavor is not needed.  The pseudo flavor is needed for NFS
   version 3 since the security negotiation is done via the MOUNT
   protocol.

   For a discussion of NFS' use of RPCSEC_GSS and Kerberos V5, please
   see [RFC2623].

3.2.1.2.  LIPKEY as a security triple

   The LIPKEY GSS-API mechanism as described in [RFC2847] MUST be
   implemented and provide the following security triples. The
   definition of the columns matches the previous subsection "Kerberos
   V5 as security triple"

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1      2        3                    4              5
-----------------------------------------------------------------------
390006 lipkey   1.3.6.1.5.5.9        negotiated  rpc_gss_svc_none
390007 lipkey-i 1.3.6.1.5.5.9        negotiated  rpc_gss_svc_integrity
390008 lipkey-p 1.3.6.1.5.5.9        negotiated  rpc_gss_svc_privacy

   The mechanism algorithm is listed as "negotiated".  This is because
   LIPKEY is layered on SPKM-3 and in SPKM-3 [RFC2847] the
   confidentiality and integrity algorithms are negotiated.  Since
   SPKM-3 specifies HMAC-MD5 for integrity as MANDATORY, 128 bit
   cast5CBC for confidentiality for privacy as MANDATORY, and further
   specifies that HMAC-MD5 and cast5CBC MUST be listed first before
   weaker algorithms, specifying "negotiated" in column 4 does not
   impair interoperability.  In the event an SPKM-3 peer does not
   support the mandatory algorithms, the other peer is free to accept or
   reject the GSS-API context creation.

   Because SPKM-3 negotiates the algorithms, subsequent calls to
   LIPKEY's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality
   of protection value of 0 (zero).  See section 5.2 of [RFC2025] for an
   explanation.

   LIPKEY uses SPKM-3 to create a secure channel in which to pass a user
   name and password from the client to the user.  Once the user name
   and password have been accepted by the server, calls to the LIPKEY
   context are redirected to the SPKM-3 context.  See [RFC2847] for more
   details.

3.2.1.3.  SPKM-3 as a security triple

   The SPKM-3 GSS-API mechanism as described in [RFC2847] MUST be
   implemented and provide the following security triples. The
   definition of the columns matches the previous subsection "Kerberos
   V5 as security triple".

1      2        3                    4              5
-----------------------------------------------------------------------
390009 spkm3    1.3.6.1.5.5.1.3      negotiated  rpc_gss_svc_none
390010 spkm3i   1.3.6.1.5.5.1.3      negotiated  rpc_gss_svc_integrity
390011 spkm3p   1.3.6.1.5.5.1.3      negotiated  rpc_gss_svc_privacy

   For a discussion as to why the mechanism algorithm is listed as
   "negotiated", see the previous section "LIPKEY as a security triple."

   Because SPKM-3 negotiates the algorithms, subsequent calls to SPKM-
   3's GSS_Wrap() and GSS_GetMIC() by RPCSEC_GSS will use a quality of
   protection value of 0 (zero).  See section 5.2 of [RFC2025] for an
   explanation.

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   Even though LIPKEY is layered over SPKM-3, SPKM-3 is specified as a
   mandatory set of triples to handle the situations where the initiator
   (the client) is anonymous or where the initiator has its own
   certificate.  If the initiator is anonymous, there will not be a user
   name and password to send to the target (the server).  If the
   initiator has its own certificate, then using passwords is
   superfluous.

3.3.  Security Negotiation

   With the NFS version 4 server potentially offering multiple security
   mechanisms, the client needs a method to determine or negotiate which
   mechanism is to be used for its communication with the server.  The
   NFS server may have multiple points within its file system name space
   that are available for use by NFS clients.  In turn the NFS server
   may be configured such that each of these entry points may have
   different or multiple security mechanisms in use.

   The security negotiation between client and server must be done with
   a secure channel to eliminate the possibility of a third party
   intercepting the negotiation sequence and forcing the client and
   server to choose a lower level of security than required or desired.

3.3.1.  Security Error

   Based on the assumption that each NFS version 4 client and server
   must support a minimum set of security (i.e. LIPKEY, SPKM-3, and
   Kerberos-V5 all under RPCSEC_GSS), the NFS client will start its
   communication with the server with one of the minimal security
   triples.  During communication with the server, the client may
   receive an NFS error of NFS4ERR_WRONGSEC.  This error allows the
   server to notify the client that the security triple currently being
   used is not appropriate for access to the server's file system
   resources.  The client is then responsible for determining what
   security triples are available at the server and choose one which is
   appropriate for the client.

3.3.2.  SECINFO

   The new SECINFO operation will allow the client to determine, on a
   per filehandle basis, what security triple is to be used for server
   access.  In general, the client will not have to use the SECINFO
   procedure except during initial communication with the server or when
   the client crosses policy boundaries at the server.  It is possible
   that the server's policies change during the client's interaction
   therefore forcing the client to negotiate a new security triple.

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3.4.  Callback RPC Authentication

   The callback RPC (described later) must mutually authenticate the NFS
   server to the principal that acquired the clientid (also described
   later), using the same security flavor the original SETCLIENTID
   operation used. Because LIPKEY is layered over SPKM-3, it is
   permissible for the server to use SPKM-3 and not LIPKEY for the
   callback even if the client used LIPKEY for SETCLIENTID.

   For AUTH_NONE, there are no principals, so this is a non-issue.

   For AUTH_SYS, the server simply uses the AUTH_SYS credential that the
   user used when it set up the delegation.

   For AUTH_DH, one commonly used convention is that the server uses the
   credential corresponding to this AUTH_DH principal:

         unix.host@domain

   where host and domain are variables corresponding to the name of
   server host and directory services domain in which it lives such as a
   Network Information System domain or a DNS domain.

   Regardless of what security mechanism under RPCSEC_GSS is being used,
   the NFS server, MUST identify itself in GSS-API via a
   GSS_C_NT_HOSTBASED_SERVICE name type.  GSS_C_NT_HOSTBASED_SERVICE
   names are of the form:

         service@hostname

   For NFS, the "service" element is

         nfs

   Implementations of security mechanisms will convert nfs@hostname to
   various different forms. For Kerberos V5 and LIPKEY, the following
   form is RECOMMENDED:

         nfs/hostname

   For Kerberos V5, nfs/hostname would be a server principal in the
   Kerberos Key Distribution Center database.  For LIPKEY, this would be
   the username passed to the target (the NFS version 4 client that
   receives the callback).

   It should be noted that LIPKEY may not work for callbacks, since the
   LIPKEY client uses a user id/password.  If the NFS client receiving
   the callback can authenticate the NFS server's user name/password

Top      ToC       Page 23 
   pair, and if the user that the NFS server is authenticating to has a
   public key certificate, then it works.

   In situations where NFS client uses LIPKEY and uses a per-host
   principal for the SETCLIENTID operation, instead of using LIPKEY for
   SETCLIENTID, it is RECOMMENDED that SPKM-3 with mutual authentication
   be used.  This effectively means that the client will use a
   certificate to authenticate and identify the initiator to the target
   on the NFS server.  Using SPKM-3 and not LIPKEY has the following
   advantages:

   o  When the server does a callback, it must authenticate to the
      principal used in the SETCLIENTID.  Even if LIPKEY is used,
      because LIPKEY is layered over SPKM-3, the NFS client will need to
      have a certificate that corresponds to the principal used in the
      SETCLIENTID operation.  From an administrative perspective, having
      a user name, password, and certificate for both the client and
      server is redundant.

   o  LIPKEY was intended to minimize additional infrastructure
      requirements beyond a certificate for the target, and the
      expectation is that existing password infrastructure can be
      leveraged for the initiator.  In some environments, a per-host
      password does not exist yet.  If certificates are used for any
      per-host principals, then additional password infrastructure is
      not needed.

   o  In cases when a host is both an NFS client and server, it can
      share the same per-host certificate.



(page 23 continued on part 2)

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