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rfc:rfc2224

Network Working Group B. Callaghan Request for Comments: 2224 Sun Microsystems, Inc. Category: Informational October 1997

                           NFS URL Scheme

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1997).  All Rights Reserved.

Abstract

 A new URL scheme, 'nfs' is defined.  It is used to refer to files and
 directories on NFS servers using the general URL syntax defined in
 RFC 1738, "Uniform Resource Locators (URL)".
 This scheme uses the public filehandle and multi-component lookup
 [RFC2054, RFC2055] to access server data with a minimum of protocol
 overhead.
 The NFS protocol provides access to shared filesystems across
 networks.  It is designed to be machine, operating system, network
 architecture, and transport protocol independent.  The protocol
 currently exists in two versions: version 2 [RFC1094] and version 3
 [RFC1813], both built on ONC RPC [RFC1831] at its associated eXternal
 Data Representation (XDR) [RFC1832] and Binding Protocol [RFC1833].

Table of Contents

    1.    URL Syntax . . . . . . . . . . . . . . . . . . . . . . .  2
    2.    URL Evaluation . . . . . . . . . . . . . . . . . . . . .  2
    3.    Server Connection  . . . . . . . . . . . . . . . . . . .  2
    4.    NFS Version  . . . . . . . . . . . . . . . . . . . . . .  2
    5.    Public Filehandle  . . . . . . . . . . . . . . . . . . .  3
    5.1     NFS Version 2 Public Filehandle  . . . . . . . . . . .  3
    5.2     NFS Version 3 Public Filehandle  . . . . . . . . . . .  3
    6.    Multi-component Lookup . . . . . . . . . . . . . . . . .  3
    6.1     Absolute vs Relative Pathname  . . . . . . . . . . . .  4
    6.2     Symbolic Links . . . . . . . . . . . . . . . . . . . .  5
    7.    Mount Protocol . . . . . . . . . . . . . . . . . . . . .  6
    8.    Bibliography . . . . . . . . . . . . . . . . . . . . . .  7
    9.    Security Considerations  . . . . . . . . . . . . . . . .  8

Callaghan Informational [Page 1] RFC 2224 NFS URL Scheme October 1997

    10.   BNF for NFS URL Scheme . . . . . . . . . . . . . . . . .  9
    11.   Acknowledgements . . . . . . . . . . . . . . . . . . . . 10
    12.   Author's Address . . . . . . . . . . . . . . . . . . . . 10
    13.   Full Copyright Statement . . . . . . . . . . . . . . . . 11

1. URL Syntax

 An NFS URL is based on the Common Internet Scheme Syntax described in
 section 3.1 of RFC 1738.  It has the general form:
      nfs://<host>:<port><url-path>
 The ":<port>" part is optional.  If omitted then port 2049 is
 assumed.  The <url-path> is also optional.
 The <url-path> is a hierarchical directory path of the form
 /<directory>/<directory>/<directory>/.../<name>. The <url-path> must
 consist only of characters within the US-ASCII character set.  Within
 a <directory> or <name> component the character "/" is reserved and
 must be encoded as described in Section 2.2 of RFC 1738.  If <url-
 path> is omitted or consists solely of "/", it must default to the
 path ".".

2. URL Evaluation

 A client must evaluate an NFS URL by a method known as WebNFS
 [RFC2054, RFC2055]. This method provides easy passage through
 firewalls and proxy servers, as well as using a minimum number of
 messages.  The WebNFS method is defined for NFS versions 2 and 3. It
 assumes that the server registers on TCP or UDP port 2049 and
 supports the public filehandle and multi-component lookup semantics
 as described in the following sections.

3. Server Connection

 The client must first attempt to create a TCP connection to <host>
 using the <port> specified.  If :<port> is omitted, then port 2049
 will be used.  If the server refuses the TCP connection, then the
 client will use UDP.

4. NFS Version

 The client must first attempt to use NFS version 3.  If the server
 returns an RPC PROG_MISMATCH error then the client must assume that
 NFS version 3 is not supported, and retry the operation with an NFS
 version 2 public filehandle.

Callaghan Informational [Page 2] RFC 2224 NFS URL Scheme October 1997

5. Public Filehandle

 NFS filehandles are normally created by the server and used to
 identify uniquely a particular file or directory on the server.  The
 client does not normally create filehandles or have any knowledge of
 the contents of a filehandle.
 The public filehandle is an an exception.  It is an NFS filehandle
 with a reserved value and special semantics that allow an initial
 filehandle to be obtained.  A WebNFS client uses the public
 filehandle as an initial filehandle rather than using the MOUNT
 protocol.  Since NFS version 2 and version 3 have different
 filehandle formats, the public filehandle is defined differently for
 each.
 The public filehandle is a zero filehandle.  For NFS version 2 this
 is a filehandle with 32 zero octets.  A version 3 public filehandle
 has zero length.

5.1 NFS Version 2 Public Filehandle

 A version 2 filehandle is defined in RFC 1094 as an opaque value
 occupying 32 octets.  A version 2 public filehandle has a zero in
 each octet, i.e. all zeros.
  1                                                             32
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2 NFS Version 3 Public Filehandle

 A version 3 filehandle is defined in RFC 1813 as a variable length
 opaque value occupying up to 64 octets.  The length of the filehandle
 is indicated by an integer value contained in a 4 octet value which
 describes the number of valid octets that follow. A version 3 public
 filehandle has a length of zero.
 +-+-+-+-+
 |   0   |
 +-+-+-+-+

6. Multi-component Lookup

 Normally the NFS LOOKUP request (version 2 or 3) takes a directory
 filehandle along with the name of a directory member, and returns the
 filehandle of the directory member.  If a client needs to evaluate a
 pathname that contains a sequence of components, then beginning with

Callaghan Informational [Page 3] RFC 2224 NFS URL Scheme October 1997

 the directory filehandle of the first component it must issue a
 series of LOOKUP requests one component at a time.  For instance,
 evaluation of the path  "a/b/c" will generate separate LOOKUP
 requests for each component of the pathname "a", "b", and "c".
 A LOOKUP request that uses the public filehandle can provide a
 pathname containing multiple components.  The server is expected to
 evaluate the entire pathname and return a filehandle for the final
 component.
 For example, rather than evaluate the path "a/b/c" as:
      LOOKUP  FH=0x0  "a"  --->
                           <---  FH=0x1
      LOOKUP  FH=0x1  "b"  --->
                           <---  FH=0x2
      LOOKUP  FH=0x2  "c"  --->
                           <---  FH=0x3
 Relative to the public filehandle these three LOOKUP
 requests can be replaced by a single multi-component
 lookup:
      LOOKUP  FH=0x0  "a/b/c"  --->
                               <---  FH=0x3
 Multi-component lookup is supported only for LOOKUP requests relative
 to the public filehandle.
 The <url-path> of the NFS URL must be evaluated as a multi-component
 lookup. This implies that the path components are delimited by
 slashes and the characters that make up the path must be in the
 printable US-ASCII character set. Characters not in the "unreserved"
 set (see BNF description below) may be included in pathname
 components but must be escaped.
 If the <url-path> is empty or consists solely of "/", the client must
 send a multi-component lookup for the pathname ".".

6.1 Absolute vs. Relative Pathname

 A multi-component pathname that begins with a slash character is
 considered "absolute" and will be evaluated relative to the server's
 root.  A pathname that does not begin with a slash is "relative" and
 will be evaluated relative to the directory with which the public
 filehandle is associated.

Callaghan Informational [Page 4] RFC 2224 NFS URL Scheme October 1997

 Note that the initial "/" that introduces the <url-path> of an NFS
 URL must not be passed to the server for multi-component lookup since
 the pathname is to be evaluated relative to the public filehandle
 directory.  For example, if the public filehandle is associated with
 the server's directory "/a/b/c" then the URL:
      nfs://server/d/e/f
 will be evaluated with a multi-component lookup of the path
 "d/e/f" relative to the server's directory "/a/b/c" while
 the URL:
      nfs://server//a/b/c/d/e/f
 will locate the same file with an absolute multi-component lookup of
 the path "/a/b/c/d/e/f" relative to the server's filesystem root.
 Notice that a double slash is required at the beginning of the path.
 Not all WebNFS servers can support arbitrary use of absolute paths.
 Clearly, the server must not return a filehandle if the path
 identifies a file or directory that is not exported by the server.
 In addition, some servers will not return a filehandle if the path
 names a file or directory in an exported filesystem different from
 the one that is associated with the public filehandle.

6.2 Symbolic Links

 The NFS protocol supports symbolic links, which are the filesystem
 equivalent of a relative URL. If a WebNFS client retrieves a
 filehandle for a symbolic link (as indicated by the file type
 attribute) then it should send a READLINK request to the server to
 retrieve the path comprising the symbolic link.
 This path should then be combined with the URL which referenced the
 symbolic link according to the rules described in RFC 1808.  If the
 relative URL in the symbolic link text is to be resolved successfully
 then it must contain only ASCII characters and conform to the syntax
 described in RFC 1808.  Note that this allows a symbolic link to
 contain an entire URL and it may specify a scheme that is not
 necessarily an NFS URL.
 A symbolic link path that begins with a slash will be evaluated as an
 absolute path relative to the directory associated with the public
 filehandle which may not be the same as the server's system root
 directory.  If symbolic links with absolute paths are to be evaluated
 correctly on both client and server then the public filehandle must
 be associated with the system root directory.

Callaghan Informational [Page 5] RFC 2224 NFS URL Scheme October 1997

 For example, if the symbolic link is named by the URL
      nfs://server/a/b
 then the following examples show how a new URL can be
 formed from the symbolic link text:
       c                      = nfs://server/a/c
       c/d                    = nfs://server/a/c/d
       ../c                   = nfs://server/c
       /c/d                   = nfs://server/c/d
       nfs://server2/a/b      = nfs://server2/a/b

7. Mount Protocol

 The NFS URL may have limited use for naming files on servers that do
 not support the public filehandle and multi-component lookup.
 If the server returns an NFS3ERR_STALE, NFS3ERR_INVAL, or
 NFS3ERR_BADHANDLE error in response to the client's use of a public
 filehandle, then the client should attempt to resolve the <url-path>
 to a filehandle using the MOUNT protocol.
 Version 1 of the MOUNT protocol is described in Appendix A of RFC
 1094 and version 3 in Appendix I of RFC 1813. Version 2 of the MOUNT
 protocol is identical to version 1 except for the addition of a
 procedure MOUNTPROC_PATHCONF which returns POSIX pathconf information
 from the server.
 Note that the pathname sent to the server in the MOUNTPROC_MNT
 request is assumed to be a server native path, rather than a slash-
 separated path described by RFC 1738.  Hence, the MOUNT protocol can
 reasonably be expected to map a <url-path> to a filehandle only on
 servers that support slash-separated ASCII native paths.  In general,
 servers that do not support WebNFS access or slash-separated ASCII
 native paths should not advertise NFS URLs.
 At this point the client must already have some indication as to
 which version of the NFS protocol is supported on the server.  Since
 the filehandle format differs between NFS versions 2 and 3, the
 client must select the appropriate version of the MOUNT protocol.
 MOUNT versions 1 and 2 return only NFS version 2 filehandles, whereas
 MOUNT version 3 returns NFS version 3 filehandles.

Callaghan Informational [Page 6] RFC 2224 NFS URL Scheme October 1997

 Unlike the NFS service, the MOUNT service is not registered on a
 well-known port.  The client must use the PORTMAP service to locate
 the server's MOUNT port before it can transmit a MOUNTPROC_MNT
 request to retrieve the filehandle corresponding to the requested
 path.
     Client                                       Server
     ------                                       ------
  1. ————- MOUNT port ? ————–> Portmapper

←————- Port=984 ——————

  1. —— Filehandle for /export/foo ? —→ Mountd @ port 984

←——– Filehandle=0xf82455ce0.. ——

 NFS servers commonly use a client's successful MOUNTPROC_MNT request
 request as an indication that the client has "mounted" the filesystem
 and may maintain this information in a file that lists the
 filesystems that clients currently have mounted.  This information is
 removed from the file when the client transmits an MOUNTPROC_UMNT
 request.  Upon receiving a successful reply to a MOUNTPROC_MNT
 request, a WebNFS client should send a MOUNTPROC_UMNT request to
 prevent an accumulation of "mounted" records on the server.

8.0 Bibliography

 [RFC1738]       Berners-Lee, T., Masinter, L. and M. McCahill,
                 "Uniform Resource Locators (URL)," RFC 1738,
                 December 1994.
 [RFC1808]       Fielding, R., "Relative Uniform Resource Locators,"
                 RFC 1808, June 1995.
 [RFC1831]       Srinivasan, R., "RPC: Remote Procedure Call
                 Protocol Specification Version 2," RFC 1831,
                 August 1995.
 [RFC1832]       Srinivasan, R., "XDR: External Data Representation
                 Standard," RFC 1832, August 1995.
 [RFC1833]       Srinivasan, R., "Binding Protocols for ONC RPC
                 Version 2," RFC 1833, August 1995.
 [RFC1094]       Sun Microsystems, Inc., "Network Filesystem
                 Specification," RFC 1094, March 1989.

Callaghan Informational [Page 7] RFC 2224 NFS URL Scheme October 1997

 [RFC1813]       Callaghan, B., Pawlowski, B. and P. Staubach,
                 "NFS Version 3 Protocol Specification," RFC 1813,
                 June 1995.
 [RFC2054]       Callaghan, B., "WebNFS Client Specification,"
                 RFC 2054, October 1996.
 [RFC2055]       Callaghan, B., "WebNFS Server Specification,"
                 RFC 2055, October 1996.
 [Sandberg]      Sandberg, R., D. Goldberg, S. Kleiman, D. Walsh,
                 B.  Lyon, "Design and Implementation of the Sun
                 Network Filesystem," USENIX Conference
                 Proceedings, USENIX Association, Berkeley, CA,
                 Summer 1985.  The basic paper describing the
                 SunOS implementation of the NFS version 2
                 protocol, and discusses the goals, protocol
                 specification and trade-offs.
 [X/OpenNFS]     X/Open Company, Ltd., X/Open CAE Specification:
                 Protocols for X/Open Internetworking: XNFS,
                 X/Open Company, Ltd., Apex Plaza, Forbury Road,
                 Reading Berkshire, RG1 1AX, United Kingdom,
                 1991.  This is an indispensable reference for
                 the NFS and accompanying protocols, including
                 the Lock Manager and the Portmapper.
 [X/OpenPCNFS]   X/Open Company, Ltd., X/Open CAE Specification:
                 Protocols for X/Open Internetworking: (PC)NFS,
                 Developer's Specification, X/Open Company, Ltd.,
                 Apex Plaza, Forbury Road, Reading Berkshire, RG1
                 1AX, United Kingdom, 1991.  This is an
                 indispensable reference for NFS protocol and
                 accompanying protocols, including the Lock Manager
                 and the Portmapper.

9. Security Considerations

 Since the WebNFS server features are based on NFS protocol versions 2
 and 3, the RPC based security considerations described in RFC 1094,
 RFC 1831, and RFC 1832 apply here also.
 Server implementors should be careful when implementing multi-
 component lookup that the client cannot obtain unauthorized access to
 files or directories. For example: a path that includes multiple
 occurrences of "../" may locate a filesystem outside of the exported
 filesystem associated with the public filehandle.

Callaghan Informational [Page 8] RFC 2224 NFS URL Scheme October 1997

 Clients and servers may separately negotiate secure connection
 schemes for authentication, data integrity, and privacy.

10. BNF for NFS URL Scheme

 The syntax of the NFS URL is a subset of the Generic URL syntax
 described in RFC 1738.  An NFS URL does not include user or password
 components, nor does it recognize "?" query or "#" fragment
 components.
    nfsURL        = "nfs" ":" relativeURL
    relativeURL   = net_path | abs_path | rel_path
    net_path      = "//" hostport [ abs_path ]
    abs_path      = "/"  rel_path
    rel_path      = [ path_segments ]
    hostport      = host [ ":" port ]
    host          = hostname | hostnumber
    hostname      = *( domainlabel "." ) toplabel
    domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
    toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
    hostnumber    = 1*digit "." 1*digit "." 1*digit "." 1*digit
    port          = *digit
    url-path      = [ "/" ] path_segments
    path_segments = segment *( "/" segment )
    segment       = *pchar
    pchar         = unreserved | escaped | ":" | "@" | "&" | "=" | "+"
    reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+"
    unreserved    = alpha | digit | mark
    mark          = "$" | "-" | "_" | "." | "!" | "~" |
                    "*" | "'" | "(" | ")" | ","
    escaped       = "%" hex hex
    hex           = digit | "A" | "B" | "C" | "D" | "E" | "F" |
                            "a" | "b" | "c" | "d" | "e" | "f"
    alphanum      = alpha | digit
    alpha         = lowalpha | upalpha
    lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |
               "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |
               "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
    upalpha  = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
               "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
               "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
    digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
               "8" | "9"

Callaghan Informational [Page 9] RFC 2224 NFS URL Scheme October 1997

11. Acknowledgements

 This specification was extensively reviewed by the NFS group at
 SunSoft and brainstormed by Michael Eisler.

12. Author's Address

 Address comments related to this RFC to:
    brent@eng.sun.com
 Brent Callaghan
 Sun Microsystems, Inc.
 Mailstop Mpk17-201,
 901 San Antonio Road,
 Palo Alto, California 94303
 Phone: 1-415-786-5067
 EMail: brent.callaghan@eng.sun.com
 Fax:   1-415-786-5896

Callaghan Informational [Page 10] RFC 2224 NFS URL Scheme October 1997

13. Full Copyright Statement

 Copyright (C) The Internet Society (1997).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implmentation may be prepared, copied, published
 andand distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

Callaghan Informational [Page 11]

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