Protocols for Interworking: XNFS, Version 3W
Copyright © 1998 The Open Group


Open Group Technical Standard
Protocols for Interworking: XNFS, Version 3W
Document Number: C702
ISBN: 1-85912-184-5

©February 1998, The Open Group All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owners.

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This Document

This document describes XNFS, the X/Open NFS Specification. This document supersedes the previous X/Open publication Protocols for X/Open Interworking, XNFS, Version 3, Document Number C525, August 1996. The previous version was aligned with Sun's NFS Version 3 (RFC 1813). This revised version (XNFS, Version 3W) incorporates the Sun WebNFSTM; optional extensions (RFCs 1738, 1808, 2054, 2055).

The process of accessing remote files and directories as though they were part of the local file system hierarchy is commonly known as "transparent file access" (TFA). The most widely used heterogeneous TFA architecture is the Network File System (NFS), originally developed by Sun Microsystems.

XNFS provides a means of access to files and directories that are physically stored on remote systems, by extending the semantics of local system interfaces so that applications and end users can (as far as possible) ignore the distinctions between local and remote objects.

NFS has been implemented on a wide range of architectures, from personal computers to mainframes and supercomputers. The specifications for the protocols associated with NFS have been published, and there have been several independent implementations.

With the XNFS specification, X/Open offers the market a temporary but complete solution to the problem of transparent file access between X/Open-compliant systems. Temporary, because X/Open recognises the TFA standardisation effort ongoing within the IEEE P1003.1f committee, and X/Open intends to be compliant with 1003.1f TFA at such time as it becomes an IEEE standard. Complete, because X/Open now offers both protocols for interoperability (via this XNFS specification) and interfaces for application/user portability (via the XSI specifications, in conjunction with the semantic differences defined in the appendices to this document).

This specification is based in part on the X/Open (PC)NFS Specification.

The X/Open (PC)NFS Specification defines the protocols for communication between a PC client running DOS or OS/2 and an X/Open-compliant server.

The XNFS specification defines:

Since many of the protocols used are the same for PC and X/Open-compliant system clients, there is obviously a great deal of overlap between these specifications.

In the event of any inconsistency or disagreement between the two documents, this document is to be treated as authoritative. At some future date, the X/Open (PC)NFS Specification will be revised to include only those elements which are specific to PC clients, such as the pcnfsd protocol, filename and attribute mapping, and the transmission analysis.

Intended Audience
There are two intended audiences for this specification. The first includes anyone who wishes to implement XNFS as part of an X/Open-compliant system. This specification defines the protocols that are to be implemented by a conforming system, so that it may interoperate with other conforming systems. It does not, however, define the way in which these protocols are to be implemented, nor the way in which XNFS is to be integrated into the rest of the system.

The second audience is the developers of X/Open CAE applications. This group relies upon the semantics of the XSI as defined in the X/Open System Interfaces and Headers Specification (see reference XSH) and the X/Open Commands and Utilities Specification (see reference XCU) and needs to be aware of any semantic changes which the use of XNFS may introduce. These changes are described in Semantic Difference Summary for File Access , Open-System Interface Semantics over XNFS and Open System Utilities Semantics over XNFS . Obviously an XNFS implementor must be aware of this material so that their implementation does not behave in an unexpected manner.

XNFS Version 2 -> Version 3 Changes
The changes to the XNFS Issue 4 specification (document number C218, which described Sun NFS Version 2) to add the NFS Version 3 protocol comprise miscellaneous modifications to sections in the XNFS Issue 4 specification, plus addition of three new chapters 12, 13 and 14.

A summary of these changes follows:

XNFS Version 3 -> Version 3W Changes
The changes to the XNFS Version 3 specification (document number C525) to add the WebNFS extensions to the NFS protocol, comprise various additions to sections 1.6, 2.4.1, 7.2.1, 7.3, 7.3.2, 12.2, 12.2.2, 12.3.8, 12.4.4, and a new WebNFS Extensions detailing the WebNFS extensions.

Trade Marks

AT&T® is a registered trademark of AT&T in the U.S.A. and other countries.

Diablo® is a registered trademark of Xerox Corporation.

Ethernet® is a registered trademark of Xerox Corporation.

IBM® is a registered trademark of International Business Machines Corporation.

LAN ManagerTM; is a trademark of Microsoft Corporation.

MS-DOS® is a registered trademark of Microsoft Corporation.

NFS® is a registered trademark and Network File SystemTM; is a trademark of Sun Microsystems, Inc.

OS/2® is a registered trademark of International Business Machines Corporation.

PC-NFSTM; is a trademark of Sun Microsystems, Inc..

Postscript® is a registered trademark of Adobe Systems Incorporated.

VAX® is a registered trademark of Digital Equipment Corporation.

VMS® is a registered trademark of Digital Equipment Corporation.

Motif,® OSF/1,® UNIX,® and the "X Device"® are registered trademarks and IT DialToneTM; and The Open GroupTM; are trademarks of The Open Group in the U.S. and other countries.

WebNFSTM; is a trademark of Sun Microsystems, Inc.

Referenced Documents

The following documents are referenced in this specification:
Open Group Documents


CAE Specification, December 1991, Byte Stream File Transfer (BSFT) (ISBN: 1-872630-27-8, C194), published by The Open Group.

Internationalisation Guide

Guide, July 1993, Internationalisation Guide, Version 2 (ISBN: 1-859120-02-4, G304), published by The Open Group.


Developers' Specification, August 1990, Protocols for X/Open PC Interworking: (PC)NFS (ISBN: 1-872630-00-6, D030), published by The Open Group.

XBD, Issue 4, Version 2

CAE Specification, August 1994, System Interface Definitions, Issue 4, Version 2 (ISBN: 1-85912-036-9, C434), published by The Open Group.

XCU, Issue 4, Version 2

CAE Specification, August 1994, Commands and Utilities, Issue 4, Version 2 (ISBN: 1-85912-034-2, C436), published by The Open Group.

XNS (Networking Services, Issue 4)

CAE Specification, August 1994, Networking Services, Issue 4 (ISBN: 1-85912-049-0, C438), published by The Open Group.


X/Open Specification, 1988, 1989, February 1992 (ISBN: 1-872630-43-X, T921); this specification was formerly X/Open Portability Guide, seven volumes, January 1989 (ISBN: 0-13-685819-8, XO/XPG/89/000).

XSH, Issue 4, Version 2

CAE Specification, August 1994, System Interfaces and Headers, Issue 4, Version 2 (ISBN: 1-85912-037-7, C435), published by The Open Group.

International Standards

ISO 8859-1

ISO 8859-1:1987, Information Processing - 8-bit Single-byte Coded Graphic Character Sets - Part 1: Latin Alphabet No. 1.

ISO/IEC 9945-1

ISO/IEC 9945-1:1990, Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Program Interface (API) [C Language] (identical to IEEE Std 1003.1-1990).

Access to IETF RFCs
RFCs may be obtained via Email or FTP from many RFC repositories. Many of these repositories also now have World Wide Web servers. Try one of the following URLs as a starting point:

RFCs can be obtained via FTP from DS.INTERNIC.NET, NIS.NSF.NET, NISC.JVNC.NET, FTP.ISI.EDU, WUARCHIVE.WUSTL.EDU, SRC.DOC.IC.AC.UK, FTP.NCREN.NET, FTP.SESQUI.NET, FTP.NIC.IT, or FTP.IMAG.FR, using the FTP username anonymous and the FTP password guest For further information about Internet Protocols in general, please contact:

USC - Information Sciences Institute, 4676, Admiralty Way, Marina del Rey, CA 90292-6695, USA

Tel: (+1) 213-822-1511

Internet Protocol Suite RFCs

RFC 1140 - IAB Official Protocol Standards

IETF RFC 1140 gives the state of standardisation of protocols used in the Internet as determined by the Internet Activities Board (IAB). RFC 1140 was published in May 1990; this document is reissued on a regular basis, and the reader should obtain the current version as described above.

RFC 1011 - Official Internet Protocols

IETF RFC 1011 is the authoritative reference as to which document defines each protocol. RFC 1011 was published in May 1987; this document is reissued on a regular basis, and the reader should obtain the current version as described above.

The descriptions which follow are derived from RFC 1011.

RFC 791 - Internet Protocol (IP)

Status: Standard. IETF RFC 791 is the universal protocol of the Internet. This datagram protocol provides the universal addressing of hosts in the Internet.

RFC 792 - Internet Control Message Protocol (ICMP)

Status: Standard. IETF RFC 792 describes the control messages and error reports that go with the Internet Protocol.
ICMP is defined to be an integral part of IP. An implementation of IP is incomplete if it does not include ICMP.

RFC 768 - User Datagram Protocol (UDP)

Status: Standard. IETF RFC 768 provides a datagram service to applications. It adds port addressing to the IP services.

RFC 793 - Transmission Control Protocol (TCP)

Status: Standard. IETF RFC 793 provides a reliable end-to-end data stream service. Note that RFC 1011 includes many additions and clarifications to RFC 793, and refers to additional RFCs which go into greater detail on certain topics.

RFC 950 - Internet Subnet Protocol

Status: Standard. IETF RFC 950 specifies procedures for the use of subnets, which are logical sub-sections of a single Internet network.

RFC 826 - Address Resolution Protocol (ARP)

Status: Standard. IETF RFC 826 is a procedure for finding the network hardware address corresponding to an Internet Address.

RFC 997 - Internet Numbers

IETF RFC 997 describes the fields of network numbers and autonomous system numbers that are assigned specific values for actual use, and lists the currently assigned values.

RFC 1060 - Assigned Numbers

Status: Historic. IETF RFC 1060 describes the fields of various protocols that are assigned specific values for actual use, and lists the currently assigned values.

RFC 894 - Internet Protocol on Ethernet Networks

Status: Standard. IETF RFC 894 describes the representation of Internet Protocol services on Ethernet networks.

RFC 1011 (includes) Internet Protocol on IEEE 802

IETF RFC 1011 includes description of the latest policy on the transmission of IP datagrams on IEEE 802 networks.

All of the preceding material should be interpreted in accordance with the following two documents, which provide an authoritative policy on the way in which the various protocols should be implemented and administered:

RFC 1122 - Requirements for Internet Hosts - Communication Layers

IETF RFC 1122, R T Braden, October 1989. Status: Standard.

RFC 1123 - Requirements for Internet Hosts - Application and Support

IETF RFC 1123, R T Braden, October 1989. Status: Standard.

In addition, XDR, RPC and NFS are described in the following RFCs:

RFC 1014 - XDR: External Data Representation Standard

IETF RFC 1014, Sun Microsystems, June 1987.

RFC 1057 - RPC: Remote Procedure Call Protocol Specification, Version 2

IETF RFC 1057, Sun Microsystems. June 1988, Status: Informational.

RFC 1094 - NFS: Network File System Protocol Specification

IETF RFC 1094, Sun Microsystems. Mar-01-1989, Status: Informational.

RFC 1813 - NFS: Network File System Prococol, Version 3 Specification

IETF RFC 1813, B Callaghan, B Pawlowski & P Staubach, June 1995. Status: Informational.

RFC 1831 - RPC: Remote Procedure Call Protocol Specification Version 2

IETF RFC 1831, R Srinivasan, August 1995. Status: Proposed Standard.

RFC 1832 - XDR: External Data Representation Standard.

IETF RFC 1832, R Srinivasan, August 1995. Status: Proposed Standard.

RFC 1833 - Binding Protocols for ONC RPC Version 2

IETF RFC 1833, R Srinivasan, August 1995. Status: Proposed Standard.

WebNFS-relevant RFCs

RFC 1738 - Uniform Resource Locators (URL)

IETF RFC 1738, T Berners-Lee, L Masinter & M McCahill. December 1994, Status: Proposed Standard. This document describes the syntax and semantics of absolute Uniform Resource Locators, which can be used for the location and access of resources via the Internet.

RFC 1808 - Relative Uniform Resource Locators

IETF RFC 1808, R Fielding. June 1995, Status: Proposed Standard. This document describes the syntax and semantics of relative Uniform Resource Locators. Relative URLs can be used for the location and access of resources relative to an absolute URL.

RFC 2054 - WebNFS Client Specification

IETF RFC 2054, B Callaghan. October 1996, Status: Informational. This document describes the procedure that a WebNFS client uses to access an NFS server.

RFC 2055 - WebNFS Server Specification

IETF RFC 2055, B Callaghan, October 1996, Status: Informational. This document describes the features that are required of a WebNFS server.

RFC 2224 - NFS URL Scheme

IETF RFC 2224, B Callaghan, October 1997, Status: Informational. This document describes a URL scheme used to refer to files and directories on NFS servers using the general URL syntax defined in RFC 1738.

Other Documents

Andrew D. Birrell and Bruce Jay Nelson, Implementing Remote Procedure Calls, XEROX CSL-83-7, October 1983.

Danny Cohen, On Holy Wars and a Plea for Peace, IEEE Computer, October 1981.

Courier: The Remote Procedure Call Protocol, XEROX Corporation, XSIS 038112, December 1981.

Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, Bell Laboratories, Murray Hill, New Jersey, 1978.

J. Postel, Transmission Control Protocol - DARPA Internet Program Protocol Specification, RFC 793, Information Sciences Institute, September 1981.

J. Postel, User Datagram Protocol, RFC 768, Information Sciences Institute, August 1980.

Disk Operating System Technical Reference, IBM part no. 6138536.

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