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The TCP/IP Guide

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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  Network File and Resource Sharing Protocols and the TCP/IP Network File System (NFS)
           9  TCP/IP Network File System (NFS)

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NFS Server Procedures and Operations
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TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
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NFS File System Model and the Mount Protocol
(Page 2 of 3)

The Mount Protocol

Before NFS can be used to allow a client to access a file on a remote server, the client must be given a way of accessing the file. This means that a portion of the remote file system must be made available to the client, and the file opened for access. A specific decision was made when NFS was created to not put file access, opening and closing functions into NFS proper. Instead, a separate protocol was created to work with NFS, so that if in the future the method of providing file access needed to be changed, it wouldn't require changes to NFS itself. This separate mechanism is called the Mount Protocol, and is described in Appendix A of RFC 1094 (NFSv2). Note that while functionally distinct, Mount is considered part of the overall NFS package.

When NFS was revised to version 3, the Mount Protocol was similarly modified. The NFSv3 version of the Mount Protocol is defined in Appendix I of RFC 1813 (NFSv3). It contains some changes to how the protocol works, but the overall operation of the two versions of Mount is pretty much the same.

The term “mount” is actually an analog to a hardware term that refers to making a physical storage volume available. In the “olden dayse” storage devices were usually removable disk packs, and to use one you mounted it onto a drive unit. In a similar manner, NFS resources are logically mounted using the Mount protocol, which makes the shared file system available to the client. A file can then be opened and a file handle returned to the NFS client so it can reference the file for operations such as reading and writing.

Key Concept: Versions 2 and 3 of NFS do not include procedures for opening or closing resources on a remote server. Before NFS tasks can be accomplished on these versions, the special Mount protocol must be employed to mount a filesystem and create a file handle to access a file on it; the protocol is also used to unmount the file system when no longer required. The Mount protocol is implemented in a manner very similar to NFS itself, defining procedures that use RPC and XDR. In version 4 of NFS, Mount is no longer needed; the tasks it performs are implemented as NFSv4 operations.



Previous Topic/Section
NFS Server Procedures and Operations
Previous Page
Pages in Current Topic/Section
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2
3
Next Page
TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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