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)

NFS Overview, History, Versions and Standards 1 2 NFS Data Storage and Data Types, and the External Data Representation (XDR) Standard

Other Important NFS Functions

Aside from these three components, the NFS protocol as a whole involves a number of other functions, some of which I think are worth specific mention:

• Mount Protocol: A specific decision was made by the creators of NFS to not have NFS deal with the particulars of file opening and closing. Instead, a separate protocol called the Mount protocol is used for this purpose. Accessing a file or other resource over the network involves first mounting it using this protocol. The Mount Protocol is architecturally distinct, but obviously closely related to NFS, and is even defined in an appendix of the NFS standard. I describe it in the last topic of this section. (Note that in NFSv4 the functions of the Mount Protocol have been incorporated into NFS “proper”.)
  
  
• NFS File System Model: NFS uses a particular model to implement the directory and file structure of the systems that use it. This model is closely based on the file system model of UNIX but is not specific to only that operating system. It is discussed in conjunction with the explanation of the Mount Protocol.
  
  
• Security: Versions 2 and 3 of NFS include only limited security provisions. They use UNIX style authentication to check permissions for various operations. NFS version 4 greatly increases the security options available for NFS implementations. This includes both the option of multiple authentication and encryption algorithms, and many changes made to the protocol as a whole to make it more “security minded”.

Like other TCP/IP protocols, NFS is implemented in the form of client and server software that implements the functions above. The NFS standards, especially for versions 3 and 4, discuss numerous issues related to proper NFS client/server implementation, including interaction between servers and clients, file locking, permission issues, caching, retransmission policies, international support and more. Many of these issues require extensive discussion that is beyond the scope of this Guide. You will want to refer to the standards for NFS, especially versions 3 and 4, for full details.

NFS Overview, History, Versions and Standards 1 2 NFS Data Storage and Data Types, and the External Data Representation (XDR) Standard