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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)

Network File and Resource Sharing Protocols and the TCP/IP Network File System (NFS) 1 2 TCP/IP Network File System (NFS)

Networking is a pretty complicated subject—if you don't believe me, try glancing at the topic list for this Guide. To people like you, who are probably reading this Guide to learn about networks to enhance your ability to make a living in the technology world, this complexity means enhanced job security, so don't knock it. J On the other hand, the main body of “regular users” just want to be able to do things on the network, without being forced to understand how everything works underneath. This is only common sense.

A primary reason why networks and internetworks are created is to allow files and other resources to be shared between computers. Thus, in any internetworking protocol stack, we need some mechanism by which users can easily moves files across a network in a simple way. Application-layer file and message transfer protocols like FTP and HTTP were created for just this purpose: to let users access resources across a network while hiding the details of how the network operates at the layers below them.

However, even though these protocols hide the lower layers, they are somewhat “manual” in nature: they require a user to invoke an application protocol and use specific commands that accomplish network-based resource access. In fact, the problem with such protocols isn't so much that they require manual intervention, but that they make sharing more difficult because they don't allow a file to be used directly on another resource. To see what I mean, consider a protocol like FTP. It does lets me share files between machines, but draws a clear distinction between a file that is mine and a file that is someone else's. If I want to use a file on Joe's machine, I have to transfer it to mine, use it, and then transfer it back. Also, if I don't transfer the file back, Joe might never even see the updated version.

The ultimate in file and resource sharing is achieved when we can hide even the details of how the files are located and the commands required to move them around. Such a system would use an “automatic” sharing protocol that lets files and resources be used over a network seamlessly. Once set up, a network resource in such a scheme can be used in much the same way that one on a local computer is. Such protocols are sometimes called network file and resource sharing protocols.

It is this “blurring” of the line between a local file and a remote one that makes file and resource sharing protocols so powerful. Once the system is set up, a user can access resources on another host as readily as on his own host. This is an extremely powerful capability, especially in the modern era of client/server computing. For example, it allows a company to store information that is used by many individuals in a common place, such as in a directory on a server, and allow each of those individuals to access it. In essence, a “virtual file system” is created that spans network devices, instead of being simply on one storage device on a single computer.

Network File and Resource Sharing Protocols and the TCP/IP Network File System (NFS) 1 2 TCP/IP Network File System (NFS)