Please Whitelist This Site? I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :) If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads. If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK. Thanks for your understanding! Sincerely, Charles Kozierok Author and Publisher, The TCP/IP Guide

NOTE: Using software to mass-download the site degrades the server and is prohibited. If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

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 Data Storage and Data Types, and the External Data Representation (XDR) Standard 1 2 3 NFS Server Procedures and Operations

Client and Server Responsibilities in NFS

Since UDP is unreliable, the use of that protocol to transport important information may seem strange. For example, we obviously don't want data that we are trying to write to a file to be lost in transit. Remember, however, that UDP doesn't preclude the use of measures to ensure reliable communications, it simply doesn't provide those capabilities itself. UDP can be used by NFS because the protocol itself is designed to tolerate loss of transmitted data and to recover from it.

Consistent with this concept, the general design of NFS puts most of the responsibility for implementing the protocol on the client, not the server. As the NFSv3 standard says, “NFS servers are dumb and NFS clients are smart.” What this means is that the servers focus only on responding to requests, while clients must take care of most of the “nitty-gritty” details of the protocol, including recovery from failed communications. This is in fact a common requirement when UDP is used, because if a client request is lost in transit, the server has no way of knowing that it was ever sent.

As mentioned in the NFS overview, NFS servers are designed to be “stateless”. In simplified terms, this means that the NFS server does not keep track of the state of the clients using it from one request to another. Each request is independent of the previous one, and the server in essence has “no memory” of what it did before when it gets a new command from a client. This again requires more “smarts” to be put into the clients, but has the important advantage of simplifying recovery in the case that the server crashes. Since there is nothing that the server was keeping track of for the client, there's nothing that can be lost. This is an important part of ensuring that files are not damaged as a result of network problems or congestion.

Both NFS clients and servers can make use of caching to improve performance. Servers may use caching to store recently-requested information in case it is needed again. They may also use predictive caching, sometimes called prefetching. In this technique, a server that receives a request to read a block of data from a file may load into memory the next block after it, on the theory that it will likely be requested next. Client-side caching is used to satisfy repeat NFS requests from applications while avoiding additional RPC calls. Like almost everything else about NFS, caching is implemented much more thoroughly in NFS version 4 than in the previous versions.

NFS Data Storage and Data Types, and the External Data Representation (XDR) Standard 1 2 3 NFS Server Procedures and Operations