NFS ( Network File System )

• Transparent Access

Users and applications can access remote files as if they were local. They are not required to know whether the files reside on the local disk or on remote servers.


• Statelessness

NFS operates in a stateless manner using remote procedure calls (RPC) built on top of an external data representation (XDR) protocol. The RPC protocol enables version and authentication parameters to be exchanged for security over the network.
When an NFS client mounts file system the server examines the mount request to be sure that the client is authorized, then issues a magic cookie to the client for use in later accesses. The magic cookie keeps the server stateless since no record of authenticated clients needs to be kept. Unmounting and remounting an NFS filesystem changes its magic cookie. Magic cookie persist across reboots provided that you do not boot single user or play with the file systems.
Once the client has the magic cookie it uses RPC to make file requests. Because the server is stateless, it is the responsibility of the client to ensure that it has recieved acknowledgements of write requests before deleting its copy of data.


• Portability

NFS is machine and operating system independent. This allows it to be ported easily to multiple OS and hardware platforms from PCs to mainframes.


• Fast Recovery From Failure

NFS is designed to recover quickly from system failures and network problems, causing minimal disruption of service to users.


• Network Protocol Independence

NFS has the flexibility to run on multiple transport protocols instead of being restricted to just one. This allows it to utilize existing protocols today as well as new protocols in the future.


• Performance

NFS is designed for high performance so that users can access remote files as quickly as they can access local files.


• Security

The NFS architecture enables the utilization of multiple security mechanisms. This allows system administrators to choose the security mechanism that is appropriate for their distributed file sharing environment instead of being restricted to one solution. This also allows NFS to utilize new security mechanisms in the future.

• Improve access and good performance on the Internet.


• Strong security with negotiation built into the protocol.


• Good cross-platform interoperability.


• Designed for protocol extensions.

• Tag Length

The length in bytes of the tag.


• Tag

Defined by the implementor.


• Minor Version

Each minor version number will correspond to an RFC . Minor version zero corresponds to NFSv4.


• Operation Argument

Operation to be executed by the protocol.


• Operation Argument Values

The operation arg value can be one of the following:


Value	Name
3	ACCESS
4	CLOSE
5	COMMIT
6	CREATE
7	DELEGPURGE
8	DELEGRETURN
9	GETATTR
10	GETFH
11	LINK
12	LOCK
13	LOCKT
14	LOCKU
15	LOOKUP
16	LOOKUPP
17	NVERIFY
18	OPEN
19	OPENATTR
20	OPEN_CONFIRM
21	OPEN_DOWNGRADE
22	PUTFH
23	PUTPUBFH
24	PUTROOTFH
25	READ
26	READDIR
27	READLINK
28	REMOVE
29	RENAME
30	RENEW
31	RESTOREFH
32	SAVEFH
33	SECINFO
34	SETATTR
35	SETCLIENTID
36	SETCLIENTID_CONFIRM
37	VERIFY
38	WRITE

Example 1



The syntax of the NFS URL is a subset of the Generic URL syntax described in RFC 1738. 

An NFS URL does not include user or password components, nor does it recognize "?" 

query or "#" fragment components.



          nfsURL        = "nfs" ":" relativeURL

          relativeURL   = net_path | abs_path | rel_path

          net_path      = "//" hostport [ abs_path ]

          abs_path      = "/"  rel_path

          rel_path      = [ path_segments ]

          hostport      = host [ ":" port ]

          host          = hostname | hostnumber

          hostname      = *( domainlabel "." ) toplabel

          domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum

          toplabel      = alpha | alpha *( alphanum | "-" ) alphanum

          hostnumber    = 1*digit "." 1*digit "." 1*digit "." 1*digit

          port          = *digit

          url-path      = [ "/" ] path_segments

          path_segments = segment *( "/" segment )

          segment       = *pchar

          pchar         = unreserved | escaped | ":" | "@" | "&" | "=" | "+"

          reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+"

          unreserved    = alpha | digit | mark

          mark          = "$" | "-" | "_" | "." | "!" | "~" |

                          "*" | "'" | "(" | ")" | ","

          escaped       = "%" hex hex

          hex           = digit | "A" | "B" | "C" | "D" | "E" | "F" |

                                  "a" | "b" | "c" | "d" | "e" | "f"

          alphanum      = alpha | digit

          alpha         = lowalpha | upalpha

          lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |

                     "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |

                     "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"

          upalpha  = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |

                     "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |

                     "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"

          digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |

                     "8" | "9"

Example 2



If the server aited to flush data from remote requests, the client would have to save 

those requests so that it could resend them in case of a server crash.



          /*

            * Remote file service routines

            */

           program NFS_PROGRAM {

                   version NFS_VERSION {

                           void

                           NFSPROC_NULL(void)              = 0;



                           attrstat

                           NFSPROC_GETATTR(fhandle)        = 1;



                           attrstat

                           NFSPROC_SETATTR(sattrargs)      = 2;



                           void

                           NFSPROC_ROOT(void)              = 3;



                           diropres

                           NFSPROC_LOOKUP(diropargs)       = 4;



                           readlinkres

                           NFSPROC_READLINK(fhandle)       = 5;



                           readres

                           NFSPROC_READ(readargs)          = 6;



                           void

                           NFSPROC_WRITECACHE(void)        = 7;

                          attrstat

                           NFSPROC_WRITE(writeargs)        = 8;



                           diropres

                           NFSPROC_CREATE(createargs)      = 9;



                           stat

                           NFSPROC_REMOVE(diropargs)       = 10;



                           stat

                           NFSPROC_RENAME(renameargs)      = 11;



                           stat

                           NFSPROC_LINK(linkargs)          = 12;



                           stat

                           NFSPROC_SYMLINK(symlinkargs)    = 13;



                           diropres

                           NFSPROC_MKDIR(createargs)       = 14;



                           stat

                           NFSPROC_RMDIR(diropargs)        = 15;



                           readdirres

                           NFSPROC_READDIR(readdirargs)    = 16;



                           statfsres

                           NFSPROC_STATFS(fhandle)         = 17;

                   } = 2;

           } = 100003;

Example 3



These are the sizes, given in decimal bytes, of various XDR structures used in the 

protocol



          /*

              * The maximum number of bytes of data in a READ or WRITE

              * request.

              */

             const MAXDATA = 8192;



             /* The maximum number of bytes in a pathname argument. */

             const MAXPATHLEN = 1024;



             /* The maximum number of bytes in a file name argument. */

             const MAXNAMLEN = 255;



             /* The size in bytes of the opaque "cookie" passed by READDIR. */

             const COOKIESIZE  = 4;



             /* The size in bytes of the opaque file handle. */

             const FHSIZE = 32;

■ Parent layer
■ Child layer

TCP/UDP

NFS