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Unformatted text preview: ference the symbolic link (e.g.,
open) really reference the file pointed to by the symbolic link.
13. READLINK. Read a symbolic link, that is, return the name of the file to which the
symbolic link points.
14. MKDIR. Create a directory.
15. RMDIR. Delete a directory.
16. READDIR. Read a directory. Used by the Unix ls command, for example.
These procedure names actually begin with the prefix NFSPROC_, which we've dropped.
UDP or TCP?
NFS was originally written to use UDP, and that's what all vendors provide. Newer
implementations, however, also support TCP. TCP support is provided for use on wide
area networks, which are getting faster over time. NFS is no longer restricted to local area
The network dynamics can change drastically when going from a LAN to a WAN. The
round-trip times can vary widely and congestion is more frequent. These characteristics of
WANs led to the algorithms we examined with TCP - slow start and congestion
avoidance. Since UDP does not provide anything like these algorithms, either the same
algorithms must be put into the NFS client and server or TCP should be used.
NFS Over TCP
The Berkeley Net/2 implementation of NFS supports either UDP or TCP. [Macklem
1991] describes this implementation. Let's look at the differences when TCP is used.
1. When the server bootstraps, it starts an NFS server that does a passive open on
TCP port 2049, waiting for client connection requests. This is usually in addition to file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/nfs_netw.htm (13 of 23) [12/09/2001 14.47.56] Chapter 29. NFS: Network File System 2. 3. 4. 5. 6. the normal NFS UDP server that waits for incoming datagrams to UDP port 2049.
When the client mounts the server's filesystem using TCP, it does an active open to
TCP port 2049 on the server. This results in a TCP connection between the client
and server for this filesystem. If the same client mounts another file-system on the
same server, another TCP connection is created.
Both the client and server set TCP's k...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12