TCP IP Illustrated

TCP IP Illustrated

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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 use. 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.

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