Using Nfs Over Tcp - Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual

100005 1 tcp
100005 2 udp
100005 2 tcp
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100005 3 tcp
If one of the NFS services does not start up correctly, portmap is unable to map RPC requests
from clients for that service to the correct port. In many cases, if NFS is not present in rpcinfo
output, restarting NFS causes the service to correctly register with portmap and begin working. For
instructions on starting NFS, refer to
Other useful options are available for the rpcinfo command. Refer to the rpcinfo man page for
more information.

19.10. Using NFS over TCP

The default transport protocol for NFSv4 is TCP; however, the Red Hat Enterprise Linux 5 kernel
includes support for NFS over UDP. To use NFS over UDP, include the -o udp option to mount
when mounting the NFS-exported file system on the client system.
There are three ways to configure an NFS file system export. On demand via the command line (client
side), automatically via the /etc/fstab file (client side), and automatically via autofs configuration
files, such as /etc/auto.master and /etc/auto.misc (server side with NIS).
For example, on demand via the command line (client side):
mount -o udp shadowman.example.com:/misc/export /misc/local
When the NFS mount is specified in /etc/fstab (client side):
server:/usr/local/pub
When the NFS mount is specified in an autofs configuration file for a NIS server, available for NIS
enabled workstations:
myproject -rw,soft,intr,rsize=8192,wsize=8192,udp penguin.example.net:/proj52
Since the default is TCP, if the -o udp option is not specified, the NFS-exported file system is
accessed via TCP.
The advantages of using TCP include the following:
• Improved connection durability, thus less NFS stale file handles messages.
• Performance gain on heavily loaded networks because TCP acknowledges every packet, unlike
UDP which only acknowledges completion.
• TCP has better congestion control than UDP. On a very congested network, UDP packets are
the first packets that are dropped. This means that if NFS is writing data (in 8K chunks) all of that
8K must be retransmitted over UDP. Because of TCP's reliability, only parts of that 8K data are
transmitted at a time.
• Error detection. When a TCP connection breaks (due to the server being unavailable) the client
stops sending data and restarts the connection process once the server becomes available. With
839 mountd
836 mountd
839 mountd
836 mountd
839 mountd
Section 19.5, "Starting and Stopping
/pub nfs rsize=8192,wsize=8192,timeo=14,intr,udp
Using NFS over TCP
NFS".
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