Hi all, while troubleshooting an odd NFS error, I discovered that apparently
(if you can believe the man pages) the default protocol for nfs clients to
mount from servers is now TCP.

And it apparently started with SL4.7, tho I could find no mention of
such a default protocol change while perusing the release notes for
SL4.7.

The following excerpts are from the man page for nfs(5) from
a 4.6 system and then from a 4.7 system.  Note the change in the
default protocol.

Under "Options for the nfs file system type" in the man page for nfs(5),

-------------
For SL4.6 (man page comes from util-linux-2.12a-17.el4_6.1):

tcp   Mount the NFS filesystem using the TCP protocol instead of the
       default UDP protocol.  Many NFS servers only support UDP.
-------------
-------------
For SL4.7 (man page comes from util-linux-2.12a-20.el4):

tcp   Mount the NFS filesystem using the TCP protocol. This is the default.
-------------

I am currently going thru and adding "udp" to all the SL4.7 clients' fstab
entries so they will use UDP rather than TCP.

My main question is, lacking any explicit protocol designation in the fstab,
how can one tell which protocol a client is using?

And lastly, why wasn't the change documented in the release notes?

 From what I've gleaned about the two protocols from googling, it appears
that TCP has advantages on a lossy network but that's not our scenario.
It also is not a stateless protocol, like UDP, so if a server crashes in
the middle of a packet transmission, the client will hang and filesystems
will need to be unmounted and remounted.  So it would seem UDP is better,
at least in our case.

Thanks!
- Larry
-- 
P. Larry Nelson (217-244-9855) | Systems/Network Administrator
461 Loomis Lab                 | High Energy Physics Group
1110 W. Green St., Urbana, IL  | Physics Dept., Univ. of Ill.
MailTo:[log in to unmask]        | http://www.roadkill.com/lnelson/
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