On Thu, 26 Feb 2009, P. Larry Nelson wrote:

> 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?
>

mount

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

In SL.documention/RELEASE-NOTES-x86-en it states that TCP is now the 
default.  Note that the RELEASE-NOTES-x86-en were the original release 
notes for SL 4.0 from TUV.

We do not write the TUV release notes so I do not know why it was not 
documented.

>
> 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
>

-connie sieh