[K12OSN] nfs troubles

[Jon Harder]

I am having problems booting iMac clients that I believe
is related to overwhelming them with data.

This is what I am seeing as they boot up:

...
Mounting root filesystem: /opt/ltsp/ppc from: 192.168.0.254
Doing the pivot_root
nfs:server 192.168.0.254 not responding, still trying
nfs:server 192.168.0.254 OK
nfs:server 192.168.0.254 not responding, still trying
nfs:server 192.168.0.254 OK
nfs:server 192.168.0.254 not responding, still trying

and these last two lines repeat indefinitely.

Some searching reveals that this might be related to the old
computers being overwhelmed with too much UDP nfs traffic from
the server.

Originally I tested this setup with a few iMac clients and it
worked fine. Now that I want to roll it out, I purchased a new
HP ProCurve 1800-24G switch which is apparently dumping the data
from the server's Gb connection a lot faster than the switch in
my original test setup was able to do.

I hooked six of the iMacs to an old 8 port switch and they all boot
fine. Once they were up and running, I moved the connections over to
the new fast switch and they work better, but soon the oldest iMacs
freeze up.

One suggestion I found was to force the clients to connect to NFS
using TCP instead of UDP. I tried playing with 

  /opt/ltsp/ppc/etc/rc.sysinit

a little bit to force TCP, but with no apparent success. I use
tcpdump to monitor the network. The server is pushing out a lot
of UDP packets!

Can someone suggest what I might do to ensure the clients are using
TCP? Or is there a way to throttle the server so that it only sends
so much traffic to a particular client? Any help would be appreciated.

--
Jon Harder
Mountain Lake (Minnesota) Public Schools