Description of problem:
sometimes, when booting, the boot sequence stops at the script
/etc/rc.d/init.d/netfs, at the line : 
   action $"Mounting NFS filesystems: " mount -a -t nfs,nfs4

we mount nfs v3 filesystems from a NetApp (v6.3.1) or another RHEL linux 4.x
box, the /etc/fstab is like : 
nfsserver:/home     /home      nfs    defaults    0  0

defaults means : nfs 3, tcp, rw

some of our RHEL boxes here have this problem sometimes yes...  sometimes no... 
either IP address fixed or dhcp
either in a VMPS vlan or not
with ethernet cards tg3, e1000 or 3c59x
tested with differents tcp nfs options : posix, rsize, wsize, timeo...

Version-Release number of selected component (if applicable):
kernels 2.6.9-34.EL, 2.6.9-22.0.2.EL (at least)
RHEL fully updated

How reproducible:
shutdown or power off the PC, boot,
we have no information on how to reproduce it. 
We didn't notice this problem when we switch to udp in the fstab.

we have some tcpdump captures on both conditions, when it works and when the
boot sequence hangs in the netfs script.

these capture are available on request.

Solution : 
switch to udp