[K12OSN] migration question - nfs freezing?

[Antonello Facchetti]

I'm migrating my server to k12ltsp 4.2.1 (fc3), from a previous 4.0.1 (fc1).
The server has got a new gigabit nic for the terminal and a fast nic for 
the network outside.
I did a standard installation (no tweaking at all, just set ip addresses)
When I try to connect a client this is correctly recognized, it gets 
it's ip address from dhcp but it freezes after this message:

mounting root filesystem from /opt/ltsp/i386
doing the pivot_root
nfs: server 192.168.1.254 not responding. trying again

meanwhile /var/log/messages in the server says:

rpc.mountd: authenticated mount request from 192.168.1.7 (/opt/ltsp/i386)

I suppose it's a problem with nfs, but I have touched nothing in the 
server (as i said, a smooth standard install)

I thought it might be a problem with gigabit nic, but the net works 
(dhcp did his work).

Nfs is running as a service

Did I forget anything?

tia
Antonello