Make sure a firewall rule isn’t blocking NFS. If NFS is running on the server and clients _can_ mount, but it’s just really slow, then things get a little hairly. You can’t just look for a problem on a client or a fix a misconfigured server. You’ll have to look at the whole ball of wax… If MTU mismatch doesn’t seem to be a problem, try going the other way and increasing the MTU size. Use the traceroute command to look for unexpected routing hops or delays.