Okay, that helped a bit! If I run: mount.nfs 10.2.4.199:/mnt/HD_a2 /dlink -wv it mounts okay, now. But running: mount -a (as root) or mount /dlink (as root) still gives the "Protocol not supported" error. My /etc/fstab file contains: 10.2.4.199:/mnt/HD_a2 /dlink nfs rw,users,sync,exec,auto,nfsvers=4 0 0 So, I next tried removing the "nfsvers=4" from fstab line and now mount -a works, too! Thanks for solution, Thorsten Kukuk!