Problem: You’ve just upgraded to Fedora 17 (or perhaps 16) on your NFS server. Nothing is listening on port 2049 and rpc.idmapd isn’t running. You’ve already made sure nfs-server.service is running.
Solution: your old /etc/sysconfig/nfs file is messing up the NFS server. rpc.idmapd is no longer needed. (man nfsidmap). Run:
mv /etc/sysconfig/nfs /etc/sysconfig/nfs.rpmsave
mv /etc/sysconfig/nfs.rpmnew /etc/sysconfig/nfs
systemctl restart nfs-server.service
And if your client is running autofs, restart that on the client as well. Now NFS should work again.