This command is not showing anything at all showmount -a 192.168.0.81. Are you mixing nfs3 and nfs4 exports? What about -e option?
You should see list as folllows:
showmount -e 192.168.0.81
Also, run above and below one from nfs client system:
/Network Recycle Bin 1
Both of them should display output. If not than make sure all nfs server including portmap running on server side as well as client side also. Finally, tcpdump may provide you more info:
rpcinfo -p 192.168.0.81
tcpdump -n -s0 host 192.168.0.81