Hmmm..
We have a Linux NFS machine to extend the AIX Server’s chronic acute harddisk space shortage syndrome. Somehow, AIX Client could not mount the shared NFS folder from the Linux Server.
Apparently, AIX uses high ports to establish the connectivity to NFS Server. Linux NFS Server requires low ports (below 1024). So, you have to force AIX to use those reserved ports to establish the connection.
nfso -o nfs_use_reserved_ports=1
Then, the normal ‘mount’ should work from AIX after the medicine 
Enjoy
Thanks for the “cure” and the explanation. It’s so much easier to take one’s medicine when you know what it’s for.
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For permanent change use :
nfso -p -o nfs_use_reserved_ports=1