How to set NFS server to support NFSv4?

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Solaris 10 installing through NFS server
failed:
mount -F nfs -o ro 192.168.0.102:/mnt/hdc /mnt
error message:
error 7(RPC:authentication failed)

successed:
mount -F nfs -o ro,vers=3 192.168.0.102:/mnt/hdc /mnt

How to set NFS server to support NFSv4?