Information
Network File System (NFS) is one of the most popular distributed file system protocols that allows a client computer to access files on shared storage over the network. NFS version 4 (NFSv4) is an improved version of NFS protocol versions 2 and 3.
Solution
Setting this option is set to the null string. Windows users who are not mapped to a UNIX user are not allowed to log in.
Additional information: http://media.netapp.com/documents/TR-3490.pdf