RFC 2623:NFS Version 2 and Version 3 Security Issu...
RFC-Ref

UDP


Click on the red underlined text to get to the source

... client send its NFS requests from UDP or TCP source ports with values < 1024. The theory is that ...
... send the request from TCP or UDP port < 1024. There does not seem to be any value in this because the NULL procedure is of very low overhead ...



Google
Web
RFC-Ref