As discussed in
HDFS-6406, this JIRA is to track the follow update:
1. Port monitoring is the feature name with traditional NFS server and we may want to make the config property (along with related variable allowInsecurePorts) something as dfs.nfs.port.monitoring.
2 . According to RFC2623 (http://www.rfc-editor.org/rfc/rfc2623.txt):
Whether port monitoring is enabled or not, NFS servers SHOULD NOT reject NFS requests to the NULL procedure (procedure number 0). See subsection 2.3.1, "NULL procedure" for a complete explanation.
I do notice that NFS clients (most time) send mount NULL and nfs NULL from non-privileged port. If we deny NULL call in mountd or nfs server, the client can't mount the export even as user root.
3. it would be nice to have the user guide updated for the port monitoring feature.