The portmap service is a dynamic port assignment daemon for RPC services such as NIS and NFS. It has weak authentication mechanisms and has the ability to assign a wide range of ports for the services it controls. For these reasons, it is difficult to secure.
Securing portmap only affects NFSv2 and NFSv3 implementations, since NFSv4 no longer requires it. If you plan to implement a NFSv2 or NFSv3 server, then portmap is required, and the following section applies.
If running RPC services, follow these basic rules.