You should disable RPC if you do not need it.
Remote Procedure Call (RPC) is a protocol that programs can use to request services from other programs located on different computers. The portmap service controls RPC services by mapping RPC program numbers into DARPA protocol port numbers; it must be running in order to make RPC calls.
RPC-based services have had a bad record of security holes, although the portmapper itself hasn't (but still provides information to a remote attacker). Notice that some of the DDoS (distributed denial of service) attacks use RPC exploits to get into the system and act as a so called agent/handler.
You only need RPC if you are using an RPC-based service. The most common RPC-based services are NFS (Network File System) and NIS (Network Information System). See the previous section for more information about NIS. The File Alteration Monitor (FAM) provided by the package fam is also an RPC service, and thus depends on portmap.
NFS services are quite important in some networks. If that is the case for you, then you will need to find a balance of security and usability for your network (you can read more about NFS security in the NFS-HOWTO (http://www.tldp.org/HOWTO/NFS-HOWTO.html) (/usr /share/doc/HOWTO/en-txt/NFS-HOWTO.txt.gz)).
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