Portmapped

Portmapped refers to the portmapper service used in distributed computing environments that rely on remote procedure calls (RPC). The portmapper maintains a registry that maps RPC program numbers and versions to the network ports on which the corresponding services listen. This enables RPC clients to locate a service by its program number rather than by a fixed port.

In operation, an RPC server registers itself with the portmapper by providing its program number, version, protocol (TCP or UDP), and port. The portmapper listens on a well-known port (traditionally port 111) and provides a small set of operations, such as GETPORT (to retrieve the port for a given program and version), DUMP (to enumerate registered programs), and CALLIT (to request the portmapper to invoke a procedure on the client side). When a service starts or changes port, it must re-register with the portmapper to keep the registry up to date.

Historically, the term portmap described this service in many Unix-like systems, particularly those using Sun RPC. Modern Linux and Unix variants often implement rpcbind as the successor or replacement for portmap, but both serve the same fundamental purpose of mapping RPC program numbers to ports and maintaining the registry required for RPC communication.

Security considerations include the fact that the portmapper exposes information about available RPC services and ports. If not needed, the portmapper’s access can be restricted or disabled, and RPC traffic can be filtered with firewalls or limited to trusted networks.