8.  Port Mapper Program Protocol

The port mapper program maps RPC program and version numbers to transport-specific port numbers. This program makes dynamic binding of remote programs possible.

This is desirable because the range of reserved port numbers is very small and the number of potential remote programs is very large. By running only the port mapper on a reserved port, the port numbers of other remote programs can be ascertained by querying the port mapper.

The port mapper also aids in broadcast RPC. A given RPC program will usually have different port number bindings on different machines, so there is no way to directly broadcast to all of these programs. The port mapper, however, does have a fixed port number. So, to broadcast to a given program, the client actually sends its message to the port mapper located at the broadcast address. Each port mapper that picks up the broadcast then calls the local service specified by the client. When the port mapper gets the reply from the local service, it sends the reply on back to the client.

8.1.  Port Mapper Protocol Specification (in RPC Language)
const PMAP_PORT = 111;      /* portmapper port number */

* A mapping of (program, version, protocol) to port number
struct mapping {
	unsigned int prog;
	unsigned int vers;
	unsigned int prot;
	unsigned int port;

* Supported values for the "prot" field
const IPPROTO_TCP = 6;      /* protocol number for TCP/IP */
const IPPROTO_UDP = 17;     /* protocol number for UDP/IP */

* A list of mappings
struct *pmaplist {
	mapping map;
	pmaplist next;
* Arguments to callit
struct call_args {
	unsigned int prog;
	unsigned int vers;
	unsigned int proc;
	opaque args<>;

* Results of callit
struct call_result {
	unsigned int port;
	opaque res<>;
* Port mapper procedures
program PMAP_PROG {
	version PMAP_VERS {
		PMAPPROC_NULL(void)         = 0;

		PMAPPROC_SET(mapping)       = 1;

		PMAPPROC_UNSET(mapping)     = 2;

		unsigned int
		PMAPPROC_GETPORT(mapping)   = 3;

		PMAPPROC_DUMP(void)         = 4;

		PMAPPROC_CALLIT(call_args)  = 5;
	} = 2;
} = 100000;

8.2.  Port Mapper Operation

The portmapper program currently supports two protocols (UDP/IP and TCP/IP). The portmapper is contacted by talking to it on assigned port number 111 (SUNRPC [8]) on either of these protocols. The following is a description of each of the portmapper procedures:

This procedure does no work. By convention, procedure zero of any protocol takes no parameters and returns no results.
When a program first becomes available on a machine, it registers itself with the port mapper program on the same machine. The program passes its program number "prog", version number "vers", transport protocol number "prot", and the port "port" on which it awaits service request. The procedure returns a boolean response whose value is TRUE if the procedure successfully established the mapping and FALSE otherwise. The procedure refuses to establish a mapping if one already exists for the tuple "(prog, vers, prot)".
When a program becomes unavailable, it should unregister itself with the port mapper program on the same machine. The parameters and results have meanings identical to those of PMAPPROC_SET. The protocol and port number fields of the argument are ignored.
Given a program number "prog", version number "vers", and transport protocol number "prot", this procedure returns the port number on which the program is awaiting call requests. A port value of zeros means the program has not been registered. The "port" field of the argument is ignored.
This procedure enumerates all entries in the port mapper's database. The procedure takes no parameters and returns a list of program, version, protocol, and port values.
This procedure allows a caller to call another remote procedure on the same machine without knowing the remote procedure's port number. It is intended for supporting broadcasts to arbitrary remote programs via the well-known port mapper's port. The parameters "prog", "vers", "proc", and the bytes of "args" are the program number, version number, procedure number, and parameters of the remote procedure.


This procedure only sends a response if the procedure was successfully executed and is silent (no response) otherwise.
The port mapper communicates with the remote program using UDP/IP only.

The procedure returns the remote program's port number, and the bytes of results are the results of the remote procedure.