Portmapper and rpcbind

Portmapper and rpcbind are the software that supply client programs with information about server programs. Portmapper returns port numbers of server programs and rpcbind returns universal addresses. A universal address is a text string representation of the transport dependent address. A universal address for rpcbind is defined in RFC 3530 as a text string of the IP address, a dot, then the text string of the two octets of the port number. The following are examples of universal addresses for port 1024 (port 1024 = port 0x400):

9.1.1.1.4.0
::FFFF:9.1.1.1.1.4.0
2001:0DB8::10:1:1:1.4.0

You can communicate between different computer operating systems when messages are directed to port numbers or universal addresses rather than to targeted remote programs. Clients contact server programs by sending messages to the port numbers or universal addresses of remote processes. Because you make requests to the port number or universal address of a server rather than directly to a server program, client programs need a way to find this information about the server programs they are calling. Portmapper and rpcbind standardize the way clients locate information about the server programs that are supported on a network.

Portmapper and rpcbind use well-known port 111. See Well-known port assignments, for other well-known TCP and UDP port assignments.

The port-to-program information maintained by portmapper is called the portmap. Clients ask portmapper or rpcbind about entries for servers on the network. Servers contact portmapper or rpcbind to add or update entries to the portmap.