RFC 1833 (rfc1833) - Page 2 of 14
Binding Protocols for ONC RPC Version 2
Alternative Format: Original Text Document
RFC 1833 Binding Protocols for ONC RPC Version 2 August 1995
A client program needs to know the RPC program number, version
number, and the transport address corresponding to a service in order
to utilize the service. Of these, the RPC program number and version
number are usually built into the client program, as part of the
service definition. The network address component of the transport
address is usually available in a name service, or is given as a
parameter to the client program. The transport selector (ie., the
TCP or UDP port) is usually determined dynamically, and varies with
each invocation of the service. Server programs allocate a transport
address, and register it with a well-known lookup service (well-known
because it uses a fixed transport selector, and resides at the same
network address as the server). Client programs consult the lookup
service in order to obtain the server's transport address.
Such a lookup service is very desirable because the range of well-
known transport selectors is very small for some transports and the
number of services is potentially very large. By running only the
lookup service on a well-known transport selector, the transport
addresses of other remote programs can be ascertained by querying the
lookup service.
This document describes three versions of a lookup service, all of
which use the same RPC program number (100000). They all use port
111 over TCP and UDP transports. Versions 3 and 4 are described in
Section 2 ("RPCBIND Program Protocol"). Version 2 is described in
Section 3 ("Port Mapper Program Protocol").
The distinguishing characteristic of RPCBIND (versions 3 and 4) is
that this protocol uses a transport-independent format for the
transport address, known as the universal address format. An address
in universal address format is an ASCII string representation of the
transport dependent address. String representation of addresses
corresponding to a transport are defined by the addressing authority
for the transport. The RPCBIND protocol can be used for binding ONC
RPC clients and servers over any transport.
The Port Mapper (version 2), on the other hand, is an older protocol
that is specific to TCP and UDP. It handles TCP and UDP ports
directly.
2. RPCBIND Program Protocol
The RPCBIND program maps RPC program and version numbers to universal
addresses, thus making dynamic binding of remote programs possible.
The RPCBIND program is bound to a well-known address of each
supported transport, and other programs register their dynamically
allocated transport address with it. The RPCBIND program then makes
Srinivasan Standards Track