ONC RPC - short for Open Network Computing Remote Procedure Call, sometimes also called Sun RPC based on its origin, is a widely deployed (possibly most widely deployed) remote procedure call system. Initially developed for the Network File System, ONC RPC supports procedure calls over both UDP and TCP. The interface description language for ONC RPC is XDR (eXternal Data Representation) which was initially designed for description and encoding of data for cross-platform communication.

Access to RPC services on a machine are provided via a port mapper that listens for queries on a well-known port, port 111 over UDP and TCP.

ONC RPC is described in RFC 1831. Authentication mechanisms used by ONC RPC are described in RFC 2695, RFC 2203, and RFC 2623.