Which port number is used by the RPC Endpoint Mapper in Windows for RPC calls?

Which port number is used by the RPC Endpoint Mapper in Windows for RPC calls?

• A. 9
• B. 548
• C. 179
• D. 135

Answer: (D)

The fixed, well-known port for discovering RPC services is the Endpoint Mapper. It acts like a directory for all RPC interfaces: a client first contacts this mapper on its standard port to ask where a particular RPC service is listening, and the mapper replies with the actual port to connect to. That way, the server can run its RPC interfaces on dynamic ports while clients always know where to start. Correspondingly, this service listens on port 135, which is why that port is the correct answer. The other ports correspond to unrelated services—9 is the discard service, 548 is Apple Filing Protocol, and 179 is used for BGP—so they aren’t used for locating Windows RPC endpoints.

The fixed, well-known port for discovering RPC services is the Endpoint Mapper. It acts like a directory for all RPC interfaces: a client first contacts this mapper on its standard port to ask where a particular RPC service is listening, and the mapper replies with the actual port to connect to. That way, the server can run its RPC interfaces on dynamic ports while clients always know where to start.

Correspondingly, this service listens on port 135, which is why that port is the correct answer. The other ports correspond to unrelated services—9 is the discard service, 548 is Apple Filing Protocol, and 179 is used for BGP—so they aren’t used for locating Windows RPC endpoints.