Which port number is commonly associated with the Endpoint Mapper for dynamic RPC services?

• A. 445
• B. 139
• C. 1024
• D. 135

Answer: (D)

The key idea is that RPC clients first talk to the Endpoint Mapper to discover where a service is listening. The Endpoint Mapper, which handles the mapping of RPC interfaces to network endpoints, is traditionally reached on port 135 (TCP and UDP). After contacting port 135, the client asks for the endpoint of the desired RPC service, and the server responds with the dynamic port number that the service is using. The real service then communicates over that dynamic port. The other ports listed correspond to different services—445 is for SMB over TCP, 139 for NetBIOS/SMB, and 1024 is just a general entry in the dynamic range and not specifically tied to the Endpoint Mapper. So the port commonly associated with the Endpoint Mapper for dynamic RPC is 135.