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An ephemeral port is a temporary communication hub used for Internet Protocol (IP) communications. It is created from a set range of port numbers by the IP software and used as an end client's port assignment in direct communication with a well-known port used by a server.
Ephemeral means temporary or short-lived, as is the characteristic of this type of port.
In client-server processes that use Transmission Control Protocol/Internet Protocol (TCP/IP) or User Datagram Protocol (UDP), the client initiates communication with a server through one of the many well-known ports. However, because the server does not initialize communication, it should not use a well-known port to send replies to the client, just in case a server-type application is running on that client device. Instead, the server to the client uses a new, temporarily assigned port that the client provides as the source port.
After communication is terminated, the port becomes available for use in another session. However, it is usually reused only after the entire port range is used up.
Different operating systems (OS) use different port ranges for ephemeral ports. Many Linux versions use port range 32768-61000, while Windows versions (until XP) use 1025-5000, by default.
Later Windows versions, including Vista, Windows 7 and Server 2008, use the Internet Assigned Number Authority (IANA) suggested range of 49152-65535.