Ephemeral Port

What is an ephemeral port?

It is a port that is only used for short period. It is typically used by a client when it connects to a server. The range is usually 49152 through 65535 but does vary. The client end of a connection typically uses a high port number allocated for short term use.

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Other definitions:

Techopedia:
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.

Dynamic ports (private ports) are 49152 - 65535. The dynamic port numbers are the port numbers that are available for use by any application to use in communicating with any other application, using TCP or UDP. These are used by client programs and you are free to use these in client programs. When a web browser connects to a web server the browser will allocate itself a port in this range. Also known as ephemeral ports.