What is an ephemeral port?

An ephemeral port is defined as a temporary port assigned for the duration of a session. This type of port is typically used for establishing outbound connections and is not meant to be permanent. When a client application on a host needs to communicate with a server, it usually opens an ephemeral port to initiate the connection. The port is dynamically allocated from a predefined range of ports, ensuring that each session can utilize a unique port number. Once the session is completed and the communication is closed, the ephemeral port is released and can be reused for future connections.

The concept of ephemeral ports is crucial in networking, as it allows for multiple simultaneous connections from a single host without port conflicts, since the ports are transient and designated solely for short-lived communication. This behavior contrasts with permanent ports, which are consistently associated with specific network services (such as HTTP typically using port 80 or HTTPS using port 443). Thus, the nature of ephemeral ports supports efficient and scalable communication in client-server interactions.