An ephemeral port is a communications endpoint (port) of a transport layer protocol of the Internet protocol suite that is used for only a short period of time for the duration of a communication session.
Such short-lived ports are allocated automatically within a predefined range of port numbers by the IP stack software of a computer operating system.
At the server end of the communication session, ephemeral ports may also be used for continuation of communications with a client that initially connected to one of the services listening with a well-known port.
For example, the Trivial File Transfer Protocol (TFTP)[1] and Remote Procedure Call (RPC) applications can behave in this manner.
The allocation of an ephemeral port is temporary and only valid for the duration of the communication session.