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. The Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Stream Control Transmission Protocol (SCTP) typically use an ephemeral port for the client-end of a client–server communication. 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) 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. After completion of the session, the port is destroyed and the port number becomes available for reuse, but many implementations simply increment the last used port number until the ephemeral port range is exhausted, when the numbers roll over. Ephemeral ports are also called dynamic ports, because they are used on a per request basis, and are only known by number once allocated.
Range
Range Operating system 49152–65535 suggested by RFC 6335 and the Internet Assigned Numbers Authority (IANA) for dynamic or private ports.IANA port number assignments FreeBSD has used the IANA port range since release 4.6. Windows Vista, Windows 7, and Server 2008 (and subsequent versions including Windows 11) use the IANA range by default.Microsoft KB Article 929851 32768–60999 used by many Linux kernels.The effective range is accessible via procfs at node /proc/sys/net/ipv4/ip_local_port_range. 32768–65535 used by Solaris OS and AIX OS. 1024–65535 RFC 6056 1025–60000 default of Windows Server 2008 with Exchange Server 2007 installed.Microsoft KB Article 929851 In addition to the default range, all versions of Windows since Windows 2000 have the option of specifying a custom range anywhere within 1025–65535.Microsoft KB Article 929851Microsoft KB Article 196271 1024–5000 FreeBSD versions before 4.6, including the Berkeley Software Distribution (BSD). Default range of Microsoft Windows operating systems through Windows XP.Microsoft Windows Technet Library 1025–5000 used by Windows Server 2003, until Microsoft security update MS08-037 from 2008 is installed, after which it uses the IANA range by default.Microsoft KB Article 956188
Configuration characteristics If certain server software is used, that uses non-ephemeral custom port ranges for initiating some further connections, it needs to be ensured by configuration that this custom port range and the ephemeral port range do not overlap.
See also Registered port List of TCP and UDP port numbers
Notes
References
External links
RFC 6056 Recommendations for Transport-Protocol Port Randomization The Ephemeral Port Range at NcFTP.com Ephemeral Source Port Selection Strategies at DataPlane.org