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 number In computer networking, a port is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specific ...

s by the

IP stack The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the sui ...

software of a computer operating system. The Transmission Control Protocol (TCP), the

User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...

(UDP), and the

Stream Control Transmission Protocol The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the p ...

(SCTP) typically use an ephemeral port for the

client Client(s) or The Client may refer to: * Client (business) * Client (computing), hardware or software that accesses a remote service on another computer * Customer or client, a recipient of goods or services in return for monetary or other valuable ...

-end of a client–server communication. At the

server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...

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 This is a list of TCP and UDP port numbers used by protocols for operation of network applications. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) only need one port for duplex, bidirectional traffic. They usually u ...

. For example, the

Trivial File Transfer Protocol Trivial File Transfer Protocol (TFTP) is a simple lockstep File Transfer Protocol which allows a client to get a file from or put a file onto a remote host. One of its primary uses is in the early stages of nodes booting from a local area netwo ...

(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

The RFC 6056 says that the range for ephemeral ports should be 1024–65535. The Internet Assigned Numbers Authority (IANA) and RFC 6335 suggests the range 49152–65535 (2¹⁵ + 2¹⁴ to 2¹⁶ − 1) for dynamic or private ports. Many Linux kernels use the port range 32768–60999.The effective range is accessible via procfs at node /proc/sys/net/ipv4/ip_local_port_range. FreeBSD has used the IANA port range since release 4.6. Previous versions, including the

Berkeley Software Distribution The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berk ...

(BSD), use ports 1024–5000 as ephemeral ports. Microsoft Windows operating systems through

Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Windows 2000 for high-end and ...

use the range 1025–5000 as ephemeral ports by default. Windows Vista,

Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...

, and Server 2008 use the IANA range by default.

Windows Server 2003 Windows Server 2003 is the sixth version of Windows Server operating system produced by Microsoft. It is part of the Windows NT family of operating systems and was released to manufacturing on March 28, 2003 and generally available on April 24, ...

uses the range 1025–5000 by default, until Microsoft security update MS08-037 from 2008 is installed, after which it uses the IANA range by default. Windows Server 2008 with Exchange Server 2007 installed has a default port range of 1025–60000. 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 196271
/ref> Solaris OS uses 32768–65535 range.

AIX Aix or AIX may refer to: Computing * AIX, a line of IBM computer operating systems *An Alternate Index, for a Virtual Storage Access Method Key Sequenced Data Set * Athens Internet Exchange, a European Internet exchange point Places Belgiu ...

OS uses 32768–65535 range.

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.

Notes

References

External links

RFC 6056 Recommendations for Transport-Protocol Port Randomization

at NcFTP.com

at DataPlane.org {{DEFAULTSORT:Ephemeral Port Internet Standards Internet protocols

Range

Configuration characteristics

See also

Notes

References

External links