An ephemeral port is a short-lived transport protocol port for Internet Protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 (IP) communications allocated automatically from a predefined range by the TCP/IP

Internet protocol suite

The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...

 software. It is used by the Transmission Control Protocol

Transmission Control Protocol

The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

 (TCP), User Datagram Protocol

User Datagram Protocol

The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...

 (UDP), or the Stream Control Transmission Protocol

Stream Control Transmission Protocol

In computer networking, the Stream Control Transmission Protocol is a Transport Layer protocol, serving in a similar role to the popular protocols Transmission Control Protocol and User Datagram Protocol...

 (SCTP) as the port assignment for the client

Client (computing)

A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....

 end of a client–server communication to a well known port on a server

Server (computing)

In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

. On servers, ephemeral ports may also be used to continue communications with a client that initially connected to one of the server's well-known service listening ports to make the well-known port available to service requests from other clients.
The allocations are temporary and only valid for the duration of the communication session. After completion of the communication session, the ports become available for reuse.Most implementations may simply increment the last used port number until the ephemeral port range is exhausted.

The Internet Assigned Numbers Authority

Internet Assigned Numbers Authority

The Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...

 (IANA) suggests the range 49152 to 65535 for dynamic or private ports.

Many Linux kernel

Linux kernel

The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....

s use the port range 32768 to 61000.The effective range is accessible via the /proc file system at node /proc/sys/net/ipv4/ip_local_port_range. FreeBSD

FreeBSD

FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...

 has used the IANA port range since release 4.6. Previous versions, including the Berkeley Software Distribution

Berkeley Software Distribution

Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...

 (BSD), use ports 1024 through 4999 as ephemeral ports. Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 operating systems through Server 2003 use the range 1025 to 5000 as ephemeral ports. Windows Vista

Windows Vista

Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...

, Windows 7, and Server 2008 use the IANA range.

See also

• ephemeral
• Internet Protocol Suite
  Internet protocol suite
  The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
  
  
• List of TCP and UDP port numbers

External links

• The Ephemeral Port Range at NcFTP.com