An ephemeral port is a communications endpoint (

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Hamburg, Manch ...

) of a

transport layer In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end c ...

protocol of the

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

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 communication endpoint. At the software level within an operating system, a port is a logical construct that identifies a specific process or a type of network service. A port is uniquely identified by a numbe ...

s by the IP stack software of a computer operating system. The

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, th ...

(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 Network packet, packets) to other hosts on an Internet Protoco ...

(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 ...

(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 requested information for other programs or devices, called clients. Role * Waiting staff, those who work at a restaurant or a bar attending custome ...

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 The Trivial File Transfer Protocol (TFTP) is a simple Lockstep (computing), lockstep communication protocol for transmitting or receiving files in a client-server application. A primary use of TFTP is in the early stages of nodes booting on a l ...

(TFTP) and

Remote Procedure Call In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space (commonly on another computer on a shared computer network), which is written as if it were a ...

(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

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