What Are Ephemeral Ports?

An ephemeral port is a temporary network communication endpoint used to establish a connection with a server application over the internet or a local network. Ports have port numbers and numeric values used to identify communication endpoints in an IP network. Port numbers help direct network traffic to the appropriate end destination and facilitate communication. The system ensures that any other active connection does not use the selected port to avoid conflicts.

Ephemeral ports allow multiple client applications to establish simultaneous connections to a server without interfering with each other. Once the communication session between the client and server is complete or terminated, the ephemeral port is released and becomes available for reuse by other applications when necessary.

Ephemeral ports and TCP/IP communication

Transmission control protocol/internet protocol (TCP/IP) is an established procedure for transferring data and communication over the internet. These rules provide a reliable and standardised method for data transmission between devices. When establishing a TCP/IP connection, two endpoints are created, each with an IP number. An IP address is a unique string of numbers and periods assigned to each device connected to a computer network. The IP address identifies the device and network and allows for communication between devices over a network. 

The TCP connection typically has four identifiers: the server IP, server port, client IP, and client port. The server IP, server port, and client IP are generally known. When establishing this connection, you must either have a specified client port or a temporary ephemeral port number assigned. Each machine’s IP number assigns these temporary ports, using specific ranges for different purposes. After the connection ends, the ephemeral releases and can facilitate a different connection when needed.

Why are ephemeral ports important?

Ephemeral ports are critical to how the internet functions and are essential for establishing temporary connections between clients and servers. Servers typically use fixed port numbers so clients will know where to send communications. Clients usually do not need a fixed port number because servers generally don’t initiate communication with them. When the client sends a PORT command to establish a connection point, the server responds using a temporary connection point with a specified ephemeral port number. 

Organisations can restrict ephemeral port selection to enhance security. Some organisations may have protocols related to which ports employee computers use for data access and transfer. It can limit the port options and make it harder for unauthorised users to access and attack your system.

Types of ports

In networking, you might use well-known ports (0 to 1023), registered ports (1024 to 49151), and dynamic or ephemeral ports (49152 to 65535), as defined by the Internet Assigned Numbers Authority (IANA). System processes or services (like port 80 for HTTP or port 25 for SMTP) use well-known ports, while client applications use ephemeral ports during communication sessions. Depending on your operating system, the port numbers may vary, so it can be helpful to know what ranges are standard for your type of device and system.

Related terms

• Firewall

• Domain name system

• ITIL

• Debugging

Learn more on Coursera

Ephemeral ports facilitate multiple client applications to establish connections to a server simultaneously without interference. Understanding these temporary network communication endpoints is essential to exploring the digital world. To gain a better understanding of the ins and outs of networking and communication, consider completing the Google IT Support Professional Certificate on Coursera. With this Professional Certificate, you can build job-ready skills in under six months, prepare for an entry-level role in the in-demand field of IT, and earn a CV-boosting credential.