Network Port Ranges: Well-Known, Registered, and Dynamic Ports

Network port numbers run from 0 to 65535. The Internet Assigned Numbers Authority (IANA) divides them into well-known ports (0–1023), registered ports (1024–49151), and dynamic or private ports (49152–65535). These ranges describe how numbers are assigned or reserved; they do not prove which application is running on a particular port.

An IP address identifies a device, while a port number helps distinguish a service or connection on that device. Always consider the transport protocol as well: TCP port 53 and UDP port 53 have the same number but belong to separate port-number spaces.

The three port-number ranges

These boundaries come from RFC 6335, Section 6, and are also listed in the IANA Service Name and Transport Protocol Port Number Registry. IANA calls the first two ranges System Ports and User Ports, respectively.

Well-known ports: 0–1023

Well-known ports are commonly associated with widely used network services. Examples in the IANA registry include HTTP on TCP 80, HTTPS on TCP 443, and Secure Shell (SSH) on TCP 22. The Domain Name System (DNS) uses port 53 with both TCP and UDP. Check the IANA registry for the current assignment and transport protocol of a particular service.

Not every number in this range is assigned to an ordinary service. Port 0, for example, is reserved rather than a normal service port. A service can also be configured to listen on a port other than its customary one.

Registered ports: 1024–49151

Applications and services can register numbers in this range with IANA. MySQL is registered on TCP 3306, while the service commonly associated with Remote Desktop Protocol (RDP) is registered on TCP 3389. Registration provides a shared reference; it does not grant a product exclusive use of a number or force every installation to use that port.

An open TCP 3306 therefore does not, by itself, prove that MySQL is running there. Likewise, a MySQL server may be configured to listen elsewhere. When troubleshooting a connection or setting a firewall rule, check the service's actual configuration and transport protocol, not just the registry entry.

Dynamic or private ports: 49152–65535

IANA does not assign ports in this range to specific services. A program can select an available number for temporary local use. For instance, when a browser connects to a server's TCP 443, the client side of the connection also uses a separate temporary port.

Do not assume that an operating system always selects temporary ports only from 49152–65535. That range is IANA's classification; the configured ephemeral-port range on a particular system may differ. Nor is any given dynamic port guaranteed to be available at all times.

How to interpret a port number

• Read a port number together with the IP address and transport protocol, such as TCP or UDP.
• Use IANA assignments as a starting point, then verify the port on which the actual service is listening.
• Not every number in the registered-port range has been assigned or is in use.
• Before opening a firewall port, confirm the required service and direction of traffic.