UDP and TCP ports: A list of the most important ports

TCP and UDP are used to connect two devices over the Internet or other networks. However, to give data packages an entrance to the PC or server at the other end of the connection, the “doors” have to be open. These openings into the system are called ports. For both protocols, there are some known and important ports which you need to know when developing web apps.

When communicating via the Internet, the two protocols TCP and UDP establish the connection, compile data packages again after transfer, and then hand them over to the programs addressed on the recipient’s device. For this handover to work, the operating system must create entrances and open them for the transfer. Every entrance has a specific code number. After the transfer, the receiving system knows where the data has to be delivered based on the port number. The data package always includes two port numbers: the sender’s and the recipient’s.

Ports have consecutive numbers – from 0 to 65536. Some of these code numbers are standardised, which means they are assigned to specific applications. These standard ports are also called well-known ports, as the code numbers are known to all and permanently assigned. There are also registered ports, which organisations or software producers have registered for their applications. The Internet Assigned Numbers Authority (IANA) is responsible for registration. There is also a wide range of port numbers that are assigned dynamically. For example, browsers use these ports when visiting a website. The number is then free again afterwards.

Among the over 65,000 ports, there are few code numbers that are essential for Internet communication. We want to show you the most important well-known ports and registered ports. Some of these ports are only authorised for one of the two protocols (TCP or UDP). There are also ports that were not officially registered for the service in question, but have established themselves unofficially. Some ports have double assignments.