A port is the entrance to a network (or Internet) in a computer system. It can be used to manage data and communication traffic. Port enables individual users, organizations and enterprises to use computer networks to protect their confidentiality, integrity and availability. Technically, ports include network protocols and operating system standards, such as TCP/IP and UDP protocols.

The tertiary port refers to the port number of the network transport layer. Each network application uses a specific port number to send and receive data. There are two types of port numbers: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). The port number is 16 digits, ranging from 0 to 65535. TCP and UDP each use their own port number range, so that data packets can be transmitted correctly. TCP and UDP port numbers are the most common examples of tertiary ports.

Although the port number is only a small part in the process of network communication, it plays a vital role in network connection. For example, a website uses port number 80 or 8080 for HTTP communication with a web server. FTP uses port 2 1 for file transfer, and SSH uses port 22 for secure remote connection. Knowing the port number and how to manage and protect it is a compulsory skill for network administrators. The third-level port is also an important part of the work of information security engineers, because mastering the knowledge of port numbers can protect the security of the network.