2. Click the software LAN viewing tool to open the window, click the tool in the menu bar, and select the viewing port in the drop-down menu, as shown in the figure below. ?
3. Enter the network computer identification name of this computer in the text box below the search workgroup in the pop-up interface. The network computer identification name of the computer can open the computer system properties window to view the following figure. The computer name is in the red circle.
4. Click the "Refresh" button after entering, and the local IP, external IP, internal and external ports and working status in the list on the right can be seen at a glance.
"Port" Various computer services and communications communicate with external computers through specific ports, just like common WWW, FTP and Telnet services. With the development of computer network technology, the original physical interfaces (such as keyboard, mouse, network card, graphics card and other input/output interfaces) can no longer meet the requirements of network communication. As the standard protocol of network communication, TCP/IP protocol solves this communication problem. Integrating TCP/IP protocol into the kernel of the operating system is equivalent to introducing a new input/output interface technology into the operating system. Because TCP/IP protocol introduces an application program interface called "Socket". With such interface technology, computers can communicate with any computer with Socket interface through software.
With these ports, how do these ports work? For example, why can a server be a Web server, an FTP server and a mail server at the same time? One of the most important reasons is that various services provide different services by using different ports. For example, TCP/IP protocols usually stipulate that the Web uses port 80, FTP uses port 2 1, and the mail server uses port 25(SMTP service), 1 10(POP3 service). In this way, the computer can communicate with the outside world without interference through different ports.
Each computer host can have 65535 ports, but in fact there are only dozens of commonly used ports, so there are quite a few undefined ports. This is why so many hacker programs can define a special port in some way to achieve the purpose of intrusion. In order to define this port, you need to rely on a program to automatically load it into memory before the computer starts, and forcibly control the computer to open that special port. This program is the "backdoor" program. These backdoor programs are often called Trojan horses. To put it simply, these Trojan horse programs first implant a program in a personal computer by some means, open a specific port, commonly known as the "back door", and make the computer an extremely open FTP server (users have extremely high permissions), and then achieve the purpose of intrusion through the back door.