"An error occurred while opening the folder on the FTP server during Serv-U public network access. Check whether you have the permission to access this folder. Detailed information: Operation timeout Solution

Recently, I set up an FTP server (Serv-U, of course) for the company. After the server is set up, it can be accessed on the local machine, whether it is using an IP address (ftp: // 192.168.1.163 ), or domain name (such as Domain Name: ftp://www.testftp.com), are normal, but how to access the public network is the emergence of "Operation timeout" prompt, the Internet did not find information, then saw an article ArticleThe firewall is not set. I went back and checked the firewall settings. I have already set port 21. The name and IP address of the logged-on user can be seen from Serv-U, so I think it's still a problem with the firewall. After testing, I finally got it done (see the figure below to solve the problem, I would like to give a reference to my friends who have encountered this problem. Of course, I will also give myself some convenience in the future.