The proxy server fails to access Alibaba Cloud DNS.

My school's campus network is connected to the Internet with 10 Mbps of bandwidth. the servers and network management workstations in the network center access the Internet directly through routers, and all other computers access the Internet through the MS-Proxy. In the past, the Internet Access failed due to a Proxy Server failure on the campus network. Generally, You can restart the proxy server to solve the problem. This time, after receiving a call for help from a teacher who was not able to access the Internet, we immediately checked the proxy server and found that the proxy server was running normally and restarted.
The fault still cannot be ruled out when the machine is being moved. After that, we checked the Internet access status of other servers and found that the webpage could not be opened. However, we can Ping the router address of China Telecom. When I open the network management workstation to access the Internet, I find everything is normal. What is the reason?

We checked the LAN line and found that there was no problem with the network connection. Why can only one computer access the Internet? Open the "local connection" attribute of the network management station, check the network settings, and find that the preferred DNS server is "202.99.160.68", and the alternative DNS server is "202.99.166.6 ", the DNS of several other servers only has one "202.99.160.68 ". I immediately added the alternative DNS "202.99.166.6" to the faulty machine. The problem was resolved immediately. It turned out to be a DNS problem. When setting network parameters, if there is an alternative DNS, you may wish to set a valid address for both the preferred DNS and the alternative DNS to avoid unnecessary troubles caused by DNS failure.