At present, universities basically have more than three lines, education, netcom and telecommunications. Everyone knows what the speed of education is like. Everyone knows the statements of China Southern Telecom and China Northern Netcom. Before the merger of the telecommunications industry, the eight northern provinces were dominated by Netcom, and the rest were dominated by telecommunications. It is their line division that slows down the speed of China Netcom's access to telecom and the lines of telecom access to China Netcom. In order to take care of their own interests, they obviously don't have enough exports to each other. In order to solve this problem, many colleges and universities adopt multi-line access and add the function of automatically selecting operators to their routes. Education network is necessary, so when they do routing, they often use the IP of telecom or Netcom as the external network IP and NAT to protect the education IP. The advantage of this is to protect the IP of the education network, and the network speed of the education network will be very fast. When the university intranet IP accesses the external network, if it is an education network, it will directly go out of the public network without going through Netcom and Telecom. If he visits the network of China Telecom or China Netcom, he will convert the IP address of the education network into the IP address of China Netcom and China Telecom through NAT, and send it to the public network to ensure the speed and safety of Internet access. This is my opinion! Please correct me if there are any mistakes.