Strange network faults

The strange Network Fault-Linux Enterprise Application-Linux server application information. The following is a detailed description. An error occurred on a server in Dongfang. It is a linux operating system that acts as a proxy for over 40 workstations in a data center to access the campus network. The workstation can download things through the plug-in, go to QQ, ping the IP addresses of dns, gateway, and Internet, and run nslookup correctly, but it cannot open the webpage, you cannot access the Internet through ftp. You can access webpages on the campus network through an IP address, but you cannot access the Internet webpage through an Internet IP address. I can't solve it for a while. I logged on to the Agent Server linux, and checked the server again like the workstation. Check dns. That's right. Check iptable. Check the firewall of linux, the server's firewall has not been opened, and it has been restarted many times. It seems that the problem is not here for me. In baidu and google searches, some netizens reported that there was a problem with the acl. It seems that there was a problem with the acl of the upper-level switch.