How proxies and gateways can cause, and be used to troubleshoot, network errors
Proxies and gateways are devices that act as intermediaries between web browsers and servers. They exist for such purposes as
- improving performance through caching,
- providing an alternative path to servers, e.g. to provide anonymity to users or to allow users to bypass faults
- distributing the function of a web site amongst multiple machines,
- allowing controlled access to otherwise protected servers
Transparent proxies and gateways lie on the communication path between your web browser and web servers (e.g. in your ISP or at the venue that hosts the servers for a web site) and operate independently of your computer. Popular software for such proxies includes Microsoft's ISA and Apache-based software, so you may observe error messages produced by such software even if neither your web browser nor the web server that you are trying to access use such software.
Other proxies can only be used if you correctly configure your system:
- From the Internet Options control panel
- Choose the “Connections” tab
- Click on the “LAN settings” button, to view this window in which you can specify the appropriate settings:
Several web sites provide public proxy services. A useful index of such sites is proxy.org.
Using proxies for troubleshooting
Proxies can be useful for troubleshooting network problems because they provide an alternative path to a destination server, and because they may translate content between different formats that are supported by the client and the server.
For specific examples of using proxies for troubleshooting, see the pages about the following errors:
Errors generated by proxies
Transparent proxies may reveal themselves when faults occur by identifying themself in error messages.
Proxies reporting errors
Proxies may report HTTP errors 400 500 502 503 504 because of problems caused by other devices.
Proxies causing errors
Proxies may also cause Internet Explorer to complain that it Cannot find server or that The address is not valid.