Thursday, January 20, 2011

Figuring out what your proxy is

If you work in corporate America chances are you are going through a proxy when you are surfing the web. Sometimes the proxy server is specified, sometimes you have a url that then determines what proxy to go to. If the server is directly specified as shown in the Proxy Server address below (the lower yellow area), then it is easy to tell. What is there is your proxy server.

On the other hand, if you have a .pac file or out configuration script that is being used then it is hard to tell from here because the rules are in the .pac file. This would be specified in the first yellow area shown below. You can use FireFox or sometimes Internet Explorer to save the .pac if you go to it in the browser. It can be saved and opened in any text editor. You can’t change it, but you can at least see what it is doing. But the question I had was how do I confirm what proxy server the .pac file has directed me to?


No matter what these settings are you can tell for sure what you proxy server you are actually connecting to by using the command line. First make sure you have Internet Explorer open and on the page in question. Open a command prompt (Start menu | Run… | cmd.exe) and then type the following:

netstat –b –n –p tcp

Now look for iexplore.exe. You will see something like


Notice I have highlighted the proxy server and port in yellow.

If you want to know what that is from a dns name perspective, you can use nslookup to look it up.

In this example, you would type:


This will return some name of the server if you are lucky.

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