how to use proxies without the remote site being able to detect the host/host IP?

Question

I'm attempting to use a proxy, via python, in order to log into a site from a different, specific IP address. It seems that certain websites, however, can detect the original (host) IP address. I've investigated the issue a bit and here's what I found.

There are four proxy methods I've tried:

• Firefox with a proxy setting.
• Python with mechanize.set_proxies.
• Firefox in a virtual machine using an internal network, along with another virtual machine acting as a router (having two adapters: a NAT, and that internal network), set up such that the internal network traffic is routed through a proxy.
• TorBrowser (which uses Firefox as the actual browser).

For the first three I used the same proxy. The Tor option was just for additional testing, not via my own proxy. The following things are behaviors I've noticed that are expected:

• With all of these, if I go to http://www.whatismyip.com/, it gives the correct IP address (the IP address of the proxy, not the host computer).
• whatismyip.com says "No Proxy Detected" for all of these.

Indeed, it seems like the websites I visit do think my IP is that of the proxy. However, there have been a few weird cases which makes me think that some sites can somehow detect my original IP address.

• In one situation, visiting a non-US site via Firefox with a non-US proxy, the site literally was able to print my originating IP address (from the US) and deny me access. Shouldn't this be impossible? Visiting the site via the virtual machine with that same non-US proxy, or the TorBrowser with a non-US exit node, though, the site was unable to do so.
• In a similar situation, I was visiting another non-US site from a non-US proxy. If I logged into the site from Firefox within the virtual machine, or from the TorBrowser with a non-US exit node, the site would work properly. However, if I attempted to log in via Firefox with a proxy (the same proxy the virtual machine uses), or with mechanize, it would fail to log in with an unrelated error message.
• In a third situation, using the mechanize.set_proxies option, I overloaded a site with too many requests so it decided to block access (it would purposefully time out whenever I logged in). I thought it might have blocked the proxy's IP address. However, when I ran the code from a different host machine, but with the same proxy, it worked again, for a short while, until they blocked it again. (No worries, I won't be harassing the site any further - I re-ran the program as I thought it might have been a glitch on my end, not a block from their end.) Visiting that site with the Firefox+proxy solution from one of the blocked hosts also resulted in the purposeful timeout.

It seems to me that all of these sites, in the Firefox + proxy and mechanize cases, were able to find out something about the host machine's IP address, whereas in the TorBrowser and virtual machine cases, they weren't.

How are the sites able to gather this information? What is different about the TorBrowser and virtual machine cases that prevents the sites from gathering this information? And, how would I implement my python script so that the sites I'm visiting via the proxy can't detect the host/host's IP address?

Answer 1

It's possible that the proxy is reporting your real IP address in the X-Forwarded-For HTTP header, although if so, I'm surprised that the WhatIsMyIP site didn't tell you about it.

If you first visited the non-US site directly, and then later again using the proxy, it's also possible that the site might have set cookies in your browser on your first visit that let the site identify you even after your IP address changes. This could account for the differences you've observed between browser instances.

(I've noticed that academic journal sites like to do that. If I try to access a paywalled article from home and get blocked because I wasn't using my university's proxy server, I'll typically have to clear cookies after enabling the proxy to be allowed access.)