Double proxy setup

Question

I'm already behind a proxy for internet access. We have certain sites blocked on this network.

If I tell my browser to use a different proxy it doesn't work. I think this is because it needs to go through the existing proxy to get to the internet.

Is there a way I can use another proxy when I'm already behind one? How do I do that? Will the sites I try to access still be blocked if the primary proxy has the policy in place?

Answer 1

You can usually specify a parent proxy through which to route traffic from your local proxy (privoxy, squid, polipo, etc). However, if that parent proxy blocks certain websites, they'll still be blocked in your two-proxy setup.

Answer 2

You can use a web proxy in addition of your corporate proxy (sometimes also called «CGI proxy»).

Chances are public web proxies are blocked by your corporate proxy, so you may need to set-up your own home. An easier way would be to set-up your own reverse proxy redirecting to a well known web proxy.

Answer 3

The proxy at your work may be a transparent one. That means anything outgoing on port 80 (and possibly 443) is intercepted at the firewall/router level and being redirected through the proxy automatically.

First, try doing a DNS lookup manually (start -> cmd.exe -> nslookup {facebook.com} 8.8.8.8) and then entering the resultant IP instead of the site domain name in the address bar (i.e. http://173.252.110.27). If your proxy blocking software is DNS or domain based this may work.

If you use a proxy that is not on port 80 or 443, it may work.

Answer 4

If you are running Linux you can use program like Proxychains. It allows you to specify a sequence of proxy servers which will be used to run traffic. As first server you should specify your existing proxy server. As second server you should specify any proxy server which you want (if your existing proxy allows connection to them).

It will look like that:

You computer -> (port80)(corporate proxy) -> (port443)(another proxy) -> (any port)(requested resource)

Everything depends on what are the access policies on proxy servers which you will use.

Your corporate server most likely will allow you to establish connection to port 80 or 443 of external computers in the Internet. If you will find open proxy server which accepts connection on ports 443 or 80 then you can route your traffic thru it as shown above. On first look it will not be suspicious because in corporate server logs it will appear as connection of type CONNECT to the external host. Usual web surfing. But in actuality it can be any traffic.