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I am conducting a small experiment on my office network. I have setup a proxy server on my desktop machine (connected to my LAN) and I have volunteers access the internet via my proxy server. Everything is working well. The problem is people cannot connect to the proxy server through their laptops. I asked my network admin and he said the wireless network has a firewall which prevents users from connecting to my proxy. He said I could tunnel the traffic or use SSH though. I am afraid I do not understand fully what is going on. Is there a way by which users connected on the wireless network can connect to my desktop?

I am using FreeProxy on Windows as my proxy server: http://www.handcraftedsoftware.org/index.php?page=download FreeProxy allows me to create a SOCKS 4/4a/5 proxy. Is that what I need? Part of the experiment involves logging the URL requests of the users. I am doing a measurement study. So, any solution must allow me to log the URL requests of users. Also, what changes do I need to make in the browser configuration.

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2 Answers 2

up vote 1 down vote accepted

SSH uses TCP port 22, so just set up your proxy client and destination proxy server to listen on TCP port 22 and that should resolve your problem because your network administrator has implied that there is a firewall exception for TCP port 22.

(+1 for an interesting question, and also especially for getting permission from the network administrator before attempting to bypass the firewall.)

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Heh. Sneaky approach. –  Paul Nov 16 '11 at 23:55
    
@Paul: Actually, it's not uncommon for people to use non-standard port numbers for specific services like proxying. The fact that the network administrator implied that TCP port 22 is open by indicating that SSH could be used for the proxy, so I read that as approval of implicit permission to use TCP port 22 for proxying. You're right about it being "sneaky" (+1 for you) in the more typical situation where permission isn't granted. =D –  Randolf Richardson Nov 17 '11 at 0:03
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Oh for sure, I meant a sneaky approach to solving the problem rather than going through an ssh tunnelling explanation, which is what I was about to take a deep breath and try to do. –  Paul Nov 17 '11 at 0:12
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@Randolf: Thanks a lot. It worked like a charm! –  Bruce Nov 17 '11 at 0:51
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@Randolf: That is great because I wanted to make minimal changes in my participant's terminals. This is a very elegant solution. –  Bruce Nov 17 '11 at 0:59

With SSH tunnelling, you need an ssh client on each device wanting to use your proxy, and you would need an SSH server on the proxy server.

The SSH protocol supports port-forwarding any port across an ssh session, called ssh tunnelling.

You can think of this as the remote port the user wants to connect to being accessible locally on their own machine. So lets say the proxy port was 8080, the user would set their proxy settings to 127.0.0.1:8080 - in other words, port 8080 on their own machine. This would get forwarded across the tunnel to port 8080 on the proxy server.

The ssh tunnelling configuration is different for each ssh client. For the standard ssh command line client, you would use the following command to create the tunnel:

ssh -L 8080:localhost:8080 proxy-ip-address

What this is saying is create a (L)ocal port 8080, and tunnel this across the ssh session, and at the other end, send it to localhost:8080

Any packets sent to port 8080 locally would then be sent via the tunnel to the proxy server port 8080.

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+1 for making the effort to explain this for Bruce -- this is useful information. –  Randolf Richardson Nov 17 '11 at 1:06
    
@Paul: Thanks a ton! –  Bruce Nov 17 '11 at 1:22
    
No problem. Note that the destination portion of the port-forward applies to any IP address and port. You can also use Dynamic port forwarding that effectively uses the remote device as a SOCKs proxy, without the actual proxy server. So the lesson here is that if you have ssh access to a server that itself is not restricted, you can use it to access pretty much anything you want regardless of local firewall restrictions. –  Paul Nov 17 '11 at 1:26

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