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Can a firewall still block things off a tunnel going trough it ?

I am testing my proxy with Dante in China and works flawlessly but I have the same config on a proxy in Ireland that goes trough a public french network and I still get some stuff blocked. Any hints ?

Thank you.

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    Can you advise what is being blocked - if it's the entire connection then it's an easy yes with the advise of trying a different port However if it's a no then can you provide detailed information as to what functionality is lost?
    – 50-3
    Sep 4, 2013 at 7:33
  • Gaming ports and torrent ports on that public french network are blocked. So the tunneled proxy actually works but those ports are still being filtered.
    – Chroma Funk
    Sep 4, 2013 at 7:58
  • Would it be an option to change the port to something under 1024 like 443 ?
    – Chroma Funk
    Sep 4, 2013 at 8:18

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Yes, a firewall can block things with a tunnel going through it. In the generic term, a tunnel does not necessarily provide encryption, so simply doing deep packet inspection will enable the firewall to operate on the tunnel.

In the case of an SSH tunnel (which is implied from the tag you selected) it is substantially harder to do, but it can be done, for example, using a man-in-the-middle attack. You don't state where you are located, but I have reason to believe that The Great Firewall of China is capable of doing this.

Further, a tunnel only "protects or hides the path between yourself and the tunnel endpoint. If the tunnel breaks out onto the Internet it is trivially possible for the traffic to be intercepted/blocked at that point, as it appears as normal traffic, albeit originating/terminating on the tunnels endpoint rather then your location.

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  • Thank you for your answer. Actually, I can easily bypass the GFC right now with the config. The problem is on the French public network. What i do: Computer on the public french network --- ssh tunnel to proxy with Dante on Ireland ---- internet ---- back to proxy --- computer. I do the SSH connection on port 22.
    – Chroma Funk
    Sep 4, 2013 at 7:53
  • Sorry, I don't understand enough to work out whats not working, particularly the bit between the public internet and your proxy - although I wonder if this is where the problem lies. Another possibility might be that the tunnel is working fine and you have an MTU issue because the tunnel is reducing the maximum size of packets - this can cause sessions to appear to freeze.
    – davidgo
    Sep 4, 2013 at 22:21

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