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JosephLea

How to send data to virtual ip (behind proxy server) ?

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JosephLea    122
I have a problem to communicate with the client behind proxy server or firewall. How can I send data to them? UDP or TCP ? Is there any document about this subject? Thank you !!!

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JY    289
The whole thing about a proxy server is that (in many cases) it acts as a firewall. Networks tend to be set up with the private IP addresses reserved by ICANN (192.168.x.x) and the proxy server acts as an intermediary between clients on the network and the outside world.

If you want to communicate with the clients via the proxy, it must be something that the proxy supports. Many proxy servers (including ones that I have written) will allow you to map TCP ports from clients to the outside world using network address translation.

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Rube    122
Problem is, unless you control the Proxy server, you''re really limited.

Like the previous poster stated, you can create a port forward ruleset on the proxy, which will forward any communication to an IP address of your choice. Only problem is if you want to talk to multiple clients behind that proxy, then you''ll need to use a different port for each client.

If you control the Proxy, setting up a port forward is usually very simple. Just tell it what port to forward to what IP inside the Proxy/Firewall.

If you don''t control the Proxy, you''re pretty much going to have to rely on the client to ask for the data. Even then, depending on the complexity of the Proxy, you might have problems. If it''s a simple packet filter firewall, then you can just find an open port. If it''s a full application scanning proxy, then you''re going to have problems.

An example of a application scanning proxy is when the Proxy actually looks over the content of the network packet(s) to decide if it''s a telnet, FTP, HTTP, or any other supported session. If it doesn''t match that syntax, you''re not getting through.

I guess the bottom line is exactly what sort of Proxy is between you and the client. =)

R.

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