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I need a rule that will allow me to send back all traffic on port 1723 to an arbitrary, non-gateway box on the private network with all packet information intact.

The machine I need to target is acting as a gateway just for this port though it is not configured as a standard interface gateway. Things are set up this way to avoid putting in a work request to get the phone company to charge its router, sitting on client side. I need the box with the open port just to sit in the middle and forward traffic between the server and client.

The middleman is a Windows machine, but I believe it is configured correctly. Watching Wireshark, my Linux machine never sends it back the data though ip_forward is 1 and I have a DNAT rewrite rule in nat PREROUTING. :(

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I use this (output is from iptables-save) to redirect:

-A PREROUTING -p tcp -m tcp --dport 5000 -j DNAT --to-destination
-A PREROUTING -p udp -m udp --dport 5000 -j DNAT --to-destination


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