Long time user (13 years). First question posted.

I have inherited two commercial products with extremely inflexible network connectivity. One runs on Windows and requires use of a NIC with a specific NON-routable IP address. The other runs on Linux and also requires use of a NIC with a specific NON-routable address, though I can bridge it from a TAP to an eth interface.

I tried using OpenVPN but discovered there was a very specific packet bit pattern that my software exchanges which OpenVPN silently drops. Also, IT policy is going to make OpenVPN extremely difficult to deploy.

So I'm trying to setup a tunnel using netcat and ssh on Linux, and cygwin+netcat and PuTTY on Windows. I created TAP's on both ends, setup the tunnel, and transmitted some test packets, but I can't seem to get netcat to listen to the TAP. Does anybody have a sample setup?

I almost got it working with socat. I can probably get as far with netcat, but socat seems to be a little easier for what I'm doing. I verified that my UDP broadcast packages are successfully tunneling from the Linux TAP to my Windows box, but they're not making it to the Windows TAP. In fact, I don't see the packets with Wireshark at all. I know this is probably a Windows problem, not Linux. So this is what I did on the Linux side to get as far as I did.

ifconfig tap0 inet 172.16.0.1 broadcast 172.16.255.255 netmask 255.255.0.0 up
socat -x TCP-LISTEN:6667,fork interface:tap0
Start my program that binds to the tap0 adapter

On the client side, I do the following:

socat -x TCP:<server_name>:6667,fork UDP:localhost:3301

With the -x switch, I can see the packets and verify the bit patterns are making it through. I'm using socat on Cygwin. I'll find a cygwin forum to get help on the Windows side.