Tunnel between windows through linux server for sql server, possible

Assuming your linux box is accessible from the internet at 1.2.3.4 on port 23008, on an external system I would do:

external% ssh -p 23008 -L 13389:192.168.8.y:3389 username@1.2.3.4

I'd then connect to the port-forwarded RDP system with

external% rdesktop localhost:13389

If your external box isn't a linux box, there will be equivalent commands for the tools you have; the idea is still the same: to forward external's port 13389 to 192.168.8.y's port 3389, then use external's RDP client to connect to localhost:13389.

You refer to setting up the linux box's sshd correctly, but unless you've reconfigured it, the standard sshd setup is likely to support this just fine.

When upgrading to a newer Dlink Router, I had the problem of no longer being able to connect to SQL SVR between computers on my network (plugged into the Dlink Router).

I found the solution on this forum.

Disabling "Advanced DNS Service". Enabled is the default.

(Setup > Internet > Manual Internet Connection Setup > Advanced DNS Service)

According to the post that I found, it also resolves difficulties connecting RDP. The was some speculation that the SQL SVR connection requests were being sent out to OpenDNS thus preventing the desired connection.

For SQL SVR 2008, there is some additional Surface area configuration needed to allow connections including connections to named instances.

Note that with Open DNS turned on, you can enable local SQL SVR connections using the port forwarding settings of the Dlink Router. If you turn off Open DNS, the port forwarding settings are not required for connections between computers on your network. If you want to allow SQL SVR connections from the Internet to computers on your DLink Network, you need to configure this in Virtual Server settings (not Port Forwarding). Both Port forwarding and Virtual Server are found on the advanced tab.

My Router is less than a year old (DIR 655)