Have you done either of these:
Windows:In Registry Editor, locate the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Set the following registry value:
Value Name: IPEnableRouter
Value type: REG_DWORD
Value Data: 1
A value of 1 enables TCP/IP forwarding for all network connections that are installed and used by this computer.
Linux: http://www.ducea.com/2006/08/01/how-to-enable-ip-forwarding-in-linux/You're not going to run anything through your system if you don't, and you'll end up with a DoS condition.