Mandrake is a variant of RedHat. In this link, John Hardin states that we need to patch RedHat with two different patches in order to the kernel to be able to do VPN Masquerade. In it, the author states that in order to do port forwarding on a kernel 2.0.
Any help is once more appreciated.
There are probably a couple of posibilities. You are using IP Masquerading. My guess is it should end up something like this for a conservative site. Which does have its own module that is loaded into the kernel. Given the above details, I suspect I need to add to pmfirewall.