IP Forwarding is just normal Layer3 Routing. In the old NT4 systems you
enabled "routing" by enabling or disabling "IP Forwarding". It is just plain
old simple everyday Routing.
What you are probably asking about is NAT (Network Address Translation). The
term IP Forwarding is constantly abused and used to refer to NAT when that
is not accurate. NAT is simply "NAT". It has different aspects to it
depending on what you are doing with it.
What you are most likely asking about it how to have outside traffic sent to
an internal IP#,...this would be Static-NAT (or Reverse NAT) if this is only
done with a specific Port# (Port# does matter). But if the same thing is
done without any regaurd to port# then it is called One-to-One-NAT, the
traffic is always passed without reguard to Port#s.
If Port#s are involved and if those numbers are *not* identical on each
side, then you are combining NAT with PAT (Port Address Translation).
