Redirection (Port Forwarding/Relaying or Transparent Proxying)

Port forwarding redirects incoming connection requests to the NAT gateway to an arbitrary address/port. In certain configurations (port rewrite), this is referred to as transparent proxying. Also keep in mind that under certain circumstances (in/out on the same interface), it might be necessary to disable Internet Control Message Protocol (ICMP) redirects (sysctl -w net.inet.ip.redirect=0); otherwise, it might interfere with what you want to accomplish.