SMC Networks ADSL Barricade SMC7204BRA - Manual (Page 71)

Adding NAT Rules
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The following example illustrates using the RDR rule to provide
external access to your web server:
Your ADSL Barricade receives a packet containing a request
for access to your Web server. The packet header contains the
public address for your LAN as the destination IP address,
and a destination port number 80. Because you have set up
an RDR rule for incoming packets with destination port 80, the
device recognizes the data as a request for Web server access.
The device changes the packet's destination address to the
private IP address of your Web server and forwards the data
packet to it.
Your Web server sends data packets in response. Before the
ADSL Barricade forwards them on to the Internet, it changes
the source IP address in the data packets from the Web
server's private address to your LAN's public address.
To an external Internet user then, it appears as if your Web
server uses your public IP address.
Figure 23. NAT Rule - Add Page (RDR Flavor)