SMC Networks Barricade SMC7404BRA EU - Manual (Page 54)

NAT
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addresses. In other words, depending on the requested service (TCP/UDP
port number), the Barricade redirects the external service request to the
appropriate server (located at another internal IP address.)
For example, if you set Type/Public Port to TCP/80 (HTTP or Web) and
the Private IP/Port to 192.168.2.2/80, then all HTTP requests from
outside users will be transferred to 192.168.2.2 on port 80. Therefore, by
just entering the IP Address provided by the ISP, Internet users can access
the service they need at the local address to which you redirect them.
The more common TCP service ports include:
HTTP: 80, FTP: 21, Telnet: 23, and POP3: 110.
Note: The WAN interface should have a fixed IP address to best utilize
this function. If your ISP only provides dynamic IP addresses, a
search for “free dynamic IP” on any major search engine will turn
up tools that will allow you to use the same domain name even
though your IP address changes each time you log in to the ISP.