User's Manual

System Configuration
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5
NAT Configuration
Network Address Translation (NAT) is a method of mapping between a single global
address on the WAN interface to multiple local addresses on the LAN interface. For
the Gateway, the internal (local) IP addresses are those assigned to PCs or other
network devices by the DHCP server, and the external IP address is the single
address assigned to the WAN port.
Virtual Server
If you configure the Gateway as a virtual server, remote users accessing services
such as web sites or FTP servers on your local network through public IP addresses
can be automatically redirected to local servers configured with private IP
addresses. In other words, depending on the requested service (designated by the
TCP/UDP port number), the Gateway redirects the external service request to the
appropriate server (located at an internal IP address). This secures your network
from direct attack by hackers, and provides more flexible management by allowing
you to change internal IP addresses without affecting outside access to local
network services.
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 port numbers include: HTTP: 80, FTP: 21,
Telnet: 23, and POP3: 110.