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Prestige 623ME-T User’s Guide
5-2 NAT
The IP address for the SUA can be either fixed or dynamically assigned when a call is connected. In addition,
you can designate servers, e.g., a web server and a telnet server, on your local network and make them
accessible to the outside world.
If you do not define any server, SUA offers the additional benefit of firewall protection. If no server is
defined, all incoming inquiries are filtered by your Prestige, thus preventing intruders from probing your
network.
Your Prestige accomplishes this address sharing by translating the internal LAN IP addresses to a single
address that is globally unique on the Internet. For more information on IP address translation, refer to RFC
1631, The IP Network Address Translator (NAT).
5.2.1 Advantages of SUA
In summary:
SUA is a cost-effective solution for small offices with less than 20 hosts to access the Internet or other
remote TCP/IP networks.
SUA supports servers to be accessible to the outside world.
SUA can provide firewall protection if you do not specify a server. All incoming inquiries will be
filtered out by your Prestige.
UDP and TCP packets can be routed. In addition, partial ICMP, including echo and trace route, is
supported.
5.2.2 Configuring Inside Servers
The Prestige enables you to make inside servers for different services, e.g., web or FTP, visible to the outside
users, even though SUA makes your whole inside network appear as a single machine to the outside world.
The port number identifies a service, e.g., web service is on port 80 and FTP on port 21.
Let's say you want to assign ports 22-25 to one server, port 80 to another and assign a default server IP
address of 192.168.1.35 as shown in the next figure.