ZyXEL Communications P-128IMH, User Manual, Page: 68 / 191

Prestige 128IMH ISDN Modem/ Router/Hub
3-12 Internet Access
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 will be filtered out by your Prestige and 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) .
3.5.1 Advantages of SUA
In summary:
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SUA is a cost-effective solution for small offices with less than 20 hosts to access the
Internet or other remote TCP/IP networks.
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SUA supports servers to be accessible to the outside world.
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SUA can provide firewall protection if you do not specify a server. All incoming inquiries
will be filtered out by your Prestige.
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UDP and TCP packets can be routed. In addition, partial ICMP, including echo and trace
route, is supported.