ZyXEL Communications 128MH - Manual (Page 65)

Prestige 128MH PSTN Router/Hub
3-13 Chapter 3 Internet Access Application
The IP address for the SUA can be either fixed or dynamically assigned by the ISP (or other
remote node). In addition, you can also configure a server (for example, a Web server) on your
local network and make it accessible by outside users.
If you do not set a server IP address, SUA offers the additional benefit of firewall protection. With
SUA, even if no server is defined, all incoming inquiries will be filtered out by your Prestige even
if you do have a server on your network. This can prevent intruders from probing your system.
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:
l SUA is an ideal cost-effective solution for small offices with less than 20 hosts using a LAN
to concurrently access the Internet or other remote TCP/IP network.
l SUA can provide one server address to be accessed by Remote Dial-in Users, thus
controlling the incoming packets.
l SUA can provide firewall protection if you do not configure a server IP address. All
incoming inquiries will be filtered out by your Prestige protecting the servers on your
network.
l UDP and TCP datagrams can be routed. In addition, ICMP echo can also be routed.
Figure 3-4 shows an example of a small office connected to the Internet via a SUA using the
Prestige. Note that if you enable the SUA feature, your local IP address MUST be selected from
the list of IP addresses for private networks as defined by the IANA.