3Com OfficeConnect 3C16771 User Manual page 52

52 C 4: C
HAPTER
For the other settings, specify the DNS Servers. Up to three
DNS servers can be specified, although not all have to be
used. The Internet Firewall uses these servers to look up the
addresses of machines used to download the Web Site
Filter and for the built-in DNS Lookup tool.
Type the required values and click Update to send the
configuration data to the Internet Firewall. It is necessary to
restart the Internet Firewall for these changes to take
effect.
NAT Enabled
Network Address Translation (NAT) provides anonymity to
machines on the LAN by connecting the entire network to
the Internet using a single IP address. This is useful for two
purposes:
Additional security is provided because all the addresses
I
on the LAN are invisible to the outside world.
In cases where a network uses invalid IP addresses or if
I
addresses are in short supply, NAT can be used to
connect the LAN to the Internet without changing the
IP addresses of computers and other devices on the
LAN.
Remote authenticated access is not possible with NAT
enabled.
When using IP addresses on a LAN which have not been
assigned by an Internet Service Provider, it is a good idea to
use addresses from a special address range allocated for
this purpose. The following IP address ranges can be used
for private IP networks and do not get routed on the
Internet:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
Select NAT Enabled from the Network Addressing Mode
drop-down list if the network uses private IP addresses or if
addresses are in short supply. A window similar to that in
Figure 17
R
OMMAND EFERENCE
is displayed.