3Com 3036, Configuration Manual

Page: 353 / 762

Configure Network Address Translation (NAT) 349
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Check whether the transparent transmission router itself is configured with
services of the protocol transmitted transparently.
Configure Network
Address Translation
(NAT)
Network Address Translation (NAT), also known as address proxy, implements the
function for the private network to visit the external network.
Private Network Address and Public Network Address
Private address refers to the address of the internal network or the host computer.
Public address refers to the sole IP address worldwide on the Internet. The Internet
Address Allocation Organization prescribes that the following IP addresses be
retained as private addresses:
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10.0.0.0 --- 10.255.255.255
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172.16.0.0 --- 172.31.255.255
■
192.168.0.0 --- 192.168.255.255
That is to say, the addresses within the three ranges will not be allocated on the
Internet. They can be used internally in a unit or a company. The enterprises can
select appropriate internal network addresses according to their forecast of the
number of internal host computers and networks in future. The internal network
addresses of different enterprises can be the same. Disorders are most likely to
occur, if a company select the network segments outside the three ranges above
as the internal network address.
Under which condition should the address be translated
As shown in the diagram above: The address needs to be translated when the host
computer of the internal network visits the Internet or communicates with the
host computers of the external networks.
Figure 130 Schematic diagram of Network Address Translation (NAT)
The address of the internal network is 10.0.0.0 network segment, while the
formal external IP address is 203.196.3.23. The internal host computer 10.1.1.48
visits the server 202.18.245.251 outside the network by means of WWW The host
computer 10.1.1.48 sends one data message with the source port selected as
6048 and the destination port as 80. After it passes by the proxy server, the source
address and port of the data message will probably be changed to
10.1.1.48
202.18.245.251
10.1.1.10
203.196.3.23
......
Internet
www
client
www
server