D-Link DSL-504 User Manual - page 23

DSL-504 ADSL Router User’s Guide 

Please note that in the above diagram, the Gateway IP address settings for the 

local PC’s needs to be set to 192.168.0.1, the LAN IP address of the router.  

NAT manipulates the IP addresses in packet headers on a one-to-one basis. An 

outgoing data packet (a packet originating from a computer on the local LAN and 

destined for a computer outside the private network) will have its IP address 

translated as shown below. 

In the Outgoing Data Packet above, the Source IP address is the IP address that 

is translated by NAT. The Destination IP Address is the IP address of a computer 

outside the private network, on the Internet for example. And the Data portion of 

the packet is the information payload carried by the packet, for instance a 

request to view a web page. 

The router logs the changes made to the IP header in its NAT table. The NAT 

table enables the router to send replies back to the local computer as shown 

below. 

In the Inbound Data Packet above, the Destination IP Address is the IP address 

that is translated by NAT. The Source IP Address is the IP address of a computer 

outside the private network. And the Data portion of the packet is the 

information payload carried by the packet, in this case, web page contents. 

Setting Local IP Addresses 

When implementing NAT and thus creating a private network that is isolated 

from the Internet, you can assign any IP addresses to host computers without 

problems. However, the Internet Assigned Numbers Authority (IANA) has 

reserved the following three blocks of IP Addresses specifically for private 

networks: 

Class 

Beginning Address  Ending Address

A 10.0.0.0 

10.255.255.255 

B 172.16.0.0 

172.31.255.255 

C 192.168.0.0 

192.168.255.255 

It is recommended that you choose local IP addresses for use with NAT from the 

private network IP addresses in the above list. For more information on address 

assignment, refer to RFC 1597, Address Allocation for Private Internets and RFC 

1466, Guidelines for Management of IP Address Space. 

Port Redirection 

17