DI-206 ISDN Remote Router
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 borne 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 borne by the packet, for example, the contents of a web page.
The actual information in the NAT table depends whether the router is implementing NAT or NAPT.
NAT
This section discusses the NAT protocol as opposed to NAPT, which is discussed in the next section.
NAT is the initial protocol set forth by RFC 1631 and provides a means in which private networks can communicate with the Internet by using a small number of IP addresses. In our discussion, we will use the example IP addresses listed in the table below and the network diagram shown on page 51.
Global IP Addresses | Local IP Addresses |
(for use with NAT) | (assigned to computers |
| on the local network) |
200.100.50.1 | 192.168.100.2 |
200.100.50.2 | 192.168.100.3 |
200.100.50.3 | 192.168.100.4 |
200.100.50.4 | 192.168.100.5 |
200.100.50.5 | 192.168.100.6 |
| 192.168.100.7 |
| 192.168.100.8 |
| 192.168.100.9 |
| 192.168.100.10 |
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