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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
Configuration and Management
DI-206 ISDN Remote Router
85
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