DI-1162 Remote Access Router
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 at the beginning of this section.
Global IP Addresses | Local IP Addresses |
(for use with NAT) | (assigned to computers |
| on the local network) |
|
|
200.100.50.1 | 192.168.100.1 |
200.100.50.2 | 192.168.100.2 |
200.100.50.3 | 192.168.100.3 |
200.100.50.4 | 192.168.100.4 |
200.100.50.5 | 192.168.100.5 |
| 192.168.100.6 |
| 192.168.100.7 |
| 192.168.100.8 |
| 192.168.100.9 |
| 192.168.100.10 |
Please note that in the above table there are 9 users on the local network using 5 global IP addresses to access the Internet.
When a packet on the local network arrives at the router and needs to be sent to the Internet, NAT will change the source IP address (for example 192.169.100.2) to a global address (200.100.50.1, for example). If this packet generates a reply (as for example, a request to view a web page will), NAT will change the destination IP address on the reply packet back to the local IP address for delivery to the machine on the local (stub) network.
The difference between static and dynamic NAT is that once the five global addresses are assigned when using static NAT, they will never change. The only way to change them is by using the console program to manually reassign them. When using dynamic NAT, the router will map a local IP address to a global IP address whenever a request is
Configuration and Management | 79 |
