Network Address Translation (NAT) allows you to connect a private network to the Internet without obtaining registered addresses for every host. Private addresses are translated to the public address of the NAT router. NAT can be used to provide a measure of security for your private network, or to provide Internet connectivity with a limited number of registered IP addresses.
As you work with NAT, it’s important to understand the following terminology.
When you configure NAT, you have the following options on a Cisco router.
Note: When you configure NAT, be sure to use an IP address in the private IP address ranges for the inside local IP addresses. Otherwise, hosts on your network might not be able to access outside hosts with the same IP address. A Cisco router can be configured to overcome this problem, but the configuration is difficult.
Private IP addresses do not need to be registered, and fall within the following ranges:
- 10.0.0.0 to 10.255.255.255
- 172.16.0.0 to 172.31.255.255
- 192.168.0.0 to 192.168.255.255