NAT is a very versatile feature that can be used for the following purposes:

• You use private or unregistered IP addresses on your internal network, but you want to connect to the Internet. NAT provides the necessary translations of your internal local addresses to globally unique IP addresses before sending packets to the outside network.

• You must change your internal addresses, but you don't want to. NAT can be used in this case to translate these addresses.

• You want to do basic load sharing of TCP traffic. With NAT, you can map a single global IP address to many local IP addresses by using the TCP load distribution feature.

• NAT can be used as a practical solution to a connectivity problem only when relatively few hosts in a stub domain communicate outside the domain at the same time. When this is the case, only a small subset of the IP addresses in the domain must be translated into globally unique IP addresses when outside communication is necessary. These addresses can be reused when they are no longer in use.