Hi
In NAT you got to have 2 terminologies namely inside,outside.
Inside actually represents your local trusted network which is ur LAN.
Outside represents te public untrusted network which is internet.
While configuring NAT you need to mention which interface is going to face or get connected with public untrusted network and which interface is will be interfaced with your local LAN.
Configuring ip nat outside under an interface indicates that its getting connected to the outside network.
Also its a part of the outside network which can be reached from anywhere in the internetworld.
You need to have atleast a single public ip / interface (associated with the outside world)which is reachable from outside so that the same can be used by local lan to go out and access the otherside..
regds
