With IPv4 addresses all used up now, NATing has become a standard practice for my businesses and ISP's in order to spread their remaining addresses as thin as possible. Although IPv6 is becoming a more popular and available alternative, it will still be awhile before it starts to become commonplace. This is becuase it can require a complex network configuration, as well as possible new hardware, making it an expensive and time consuming approach. Most people have decided to use NATing in the mean time.
NAT stands for network address translation and, in the most basic description, is typically used to translate public, or internet routable IP addresses to private, or non internet routable IP addresses, and vice versa. A lot of people tend to confuse this technique with PAT, or port address translation. You can find a more detailed description of NATing and PATing, as well as their differences here. Basically, PATing translates multiple private IPs to a single public IP and uses ports to track the different connections from the different inside IP addresses. This technique is typically used by ISPs for residential internet service. A lot of people will use port forwarding on their home router, in order to access their PCs or other devices at home from the internet.
In the next section I will describe a technique known as policy NATing that will allow you to have a really granular way to configure your NATing and can even integrate PATing into the mix!
