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Chapter 12. Scaling IP Addressing with Network Address Translation
This chapter covers the following topics:
One of the problems facing anyone connecting to the Internet today is the depletion of IP addresses. The IP version 4 address space was originally designed so that 4,294,967,296 (232) hosts could be assigned a unique address. Because addresses are reserved for multicasting, testing, and other purposes, and because the nonreserved address space is divided into classes, this range is actually somewhere between 3,200,000,000 and 3,300,000,000 addresses. With the exponential growth of companies doing business over the Internet, IP address assignments became a major concern across the networking world.
For your computer to effectively communicate on the Internet, it must have a unique 32-bit IP address. This IP address identifies the location of your computer on a network, much like your phone number distinguishes your phone from the millions of other phones out there.
With the unpredicted popularity of the Internet and the continuing increase in the number of home and business networks, the number of available IP addresses is simply not enough. IP version 6 is being developed to eliminate these issues, but it will take several years to implement, because it will require modifying the Internet's infrastructure. Because of this lag in deployment, Network Address Translation (NAT) was defined in RFC 1631, The IP Network Translator. In the simplest of terms, NAT allows a single device to act as an agent between the Internet (or "public network") and a local (or "private") network. This allows you to use a single unique IP address to represent your entire internal network to anything or anyone outside your network. Besides NAT's obvious benefits when it comes to addressing the shortage of IP addresses, you also gain security and administrative benefits from it.
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