The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  IP Network Address Translation (NAT) Protocol

IP Network Address Translation (NAT) Protocol 1 2 3 4 5 IP NAT Address Terminology

The decision to make IP addresses only 32 bits long as part of the original design of the Internet Protocol led to a serious problem when the Internet exploded in popularity beyond anyone's expectations: exhaustion of the address space. Classless addressing helped make better use of the address space, and IPv6 was created to ensure that we will never run out of addresses again. However, classless addressing has only slowed the consumption of the IPv4 address space, and IPv6 has taken years to develop and will require years more to deploy.

The shortage of IP addresses promised to grow critical by the end of the 1990s unless some sort of solution was implemented until the transition to IPv6 was completed. Creative engineers on the Internet Engineering Task Force (IETF) were up to the challenge. They created a technique that would not only forestall the depletion of the address space but could also be used to address two other growing issues in the mid-to-late 1990s:

• Increasing Cost of IP Addresses: As any resource grows scarce, it becomes more expensive. Even when IP addresses were available, it cost more to get a larger number from a service provider than a smaller number. It was desirable to conserve them not only for the sake of the Internet as a whole, but to save money.
  
  
• Growing Concerns Over Security: As Internet use increased in the 1990s, more “bad guys” started using the network also. The more machines a company had directly connected to the Internet, the greater their potential exposure to security risks.

IP Network Address Translation (NAT) Protocol 1 2 3 4 5 IP NAT Address Terminology