CertiGuide to A+ (A+ 4 Real)  9  Chapter 14: Networks       9  What is a Network?            9  Protocol Standards

Protocol Standards 1 Network Address Translation (NAT)

Internet Protocol (IP) is the routing and naming scheme that gives each device on a TCP/IP network a unique descriptor – an “IP address” – and manages the delivery of data to its destination. Think of IP as the postal service; you are responsible for writing the letter, putting it in the envelope and addressing it correctly, but the postal service will make sure the letter gets to it’s unique destination specified by the address on the envelope. Because unique identification is the only way to find a device on a network, such as a PC, there is a mathematical limit to the number of unique devices that can exist on the largest of all networks, the Internet.

When TCP/IP was developed, it was intended for military use, and the idea of dozens of devices that would need unique IP addresses in every home and business in the world (and beyond) was not a consideration. However with the explosion in popularity of the Internet the available IP addresses have been rapidly used up, and several workarounds have been developed to handle the limitation of the small amount of available public IP addresses..

One workaround was to take three number groupings (“blocks” of “address space”) and declare them private. That means you are free to use them on your network at home or work, without directly being part of the Internet. They will never conflict with the numbers assigned to anyone else’s computers on the Internet, because by definition, they are private to the individual’s or company’s own network, and cannot be shared with the Internet. These private address blocks are defined by RFC 1918²¹⁰, and consist of the following ranges:

• 10.0.0.0 to 10.255.255.255
  
  
• 172.16.0.0 to 172.31.255.255
  
  
• 192.168.0.0 to 192.168.255.255

This allows re-use of the same set of numbers without conflict. To allow each network that uses these same numbers privately to have Internet access, the network uses a single, unique public address as a doorway (correctly known as a “gateway”) to the Internet. Nevertheless, how can an organization use multiple private IP addresses internally, only one public IP address externally and still give all internal clients’ access to the Internet?

Protocol Standards 1 Network Address Translation (NAT)