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

Advantages of NAT

NAT is one of those technologies that has a long list of both advantages and disadvantages. This means it can be extremely useful in a variety of scenarios, but also problematic in others. The main advantages are:

• Public IP Address Sharing: A large number of hosts can share a small number of public IP addresses. This saves money and also conserves IP address space.
  
  
• Easier Expansion: Since local network devices are privately addressed and a public IP address isn't needed for each one, it is easy to add new clients to the local network.
  
  
• Greater Local Control: Administrators get all the benefits of control that come with a private network, but can still connect to the Internet.
  
  
• Greater Flexibility In ISP Service: Changing the organization's Internet Service Provider (ISP) is easier because only the public addresses change. It isn't necessary to renumber all the client machines on the network.
  
  
• Increased Security: The NAT translation represents a level of indirection. Thus, it automatically creates a type of firewall between the organization's network and the public Internet. It is more difficult for any client devices to be accessed directly by someone malicious because the clients don't have publicly-known IP addresses.
  
  
• (Mostly) Transparent: NAT implementation is mostly transparent, because the changes take place in one or perhaps a few routers. The dozens or hundreds of hosts themselves don't need to be changed.

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