Network Address Translation

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Network Address Translation
Design and Implementation

Abstract—This is the final report for a research project covering network address translation (NAT). Research topics include: the history and necessity for NAT, overall design, implementation, the different types, and examples of its use.
Keywords—NAT; networking; project; research
Necessity
IP addresses were originally designed to be globally unique. In an IP network, each computer is allocated a unique IP address. In the current version of IP protocol (IPv4) an IP address is 4 bytes, and because an address is 4 bytes, the total number of available addresses is 2 to the power of 32, which is 4,294,967,296. This represents the total theoretical number of computers that
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RFC 1287 also discussed possible ways to extend IP address space. The first suggested a direction similar to current NATs:
Replace the 32-bit field with a field of the same size but with a different meaning. Instead of being globally unique, it would be unique only within some smaller region. Gateways on the boundary would rewrite the address as the packet crossed the boundary.
Shortly after RFC 1287 was published, RFC 1335 introduced a clearer description of the use of internal IP addresses as a solution to IP address exhaustion. The NAT idea was first described in the article “Extending the IP Internet through Address Reuse” which appeared in the January 1993 issue of ACM Computer Communication Review and was later published as RFC 1631. The invention of the Web in the early 1990s underlined the urgency to take action toward solving both the routing scalability and the address shortage problems. Long-term solutions require a long lead time to develop; therefore efforts began to develop both a short-term and a long-term solution to those problems.
As a short term solution, Classless Inter-domain Routing (CIDR) was proposed, which removes the class boundaries embedded in the IP address structure. This enables more efficient address allocation, helping to extend the lifetime of IP address space. Address space was poorly utilized with the "Classful" addressing approach, CIDR helped in extending the lifetime of
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