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
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 can be directly connected to the Internet. This property of the IP address is fundamental in supporting the end-to-end architecture of the Internet. Until recently, almost all of the Internet protocol designs were based on the original IP address model. However, the explosive growth of the Internet during the 1990s made clear the danger of IP address space exhaustion. This also created an instant demand on IP addresses. Connecting large numbers of user networks and home computers demanded IP addresses instantly and in large quantities. The regular IP address allocation process could not possibly meet such a demand. IP increasingly became the standard for networked digital communication; the wide-spread mobile phones have become viable internet hosts. The introduction of broadband Internet access increased IP penetration. These connections are always active and are rarely turned off compared to what was common in dial-up networks. Inefficiencies caused by subnetting made it difficult to use all addresses in a block. [RFC 3194] defines the host-density ratio; it is a metric for utilization of IP address blocks used in allocation policies. The advanced hardware infrastructure made it possible to host many instances of an operating system on a single unit; each of these may require a unique public IP address. Network address translation began to be developed to meet this instant high demand, and products featuring NAT were quickly developed to meet the market demand. NAT is a technology which is featured on devices like routers, servers, and firewalls. NAT makes it possible for LAN devices with private IP addresses to communicate with the devices on the public network. Devices which are configured with private IP addresses are not able to communicate with devices that have public IP addresses because private IP addresses are not routable on the internet. This implies that devices on the LAN will not be able to communicate with devices on the public network directly. Traffic that is initiated from a private network must go through the appropriate NAT devices to make them routable on the public network. With NAT it is possible to share a single address between multiple computers and connect them all at the same time to the Internet. Moreover, users who do not require external communication with the outside network (Internet) do not consume public IP addresses. NAT did not only offer a solution for the increased demand and cost of IPv4 addresses, but also improved the overall security of networks by forming a first line of defense against external attacks. The main idea was to set up individual private networks that are connected indirectly to the Internet. NAT routers will translate the addresses in the datagram from the private network to the public internet and vice versa. One of the main reasons NAT is so widely spread is because it provides the ability to manage and monitor the network on a large scale. Administrators can still enjoy the control benefits that come with a private network and still be able to connect to the Internet. It is easy to add clients and even change the main Internet service provider as the change will only happen on the public addresses. History
The first RFC...
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