The enormous success of the Internet came as a surprise to most all of its early developers, and that certainly holds true for the developers of IPv4. No one expected that the 32-bit IPv4 address space would be insufficient to accommodate the future needs of what was then a small research network. But by the mid-1990s the steadily increasing demand for IP addresses threatened the remaining supply. Many predicted that the available IPv4 addresses would last for only a few years more.
The long-term solution to the IP address depletion problem was to create a new version of IP with an expanded address space. Originally called IPng for IP next generation, this proposed version eventually became IPv6. However, short-term workarounds were required to slow the rate of IPv4 address depletion until the work on IPv6 could be completed. One short-term solution was Network Address Translation (NAT). Also known as IP masquerading or Port Address Translation (PAT), NAT resides between the Internet and a group of hosts on a server, firewall, or router. Through a clever manipulation of port numbers, NAT allows a large number of hosts to share a single unique IPv4 address.
Fueled by the lack of public IP addresses, 70% of Fortune 1000 companies have been forced to deploy NATs (Source: Center for Next Generation Internet). NATs are also found in hundreds of thousands of small business and home networks where several hosts must share a single IP address. It has been so successful in slowing the depletion of IPv4 addresses that many have questioned the need for IPv6 in the near future. However, such conclusions ignore the fact that a strategy based on avoiding a crisis can never provide the long-term benefits that solving the underlying problems that precipitated the crisis offers.
However, NAT was never intended as a long-term solution, and it presents a number of problems in modern networks. Most significantly, NAT destroys a key benefit of the Internet as a network of 'always-on, equally-connected, easily-reachable' peers. Peer-to-peer capability provides a powerful tool, empowering users to become active contributors to the Internet, rather than just consumers. Peer-to-peer systems assume that a user can find and connect to another user, but if a user is hidden behind a NAT device this assumption is not valid. As a result, present peer-to-peer systems utilize an extra level of complexity made necessary only to circumvent NAT obstacles.
NAT also presents challenges for many applications that incorporate the host's IP address in the application-layer data. This issue is particularly problematic for security protocols such as IPSec. If the Internet is to become a community of peers, strong security is essential. Additionally, NAT is a roadblock for applications requiring Quality of Service (QoS) such as Voice over IP (VoIP) and real-time video. NAT is recognized as one of the single largest roadblocks to the widescale adoption of VoIP with its promised cost savings and enhanced communication services. However, NAT was helpful in delaying a global IP address crisis, but in return has extracted a proportional 'pound of flesh' by delaying uncounted peer-to-peer network innovations and their associated cost savings.
The adoption of IPv6, with its abundance of addresses, eliminates any need for NAT and, by extension, eliminates the roadblocks to Internet progress that NAT represents.
By IPv6 Forum
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