Much of the reason for this apparent contradiction between the addressed device population of the IPv4 Internet and the actual count of connected devices, which is of course many times larger, is that through the 1990's the Internet rapidly changed from a peer-to-peer architecture to a client/server framework. Clients can initiate network transactions with servers but are incapable of initiating transactions with other clients. Servers are capable of completing connection requests from clients, but cannot initiate such connections with clients. Network Address Translators (NATs) are a natural fit to this client/server model, where pools of clients share a smaller pool of public addresses, and only require the use of an address once they have initiated an active session with a remote server. NATs are the reason why a pool of excess of 30 billion connected devices can be squeezed into a far smaller pool of some 3 billion advertised IPv4 addresses. Services and Applications that cannot work behind NATs are no longer useful in the context of the public Internet and no longer used as a result. In essence, what we did was to drop the notion that an IP address is uniquely associated with a device's identity, and the resultant ability to share addresses across clients largely alleviated the immediacy of the IPv4 addressing problem for the Internet.

However, the pressures of this inexorable growth in the number of deployed devices connected to the Internet implies that the even NATs cannot absorb these growth pressures forever. //

There is a larger question about the underlying networking paradigm in today’s public network. IPv6 attempts to restore the 1980’s networking paradigm of a true peer-to-peer network where every connected device is capable of sending packets to any other connected device. However, today’s networked environment regards such unconstrained connectivity as a liability. Exposing an end client device to unconstrained reachability is regarded as being unnecessarily foolhardy, and today’s network paradigm relies on client-initiated transactions. This is well-suited to NAT-based IPv4 connectivity, and the question regarding the long-term future of an IPv6 Internet is whether we want to bear the costs of maintaining end-client unique addressing plans, or whether NATs in IPv6 might prove to be a most cost-effective service platform for the client side of client/server networks. //