Bob left a lengthy comment arguing with the (somewhat black-and-white) claims I made in the Rise of NAT podcast. Let’s start with the any-to-any connectivity:

From my young millennial point of view, the logic is reversed: it is because of NATs and firewalls that the internet became so asymmetrical (client/server) just like the Minitel was designed (yes, I am French), whereas the Internet (and later the web, although a client/server protocol, was meant for everyone to be a client and a server) was designed to be more balanced.

Let’s start with the early Internet. It had no peer-to-peer applications. It connected a few large computers (mainframes) that could act as servers but also allowed terminal-based user access and thus ran per-user clients.

The client/server dichotomy became more evident as we started connecting low-end machines (IBM PCs and the like) to IP networks. The low-end machines did not have enough resources to be (reasonably good) servers¹, and once you could run Internet applications on your personal computer and drag an email into a trash bin, terminal access quickly seemed bizarrely outmoded. Even though every device was an IP host, the split into primarily clients and mostly servers IP hosts happened without any pressure from the network side.

Of course, we always had people running web- and SMTP servers² in their basements, but they were always a tiny (but very vocal) minority.

It’s also worth mentioning that all networking technologies³ (apart from IBM SNA) available in the early 1990s used a single address space and provided any-to-any end-to-end connectivity. IP wasn’t either unique or better than the others; it just happened to have a big enough address space and a global address allocation mechanism. The sacred cow of any-to-any connectivity was created primarily as an argument for the almost infinite advantage of IPv6⁴ after we had no other option but to start using NAT.

It’s also worth noting that most residential customers didn’t care at all about those technical details (as long as they could read emails and browse the web), and large organizations viewed NAT as a welcome demarcation point between internal and public networks. The only people preaching the benefits of unlimited, any-to-any connectivity were the IPv6 True Believers.

The rise of NAT was thus not an evil conspiracy by Big Tech or the cause for the client-server asymmetry. It was a pragmatic consequence of the fact that most paying customers accessed Internet services from clients that were not also servers while IETF was dragging its feet⁵, suffering from the not invented here syndrome, and throwing all sorts of crazy ideas into the kitchen sink called IPv6 instead of reusing an already-deployed protocol as the basis for the next-generation Internet.