35 years ago, mainframes, single-protocol networks (be it SNA or DECnet), and centralized architectures that would make hard-core SDN evangelists gloat with unbridled pride were all the rage. If you’re old enough to remember IBM SNA, you know what I’m talking about.
Local area networks (starting with cheap ARCnet and then thin-coax Ethernet), personal computers, and a bit later x86-based servers totally changed the networking landscape. All of a sudden we had to deal with half a dozen protocols and tons of unpredictable peer-to-peer traffic.
Most networking engineers eventually adapted and got operational experience running multiprotocol networks, and started treating peer-to-peer traffic and end-to-end principle as business-as-usual.
The old-timers had a really hard time adapting to the new world (it took IBM years to retrofit peer-to-peer communication using LU6.2 into their SNA protocol stack), and some of them retired before ever having to touch an Ethernet cable.
More recently, we’ve experienced another shift, this time in a totally different direction. All network-layer protocols but IP died, application architectures became ever more centralized (cloud is nothing else but a mainframe with distributed internal architecture), and end-to-end principle slowly died by thousand cuts made by kludges ranging from NAT and ALG to DPI and WAN acceleration.
We got to a point where people entering networking in the last 10+ years have no operational experience running multiprotocol networks, might view end-to-end principle as a security hole instead of an architectural simplification, or use network designs that rely heavily on NAT to get the job done. We’ve lost approximately 20 years of progress (or whatever).
With this in mind, it’s no wonder we’re experiencing outright denials of the need for IPv6, and dismal IPv6 adoption in enterprise networks – a lot of people running them are in exactly the same position as the SNA networking engineers were when they faced the inevitable need to deploy IP or IPX in their enterprise network.