I was at some of those IETF meetings in the mid-1990s and attended some early IPv6 working group sessions. We knew the conversion would take time, but I don’t think any of us thought it would be this slow. I was involved with multiple L3 switches and routers from 1997 through 2010. The issue was always that IPv6 basically required lots of boxes in the middle to understand it in order to roll it out, so when would it be commercially necessary? Yes, you can do tunneling and NAT at various points, but it always requires more than just the endpoints. It shows up in DNS and socket APIs. There’s no easy way to determine if a path supports it, and the path can change in an instant due to a route change. All that is very different than SSL or QUIC where only the endpoints have to be involved. That’s why QUIC uses UDP, for instance, so old intermediate devices just see it as a protocol they already know. SSL just assigned port 443 and the “https” protocol in the web URL. If a web client contacts a server on port 443 that doesn’t use SSL, it just fails. To put it another way, the level of the stack that you’re changing matters. SSL and QUIC are really L5+. IPv6 is squarely L3. There are no protocol negotiation mechanism available at L3. So, from a business standpoint, when do you take the hit and integrate it all into the processing pipeline? How do you do that in a way that doesn’t impact your IPv4 forwarding performance, because that’s what the near-term market will judge you on? How do you afford the development and test cost associated with a whole other development (almost double)? If you’re doing software forwarding, the answers are a lot easier. As soon as you’re designing silicon, it’s a lot harder. When you’re under a lot of commercial pressure, it’s difficult to be the one who goes first. And remember that this hardware evolves on roughly 10 year cycles (2 years for design, 3-5 year market sales, 3-5 year depreciation at the customer before they buy new ones). Oh, and customer rollout of IPv6 is a major project with lots of program management and testing, not just buying a box or two. So, yea hindsight is easy. Eventually you get there, but it’s a long road.