I think a lot of other commenters complaining about the parent commenter missing the IPv4/6 header size are missing the forest for the trees here. The main prob

I think a lot of other commenters complaining about the parent commenter missing the IPv4/6 header size are missing the forest for the trees here. The main problems with IPv6 (that are why most customer-facing components are not switching to it anytime soon) are simple: 1. The address space is ludicrously unwieldy. Humans are good at remembering long numbers. We're quite bad at remembering random strings outside of pure muscle memory. For the cases where you're manually fiddling with IPv6 space in situations where a domain name isn't mapped to an IP (ie. home networks), the reality is that IPv6 is only a negative. Telling people to go to "192.168.2.1" to log in on their router is easy. Telling them to punch in a long IPv6 address that includes the A-F range isn't. (And that's without getting into colon collapsing 0000 ranges which just reeks of "did anyone run this past a human being", because this makes even less sense to people who barely get "I need to type the address on the ISP router sticker in my browser"). 2. The complete lack of even a one-way compatibility layer with IPv4 (so communicating from an IPv6 to an IPv4, which should be possible in a tech stack) means that even if you take the slow movement of hardware to IPv6 space into account, the offering simply isn't worth it until everyone switches over. Right now the standard offer for home ISPs is CGNAT + IPv6 if they offer the latter, is not solving anything - the reality is that if you give an IPv6-only offer, your customers just straight up can't access ~40% of the internet (and by law of institutions, that will include parts of the internet they really need because the people running it are restricted by yellow tape and budgets to also move to IPv6), so all we get is the worst of both worlds where IPv4 is still running out of space and IPv6 isn't ready to replace it. Would it really have been too much work to slightly compromise on address space for IPv6 to just allocate a region to old IPv4 addresses, where the relevant low-level bits of the stack just switches over to the IPv4 protocol if it detects that region? If that were the case, the transition process would go much smoother and we probably wouldn't be haranguing about getting public entities to sell off their address space, just to delay the inevitable. Those are the reasons why IPv6 isn't replacing anything beyond a slow crawl of "maybe I should set an AAAA record" (and considering like 80% of the DNS+VPS providers I've used in the past decade just dump the /16 when you pick a VPS from a dropdown in the address, which obviously fails to work, it's also clear that hosting companies don't consider it a real priority either). When it comes to core infrastructure like this, backwards compatibility isn't a "nice to have" or to be "thrown out because it was based on bad ideas". It's a requirement, no matter how insane the original product might have looked.