No Stupid Questions

Inertia. IPv4 still works, every service on the internet still available over it. You can just be lazy and things will be ok.

Complexity. IPv6 is complex in the areas where v4 sucks. Ran out of address space? Here's a lot more address space. Multiple routers offering multiple routes? Just grab them all, have as many addresses as you want. No method to find peers on the same subnet? Here's like three methods to find peers on the subnet. All this is stuff you gotta learn!

Workarounds. Initially, ISPs thought that people turned their PC off at night and they'd get the IP address back. Then, they were leaving multiple devices on all day! So they came up with a hack that pretends everyone is behind one IP address, now all your devices are just one IP. But that IP still stays up and occupied all the time, they're not getting it back, so they put all their customers under another (CG)NAT. It's just NAT all the way down whenever they run out, and this way they never run out.

Because people are slow to fix something unless it is an impending problem.

Take the Y2K bug. Did you know the original person who made the bug was telling people in the 70s that is needs fixing? And it wasn't actually fixed till the second half of the 90s.

2038 is going to be a fun year with all the 32bit clocks overflowing to 1970

we did a few tricks to get more use out of ipv4 address. take 192.168.100.1 that is a private ipv4 address it can not connect directly to the internet. Most home routers will have a single public ipv4 address and assign some private address to each device connected to it. So now each home can have 1 device with 192.168.100.1. This means we kept using ipv4 for a long time after ipv6 came out.

Second updating all the old routers and switches. At this point in time it is unlikely you will find a router in the wild that can't use ipv6. Someone let me know the last time you found a device on some job site. But it took a while to get there because its expensive to replace them and no one was going to cough the massive amount of money to get it done in just a year or two.

Here is a full ipv6 address 2001:0db8:85a3:0000:0000:8a2e:0370:7334, yes it can be shortened to 2001:db8:85a3::8a2e:370:7334. That's still a pain to type out and yes it did make a mistake just typing that one address. It is just more error prone to write and type out ipv6 addresses.

Why is this?

Most corporations have the inertia of a rock when it comes to changes. There is no real reason behind it. Implementing IPv6 is a no-brainer. Same with NATing legacy systems so they can continue using IPv4.

Instead of manually juggling IP addresses, properly set up environments use hostnames and handle DNS automatically.

It’s basically “we/I don’t see any short-term benefit from it, it causes some setup work, and it is not important because everything still works”.

The first and biggest reason is network effects. If nobody else is using IPv6, then there's little benefit to switching. Corporations and governments are always resource constrained and there's not really a business case for switching just because it might be necessary someday. Being that corporations and governments are the ones providing the vast majority of services on the internet, that means there's not as much reason for switching for end users as well.

Part of the reason that switching didn't end up being necessary was that NAT did a really good job of solving the address problem. NAT let you have an internal network behind a single IP address which vastly reduced the amount of public IPs necessary. Even most people in tech probably wouldn't realize that the concept of public vs internal network didn't exist back in the day. Everything connected to the Internet had a publically reachable IP. When even that wasn't enough, they just did it again and had CGNAT, carrier grade NAT. Now you could have multiple households and businesses behind a single IP.

The final reason is that IPv6 is just different from IPv4. Things like router advertisements and SLAAC require you to learn new things and rethink how you do things. What doesn't help matters is that until you get everyone switched over to IPv6, you still have to support IPv4 in some way. Dual stack, where you run both IPv4 and IPv6 in parallel, is the most compatible way, but it's also the most complicated to administrate. There are ways for an IPv6-only network to communicate with IPv4 clients, such as NAT64, but they each have their own caveats. These differences can result in small annoyances to administrators that add up, such as like you mentioned that IPv6 addresses are just not as memorable as IPv4. The natural fix for this is DNS. But like I said, that requires you to rethink your network. DNS goes from being a nice to have to being essential even for small networks.

Despite all these issues, IPv6 adoption is still marching along. France, India, and Germany have some of the highest rates of IPv6 capable devices, at 83.97%, 78.81%, and 74.30%. (IPv6 Adoption) Globally, we're sitting around just under 50%. (Google IPv6 Tracker) Some sectors also have higher adoption rates. Mobile carriers are mostly IPv6-only these days. A lot of residential routers also ship with IPv6 enabled.

In a nutshell: https://github.com/becarpenter/misc/blob/main/why6why.md

surely that has to be a bigger problem in the modern day?

The problem already exists. We have run out of IPv4 addresses for years now and e. g. cloud computing/VPS providers have started charging additional fees for IPv4 addresses.

Maybe because a 128-bit hexadecimal address is impossible to memorise. I know all (6) my IPV4 addresses.

I think people are missing a main point here. There is nothing wrong with IPv4, it works. It just can't scale globally anymore, it doesn't have enough space.

If you are running a worldwide network with millions of nodes, IPv6 is essential. But for things that are smaller than that, it becomes less essential. But what's the best metric for adoption, how many small offices or home labs adopt it? Or how many large, worldwide networks?

V4 is easier to work with (not using long hex addresses and it's concepts are more familiar) and works fine for most everyone's use cases. So if it ain't broke don't fix it and low return on investment for most businesses. If you switch you have you do some awkward stuff where you maintain both.

What are these many advantages you speak of, other than global address space? If I'm an average business and may need one to three external ipv4 addresses, which are around $30/yr each, how much labor is it going to cost to migrate and when will I break even? Surely my sysadmin's time is better spent on things like security hardening?

The main reason is money.

Some companies don't want to do additional work and IPv4 is "good enough" (although it isn't) so they do nothing and we are stuck with it.

I think you might be underestimating uptake. Google suggests upwards of 50% usage. Also I'm fairly certain that a lot of residential infrastructure has been slowly moving to IPv6 in Australia at least. Not an overnight process, but it's happening. Over here we have a lot of newer mobile plans offering IPv6 as well.

I think a big holdback is that a lot of larger corporations will still use IPv4/NAT setups at the top level, even if all of the hardware in the network supports it. "If it's not broke don't fix it." The result is huge amounts of daily traffic coming from these institutions being IPv4 by default, with all devices in WiFi, etc, being lumped into the same group.

Lots of servers these days run only on IPv6

For me personally it's unfamiliarity. Technically all my devices and networks use IPv6. But I just enabled it in my router and used my hosting company's configuration.

But one of my servers at home should be reachable from the internet but that is only through IPv4. Configuring port forwarding through my router was intuitive and straight forward. But for IPv6 I have to allow the port to be open, but I don't want it to be the standard port so I have to configure the corresponding service on the machine itself to listen with a specific port on a specific address. But I have no idea what each of the addresses it has mean.

I think some of them are purely internal, some temporary, some less so. And if I ever found out what to use I would then have to configure my DynDNS, which is currently just pointing to the public IPv6 address of my router but not to the server I would want to reach.

I could learn all these things. But I just can't be bothered because the IPv4 stuff still works.

There are a number of points:

If you build a networking devices, you have to have IPV4. You may or better should have IPV6, too, but without IPV4, you'll have a bad start.

If you build an embedded system, like an "internet of things" sensor or actor, memory is at premium, so having to take care of a small and a large IP stack might be challenging.

Some systems are old that their software libraries don't even offer an IPV6 option.

My current project uses IPV4 only, because I don't need anything fancy. I just span a 10/8 network with 10.0.0.1 being the server. No routing, not even DNS. Using IPV6 for that application would be wasted.