My frustration is because using a private CA is more difficult than it should be.

You can't just add the CA to system trust stores on each device, because some applications, notably browsers and java, use their own trust stores, you have to add it to.

You also can't scope the CA to just .internal, which means in a BYOD environment, you have to require your employees to trust you not to sign certs for other domains.

And then there is running the CA itself. Which is more difficult than using let's encrypt.

The Name Constraints extension can limit the applicability of a CA cert to certain subdomains or IP addresses.

How well supported is that?

It's hard to say, but I'm super interested if anyone has statistics. Netflix built https://bettertls.com/ to answer these sorts of questions, but somehow forgot to validate constraints set at the root: https://github.com/Netflix/bettertls/issues/19

Anecdotally, I've seen name constraints kick in for both Firefox and Chrome on a Linux distro, but I can't comment more broadly.

It's required by RFC 5280 (and predecessor), so it’s fairly well supported.

Do you have any references for that? There are lots of RFCs that are weakly adopted or even ignored. When I tested Chrome they didn't support name constraints, but have since added support. I suspect other software is still lagging.

From the issue for support on chrome, it sounds like RFC 5280 requires it for intermediate CAs, but is ambiguous on whether it is required for root CAs (which in this case, is where you want it). So chrome didn't support it on root CAs until recently, at least on Linux.

Although, ideally, it would be possible to limit the scope of a CA when adding it to the trust store, and not have to rely on the creator of the CA setting the right parameters.

the frustration comes when non-corporate-provisoned clients get on the .internal network and have trouble using the services because of TLS errors (or the problem is lack of TLS)

and the recommendation is to simply do "*.internal.example.com" with LetsEncrypt (using DNS-01 validation), so every client gets the correct CA cert "for free"

...

obviously if you want mTLS, then this doesn't help much. (but still, it's true that using a public domain has many advantages, as having an airgapped network too)

I'll add that anyone using VMs or containers will also run into trust issues too without extra configuration. I've seen lots of contractors resort to just ignoring certificate warnings instead of installing the corporate certs for each client they work with.

You’re basically saying that .internal can cause frustration when it is used without good reason. Fair enough, but also not surprising. When it is used for the intended reasons though, then there’s just no other solution. It’s a trade-off between conflicting goals. “Simply do X instead” doesn’t remove the trade-off.

What do you see as the intended reasons with no other solutions?

The biggest benefit of .internal IMO is that it is free to use. Free domains used to be a thing, but after the fall of Freenom you're stuck with free subdomains.

If `.internal` is for private-use only, they must be resolved by some sort of private or internal DNS. In that case, all domains are free for private-use anyway.

Unfortunately, that's not true in general. Google proved this with their handling of the .dev TLD. Security settings like the HSTS preload list can impact your internal network if you "squat" on a domain you don't own. Google added all of .dev to the HSTS preload list and now, if you use any domain under that, you browser will force you to use HTTPS.

The reasons are explained in https://itp.cdn.icann.org/en/files/security-and-stability-ad....

As a side point, there _needs_ to be something equivalent. People were doing all sorts of bad ideas before, and they had all the problems of .internal as well as the additional problems the hacks were causing -- like using .dev and then dealing with the fallout when the TLD was registered.