If they don’t have an v4 address then they don’t have that problem.
NPT solves the issue of your devices losing global addresses.
Ideally you wouldn’t need NPT, and you should have an RA for the ULA and an RA for the GUA and then use the ULA locally... but then you end up with a different problem (and why I didn’t do it at home). Doing this means you have little control about which upstream ISP gets chosen. I have two ISPs at home, and router will failover between them; however, even though I have PI IP space, finding a residential ISP that will let me use it is nearly impossible (good luck finding someone there who even knows what BGP is).
So the tradeoff here for me is not letting my devices have a GUA so that my router can control outbound traffic policy completely (like it can with v4), and just NPT it to what I need it to be externally. Works great (but again, if you only have one global prefix you need to deal with, separate RAs for ULA/GUA do work better).
> You're half right. The devices will work fine because they won't be using IPv6 at all.
Not if they don’t have an IPv4 address to begin with!
You can also coax your local DNS resolver to... just not let A records through if the name also has an AAAA record.
Even better than that would be out of the box like magic 464XLAT in home routers / ISPs. As it is 464XLAT is not the nicest thing in the world to configure; however, it does work very well, and does allow for a network to be entirely v6 except at the very edge. Heck, I’d love it if enterprise gear had “like magic” 464XLAT too. Would make a lot of things easier.
> How do I know that? I made a personal goal to create a dualstack demo network that is fully standards compliant and supports the bare minimum functionality that I would expect from a SOHO network. So far, I keep finding new and exciting breakages on every level.
If you really want to accomplish that, completely forget about trying to make dual stack work throughout the network. It’s an exercise in frustration, mostly in needing to duplicate config in v4 and v6, and you will inevitably have them end up out of sync with each other.
464XLAT is good standard here, DNS64 with a NAT64 does also work... for things with names at least.
One of the other comments around here about not providing a “migration plan” does have a lot of truth to it. If, 30 years ago, they envisioned 464XLAT and made it part of the default features a v6 capable router should have, I bet v4 would be long dead (or nearly there) by now.
But anyway, ULA vs. GUA preference is mostly an academic question. In practice, you can just squat on an unused IPv6 range and avoid the precedence issue.
The deeper problem is that the solution to IPv6 problems appears to be NAT. And we're switching from IPv4 to avoid NAT. And you'll need a stateful firewall for IPv6 anyway (it's a recommendation for SOHO, there's an RFC for it, too lazy to dig it up now).
I'm stubborn, so my house now has its own ASN, a PI block, and a DIA connection to two ISPs. Which is the only NAT-less way to achieve my goal.
> One of the other comments around here about not providing a “migration plan” does have a lot of truth to it. If, 30 years ago, they envisioned 464XLAT and made it part of the default features a v6 capable router should have, I bet v4 would be long dead (or nearly there) by now.
464XLAT (and its evil twin IPv6 RD) were envisioned in the early 2000-s. Along with about 20 various "migration plans". They all missed the point, though. Some people are still missing it.
The key to migration has never been some form of tunneling. The key to migration is making IPv4 and IPv6 coexist side-by-side, in other words, the Happy Eyeballs algorithm. It should have been reified to the TCP level in the late 90-s. So that applications could just do: `connect("somehost.com", 80)` and transparently get either an IPv4 or IPv6 connection, depending on whichever one works better locally. Other operational headaches like the ULA priority would have surfaced much earlier then.