This is an option, but ULAs are ranked _below_ IPv4 in address selection preferences. So your network will essentially operate in IPv4 mode: https://www.ietf.org/archive/id/draft-buraglio-6man-rfc6724-...
Moreover, some devices will refuse to connect to IPv6 GUA with ULA addresses altogether.
> Yes, your local devices will use the ULA to attempt to connect to Internet destinations if that’s the only v6 address they have. It works fine.
You're half right. The devices will work fine because they won't be using IPv6 at all.
As I said, IPv6 is a recursive WTF.
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 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.