I keep hearing this and it never makes sense to me.
If your provider will assign you a static /48, then, you have stable addresses when your provider link is down in GUA. Who needs ULA?
You used the word "if". Reverse the sense of the "if" and see if it still doesn't makes sense to use ULA addresses. I get a mostly stable IPv4 address from my cable provider (DHCP). That address changes without notice about once a year. I can configure a 6to4 prefix based on that address (effectively a PA prefix). I use ULA addresses internally and 6to4 (PA) externally. Same for 6rd. Same for PD.
I use the dynamic address from my cable provider to terminate a set of GRE tunnels to my colo routers. I use the static address from my DSL provider to terminate other GRE tunnels to my colo routers. The DSL tunnels are all carrying both IPv4 and IPv6. When the cable address changes, the BGP sessions over those GRE tunnels drop and my network connection slows down. When I repair the tunnels with the new end-point address, everything goes back to fast.
DHCP derived 6to4, DHCP derived 6rd, DHCP derived Terado and PD all give you leased prefixes. They are not guarenteed to be STABLE. For internal communication you really do want stable prefixes. ULA gives you those stable prefixes.
Yep... Makes much more sense to have at least one provider with static and do native IPv6 than to use 6to4, 6rd, Teredo, or PD.
You talk to the world using PA addresses, directly for IPv6 and indirectly via PNAT for IPv4. These can change over time. =20 Or, if you don't want your IPv6 addresses to change over time, you can get a prefix from your friendly RIR.
You really think I'm going to go to my RIR and get a addresses block for my home network then my cable provider will route it for me?
No... I think you might go to your RIR and get an address block for your home network then find a way to use your cable provider for L2 transport and route it. That solution works quite well for me.
Similarly, ULA + 6to4 works well provided the 6to4 works when you are connected. When your IPv4 connection is renumbered you have a new external addresses but the internal addresses stay the same. =20 That's a big "provided that"...
Not really. It works for lots of people.
Then how come I hear a lot more 6to4 horror stories than 6to4 success stories? It's not like I don't talk to lots of people using these protocols on a daily basis.
And you expect the routing system to cope when 2 billion homes do the same thing?
As a matter of fact, I think the routing system damn well better start planning to cope with just that scenario. I think it is inevitable in one form or another. Owen