On 2012-01-26, Owen DeLong wrote:
If you can't point to some specific advantage of ULA over secondary non-routed GUA prefixes, then, ULA doesn't have a reason to live.
My biggest concern with secondary non-routed GUA would be source address selection. If you're trying to talk to something in 2000::/3, it's obvious to the OS that it should be using its address in 2000::/3 rather than the one in fc00::/7. When both the "external" and "internal" addresses live in 2000::/3, more care has to be taken to ensure the system DTRT.
I'm not sure where DNS64/NAT64 comes into play here for v6 to v6 communication. For IPv4, I don't see any advantage in ULA+NAT64 vs. the more reliable and easier RFC-1918 with NAT44 possibilities, even if you have to run multiple RFC-1918 domains to get enough addresses, that will generally be less complicated and break fewer things than a NAT64 implementation.
My best guess there is the ability to a) only manage a single-stack network (I really wish more software supported IPv6 so this could be a more feasible reality), and b) use the same NAT64 prefix across various NAT64 instances (64:ff9b::/96 is a blocker if you actually want to allow NAT64 to RFC1918 space). While I can see the potential appeal of the second point, I'm not sure I'd agree with it myself. Jima