aside from the difficulties pointed out during this thread regarding enforcement of ULA terms vs. PI terms, there are two other things that prevent me from thinking well of ULA. first, ARIN does not currently consider routability when allocating address space. non-routable space comes from ietf/iana, not the RIRs. so, for ARIN to start allocating nonroutable space is a big change. we would have to define "routable", we could face implied liability for routability on "normal address space" (even if we continue to disclaim it in the NRPM as we do now), and we would then walk the slippery slope of the changing definition "largest" with respect to breidbart's maxim: >> But what *IS* the internet? > It's the largest equivalence class in the reflexive transitive > symmetric closure of the relationship "can be reached by an IP > packet from". --Seth Breidbart second, even with the rampant EUI64 wastage of the bottom 64 bits of the IPv6 address space, there's still a lot of space, and it's not hard to get. it's perfectly reasonable for all addresses to be unique even if some are never expected to be "routed" or are only "privately routed" or whatever. so while i think that ietf/iana ought to allocate a "private" block of space for IPv6 since a lot of the world loves their IPv4 NAT and wants to be able to do the same thing with IPv6, one block ought to be enough. (heck, maybe the old site-local prefix is still available.)