> Even in so far as the local bit being 1, there have been at least two attempts to create a "voluntary global registry" for your randomly generated prefix, mostly for the same "collision avoidance" stated above.
Like most things people don't like about IPv6, you don't like this because you misunderstand how it's supposed to work.
There is no need for a ULA registry because you're supposed to pick a random prefix within the ULA space. The ULA space has 7 bits already defined, so you're picking a random prefix from a space 57 bits big. The chance that you will pick the same prefix as some other specific person is effectively zero.
(the birthday paradox does not apply because we don't care if your prefix matches anyone else on earth, just the one specific person/organization that you want to merge networks with).
> In either case, somewhat unintuitively, those are still _global_ addresses, and don't have the same level of "non local routing" restrictions that the RFC1918 address space explicitly gained.
Err, what? ULAs are routable and "global" addresses in exactly the same way that RFC1918 addresses are routable and global. They are valid addresses within the address space and the only thing that makes them "not globally routable" is that all routers have certain prefixes baked into the firmware as non-routable. If you don't trust your router not to route them for IPv6, why do you trust it for IPv4?
> Like most things people don't like about IPv6, you don't like this because you misunderstand how it's supposed to work.
Thanks for explaining my own motivations to me, while at the same time denying that any discussed changes are relevant to anyone.
> There is no need for a ULA registry
I was merely summarizing what the public opinion on the matter happens to currently be. Which suggests that the current recommendation to pick a random address and be happy with it is inadequate. The original posts dissatisfaction with being able to deploy IPv6 _conveniently_ also hints that improvements would be welcome by most people.
> ULAs are routable and "global" addresses in exactly the same way that RFC1918 addresses are routable and global.
RFC1918 explicitly defines it's addresses as local and not globally unique. RFC4193 specifies that these addresses are meant to be globally unique. RFC1918 requires a more specific level of filtering than RFC4193, and the definition of "site local" has always had some ambiguity to it.
So, within the very specific and nuanced points I was trying to make, no, they're different.
Agree with the parent that there is no need for a ULA registry for locally assigned addresses under RFC 4193 (which is every one I've ever seen). But there is that option for globally assigning addresses that I'd be intrigued to see if anyone does anything with...
Also important to note that while RFC1918 is roughly equal to RFC4193/ULA, that "site local" is another beast entirely (FECO ) that was, as you noted, ambiguous and was deprecated in rfc3879
Well -that's not entirely true. RFC4193/ULA has a Local Bit that, in my experience, is almost set to 1, so the prefix is FDxx.... At a prior company we rolled out about 25 million nodes all in RFC4193 space (non-routability was a design objective) - and, just to be within spec, we did indeed grab a random /48 for each customer instance we rolled out (and made very good use of the 65K networks we had available within that /48).
But - what if that Local bit is set to 0 - then:
Set to 1 if the prefix is locally assigned.
Set to 0 may be defined in the future.
Presumably there was some thought that there might be a Global Registry that the OP was referring to?
Concur with the rest- and, honestly, RFC 4193 is one of the simply written RFCs out there - understandable within 30 minute read - I'd encourage everyone to dig into it.
Like most things people don't like about IPv6, you don't like this because you misunderstand how it's supposed to work.
There is no need for a ULA registry because you're supposed to pick a random prefix within the ULA space. The ULA space has 7 bits already defined, so you're picking a random prefix from a space 57 bits big. The chance that you will pick the same prefix as some other specific person is effectively zero.
(the birthday paradox does not apply because we don't care if your prefix matches anyone else on earth, just the one specific person/organization that you want to merge networks with).
> In either case, somewhat unintuitively, those are still _global_ addresses, and don't have the same level of "non local routing" restrictions that the RFC1918 address space explicitly gained.
Err, what? ULAs are routable and "global" addresses in exactly the same way that RFC1918 addresses are routable and global. They are valid addresses within the address space and the only thing that makes them "not globally routable" is that all routers have certain prefixes baked into the firmware as non-routable. If you don't trust your router not to route them for IPv6, why do you trust it for IPv4?