Re: [v6ops] Scope of Unique Local IPv6 Unicast Addresses (Fwd: New Version Notification for draft-gont-6man-ipv6-ula-scope-00.txt)

[Brian E Carpenter <[e-mail]>]

On 15-Feb-21 10:54, Fernando Gont wrote:
> On 14/2/21 18:34, Ted Lemon wrote:
>> On Feb 14, 2021, at 4:14 PM, Fernando Gont <[e-mail] 
>> <mailto:[e-mail]>> wrote:
>>> That's not a legitimate use for GUAs.  Whereas in the case of ULAs, 
>>> that the *intended* usage.
>>
>> Untrue. ULAs are intended to be globally unique. 
> 
> Could you compute the birthday paradox for *all ULAs* on the internet, 
> and share the math/results?

I'm not Ted, and my preferred formulation is:

   ULAs are intended to be globally unique for all practical purposes.

Although there is a high probability of some ULA prefixes somewhere
being equal, the probability of your ULA prefix being equal to your
next-door neighbour's is extremely small.

There's no equivalent statement that can be made for RFC 1918 addresses,
nor for the deprecated IPv6 Site Local addresses.

BTW, RFC 4193 seems very clear on this to me:

>>       - Globally unique prefix (with high probability of uniqueness).
...
>>       - In practice, applications may treat these addresses like global
>>         scoped addresses.

    Brian