Re: [v6ops] I-D Action: draft-ietf-v6ops-ula-usage-recommendations-02.txt

[Owen DeLong <[e-mail]>]

On Feb 19, 2014, at 6:35 PM, Mark Andrews <[e-mail]> wrote:

> 
> In message <[e-mail]>, Lorenzo Colitti writes:
>> On Thu, Feb 20, 2014 at 10:52 AM, Brian E Carpenter <
>> [e-mail]> wrote:
>> 
>>>> 2. A piece of remarkably bad luck, rather less likely than
>>>>> winning any lottery I'm aware of.
>>> 
>> 
>> Can you elaborate on exactly how bad this luck is as a function of how many
>> ULA prefixes you use your organization?
> 
>> From RFC4193 (1 in x added by myself).
> 
>      Connections      Probability of Collision
> 
>          2                1.81*10^-12 (1 in 552486187845)
>         10                4.54*10^-11 (1 in 22026431718)
>        100                4.54*10^-09 (1 in 220264317)
>       1000                4.54*10^-07 (1 in 2202643)
>      10000                4.54*10^-05 (1 in 22026)
> 
>> For example - if two large organizations that each use 200 ULA /48s (one
>> per site) merge, what is the chance that one of them will collide?
>> 
>> I don't feel it's satisfactory to say "the probability of a collision is
>> low" without saying how low it actually is. In fact, I think the draft
>> should not be published without giving a few examples of these numbers. If
>> *nobody* among the authors or on this list knows what the numbers actually
>> are, then we should not advocate using ULAs. It is not good engineering
>> practice to recommend something that you do not understand.
>> 
>>> You assume that people will actually follow the rules instead of saying
>>>> "let's just do this like IPv4, and use NAT at the border".
>>> 
>>> If CERs do the right thing the ULA prefix will be generated
>>> correctly. But you're right, there will be a generation of
>>> old-time IPv4 operators who will do exactly that whatever we
>>> put in RFCs.
>> 
>> I'm not talking about home networks here, I'm talking about corporate IT
>> environments.
> 
> Which should have trained staff who should know better.

In an ideal world, sure… In the real world where some of us have to live…

I think Lorenzo’s use of the term hopelessly optimistic is kind. I would go so far as to say somewhat detached from reality.

Owen