Re: Status of Privacy Extensions for Stateless Address Autoconfiguration in IPv6

[Fernando Gont <[e-mail]>]

On 2/4/20 10:32, Alexandre Petrescu wrote:
> 
> Le 02/04/2020 à 15:16, Fernando Gont a écrit :
>> Alexandre,
>>
>> On 2/4/20 09:54, Alexandre Petrescu wrote:
>>> Le 02/04/2020 à 14:39, Fernando Gont a écrit :
>>>> On 2/4/20 09:25, Alexandre Petrescu wrote:
>>>>> would it it be possible to specify this:
>>>>>> However, the method discussed in
>>>>>>           this document could be employed for generating Interface 
>>>>>> IDs
>>>>>>           of any arbitrary length, albeit at the expense of reduced
>>>>>>           entropy (when employing Interface IDs smaller than 64 
>>>>>> bits) or enhanced entropy (when IID len longer than 64)
>>>>>
>>>>> (note 'IID longer than 64')
>>>>
>>>> Not sure what you mean.
>>>> 1) That's of course implied
>>>> 2) 2**64 is enough entropy for this kind of thing. Why would anyone 
>>>> do that??
>>>>
>>>> I miss the point you are trying to make...
>>>
>>> At some point you say less than 64 entropy might not be enough, and 
>>> that a limit is not clear.
>>
>> Nope neither me nor the document says that. The document says the 
>> obvious: the algorithm does not have any inherent requirement 
>> regarding the IID length. Of course, if you change the IID length, you 
>> change the entropy (the search space). (e.g., if you reduced the IID 
>> length, the entropy would be reduced).
>>
>>
>>> But similarly, more than 64 entropy might be more than enough - you 
>>> just dont say it.
>>
>> Let me put it bluntly: even 32 bits would be more than enough for this.
> 
> Yes, write that down.  I agree with you.  I do not know why not writing 
> it down.

Because this is not a document to discuss IID lengths. The current specs 
mandate /64. If that's changed, such document should do the appropriate 
analysis. There's no reason for this document to do that.




>>> You say 'it is implied', but there is silence, actually.
>>>
>>> There is nothing in I-D RFC4941bis, nor in RFC7421, that talks about 
>>> IID length longer than 64.
>>
>> 1) The current architecture doesn't have such a thing
> 
> All IPv6-over-foo docs request it, and the IPv6 Addr Arch requests it.

Exactly. There's no point in getting into a discussion about something 
that's not even allowed in the current specs.



[...]
>> 2) I personally don't think anybody would even think about IIDs longer 
>> than 64 bits. 64-bit IIDs already waste a big part of the address space.
> 
> ??  No, I dont think so.
> 
> I personally think IIDs longer than 64bit are absolutely necessary in 
> some contexts.  A SLAAC where a router that advertises a /56 in an RA, 
> might need the Host  to form a 72bit IID.

Write a draft, and propose that change. Until that, this document need 
to stick to existing specs.

Thanks,
-- 
Fernando Gont
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