Re: router behaviour with prefixes longer than /64

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

Peter,

On 18/03/2014 08:54, Peter Dordal wrote:
> On 03/17/2014 02:17 PM, David Farmer wrote:
>> On 3/17/14, 12:45 , Manfredi, Albert E wrote:
>>> From: Lorenzo Colitti [mailto:[e-mail]]
>>>
>>>>> I didn't miss that. People seem to be reading this clause backwards.
>>>>>
>>>>> I'm saying that "those that start with binary value 000" are the vast
>>>>> majority of potential IPv6 global unicast addresses.
>>>
>>>> No, the way to read it is exactly the way it's written: for *all*
>>>> unicast addresses, except those that start with 0 or 1, IIDs are 64
>>>> bits long, period.
>>>
>>> Are you disagreeing that unicast addresses starting with 000 are the vast 
>>> majority of potential future unicast addresses?
>>
>> The only currently defined IPv6 addresses that start with the binary value 
>> 000, are special-purpose addresses, all other addresses that meet this 
>> definition are reserved, and not currently available for allocation, though 
>> they are reserved for future unicast allocation.
> 
> My understanding of the 0::/3 block has always been that it represents a fallback
> in case 64-bit prefixes don't work out for some reason. This address block is 
> "held in reserve".

No. It's partially used for special purpose addresses. The reserve is in the fact
that only 2000::/3 (1/8 of the total space) has been released to IANA for unicast
allocations.

   Brian

> That is, if we run out of /64 IPv6 address prefixes, we can always divide up the 
> 0::/3 block using, say, /96 prefixes.

> (And then at that point figure out how to manage with 32-bit interface IDs.)
> 
>> ...
>> There has never been any general-purpose unicast addresses that start with the 
>> binary value 000, only the current and historic special-purpose addresses.
>>
> But this /could/ change in the future, though that would be likely only if there 
> were a problem with the 64/64 division.
> Which is to say not very likely at all.
> 
> Peter Dordal
> Loyola Univ Chicago CS Dept
> 
> 
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