Re: slaac-renum: New rev of draft-gont-6man-slaac-renum (Fwd: New Version Notification for draft-gont-6man-slaac-renum-08.txt)

[Fernando Gont <[e-mail]>]

Hi, Brian,

On 20/5/20 17:57, Brian E Carpenter wrote:
[....]
>>
>> So in my opinion, the algorithm has to work correctly without knowledge
>> of ULA.
>>
>>> When a prefix is missing, that's an indication that the prefix has
>>> become stale. Now, you might process the RAs irrelevant of ULA nad
>>> non-ULA, and it would also be fine.
>>>
>>> But the logic here is that it is better to have one stale address of
>>> each type, than no address of that type. If you want, this is the
>>> algorithm being more conservative.
>>
>> Again, without special treatment of ULAs, the algorithm is dangerous. It can
>> take an RA with a ULA to invalid all non-ULA prefixes.
> 
> I'm finding this hard to understand, since the text says:
> 
>    "o  Only RAs that advertise Global Unicast prefixes may deprecate
>        Global Unicast Addresses (GUAs), while only RAs that advertise
>        Unique Local prefixes may deprecate Unique Local Addresses (ULAs)."
> 
> Perhaps that should be reformulated with MUST NOT terminology to make it
> clearer:
> 
>     o  RAs that advertise Global Unicast prefixes MUST NOT deprecate
>        Unique Local prefixes, and RAs that advertise Unique Local
>        prefixes MUST NOT deprecate Global Unicast prefixes.
> 
>> So, the ULAs need to be treated specially to make it to work at all.
> 
> Yes, of course. They *are* special. They work even if the WAN side drops
> and even if the WAN prefix changes.

FWIW, this text is meant to describe what the algorithm does, as opposed 
to actually specifying anything. i.e., it's goal is to "explain" the 
algorithm. I don't mind changing the text, though.


>> This
>> locks us into a situation where ULA, non-ULA is all that can exist.
>> Introducing a third type of addresses would cause this algorithm to fail.
> 
> Yes. If there was a 4th type of address (we already have three, counting
> link-local), every router in the universe would need a fix.

In fact, if there was a 4th type of address probably all nodes would 
need a fix (including source address selection and others).

Thanks!

Cheers,
-- 
Fernando Gont
SI6 Networks
e-mail: [e-mail]
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