As I understand it, the original intent with the U bit was to provide an
easy way to create IID that were highly likely to be distinct from all
other IIDs (on the link). As IEEE reserves the G bit, we marked that as
special as well when the U bit was set.
Changing the meaning of U=1, G=0 seems a major chane with no particular
benefit.
When we defined it, we were unclear about the U=1, G=1 case. Given the
way the U bit is defined, U=1, G=1 can not occur in the normal course of
events. We can ignore it. we can define it. We can reserve it and thn
sit on our hands. But given taht we have text already, and that text is
ambiguous, it seems like we should at least clear up the ambiguity.
Yours,
Joel
On 12/18/2012 7:35 PM, Fred Baker (fred) wrote:
Why do we care about u and g in the first place? Is there code in an IPv6
router or host that interprets them?
On Dec 18, 2012, at 3:50 PM, Joel M. Halpern wrote:
In reading the discussion,a nd trying to think through what I understand to be
correct, it seems that there is an unforeseen ambiguity in the way the current
documents about IPv6 IIDs are written.
I think that there are two possible meanings, ad we should decide explicitly
which one we want.
1) u=1 means that the IID is derived from an IEEE OUI (of some form). With that
meaning, u=1, g=1 is clearly some sort of multi-entity identifier. And we
should say that somewhere.
2) u=1, g=1 was unforeseen, and we don't know what it means. In that case, we
ought to figure out how we want that portion of the IID space used, and write
it down clearly. It seems to me that allowing this space to be used for
special-semantic IIDs (with suitable care so that the entire ecosystem is not
affected by them) is a very reasonable path.
It seems unlikely that there is actual practice in the wild with u=1, g=1 under
either interpretation. We do now have a request to start using it (4rd). So
we should decide.
Yours,
Joel
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