Joel,
On 02/02/2013 00:41, Joel M. Halpern wrote:
> With regard to section 3, I would ask the question in the reverse.
> (which may actually be the same quewstion Fernando is asking.)
>
> If we assume that there is value in being able to perform the diagnostic
> operation described, then it seems that one needs to be able to tell
> when it can be applied.
> Currently, that is u==1 in the IID field.
> The text says that u==1 must be used n the IID field for IIDs derived
> from EUI-64.
> But it the goes on to say that u=1 can be used by other addresses.
> If u=1 can be used by addresses not derived from EUI-64, then the
> diagnostic operation can not be applied without a-priori knowledge.
> And in the presence of such knowledge, the u bit does not seem to help.
Correct. Semantically, it's a dead duck. That's already true, whatever
words are written in RFCs - the fact that u=1 does not prove the IID
comes from a MAC address with u=0, and vice versa.
> The obvious answer is that to enable the diagnostic, and because there
> is no need to make a gratuitous change, we stick with u=1 being used
> always and only for addresses derived from EUI-64.
But that doesn't mean that the IID was derived from a MAC address,
so its value is limited.
> The other alternative I can understand, although I do not favor it, is
> to not allow the diagnostic at all.
The alternative is what we have today: *assume* that an IID that looks
as if it came from a MAC address in fact did so.
Brian
>
> Yours,
> Joel
>
> On 2/1/2013 3:13 PM, Fernando Gont wrote:
>
>> Section 3:
>>> It should be noted that IIDs known or guessed to have been created
>>> according to RFC 4941 could be transformed back into MAC addresses,
>>> for example during fault diagnosis. For that reason, keeping the
>>> "u"
>>> and "g" bits in the IID has operational value. Therefore, the
>>> EUI-64
>>> to IPv6 IID transformation defined in RFC 4941 MUST be used for all
>>> cases where an IID is derived from a MAC address.
>>
>> How can you tell whether an IID was really derived from a MAC address,
>> or you just had pretty bad luck with your IID randomization -- such tha
>> it *looks* like derived form a mac address?
>>
>> Thanks!
>>
>> Cheers,
>>
>
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