Re: <draft-ietf-6man-rfc4291bis-09.txt>

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

On 20/07/2017 14:14, Manfredi, Albert E wrote:
> From: ipv6 [mailto:[e-mail]] On Behalf Of Brian E Carpenter
> 
>> But what is needed is clarity in definitions, which is why
>> I've been asking what the low order bits in an IPv6 address
>> are called in cases where people claim they are not called an
>> IID.
>>
>> (My answer fwiw is that they are always called an IID, because
>> once you're on the final link, those bits serve only to deliver
>> the packet to the intended interface, so they must uniquely
>> identify that interface.)
> 
> That's certainly my answer too. But more to the point, I don't understand what other answer could be valid, or said another way, why ask the question?

a) Because of the several subtly different meanings of 'prefix' in IPv6.
b) Because some people seem to be limiting their use of 'IID' to the SLAAC meaning of 'prefix'.

    Brian

> 
> RFC 4291 wasn't ambiguous about this, was it?
> 
> 
>    |          n bits               |           128-n bits            |
>    +-------------------------------+---------------------------------+
>    |       subnet prefix           |           interface ID          |
>    +-------------------------------+---------------------------------+
> 
> That isn't limited to 64 bits? It says:
> 
>    For all unicast addresses, except those that start with the binary
>    value 000, Interface IDs are required to be 64 bits long and to be
>    constructed in Modified EUI-64 format.
> 
> We've been over the broadening of the exceptions in 4291-bis, but even as written, the IID isn't constrained to being just 64 bits.
> 
> Bert
> 
> 
>