Re: Question about Interface ID length

["Stephen Sprunk" <stephen@sprunk.org>]

Thus spake "Barany, Pete" <pbarany@qualcomm.com>
> ... RFC 3513 ... Section 2.5.1:
> -----
> "For all unicast addresses, except those that start with binary value
> 000, Interface IDs are required to be 64 bits long and to be constructed
> in Modified EUI-64 format."
>
> ... RFC 2526 ... Section 2:
> -----
> "For other IPv6 address types (that is, with format prefixes other than
> those listed above), the interface identifier is not in EUI-64 format
> and may be other than 64 bits in length; these reserved subnet anycast
> addresses for such address types are constructed as follows:"
> |              n bits             |    121-n bits    |   7 bits   |
> +---------------------------------+------------------+------------+
> |           subnet prefix         | 1111111...111111 | anycast ID |
> +---------------------------------+------------------+------------+
>                                   |   interface identifier field  |
> -----

Different angle...

RFC 3513 and RFC 2526 both seem to outlaw* the common and logical practice
of using /127 networks (and thus a 1-bit Interface ID) for point-to-point
and tunnel links, because the IID isn't long enough and there's no space for
the 7-bit anycast ID, respectively.  Can we put some sort of exception for
/127 networks in the RFC updates?

* at least in format prefix 001, which is what operators will want to use.

S

Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking


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