Subject: Question about Interface ID length

From: "Barany, Pete" <[email-masked]>
Date: Tue, 16 Dec 2003 15:32:50 -0800

Hi,

--> For the RFC 2462bis I-D there was a list of issues sent out during
Oct. 2003 and one of the issues was:
-----
"If RFC2462 requires 64bit IFID
by several people, several times."

So far in the RFC 2462bis I-D the answer appears to be "No" since no
changes in the I-D indicate otherwise.
-----

--> Referring to RFC 3513 (and now also RFC 3513bis), the following
statement is made in 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."

So here it appears that the answer to the question in RFC 2461bis should
be "Yes"?
-----

--> There seems to be an inconsistency here. I am concerned that this
issue may also have ramifications for other RFCs. For example, in RFC
2526, the following statement is made in 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  |
-----

--> How is this to be resolved? Thanks.

Regards,

Pete

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---

From: Brian Haberman <[email-masked]>
Date: Wed, 17 Dec 2003 06:28:20 -0500

Pete,
      2462bis does not contain any changes as of yet.  The document
exists currently to document the issues that need to be addressed.
So, the point on IID length should be addressed in 2462bis at some
point.

Brian

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From: "Stephen Sprunk" <[email-masked]>
Date: Sat, 20 Dec 2003 09:44:29 -0600

Thus spake "Barany, Pete" <[email-masked]>
> ... RFC 3513 ... Section 2.5.1:
> -----
> ... RFC 2526 ... Section 2:
> -----

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

---

From: Brian Haberman <[email-masked]>
Date: Sat, 20 Dec 2003 11:52:00 -0500

I would suggest reading RFC 3627.

Regards,
Brian