Subject: MAC-Derived Interface-id

From: "Sellers, Julian P" <[email-masked]>
Date: Fri, 18 Feb 2000 16:14:31 -0500

I have a requirement that IPv6 addresses be configurable per application.
It would be very convenient to configure for an application a 16-bit value
that would replace the FFFE in the middle of the MAC-derived EUI-64
interface-id.  These V6 addresses would be just as unique as those with the
FFFE (but I wouldn't mind setting the univeral/local bit if that were
required).  This uniqueness property is nice because 1) I also have to allow
multiple interfaces to the same network, and 2) it would eliminate most
conflicts with manually configured V6 addresses of other nodes on the same
network.

When RFC 2373 (Addr Arch) describes the formation of EUI-64 identifiers from
MAC addresses, it refers to an IEEE document called "Guidelines for 64-bit
Global Identifier (EUI-64) Registration Authority."  I'm trying to find a
copy of that to see if I can find any reason why I shouldn't form
interface-ids from MAC addresses with other than FFFE in the middle.  Does
anyone know of a reason why I should not do that?  It sure seems better than
::1, ::2, etc.

Julian
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From: "Matt Crawford" <[email-masked]>
Date: Fri, 18 Feb 2000 15:50:44 -0600

> required).

The FFFE is there as part of an IEEE-defined mapping from their old
48-bit identifiers to the new EUI-64 format.  Manufacturers can and
do issue 64-bit identifiers with the values 0000-FFFD in that
position.

However, if you flip the universal/local bit, you're OK.  You get no
promise that some entireley different node on the link (or some other
application on your node!) isn't inventing its own "local"
identifiers, of course, and they could just possibly collide, so
you'd be well advised to do DAD on each new address.

> interface-ids from MAC addresses with other than FFFE in the middle.

http://grouper.ieee.org/groups/802/secmail/msg00396.html

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From: Francis Dupont <[email-masked]>
Date: Fri, 18 Feb 2000 23:44:27 +0100

In your previous mail you wrote:

=> I believe ports are here for this purpose?

   interface-id.

=> you can do what you want when the global bit is reset/reversed.

   It sure seems better than ::1, ::2, etc.

=> I'd prefer this (1, 2, ...) because this is so simple (:-).
In fact you can do anything when you need far less than 3037000499
addresses!

Regards

[email-masked]