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Re: [ieee-ietf-coord] Rationale for 0xFFFE as octets 4 and 5 pf EUI-64?

Geoff Thompson <thompson@ieee.org> Mon, 25 June 2018 01:27 UTC

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From: Geoff Thompson <thompson@ieee.org>
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Date: Sun, 24 Jun 2018 18:27:38 -0700
Cc: Geoff Thompson <thompson@ieee.org>
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To: Donald Eastlake <d3e3e3@gmail.com>, Charlie Perkins <charles.perkins@earthlink.net>, "ieee-ietf-coord@ietf.org" <ieee-ietf-coord@ietf.org>
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Subject: Re: [ieee-ietf-coord] Rationale for 0xFFFE as octets 4 and 5 pf EUI-64?
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Inserting "0xFFFF to convert a MAC-48 to and EUI-64" or "0xFFFE to convert an EUI-48 to an EUI-64"
does not actually "convert" anything in a useful way except to to make a "EUI-48" readable in a 64 bit system.

The purpose of developing EUI-64 was to have a larger address space that could be used for (among other things) software instances.
Having a fixed 16 bit value in a 64 bit address does nothing towards achieving that goal or slowing down the usage of 48 bit addresses to extend the life of 802 physical networks.

Geoff Thompson


> On Jun 24, 2018, at 5:52 PMPDT, Donald Eastlake <d3e3e3@gmail.com> wrote:
> 
> Hi Charlie,
> 
> As I recall, there is/was this distinction between MAC-48 and EUI-48 addresses. I think MAC-48 was just for hardware and EUI-48 was for other devices and software. Anyway, you inserted 0xFFFF to convert a MAC-48 to and EUI-64 and 0xFFFE to convert an EUI-48 to an EUI-64. The RFCs that talk about extending a 48 bit address to 64 bits to use as the low order bits of an IPv6 address say that 0xFFFE was used by mistake and that 0xFFFF should have been used (see for example the Note on page 22 of RFC 4291) but it was decided to stick with 0xFFFE for that purpose. Hope this helps.
> 
> Thanks,
> Donald
> ===============================
>  Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
>  155 Beaver Street, Milford, MA 01757 USA
>  d3e3e3@gmail.com <mailto:d3e3e3@gmail.com>
> On Fri, Jun 22, 2018 at 9:54 PM, Charlie Perkins <charles.perkins@earthlink.net <mailto:charles.perkins@earthlink.net>> wrote:
> Hello folks,
> 
> Does anyone here remember why 0xFFFE were chosen to be the filler bits (i.e., bytes 4 and 5 of 8) when expanding a 48-bit MAC address to be EUI-64?  It is not explained in RFC 2464.
> 
> Or maybe there was not a reason...?
> 
> Thanks in advance,
> Charlie P.
> 
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