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Re: 64bit MAC addresses and SLAAC

Fernando Gont <fgont@si6networks.com> Wed, 17 June 2020 15:30 UTC

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Subject: Re: 64bit MAC addresses and SLAAC
To: Alexandre Petrescu <alexandre.petrescu@gmail.com>, Bob Hinden <bob.hinden@gmail.com>
Cc: IPv6 List <ipv6@ietf.org>
References: <e8a25961-5ac9-d35e-77dd-bf86f45cd077@gmail.com> <a17ae9f3-001c-07f6-84f9-a0ca583e6a00@gmail.com> <7AE5B6D0-AB01-4077-A9EF-5BD86F428681@gmail.com> <7a3b839f-099e-8fd3-35a2-4625df3c369e@gmail.com>
From: Fernando Gont <fgont@si6networks.com>
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Date: Wed, 17 Jun 2020 12:20:38 -0300
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On 17/6/20 08:39, Alexandre Petrescu wrote:
> Le 15/06/2020 à 23:01, Bob Hinden a écrit :
>> Alexandre,
>>
>>> On Jun 15, 2020, at 1:23 PM, Alexandre Petrescu 
>>> <alexandre.petrescu@gmail.com> wrote:
>>>
>>> Hi,
>>>
>>> Before the sanitary situation I was studying an issue at ISO.
>>>
>>> The issue is about 64bit MAC addresses and SLAAC.
>>>
>>> SLAAC needs a 48bit MAC addresses in order to work, and it can not 
>>> work with a 64bit MAC address; (but yes, it can with 64bit IIDs).
>>
>> SLACC does not specify the length of the Interface ID, it does not 
>> require require 48-bit MAC addresses, and the reason for Modified 
>> EUI-64 Format Interface Identifiers in RFC4291 was to support 64bit 
>> EUI-64 Identifiers.   We have since moved away from using MAC 
>> addresses as Interface IDs.  See RFC 8064.
> 
> Bob,
> 
> RFC8064 says "this document [...] recommends against embedding stable
> link-layer addresses in IPv6 Interface Identifiers".
> 
> But a 64bit MAC address could be a random number as well, not
> necessarily stable.  Windows randomizes some of its MAC addresses.

Reusing IDs in multiple contexts is known to be a bad idea. See e.g.: 
https://tools.ietf.org/html/draft-irtf-pearg-numeric-ids-generation and 
https://tools.ietf.org/html/draft-gont-numeric-ids-sec-considerations

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492

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