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Re: RFC4941bis implementations

otroan@employees.org Thu, 02 April 2020 22:20 UTC

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Subject: Re: RFC4941bis implementations
From: otroan@employees.org
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Date: Fri, 03 Apr 2020 00:20:14 +0200
Cc: Florian Obser <florian@openbsd.org>, Alexandre Petrescu <alexandre.petrescu@gmail.com>, 6man WG <ipv6@ietf.org>
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To: Mark Smith <markzzzsmith@gmail.com>
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Mark,

> > Does it work with a plen 65 in RA?
> 
> I'm happy to report that slaacd(8) in OpenBSD does not care about the plen.
> It just forms a 128 bit random number and overwrites the front with
> the prefix.[1]
> So if you put your whole /29 onlink you can have 99 bits of entropy!
> 
> Or 1 bit of entropy if you use a 127.
> 
> Might be worth issuing a warning about the privacy properties of an RFC4941 address if the prefix length gets to long.
> 
> A false sense of privacy is probably just as bad as a false sense of security.

4941bis is for SLAAC. SLAAC uses 64 bit IIDs.
I don't think we need to get into this discussion. See also 7421.

Note also the title change.
These are temporary addresses. I believe the document does not make any exaggerated claims about privacy.
I.e. it claims very little in that respect...

Best regards,
Ole

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