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SubjectRe: [PATCH 1/2] UUID: set multicast bit in pseudo-random MAC address
Date
On Sunday 21 October 2007, Theodore Tso wrote:
> On Sat, Oct 20, 2007 at 09:58:40PM +0200, Helge Deller wrote:
> > Fix a bug in the current random UUID generator:
> >
> > Section 4.1.6 of RFC 4122 states regarding the "NodeID" of a UUID:
> > : For systems with no IEEE address, a randomly or pseudo-randomly
> > : generated value may be used; see Section 4.5. The multicast bit must
> > : be set in such addresses, in order that they will never conflict with
> > : addresses obtained from network cards.
> >
> > So up to now it was just pure ("random") luck if this bit was set or not.
> > This tiny patch sets the bit explicitely.
>
> NACK. Your patch degrades the random UUID by a bit, for no good reason.
>
> The part of Section 4.1.6 which you quoted only applies to version 1
> UUID's --- i.e., MAC and time based UUID's. Random uuids are version
> 4 UUID's, and are already distinguished from version 1 UUID's by the
> high 4 bits of the time_hi_and_version field, in octets 6-7 of the
> URL. Hence, there is no danger of conflict. If you had looked 3
> paragraphs later section 4.1.6:
>
> For UUID version 4, the node field is a randomly or pseudo-randomly
> generated 48-bit value as described in Section 4.4.
>
> And the summary can be found in Section 4.4 of RFRC 4122:
>
> 4.4. Algorithms for Creating a UUID from Truly Random or
> Pseudo-Random Numbers
>
> The version 4 UUID is meant for generating UUIDs from truly-random or
> pseudo-random numbers.
>
> The algorithm is as follows:
>
> o Set the two most significant bits (bits 6 and 7) of the
> clock_seq_hi_and_reserved to zero and one, respectively.
>
> o Set the four most significant bits (bits 12 through 15) of the
> time_hi_and_version field to the 4-bit version number from
> Section 4.1.3.
>
> o Set all the other bits to randomly (or pseudo-randomly) chosen
> values.
>
> See Section 4.5 for a discussion on random numbers.

Hi Ted,

Thanks for looking into it and pointing to the important RFC pieces.
Of course you are right and I mixed that up.

Herewith I withdraw this patch.

Helge
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