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    SubjectRe: [PATCH 1/2] UUID: set multicast bit in pseudo-random MAC address
    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

    See Section 4.5 for a discussion on random numbers.

    - Ted
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