On 03 May 2012 00:38, Richard Wilson wrote:
As for "The UUID is unique as an identifier across all time and
space" In a site with more than 1 box I'd trust that about as far as
I could throw a politician
While I would consider the quote within the above quoted message to
be hyperbole, in consideration of a "site with more than 1 box" the
uniqueness is established additionally within a component of the UUID
which should, according to /networking/ concepts [which already
necessitates further uniquely identify each "box"], similarly extend the
uniqueness to each "box".
A more appropriate claim might be either of "A UUID is 128 bits long,
and *can* guarantee uniqueness across space and time" from
or "is either guaranteed to be
different from all other UUIDs/GUIDs generated until 3400 A.D. or
extremely likely to be different (depending on the mechanism chosen)"
A quick web search found the above links, and the following links.
The following link may be an appropriate description; see "The node ID":
"... The node ID should <ed: preferably be> an IEEE 802 MAC address ...
If no IEEE 802 address is available one can also generate a random part
for this address, in this case the multicast bit (least significant bit
of the first byte) must be set to 1, this to avoid clashes with
legitimate IEEE 802 addresses. In case a random address is used,
uniqueness cannot be guaranteed."
Corroborated at least somewhat by:
"A UUID (Universal Unique Identifier) is a 128-bit number used to
uniquely identify some object or entity on the Internet. Depending on
the specific mechanisms used, a UUID is either guaranteed to be
different or is, at least, extremely likely to be different from any
other UUID generated until 3400 A.D. The UUID relies upon a combination
of components to ensure uniqueness. A guaranteed UUID contains a
reference to the network address of the host that generated the UUID, a
timestamp (a record of the precise time of a transaction), and a
randomly generated component. Because the network address identifies a
unique computer, and the timestamp is unique for each UUID generated
from a particular host, those two components should sufficiently ensure
uniqueness. However, the randomly generated element of the UUID is added
as a protection against any unforeseeable problem. ..."
And of course from the expected domain, where Version 1 concurs, but
mention of up to a Version 5:
Version 1 (MAC address)
Conceptually, the original (version 1) generation scheme for UUIDs was
to concatenate the UUID version with the MAC address of the computer
that is generating the UUID ...
Version 5 (SHA-1 hash)
Version 5 UUIDs use a scheme with SHA-1 hashing; otherwise it is the
same idea as in version 3. RFC 4122 states that version 5 is preferred
over version 3 name based UUIDs, as MD5's security has been compromised. ...