GUID:Globally Unique IDentifier ; UUID: Universally Unique IDentifier ; RFC4122

Universally Unique IDentifier

Defined at RFC4122

Generating a UUID does not require a registration authority
UUIDs are inherently very difficult to resolve in a global sense.
That is, given a UUID, determining who or what it belongs to is difficult.

Generating UUID using one of three algorithms

use unique values of 802 MAC addresses (Network Interface Card ) to guarantee uniqueness,
uses pseudo-random number generators,
cryptographic hashing and application-provided text strings

Using the timestamp / nodeid version (version 1), where the nodeid comes from network equipment (Like a UUID generated using the uuidgen -t command.)

 v= 1      time-based 
    2      DCE Security , with embedded POSIX UIDs.
    3      name-based    uses MD5 hashing.
    4      randomly or pseudo-randomly generated  
    5      name-based    uses SHA-1 hashing.

UUID =	time_low 4	-	time_mid 2	-	version + time_high 2	-	clock_seq + reserved + clock_seq_low 2	-	node 6
or by hexDigits	llllllll	-	mmmm	-	vhhh	-	rcll	-	nnnnnnnnnnnn

                            8 Octets (Bytes) total
time_low                    4 hexOctets                          6A3C6342
time_mid                    2 hexOctets                          D97C
version_and_time_high       2 hexOctets   
               v              hexDigit                           1
                hhh           hexDigit+hexOctet                  1DB

The timestamp is a 60-bit value.
For UUID version 1, this is represented by Coordinated Universal Time (UTC)
as a count of 100-nanosecond intervals since 00:00:00.00, 15 October 1582
(The date of Gregorian reform to the Christian calendar).

clock_seq_high + reserved    1 hexOctet                             
 reserved                 3 bits !  (aka variant aka type )
                          0-7 NCS ; backward compatibility
                          8-B current variant of UUID;        8 
                          C-D Microsoft
                          E-F furture
clock_seq_high            bit + hexDigit                      3
clock_seq_low             hexOctet                            14
node                      6 hexOctet                          0800200C9A66
hexOctet (aka byte)     = hexDigit hexDigit
hexDigit                = 0 : F

see RFC4122 section 4.3 for generation of Name Based UUIDs, Section 4.4 for using random numbers.

- v - - time-based 6A3C6342-D97C-11DB-8314-0800200C9A66 generated on: Friday, March 23, 2007 8:23:51 PM GMT
- v - - random 1CBE3804-20DF-48DA-B048-895C206E80A5

Generate your own version:1 (time based) UUID at Famkruithof.net/uuid/uuidgen

Extract the time from a version 1 UUID

Some Examples


--- Winsock Layered Service Provider list ---
 MSAFD Tcpip [TCP/IP]
GUID: {E70F1AA0-AB8B-11CF-8CA3-00805F48A192}
 %SystemRoot%\system32\mswsock.dll
 NT/2k/XP IP protocol
DB  %SystemRoot%\system32\mswsock.dll               DB protocol: MSAFD Tcpip[*]

 MSAFD Tcpip [RAW/IP]

 RSVP UDP Service Provider
GUID: {9D60A9E0-337A-11D0-BD88-0000C082E69A}
 %SystemRoot%\system32\rsvpsp.dll
 NT/2k/XP RVSP
DB  %SystemRoot%\system32\rsvpsp.dll                DB protocol: RSVP * Service Provider

 RSVP TCP Service Provider

 MSAFD nwlnkipx [IPX]
GUID: {11058240-BE47-11CF-95C8-00805F48A192}
 %SystemRoot%\system32\mswsock.dll
 NT/2k/XP Novell Netware UPX protocol
DB  %SystemRoot%\system32\mswsock.dll           DB protocol: MSAFD nwlnkipx *

 MSAFD nwlnkspx [SPX]
GUID: {11058241-

 MSAFD nwlnkspx [SPX] [Pseudo Stream] 
 MSAFD nwlnkspx [SPX II] 
 MSAFD nwlnkspx [SPX II] [Pseudo Stream]

 MSAFD NetBIOS [\Device\NwlnkNb] SEQPACKET 3
GUID: {8D5F1830-C273-11CF-95C8-00805F48A192}
8D5F1830-C273-11CF is Mon, 10 Jun 1996 03:52:56 +0000 
 %SystemRoot%\system32\mswsock.dll
 NT/2k/XP NetBios protocol
DB  %SystemRoot%\system32\mswsock.dll           DB protocol: MSAFD NetBIOS *

MSAFD NetBIOS [\Device\NwlnkNb] DATAGRAM 3
MSAFD NetBIOS [\Device\NetBT_Tcpip_{5E9F90A2-3DAC-477B-AE25-81B8ED1CE696}] SEQPACKET 0
MSAFD NetBIOS [\Device\NetBT_Tcpip_{5E9F90A2-3DAC-477B-AE25-81B8ED1CE696}] DATAGRAM 0
MSAFD NetBIOS [\Device\NetBT_Tcpip_{FBC2E32E-ABD0-4C56-AD81-8F947E1D3172}] SEQPACKET 1
MSAFD NetBIOS [\Device\NetBT_Tcpip_{FBC2E32E-ABD0-4C56-AD81-8F947E1D3172}] DATAGRAM 1
MSAFD NetBIOS [\Device\NetBT_Tcpip_{DC584667-773B-4D03-84F4-C834EEB4612E}] SEQPACKET 2
MSAFD NetBIOS [\Device\NetBT_Tcpip_{DC584667-773B-4D03-84F4-C834EEB4612E}] DATAGRAM 2

Namespace Provider 0: Tcpip
GUID: {22059D40-7E9E-11CF-AE5A-00AA00A7112B}
 %SystemRoot%\System32\mswsock.dll
 NT/2k/XP TCP/IP name space provider
DB  %SystemRoot%\system32\mswsock.dll               DB protocol: TCP/IP

Namespace Provider 1: NTDS
GUID: {3B2637EE-E580-11CF-A555-00C04FD8D4AC}
 %SystemRoot%\System32\winrnr.dll
 NT/2k/XP name space provider
DB  %SystemRoot%\system32\winrnr.dll                 DB protocol: NTDS

Namespace Provider 2: Network Location Awareness (NLA) Namespace
GUID: {6642243A-3BA8-4AA6-BAA5-2E0BD71FDD83}
 %SystemRoot%\System32\mswsock.dll
 NT/2k/XP name space provider
DB  %SystemRoot%\system32\mswsock.dll               DB protocol: NLA-Namespace

Namespace Provider 3: NWLink IPX/SPX/NetBIOS Compatible Transport Protocol
GUID: {E02DAAF0-7E9F-11CF-AE5A-00AA00A7112B}
 %SystemRoot%\System32\nwprovau.dll
 NT/2k/XP Novell Netware name space provider
DB  %SystemRoot%\system32\nwprovau.dll              DB protocol: NWLink IPX/SPX/NetBIOS*