UUID

RFC 4122 generate

128-bit number used to identify information in computer systems

There 5 different versions of UUID's.

UUID v1

Time-based with host identifier (MAC adress)

UUID v2

Time-based with host identifier (MAC adress) + segment of a local domain number

UUID v3

Name-based with MD5 hashing

UUID v4

Random-based

UUID v5

Name-based with SHA-1 hashing