![]() ![]() But their MAC address had the first bit (indeed the first 24 bits) all set! Remember I said that in real MAC addresses, the first bit is zero, indicating a unicast destination. Their systems had a virtual network card, and the driver for the virtual network card generated a MAC address where the Organizationally Unique Identifier (OUI) was FFFFFF. It took a lot of investigation, but the team finally got to the root of the problem. (In real MAC addresses, the first bit is zero, indicating a unicast destination.) So why wasn’t the MAC address being used in the UUID? Instead, the high bit of the first byte of the MAC address was set, indicating that this was a pseudo-random MAC address rather than a real one. The timestamp is incremented to produce sequential UUIDs. Sequentially-generated UUIDs are so-called Version 1 UUIDs: A combination of a timestamp and a MAC address. A customer reported that the UuidCreateSequential function was generating UUIDs that did not place the network card’s MAC address in the final bytes of the UUID. ![]()
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