What this means
The IEEE assigned the MA-L block 00123C to Second Rule LLC. Every network interface they manufacture under this block has a MAC address beginning with these digits, followed by a unique per-device identifier. If a device on your network shows a MAC starting 00:12:3C, it is Second Rule LLC hardware.
Frequently Asked Questions
Who owns MAC prefix 00123C?
00123C is registered to Second Rule LLC in the IEEE MA-L registry.
What does the MA-L registry type mean?
An MA-L assignment, the IEEE's original OUI format, gives the vendor the first three octets and 16,777,216 device addresses under them. Second Rule LLC's block covers 16,777,216 addresses.
What devices use 00123C?
Any network device with a MAC address starting 00:12:3C was manufactured by or for Second Rule LLC.