What this means
The IEEE assigned the MA-L block C42C7B to VIETNAM POST AND TELECOMMUNICATION INDUSTRY TECHNOLOGY JOIN STOCK COMPANY. 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 C4:2C:7B, it is VIETNAM POST AND TELECOMMUNICATION INDUSTRY TECHNOLOGY JOIN STOCK COMPANY hardware.