What this means
The IEEE assigned the MA-L block 74DDF0 to SHEN ZHEN TENDA TECHNOLOGY CO.,LTD. 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 74:DD:F0, it is SHEN ZHEN TENDA TECHNOLOGY CO.,LTD hardware.