The port status of the switch is up, but the MAC address under this port is queried as empty

(the computer is turned off) the port status of the computer and the switch is still up, but the MAC address under query for this port is empty .

Preliminary suspicion causes:

Wake-on-lan (computer shutdown, network card is still working)

Wake-on-lan, known as WOL, is a power management feature that allows a device to wake the operating system from standby or Hibernate mode if there is network activity. Many motherboard vendors support IBM's proposed network wake-up standard. This standard allows the network administrator to remotely turn on the PC power.

Wake-on-lan implementation, mainly to the target host to send a special format of the packet, is produced by AMD Magicpacket this software to generate a network wake-up required special data packets, commonly known as Magic Packet. Although the Magicpacket format is an AMD-developed technology that is not universally accepted, it is still supported by many network card manufacturers, so many NICs with Wake-on-LAN capabilities are compatible.

In addition to the Magic packet, some network cards also support wake up frame.

MP is the abbreviation of the English Magic Packet, to wake up another computer with a special packet (AMDR "Magic Packet"), which will contain 16 consecutive Mac Address in the AMDR "Magic Packet". PM is the abbreviation for pattern match, which basically wakes up another computer with the pattern frame of MicrosoftR "wake-up frame".

The port status of the switch is up, but the MAC address under this port is queried as empty