How can I trace the following MAC addresses and find out who they are or belong to:
When checking my router, these MAC addresses were in the drop-down menu.
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MAC addresses are only locally unique and it could be a spoofed address (if it an attack) as well. Therefore if you are referring to an attack, the best thing is to look at MAC addresses later.
If you have a chance to analyze ARP packets from your router you will be able to find the related IP addresses.
If you suspect an inside attacker, you can check your ARP/RARPtable. Or block these MAC addresses using MAC filtering. Users will complain when they are not able to use the internet. Before that, make sure all critical users are not using these MAC addresses.
In addition to that, try to identify the product vendor using a MAC lookup tool to look for the devices.
But It is really hard to find your network devices if they are connecting through multiple ways.