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I have run into a snag regarding MAC addresses, or retrieving them from devices. I don't know if this is the correct forum for this question, but it is the best that comes to my mind. Background: I have created a GUI that communicates with a PCB that has a standard Ethernet port (wired). My GUI searches for available IP addresses, and then retrieves the MAC address for each of these, using the WinAPi.IpHlpApi SendARP function. The 36 most significant bits of the MAC address are then used for filtering. Recently, my lab has been moved to a new location, with no wired access to the Router / DHCP server. Since my PCB only has a standard wired Ethernet port, I have set up an access point in "client mode", to make a tiny wired network in the lab. (TP-Link WA801N) This seems to work nicely, except... The problem: My GUI cannot find the PCB, and I've figured out that the reported MAC address is wrong when the PCB is connected to the access point. I can find the board's IP address with Advanced IP Scanner, but the reported MAC address is the same as the access point's MAC address. For security, I have partially obscured the MAC addresses, but the two MAC addresses marked with yellow are identical. The DOS command arp -a says basically the same thing. However, if I connect a computer to the same ethernet switch as my PCB (with a network cable), then I get the correct MAC address through that connection. Can anyone explain what is going on here? Is it natural that an access point overrides the MAC addresses of the connected devices? Could there be some obscure setting that I need to change? Or is there something wrong with the access point? Any help will be greatly appreciated.