Access point changes my device's MAC address

[ErikT 1]

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.

[DelphiUdIT 275]

 

This is in Italian, you must go in "Settings/Networks an Internet", there is a "casual hardware address" setting ... if it is set I think that for every connection Windows generate a new MAC ...

[Brian Evans 138]

It is your device changing its own MAC address not the access point. It is meant as a privacy feature to prevent easy tracking of user devices. 

 

Windows 10/11 : How to use random hardware addresses in Windows - Microsoft Support

 

On second thought - it looks like the access point is setup as a router not an ethernet bridge. That means packets all come from the router as it routes / passes on IP packets not ethernet frames.  

Edited February 29, 2024 by Brian Evans

[ErikT 1]

@DelphiUdIT

Thanks, but I am not quite sure what I am looking at.

[ErikT 1]

@Brian Evans

Yes, sounds plausible. A very good guess. Thank you for that!

I think I'll write to the manufacturer of the access point and ask what is going on, and if there is a way to make it behave.

 

My device is definitely not changing its MAC address by itself, as the firmware isn't designed to do that.

Edited February 29, 2024 by ErikT

[Attila Kovacs 695]

turn on WDS

[ErikT 1]

@Attila Kovacs

Thanks, but I have no idea how to do that in the Sagecom router that I have. Cannot find any menu item like that.

 

However, it won't really make a difference, because if this can happen at my place, then it can happen at the customers as well. So even if I do get it solved here, it won't be a general solution.

I will just have to use a different method to identify the devices.