MAC address not unique to device

[asicguy]

I realize how a MAC address works in terms of each device connected to a network has a unique MAC address that is associated with the device from it's manufacturer.

What I am seeing on my ASUS router is that three devices are sharing the same MAC address, the GUI even highlights a number icon to indicate that multiple devices are being used on the same MAC address that is listed.

The MAC address is for the RT-AC56U router. The other two devices are an iPhone and a gaming computer.

I should add that the other two devices aren't showing up in the client table.

How is this possible? I thought the source MAC address was embedded in the ethernet frame. If I'm setting parent access for the 'real' MAC address associated with the device, will the device pass through the router because it's being associated with this other MAC address?

 

[bill001g]

It may be related to a repeater/extender. These use WDS which uses a single mac address of the repeater for encryption and then passes the other mac addresses in a field for WDS.

If the devices connect directly via wireless the mac is used as part of the encryption key so it is very difficult for multiple devices to have the same mac.

Still a mac is not unique in any way. The manufactures only have a limited..but huge..number. They reuse the mac addresses but it would be highly unlikely you get 2 devices with the same mac. In a large corporation that buys 50,000 of the same laptop the odds get pretty good you get a duplicate.

Even then the mac is just a value sent in the hardware. The mac that is embedded in packets is set by software. Almost every ethernet nic driver had the ability to change the mac to anything you want. A few wireless nics have this ability also. Under linux based systems it is trivial to set the mac to anything you please.

 

[asicguy]

Yeah, I have less than ten devices, and the MACs are mutually exclusive when I inspect them manually.

I do have a repeater attached. What's odd is that it doesn't show in the network map, I have to assign a static ip address to it and connect to it directly.

I can't picture how a repeater would affect or merge the MAC value. Isn't there a source MAC address in the ethernet packet?

 

[bill001g]

There is but I forget exactly how WDS works. I know it copies the mac into a different field in the wireless header. To work the router obviously has to copy the value back into the real packet before it would send it to say a lan attached device since that header does not exist in ethernet.

I suspect this is one of those strange display problems...since technically there is no way devices can share a mac other than with a NAT router and even if they did how would the router know they did it.

 

[asicguy]

There is but I forget exactly how WDS works. I know it copies the mac into a different field in the wireless header. To work the router obviously has to copy the value back into the real packet before it would send it to say a lan attached device since that header does not exist in ethernet.

I suspect this is one of those strange display problems...since technically there is no way devices can share a mac other than with a NAT router and even if they did how would the router know they did it.

 

[asicguy]

I'll look into WDS a bit more. I have a lot of patents at the PHY layer, but not familiar with anything above that.