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I have a Thunderbolt to Ethernet adapter for a Macbook Air and I need to assign a static IP address to it.

I assume the MAC address is embedded in a given adapter... and by convention I would assume that the MAC address would be written somewhere on the device, but it is not. Does the MAC address have more to do with the adapter of the MAC itself?

In other words if I swap adapters will the MAC address change, or will it stay the same? What if I swap thunderbolt ports it's plugged into (for Macbook Pro Retna)?

Does the same logic above apply to Thunderbolt displays since they have Ethernet?

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up vote 6 down vote accepted

The MAC Address is unique and a property of the actual network hardware (although it can be spoofed). So your adapter has its own MAC address, as does the the network interface in a Thunderbolt display, and the Wi-Fi in your MacBook Air.

Different Thunderbolt to Ethernet adapters will have different MAC addresses, but moving one between different ports won't change it.

You can view the MAC address of any network interface attached to your Mac by using Network Utility, which you'll find in the Utilities folder within your Applications folder. It calls it a Hardware Address, but it's the same thing.

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On a rMBP 11.3 (Mid 2014) with 2 Thunderbolt ports and yet no Thunderbolt/Ethernet adapter connected, querying ifconfig returns en0 (Airport) and en1 (Thunderbolt, MAC address ending in …e0) and en2 (Thunderbolt, MAC …:e1). Am not sure whether these MAC addresses are generic placeholder numbers -- googling them found 0 results, indicating that they are likely unique or no-one discussed this generic MAC address scheme yet -- or the actual MAC addresses, and wether dongles have their own address & wether the network device intelligence resides in the dongle or the Thunderbolt controller. – porg Feb 25 '15 at 8:59

If you connect the Thunderbolt-Ethernet adapter and connect an ethernet cable, the MAC address immediately appears in the Network -> Advanced -> Hardware tab.

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I looked into it further, and the mac address from the System Information is not the mac address that is used by the ethernet dongle.

  1. MacHD > Applications > Utilities >
  2. ifconfig -a
  3. look for bridge0, that is the mac address of your dongle.


You can also access by going to

  1. apple menu (top left) > About This Mac
  2. Click on "More Info..."
  3. Click on "System Information"
  4. Under Hardware look for Ethernet Cards
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