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I have a "black-box device" (a credit card reader, to which some klutz lost the admin unlock card...) running an unknown, but primitive, operative system. I need to find it's MAC address.

At my disposal, I have the device itself (but no access to its admin interface), a computer running Ubuntu 12.04 (where I have full sudo rights), and a regular ethernet cable. If necessary, I can probably shake up an ethernet switch, too.

How do I go about to find the MAC address of the card reader?

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2 Answers 2

up vote 1 down vote accepted

By the help of a friend, I now resolved this! =) This is what I did:

  1. Install Wireshark, which is available in the software repositories: sudo apt-get install wireshark

  2. Start the program with root permissions: sudo wireshark

  3. Start capturing on the eth0 device (piece of cake - click the button on the top left of the interface, select the device in the dialog and click OK).

  4. Connect the "black-box device" and turn it on. The devices will send a large amount of packages back and forth trying to establish a connection. Wireshark will capture them all.

  5. Find a packet originating from the "black-box device". Wireshark displays the originating MAC address. Voila!

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If it does connect, nmap can perform a scan.

sudo nmap -PN

Also, more obscurely, if the device has a serial port you may get it to spill its guts on boot, and this might reveal static ip details as well.

Granted, this requires a cable, and guessing or obtaining the protocol attributes.

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