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Old 23rd October 2007, 06:37 PM
philp Offline
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Join Date: Aug 2006
Posts: 23
MAC address directly from network card

I would very much like to obtain the raw MAC address directly from the network card. I know the MAC address can be changed on Fedora, but I would like to read the MAC address directly from the ethernet card. It obviously does this at boot time, but is it at all possible to read it at run-time. I was trying to use the MAC address as a form of restriction to stop programs from being run on more then the one PC, but then I found out the MAC address can easily be changed and so it could easily be defeated. Is it possible to access the MAC address directly from the ethernet card?

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Old 23rd October 2007, 08:27 PM
stevea Offline
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Join Date: Apr 2006
Location: Ohio, USA
Posts: 9,069
Typically the interface hardware gets the original MAC from a
tiny eeprom, and often the sofware can read (and with difficulty
wrte) the eeprom. It;s also possible to change the MAC from
the driver software like ...
ip link set dev eth0 address 42:42:42:42:42:42

The original remains in the eeprom, but at no regular location.
This one has the original MAC at offset 0, but it's chipset
dependent. [00 0d 60 fd 8c 77].

[root@nidula ~]# ethtool -e eth0
Offset Values
------ ------
0x0000 00 0d 60 fd 8c 77 00 0b ff ff ff ff ff ff ff ff
0x0010 00 00 00 00 0b 66 49 05 14 10 1e 10 86 80 a5 b1
0x0020 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
0x0030 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
0x0040 cf 00 61 78 0b 14 00 00 c8 04 ff ff ff ff ff ff
0x0050 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 02 06
0x0060 2c 01 00 40 11 12 ff ff ff ff ff ff ff ff ff ff
0x0070 ff ff ff ff ff ff ff ff ff ff ff ff ff ff 05 c0
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Old 24th October 2007, 09:35 AM
philp Offline
Registered User
Join Date: Aug 2006
Posts: 23
Thanks for that. It's what I half expected. So I presume that the ethernets device driver reads the MAC address from a device specific location on the card and somehow passes that to the kernel which then stores it away somewhere. There is no means (ioctl or whatever) of interfacing directly to the device driver to read the eeprom (I appreciate that even then it can be defeated by modifying the eeprom, but I'm hoping that would be more difficult then simply using the ip command)?

Thanks for your help
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address, card, directly, mac, network

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