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i wanna know how exactly the kernel changes the mac address on the hardware. does it take the mac adress from the user then instruct the hardware to change the ...
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  1. #1
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    change in mac address


    i wanna know how exactly the kernel changes the mac address on the hardware.
    does it take the mac adress from the user then instruct the hardware to change the mac address on it..
    or mac address is purely a software thing as seen by the L2 and is just a matter of changing the mac address value on the ifconfig

  2. #2
    Administrator jayd512's Avatar
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    Hello and Welcome!

    The MAC address would typically be part of a sub-layer of the physical layer of the TCP/IP stack. That would be level 1.
    It is pretty much burned into the ROM of the NIC or wireless card (or whatever you are using) and then the information is loaded to RAM when the OS boots.
    The interactions that follow (concerning the upper model layers of TCP/IP) can be followed in any literature found in the library or online.

    Why do you ask?
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    my doubt is that if the mac address is something that is burned on the NIC, how are we able to change it using "ifconfig hw ether xxx"

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    Administrator jayd512's Avatar
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    You'll never be able to change the MAC that a piece of hardware uses.
    You may be able to spoof it, and the how-to for that can be found in several sources (CCNA or MCSE guides... MAC Address Spoofing).
    The NIC will always associate itself with the MAC that is burned into the ROM of the device... ifconfig hw ether xxx only tells the OS what to do...
    The ROM on a NIC or wireless card can't actually be over-written.

    Period.
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  6. #5
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    hi, jayd512

    thanks, that was quite helpful but my doubt still remains.
    so i change the mac using ifconfig. now the OS knows the changed mac but the NIC hardware knows its original (burned) mac. obviously the OS will reply to ARP requests with the changed mac.
    so how does the NIC recieve frames from now

  7. #6
    Administrator jayd512's Avatar
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    I'm hesitant to try to explain it online for fear of mucking up the explanation

    But take a look at levels 1 & 2 of the OSI model. These are the Physical and Data Link layers, respectively. Layer 3, however (Network), plays a hand in this as well.

    Look through the Wikipedia page, and check some of the sources at the end... Most of your detailed information, though, is going to come from something like a CCNA reference guide... especially the chapters dealing with the OSI models.


    *EDIT*

    This may help as well...MAC address - Wikipedia, the free encyclopedia
    Last edited by jayd512; 10-15-2010 at 04:26 PM.
    Jay

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