Re: how to detect MAC address

Discussion in 'Java' started by Rene, Jun 28, 2003.

  1. Rene

    Rene Guest

    Sudsy <> wrote:
    > I'm amazed by how many times this topic arises. I can only surmise
    > that people are trying to use the MAC address for some licensing
    > scheme. I almost hate to tell them that there are ethernet cards
    > out there which allow you to reconfigure the MAC address. As long

    Well that's a driver / software thingie. Almost any card can do it.
    Actually, I've never seen one that couldn't do it.

    It is just that the rumor that the MAC addresses are unique and
    unchangeable without an eprom burner still floats around.

    But that is simply wrong.

    The MAC address *is* set statically in a NIC, so much is true. It is
    further true that in most cases the MAC address can only be changed by
    exchanging the eeprom. However, the MAC address is only read out of the
    card once at boot time (or rather, the time when the NICs driver starts and
    initializes the card) and then the MAC address is stored in memory in the
    OS network driver.

    The driver puts together data packets, not the NIC, the NIC has to bring
    the data on the wire, but the OS "fills in" the data into the frame. So its
    a pure driver thing. All you need is a driver which allows you to override
    the default value that is provided by the NICs eeprom.

    And most drivers do, since without that feature, you couldn't do failover
    and other high-availability functions.

    > as you don't have more than one machine on the LAN segment with
    > the same MAC then you don't have a problem with routing.

    You can always override the value and create a collision by hand. There are
    some very specific and rare cases where it makes sense to do so. Generally
    its a very bad thing. But it can be done. You shouldn't though, unless you
    know exactly what you do.

    The bottom line for everyone else is: Trusting on a static never changing
    MAC address is no more secure than trusting on a static, never changing IP
    address. (there are people around who tell you to configure a firewall to
    filter on MAC address instead of IP addresses, since MAC addresses are
    static. This is very untrue)



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    Rene, Jun 28, 2003
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