LAN Card Lunacy - MAC id changing by itself

Discussion in 'Hardware Q&A' started by kumarmohit, Apr 30, 2006.

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  1. kumarmohit

    kumarmohit New Member

    May 23, 2005
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    OK Guyz

    I have a Realtek RTL 8139/810x Family Fast Ethernet NIC (DLink make).
    besides that I have SUSELinux 10.0, WinXP Home SP2 and Win 98 installed so a tripple boot PC.

    The LAN CArd has gone crazy and every time is start my PC it reports different MAC id.

    The WinXP is configured to access internet thru SIfy services. As all sify users know that sify has IP Macid binding so every time I want login the net I have to call sify ppl to release MAC so that I can login

    As far as I know MAC id is stored in ROM and can therefore not change by itself am I wrong in this regard and can any one give me any idea why does the mac id change by itself and is there any way I can force sify server to believe that I have not changed LANcard or anything else and save me of the trouble of calling them every time i try to login
  2. mod-the-pc

    mod-the-pc Back to School Mr. Bean !

    Apr 1, 2004
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    Try this From

    Changing MAC addresses

    Although physical MAC addresses are permanent by design, several mechanisms allow modification, or "spoofing", of the MAC address that is reported by the operating system. This can be useful for privacy reasons, for instance when connecting to a Wi-Fi hotspot, or to ensure interoperability. Some internet service providers bind their service to a specific MAC address; if the user then changes their network card or intends to install a router, the service won't work anymore. Changing the MAC address of the new interface will solve the problem. Similarly, some software licenses are bound to a specific MAC address. Changing the MAC address in this way is not permanent: after a reboot, it will revert to the MAC address physically stored in the card.

    As a MAC address can be changed, it can be unwise to rely on this as a single method of authentication. IEEE 802.1x is an emerging standard better suited to authenticating devices at a low level.


    Under Linux, the MAC address of a Network Interface Card (NIC) can be changed by doing the following: (You must be root in order for this to work)

    /etc/init.d/networking stop
    ifconfig eth0 hw ether 02:01:02:03:04:08
    /etc/init.d/networking start

    NOTE: You cannot do this if using a DSL modem.

    In Red Hat Linux and other similar systems (Fedora Core, etc) an easy way to make it "permanent" across reboots is to just add a variable like this to your ifcfg-eth0 or similar file:


    (upper or lower case on the MAC address are fine, because the network function does a "toupper" on it)

    and service network restart for prompt results.


    Under Windows XP, the MAC address can be changed in the Ethernet adapter's Properties menu, in the Advanced tab, as "MAC Address", "Locally Administered Address", "Ethernet Address" or "Network Address". The exact name depends on the Ethernet driver used; not all drivers support changing the MAC address in this way.

    However, a better solution - requiring Administrative User Rights - is to pass over the System Registry Keys under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}. Here settings for each network interface can be found. The contents of the string value called 'NetworkAddress' will be used to set the MAC address of the adapter when next it is enabled. Resetting the adapter can be accomplished in script with the freely available command line utility devcon from Microsoft, or from the adapters context menu in the Network Connections control panel applet.

    There is a nice tool to change the MAC address for all cards (even those that can't be changed through the adapter's Properties menu): SMAC MAC Address Changer

    Note: to check your MAC address easily on a Windows XP box, go to Run, type CMD, then type "ipconfig /all" without quotation in the command prompt. The number under physical address is the MAC address. If multiple IP are displayed, you should look under the label "Ethernet adapter x", where x is the name of your connection (which is Local Area Connection by default).
    Last edited: May 2, 2006
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