Thread: MAC addresses

  1. #1
    & the hat of GPL slaying Thantos's Avatar
    Join Date
    Sep 2001

    MAC addresses

    Ok bare with me, I'm having an idea that came to me while I was trying to fall asleep.

    My router displays the mac addresses for all the computers that it provides DHCP services to. I would like to know how it does that.

    Reason: A lot of messageboards I go to are limited to banning people by username and then IP address. Since IP address banning will likely result in someone else getting affected also its a not so nice approach. But if we could ban the MAC address then all would be good (until they got a new card).

    This of course requires that each device has a completly unquie mac address which IIRC is the case.

    Quick search of this forum and google didn't come up with anything. I'll try again once I wake up.

    But if any of you know a way please let me know. Thanks

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    As far as I know, the MAC addresses are only obtainable at both ends of the same piece of wire.
    If you have and on the same LAN, then it's the MAC addresses of those two machines which tells them apart.

    Once you go through any kind of hub or switch to a different network segment, the routing of messages is done by IP.

    > A lot of messageboards I go to are limited to banning people by username and then IP address
    So use authenticated email addresses.
    You can only post if you give a valid address and return the cookie back to the website to complete your registration.
    Then you exclude all the free hotmail / yahoo's of the world as being valid.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Yes, my avatar is stolen anonytmouse's Avatar
    Join Date
    Dec 2002
    Consider the internet as a series of ethernet networks for a second.

    I want to send a packet to []

    My computer sees the address is not on its subnet.

    So it sends it to the gateway.
    -->The from mac address is my computer.
    -->The to mac address is the gateway.

    The gateway(typically a home router or a router at the ISP) sees that the packet is not on its subnet so routes it (sends it to a node closer to
    -->The from mac address is the gateway.
    -->The to mac address is the destination node mac address.

    and so on until we reach

    Of course the internet is not all ethernet networks. It can run on many underlying communication infrastructures. The internet routers must understand IP addresses and therefore do not need a mac address equivalent.

    Imagine if tracking of mac addresses by internet sites was possible. An web ad company can track wherever you go over a period of several years!

    >>Then you exclude all the free hotmail / yahoo's of the world as being valid.<<

    What if you don't have anything else?

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