Technical Cable Modem Q

Discussion in 'The Barracks' started by Fox, Feb 24, 2003.

  1. Derelict

    Derelict Retired Administrator

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    DHCP IP allocations are based off MAC addresses of a particular network adapter trying to access the network.

    The cable modem has a MAC address just as your network card has. Your reinstall wouldn't have changed the MAC address - as it's hardcoded into a ROM chip.

    Basically the DHCP server at the Optus end had previously registered your MAC address from the cable modem and when the same MAC address asked the server for an IP address, since the lease was still valid for the server, then the server just tells the modem the same IP as it previously had before and off it goes.

    For the server, all that happened was the cable modem was off the network for a few hours, nothing more.
     
  2. Hethrir

    Hethrir Getting Started

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    I get that, it's just that Fox said that for some reason the driver re-install gave him a new IP address :? So i re-install windows and tried it for myself...
     
  3. SnakeTails

    SnakeTails Well-Known Member

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    Ok Derelict, explain this one.

    I know its DHCP allocation off MAC addresses and all that... but how do you get 1 IP address with 1 version of Linux, then another IP address with another version, then back again when the original is rebooted.....

    Which MAC address?

    MAC of the firewall Network card
    MAC of the cable modem?

    The MAC of the network card can be easily changed, but for the cable modem, the configs are accessable from the cable side of the network, not the UTP (Ether) side
     
  4. Warbear.Prime

    Warbear.Prime Well-Known Member

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    It does it because on a standard Network the MAC adress is correct as derelict says for addressing, but on the broadband connection the MAC address is not used, simply because of the size of the network. So it has a "pool" of IP addresses it uses, and assignes them by account, which is connected to a combination of things like machine name, router it is off, type of network card AND the mac address - which it randomly assigns and IP to.

    If you want to change the IP, plug it into a different nic, with dhcp enabled and get an IP - it will be different. Go back to the original card, and it will change to another IP again (unless you get unlucky).

    I do this to avoid people that ban my IP.
     
  5. Hethrir

    Hethrir Getting Started

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    ...and this happens on a regular basis :p
     
  6. Warbear.Prime

    Warbear.Prime Well-Known Member

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    Not as often as people would think!
     

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