IP Conflict?

  • I have a Windows 2000 network running Windows 2003 Domain Controllers, for which we run a DHCP scope on.


    We have laptops configured to DHCP only but they are always receiving 'dummy' IP Conflicts. I say they are 'dummy' for 2 reasons:


    1) It doesn't disconnect you from anything
    2) Is it even possible?


    Any advise? These are random machines.

  • Ip conflicts can only happen if something on the network has a fixed address. If ANY equipment (routers, wireless access points or range extenders, printers) has a fixed IP it must be outside the range of the dhcp pool. Also set policies blocking users from setting their IP addresses, a lot of users have a habit of changing their addresses in an attempt to access blocked sites (gaming or chat) or to hide their identity when browsing particular sites. It does not help them, but this is a far wider problem then anyone would imagine.

  • An IP conflict would not disconnect your system from the network as it means that there are two (or more) systems with the same IP address on your subnet. What can happen is that transfers between the machines are very slow, or fail unexpectedly. You can also have long connection times between systems. It can also possibly mess up your network's internal router's routing table depending on how you have your internal network set up.


    It is easily possible to have an IP conflict. For DHCP to properly work you have to have all systems that do not have statically assigned IP addresses using your DHCP server. If someone with a laptop that has a statically-assigned IP address plugs into your network, then it could easily conflict with a dynamically assigned address. This is because the DHCP server will only really know about the addresses that it managaes from its address pool.


    Ways around this are to reserve IP addresses for known laptops from the DCHP server's dynamic pool. That way, a laptop ends up with a certain set IP address each time it connects.


    It does not cancel out that laptops brought in from outside the network could still cause a conflict. One way to get around that is to use MAC address filtering on your routers so that only know laptops can access your network. That way, if someone just jacks into your network they'll get no connection or access to anywhere. They would then have to request access to the network, you would allows their laptop's MAC address and it would then run from the DHCP server.

  • Had the same problem. The easiest way to solve it is fixed IP on the clients. Has to do with the server DHCP pool refresh rate versus client demand rate and number of allocated addresses in the pool.

  • ukman_2001_uk,
    Are you the administrator of the Windows Server 2003 Domain Controllers?
    Perhaps you could consider these steps:
    1.) How many Domain Controllers in your domain, and which Domain Controllers that take care of the DHCP? For simplicity, it should be only one Domain Controller that runs the DHCP; if not it'll take more time to locate the source of this "dummy IP" conflict you have.
    2.) Have you check every laptops and computers (their TCP/IP v4) that connect to the domain? Again for simplicity, you should click the radio button of "Obtain IP address automatically" & "Obtain DNS address automatically".


    My best guess is that there is/are machine(s) using same IP address assign to them manually in it's/their TCP/IP v4 setting, or the DHCP server assigns an IP address (automatically) and another machine is using that same IP address (manually).
    It'll take a while for you or the IT administrator to check each and every machines that connect to the domain for these "dummy-IP(s)". But better do it right away than waiting something went wrong and costs you more...
    Maybe someone in your network have modify their TCP/IP settings when they tried to connect to another networks, and they forgot to click the "Obtain IP address automatically" radio button.
    Cheers and good luck!

  • Step to solve:
    1. disable and enable network card
    2. enable network card, then use command promt "ipconfig /release" and "ipconfig /renew"

  • Quote from christy

    Ip conflicts can only happen if something on the network has a fixed address. If ANY equipment (routers, wireless access points or range extenders, printers) has a fixed IP it must be outside the range of the dhcp pool. Also set policies blocking users from setting their IP addresses, a lot of users have a habit of changing their addresses in an attempt to access blocked sites (gaming or chat) or to hide their identity when browsing particular sites. It does not help them, but this is a far wider problem then anyone would imagine.


    Hi,
    I agreed with Christy. You can resolve the problem by removing all the cookies and set a fixed ip.