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Continued DHCP Headache...

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  • Continued DHCP Headache...

    I'm having the strangest DHCP problem and it's driving me mad!!

    I have two domains located on the same network segment.

    Domain1 is an NT 4.0 domain - let's call the domain ABC.
    Domain2 is a Windows Server 2003 domain - let's call it abc123.local.

    There is a two-way trust between the domains.

    Each domain now has a DHCP server. The DHCP server in domain ABC serves a scope of 10.1.4.x while the DHCP server in domain abc123.local serves the scope 10.1.8.x.

    The NT domain, ABC, is really the domain with active users. I'm in the middle of a domain migration project and I'm still just testing things on the Windows Server 2003 domain.

    Users logging into the NT domain may get either a 10.1.4.x or a 10.1.8.x IP address depending on which DHCP server responds first.

    The problem is this:

    I'm testing 2 computers on the Windows Server 2003 domain. When I boot these computers, they both will USUALLY come up with an APIPA address. Usually, but not always. Sometimes they get a 10.1.8.x IP address as I would expect.

    Maybe 80% of the time, they boot with an APIPA address. If I run a packet trace on these machines while in this state, I see DHCP Discover packets going out at about 5 minute intervals (this is how DHCP should behave) but I see no other DHCP packets (no Offer, Request, ACK packets). All of this leads me to believe that the computer cannot find a DHCP server. That would make sense except for the fact that after a few reboots it generally DOES find a DHCP server and it gets an IP address.

    The network setup is very simple. Cabling runs from each office into a patch panel in the server room and then into a series of Bay Networks switches. The cabling from the servers runs directly into the same switches.

    I cannot seem to find anything that sheds light on this subject. Anyone with insight into this problem will have my eternal gratitude!!


  • #2
    Re: Continued DHCP Headache...

    You cant use two DHCP servers in the same network. Please create a seperate VLAN to each network & connect then with layer 3 switch (Thats block DHCP traffic). You can use also other products to block the DHCP broadcast from one side to another - but the best way is to create unique segment to each domain.


    Best Regards,

    Yuval Sinay

    LinkedIn:, Blog:


    • #3
      Re: Continued DHCP Headache...

      Hi Yuval,

      Thanks for your reply.

      I should mention that the second DHCP server (scope = 10.1.8.x) is a very recent addition. I only added it last week in an attempt to solve the problem. Someone on this forum in a previous post suggested this course of action.

      The 2nd DHCP server doesn't actually seem to be causing any problems in general.

      My servers all have static 10.1.1.x addresses.
      My NT 4.0 DHCP server gives out 10.1.4.x addresses.
      And the new Windows Server 2003 DHCP server gives out 10.1.8.x addresses.

      The only routers I have in place are:

      1. A Cisco router that connects us to the internet (outside of the firewall)
      2. A multihomed NT server with 2 NICs that acts as a router and sits just inside our firewall.

      The bottom line is that the DHCP problem predates the second DHCP server.

      I should perhaps clarify. Our NT domain is functioning properly. I also have my Windows Server 2003 domain running on the same cabling system. It's only when I began testing machines to connect to this new domain that I began experiencing problems.

      The only machines that have any DHCP problem are machines that have the Windows Server 2003 domain specified as their computer's domain.

      The really strange thing is that it doesn't happen all of the time. Sometimes when I boot the machines they contact the DHCP server and get their address with no problem. At other times, they don't and I get an APIPA address.

      I can find no reason why this is sometimes the case. It's really maddening!

      Thanks for your help!!


      • #4
        Re: Continued DHCP Headache...

        You need to add the NT4 scope range into Windows Server 2003 DHCP and viceverse. Add the 2003 scope range into NT4 DHCP Server to provide redundant DHCP service for all client computers on both subnets.