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  • Need help with DHCP Configuration

    Our company was recently split in half to form two smaller ones. Our domain however was never changed.

    Now, as is always the case, politics have started to create a rift between the two new companies and we want to prepare for an inevitable split. In order for us to do this, we've decided to create two completely separate domains and create a trust between them so that cross company file access is still possible.


    Creating the new domains will be simple, however, the problem lies in our networks IP range. What we would like to do is have a single DHCP server on Domain A. As this domain broadcasts across the entire network, Domain B should have no trouble getting IP leases from the server.

    The problem we have however is in the configuration of the DHCP server.

    What we thought we would do is have three Scope's, one for unclassified PC's (i.e visitor's laptops connecting to the network), one for Domain A and a third for Domain B

    The unclassified scope would be from 192.168.0.1 - 192.168.0.255
    The scope for Domain A would be from 192.168.1.1 - 192.168.2.255
    The scope for Domain B would be from 192.168.3.1 - 192.168.4.255

    We would then use exclusion ranges for Domain A/B's entire scope and use reservations for the PC's on Domain A/B. This is so that PC's we've identified would have the correct DNS settings configured in the Scope Options...

    Does this sound viable?

    The problem I'm having is that when I try creating a second scope using the same subnet as the first (255.255.0.0) but a different IP range, it tells me that there's a conflict...

    So, I'm a bit stuck now and was wondering if anybody could offer me some wisdom Smile

    Cheers
    Niels

  • #2
    Re: Need help with DHCP Configuration

    Did you check with the DHCP server IP first?

    There may be a possibility that your DHCP's ip comes into that range.

    Comment


    • #3
      Re: Need help with DHCP Configuration

      Yes- my DHCP's server IP is 192.168.10.100

      I still get the message 'The address range and mask conflict with an existing scope.'

      The Subnet mask we use throughout the company is currently 255.255.0.0

      Our servers are in the x.x.10.x range
      Our Workstations are currently in the x.x.0.x - x.x.4.x range using a single scope (this is because we currently only have the one domain to manage)

      Because of the two domain plan on the same network, we'll need to get two scopes so that the correct PC's on DOMAIN A get the correct DNS settings from the DHCP SCOPE A options. Likewise for DOMAIN B

      Any more ideas?

      Cheers
      Niels

      Comment


      • #4
        Re: Need help with DHCP Configuration

        Ok, let us give another try.

        Try to give the IP range from 1 to 254.

        Norbert.

        Comment


        • #5
          Re: Need help with DHCP Configuration

          you need to start subnetting.
          Also see this topic:
          http://forums.petri.com/showthread.php?t=20176

          Most of you're questions is already answered over there. If you have any questions left, please feel free to ask.
          Marcel
          Technical Consultant
          Netherlands
          http://www.phetios.com
          http://blog.nessus.nl

          MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
          "No matter how secure, there is always the human factor."

          "Enjoy life today, tomorrow may never come."
          "If you're going through hell, keep going. ~Winston Churchill"

          Comment


          • #6
            Re: Need help with DHCP Configuration

            But after Subnetting I think we need a Router to connect the two domains. Without subnetting wont that Scope work?

            Comment


            • #7
              Re: Need help with DHCP Configuration

              Because your subnet mask is 255.255.0.0 your network address is 192.168.0.0 so anything 192.168.x.x is in the same network and therefore in the same scope. To make it work with your current subnet you will need to create one scope and create reservations for each computer on each domain. This might not work if the computers from domain a and b need to use different DNS servers as I don't know if it's possible to specify multiple values for DHCP option 15 (DNS Domain Name). You may be forced to subnet the 192.168.0.0 as stated previously and then you would need to use a router or layer 3 switch to route traffic from one subnet to another.

              Comment


              • #8
                Re: Need help with DHCP Configuration

                norbert.ranjith:

                As joeqwerty said, all the scopes mentioned by "thesixuk" seems to be in different subnet but due to 255.255.0.0 mask they are in the same subnet.

                In DHCP we can not create multiple scopes for same subnet.

                Regards,
                Kapil Sharma
                ~~~~~~~~~~~~~
                Life is too short, Enjoy It.

                Comment


                • #9
                  Re: Need help with DHCP Configuration

                  Originally posted by norbert.ranjith View Post
                  But after Subnetting I think we need a Router to connect the two domains. Without subnetting wont that Scope work?
                  If you start subnetting then you have to setup some kind of routing and dhcp helpers. It can be a router but it's also possible with layer 3 switches.

                  It's not possible to create multiple DHCP scopes within the same subnet.
                  So if thesixuk want's to create multiple DHCP scopes, he has some choices.
                  Start subnetting the /16 to smaller networks or use network ranges outside the current subnet, eq 17.16.x.x /16 subnet.

                  This example directly shows my personal dislike to use large networkscopes when you don't need them.

                  It's silly to use a /16 subnet if you have only has a need for example 200 or even 500 ip addresses.
                  Marcel
                  Technical Consultant
                  Netherlands
                  http://www.phetios.com
                  http://blog.nessus.nl

                  MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                  "No matter how secure, there is always the human factor."

                  "Enjoy life today, tomorrow may never come."
                  "If you're going through hell, keep going. ~Winston Churchill"

                  Comment


                  • #10
                    Re: Need help with DHCP Configuration

                    The problem we have is that if we use subnetting then our servers on the 192.168.10.x range wont be able to communicate with the clients without a router.

                    My Subnetting skills are also a little weak and while I can use various online subnet calculators to work out the subnet for 254 hosts (the range for the unclassified PC's). I cant figure out the subnet needed for the two domain scopes.

                    Are there any other options?

                    Niels

                    Comment


                    • #11
                      Re: Need help with DHCP Configuration

                      Don't you have layer 3 devices?
                      Learn to subnet is quite critical.
                      Marcel
                      Technical Consultant
                      Netherlands
                      http://www.phetios.com
                      http://blog.nessus.nl

                      MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                      "No matter how secure, there is always the human factor."

                      "Enjoy life today, tomorrow may never come."
                      "If you're going through hell, keep going. ~Winston Churchill"

                      Comment


                      • #12
                        Re: Need help with DHCP Configuration

                        The easy way to subnet this network would be to use a 255.255.255.0 mask which would create 192.168.x.0 subnets (192.168.1.0, 192.168.2.0, etc.). You would need to use a router to route traffic between the subnets. You could use a "router on a stick" or use a layer 3 switch.

                        Comment

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