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PUZZLED: Multiple DHCP

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  • PUZZLED: Multiple DHCP

    Hi Guys,

    Had a look around and cant find a specific answer so hoping someone can help

    We are in the process of a network change.

    At the moment we have an old network 192.168.0 \24. We ran out of addresses about 6 months ago so added a second scope 192.168.1\24.

    We now wish to move to a new network, breaking it up into Vlans, and having one scope per vlan.

    e.g. vlan 101 will have the scope of 10.20.101/24.
    vlan 102 will have the scope of 10.20.102/24 and so on.

    The Vlans are setup on new cisco switches, and have the IP helper set to the IP address of our windows dhcp server which is on the old network with a 192.168 address.

    Both the 192.168.and 10.20 networks can see and talk to each other as we are using a sonicwall nsa (firewall) that sits between them and allows them to talk.

    The DHCP server, has multiple scopes setup within a superscope for the new VLANs i.e. 10.20.101/24, 10.20.102/24 as well as the old 192.168.0/24 & 192.168.1/24 scopes.

    If I plug into a switch that is on the 10.20 side and configured to say VLAN 101 then I succesfully get an IP address of 10.20.101.4 (I've excluded 10.20.101.1 - .4).

    The problem I have is that the old network, which the majority of my company still sits on, when a client looks for a lease (when plugged into an old switch) it somehow gets leases from the wrong scope i.e. 10.20.101/24. When it needs to get a lease from one of the 192.168 scopes.

    Please can someone give me a few pointers to check !? My understanding is the lease allocation is decided by the gateway IP that the request comes from?! I cannot for the life of me figure out why leases are going into the wrong scope!

    PLEASE HELP

    Thanks
    Dom

  • #2
    Re: PUZZLED: Multiple DHCP

    Note: If you've excluded 10.20.101.1-4, then you shouldn't get 10.20.101.4 from DHCP
    ** Remember to give credit where credit is due and leave reputation points where appropriate **

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    • #3
      Re: PUZZLED: Multiple DHCP

      Create 2 seperate broadcast domains.

      Comment


      • #4
        Re: PUZZLED: Multiple DHCP

        Thanks wullieb1, is that basically the same as creating a new Superscope !?

        Apologies if not, but can you explain a bit more - thanks in advance

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        • #5
          Re: PUZZLED: Multiple DHCP

          Would Option 28 help me out here at all ?! Does that help tie up the range to issue a lease from with the requesting device ?

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          • #6
            Re: PUZZLED: Multiple DHCP

            No.

            Read this for more info on SuperScopes

            http://technet.microsoft.com/en-us/l...14(WS.10).aspx

            I think you need to explain in better detail exactly what it is that you want to achieve.

            From my understanding you want a specific set of machines to get a set of IP details relevant to that network.

            So lets break it down.

            Subnet A is 10.20.101.x and Subnet B is 192.168.0.x

            All PC's on subnet B should get a 192.168.0.x address and subnet A should get a 10.20.101.x address. Is this correct???

            You mention you have VLAN's setup. How are they configured and have you used the IPHELPER command to forward DHCP requests to the server??

            As you know DHCP will not pass over a router, broadcast domain, so what in effect you need to do is create 2 separate broadcast domains inside your router. This can be achieved using VLAN's on a layer 3 switch and setting the correct IP details.

            Ultimately though we will need more information from you on your current setup and requirements before we can go any further.

            Comment


            • #7
              Re: PUZZLED: Multiple DHCP

              I have multiple subnets, but best if I refer to one batch of subnets as the new network and one batch as the old.

              The New Network is going to be 10.20.x.x each subnet will be /24 but the thrid octet will be defined by the VLAN it is in. For example VLAN 101 will have leases 10.20.101.1 - 10.20.101.254. Vlan 51 will have 10.20.51.1 - 10.20.51.254.

              Each Vlan has been setup, with the IP details and the IP helper pointing towards our 1 dhcp server (192.168.0.4)

              The same DHCP server also manages requests from what I will refer to as our old network. This has 2 scopes within a Super Scope of 192.168.0/24 and 192.168.1/24.

              A Sonicwall NSA 5000 sits between the two networks which is also our firewall. (note, this is not our DHCP server).

              I've setup a couple of scopes for our new network, and this works fine. Clients I plug into the switches with the relevent VLAN's pickup 10.20.101.x addresses, and can see clients on the 192.168 network and viceversa, clients on the 192.168 network can see clients on the 10.20 network.

              My problem - Some clients that are plugged into the old network somehow are getting addresses from the 10.20. range, despite not being in any VLAN. Basically it looks like they go across to the dhcp server and that randomly chooses a scope to issue a lease from - I do not want this, I want the old network to stick with the 192 addresses and the new network to stick with 10.20.

              Please help!

              Thanks
              Dom

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              • #8
                Re: PUZZLED: Multiple DHCP

                Hi Guys,
                Would a multicast scope help here?!
                Thanks
                Dom

                Comment


                • #9
                  Re: PUZZLED: Multiple DHCP

                  Can you do a diagram of how you network is setup.

                  Comment


                  • #10
                    Re: PUZZLED: Multiple DHCP

                    Hi Here is a picture of our network

                    thanks
                    Attached Files

                    Comment


                    • #11
                      Re: PUZZLED: Multiple DHCP

                      What is the old network that you are referring to???

                      Comment


                      • #12
                        Re: PUZZLED: Multiple DHCP

                        The old network is 192.168 the new is 10.20.x

                        Comment


                        • #13
                          Re: PUZZLED: Multiple DHCP

                          Your machines on the old network will pick up IP address on the 192 network due to the fact that they are still on the same local LAN as the DHCP server.

                          For the clients to pick up the correct 10 addresses they either need to be in a VLAN with the relevant netork details setup and IP help address configured or you need to change the IP of you DHCP server and remove the old scopes.

                          You can have your DHCP server sat in its own VLAN as long as your switches have the correct VLAN's setup.

                          IMO you don't need a SuperScope or a MultiCast scope setup but you will need the relevant number of scopes as you need.

                          Hope that makes sense to you.

                          Comment


                          • #14
                            Re: PUZZLED: Multiple DHCP

                            Yes that makes sense but I dont think you understand my problem - the clients plugged into the 192.168 network are getting addresses from the 10.20 scopes

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                            • #15
                              Re: PUZZLED: Multiple DHCP

                              Remove the Superscope and have individual scopes.

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