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DHCP Classes - Win 2K8

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  • DHCP Classes - Win 2K8

    Alright... I don't know what I'm missing here. We have a network that's 10.10.50.X... I expanded everything to 10.10.X.X since we were running out of IP's.

    The original DHCP is 10.10.50.50-200. I added a new scope for 10.10.30.50-200, I want computers in our computer lab to use the 30 scope. I assigned classes to all the machines, and set the scope options on the .30 to only apply to the 'Labs" class. But, no matter what I do I cannot get the clients with the 'Labs' class assigned to use this scope... the only time it ever happens is if i delete the .50 scope.

    What could I be missing? I swear i tested this a week ago with identical settings on a Win 2000 DHCP and it worked.

  • #2
    Re: DHCP Classes - Win 2K8

    Not sure what your infrastructure looks like but to route between different subnets requires a router or another layer 3 device (Layer 3 switch). On the layer 3 interfaces you need to specify the dhcp relay agent to forward the dhcp broadcasts from your clients to the dhcp server. Devices on the same subnet as the dhcp server dont require this just devices that are on different subnets as the dhcp server.

    On a cisco device this would look like

    int vlan 20
    ip helper-address x.x.x.x (address of your dhcp server)

    Are you clients switchports in the correct vlan?

    Is the new scope authorized and running?
    CCNA, CCNA-Security, CCNP
    CCIE Security (In Progress)

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    • #3
      Re: DHCP Classes - Win 2K8

      I'm just taking over this school... they're basically out of IP's and have a boatload of switches all over the place. They're running out of IP's literally right now... so I expanded everything to a /16. I simply dont have the time to implement VLAN's yet.

      The new scope is authorized and running. So please correct me if I'm wrong but since its all a /16 everyone will end up at the same DHCP Server (only one server is running) since DHCP is Broadcast. But then, can't I define multiple scopes and use classes to assign certain computers to each scope?

      I have one scope 10.10.50.x - with a class set to default
      I have another scope 10.10.30.x - with a class set to Labs

      On all the lab machines I then ran ipconfig /setclassid "Local Area Connection" Labs. So shouldn't those machines grab IP's from the 30 scope? Or is my understanding of classes wrong? (I have a sneaking suspicion this might be the case! )

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      • #4
        Re: DHCP Classes - Win 2K8

        I have one scope 10.10.50.x - with a class set to default
        I have another scope 10.10.30.x - with a class set to Labs


        Your correct in saying if you changed the subnet mask to /16 then yes all machines will be in the same broadcast domain (Same Layer 2 domain)

        The problem is that since its one flat layer 2 network how does your dhcp server determine which pool to pull from? It cant. The client is going to accept the first DHCP offer it gets, whether it be from the .50 pool or the .30 pool. In reality you could just have one pool for all clients. The reason to create different pools is for Layer 2 segragation, ie vlans. Vlan's separate broadcast domains. I would highly you recommend implementing vlans in your infrastructure. Not sure how many clients you have but since they are all on the same layer 2 network, all machines on that network will hear every broadcast etc. which wastes bandwidth etc. Also not to mention that your using a whole /16 network which is a waste of ip addresses.

        The only way I think this will work is if you implement mac filtering (reservations) on the dhcp server. So you are assigning an address per a specific client mac address


        I highly suggest looking at vlans. It will help out in the long run.
        CCNA, CCNA-Security, CCNP
        CCIE Security (In Progress)

        Comment


        • #5
          Re: DHCP Classes - Win 2K8

          Yea, thats what I thought the answer might be :/

          I was originally thinking I could use DHCP Classes on the DHCP Server to assign machines to specific scopes. I'm definitely going to have to take a look at VLAN's. The current switching environment seems to be a bit of a mess its gonna take some time to sort out before I'll be able to implement them. I mean... they have a ~2 dozen or so switches over 4 floors and over 100 rooms. I'm not even sure how to begin to tackle that.

          In the meantime I used your recommendation and just set reservations for them on the desired scope.

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