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how to configure DHCP backup between subnets?

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  • how to configure DHCP backup between subnets?

    Hi

    I have 1 domain with 2 sites
    Each site has its own 2008 server acting as DC running DHCP for the subnet

    The subnets are 192.168.0.0 and 192.168.1.0

    I'm looking for a way that if one server is down, the other server ( from the other subnet ) will answer to DHCP requests.


    Thanks
    Yaniv

  • #2
    Re: how to configure DHCP backup between subnets?

    Setup both scopes on both servers.

    Setup a DHCP relay agent on both sides that will hande requests when the DHCP server goes down.

    Alternatively if there is an option on your switch or firewall to allow for an IP Helper then ues that.

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    • #3
      Re: how to configure DHCP backup between subnets?

      To add to wullieb1's answer - make sure you have configure both scopes on both DHCPs. Then, configure each scope to exclude 20% of the range, and only work with 80% of it. This number can be changed to meet your needs.

      DHCP 1
      Local scope - 80% active - 20% exclude
      Remote scope - 20% active - 80% exclude

      DHCP 2
      Local scope - 80% active - 20% exclude
      Remote scope - 20% active - 80% exclude

      If one DHCP fails, the DHCP Relay Agent will fwd the request to the other DHCP, and that one will assign one of the 20% it has for the other scope.
      Cheers,

      Daniel Petri
      Microsoft Most Valuable Professional - Active Directory Directory Services
      MCSA/E, MCTS, MCITP, MCT

      Comment


      • #4
        Re: how to configure DHCP backup between subnets?

        Thank you both

        I'll configure it and test it.

        I'll post my results soon

        is there a way to use reservation using that method?


        Yaniv

        Comment


        • #5
          Re: how to configure DHCP backup between subnets?

          Originally posted by Yaniv Hoobian View Post
          is there a way to use reservation using that method?
          You'll have to use the same reservations on both scopes.

          Ta
          Caesar's cipher - 3

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          SFX JNRS FC U6 MNGR

          Comment


          • #6
            Re: how to configure DHCP backup between subnets?

            Originally posted by danielp View Post

            If one DHCP fails, the DHCP Relay Agent will fwd the request to the other DHCP, and that one will assign one of the 20% it has for the other scope.
            Just wanted to clarify.

            If I'm installing the DHCP relay agent on the server, and the server ( not only the DHCP ) fails, how the clients will find the other dhcp server?

            Yaniv

            Comment


            • #7
              Re: how to configure DHCP backup between subnets?

              You don't set up the DHCP relay on the server, you set it up on the router that separates the two networks.

              Comment


              • #8
                Re: how to configure DHCP backup between subnets?

                Originally posted by danielp View Post
                To add to wullieb1's answer - make sure you have configure both scopes on both DHCPs. Then, configure each scope to exclude 20% of the range, and only work with 80% of it. This number can be changed to meet your needs.

                DHCP 1
                Local scope - 80% active - 20% exclude
                Remote scope - 20% active - 80% exclude

                DHCP 2
                Local scope - 80% active - 20% exclude
                Remote scope - 20% active - 80% exclude

                If one DHCP fails, the DHCP Relay Agent will fwd the request to the other DHCP, and that one will assign one of the 20% it has for the other scope.
                Thanks Daniel.

                I forgot to add that bit in.

                Comment

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