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  • Serving DHCP to different network segments

    I've got a flat network and one DHCP server. I need to segment the traffic coming from one floor of the building so that it gets special DHCP scope options.

    I assume I'll need to have our network guy create a vlan for that floor of the building but how do I setup my DHCP server so it only sends the special options to traffic from that single floor? Is it as simple as sticking second NIC in the server and mapping it to the subnet of the second vlan? Will I have to create a second scope?

    Thanks.

  • #2
    Re: Serving DHCP to different network segments

    Pretty easy if you switch supports IP helper commands.

    If it does then ask your network guy to VLAN your switch then add the IP Helper address for DHCP to point to the DHCP server then create the relvant scope with options on your DHCP server.

    We have our DHCP server servicing 4 scopes at the moment and it works a treat.

    ***EDIT***

    I shouold also add that if your switch doesn't support IP Helper then you'll need a DHCP Relay Agent install on the VLAN'd subnet to capture all DHCP requests and forward them to the server.

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    • #3
      Re: Serving DHCP to different network segments

      If you want to keep them on the same subnet then you can use DHCP classes to give a subset of computers different scope options. Check out this link http://thelazyadmin.com/blogs/thelaz...r-Classes.aspx

      Otherwise you'll need to setup a new subnet and a scope for the new subnet on the DHCP server and follow Wullie's advice. You could also slap another NIC in the DHCP server and connect it to the new VLAN if you wanted.

      Note that if you have to setup a new subnet you'll need to configure a router (maybe your switch is an L3 switch that can do the routing) between the two subnets.
      Regards,
      Jeremy

      Network Consultant/Engineer
      Baltimore - Washington area and beyond
      www.gma-cpa.com

      Comment


      • #4
        Re: Serving DHCP to different network segments

        That class ID setting sounds pretty slick but won't work for me because I'm trying to get my special options to voip phones located on one floor of the office. I don't think I can change their class ID. Even if I could, it doesn't sound like it'd save me any time over entering the settings on each phone manually

        So, with IP helper commands or not, I've got some device forwarding DHCP requests from my vlan to my DhCP server. I know how to create an additional scope, but I don't know how to make the server hand out IPs from that scope to only requests from that vlan.

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        • #5
          Re: Serving DHCP to different network segments

          The separate VLAN requires that it be on a different subnet. The relay agent will be on the new subnet and the DHCP server will see what subnet the request is coming from and assign an IP address accordingly.
          Regards,
          Jeremy

          Network Consultant/Engineer
          Baltimore - Washington area and beyond
          www.gma-cpa.com

          Comment


          • #6
            Re: Serving DHCP to different network segments

            Lucky for me, looks like they've decided to separate the two networks physically and provide dhcp to the new network (voice) through the switch.

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            • #7
              Re: Serving DHCP to different network segments

              Cool. Thanks for the follow up. Let us know if you have any questions.
              Regards,
              Jeremy

              Network Consultant/Engineer
              Baltimore - Washington area and beyond
              www.gma-cpa.com

              Comment


              • #8
                Re: Serving DHCP to different network segments

                Hi

                Just for information purposes. I had a simular issue. I had a scope of address that serve ips to phones and workstations; however the phones require a vedor id which was the same vendor id that the imaging server requires. So the work around was to create a new vendor class in DHCP and specify the mitel phones vendor information.

                Therefore everything worked in the end.

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