No announcement yet.

Secondary DHCP Server is not Assigning Addresses

  • Filter
  • Time
  • Show
Clear All
new posts

  • Secondary DHCP Server is not Assigning Addresses

    I want to create a secondary backup DHCP server in the event our primary server is down and cannot assign ip addresses. But the secondary server is not assigning IP addresses when I turn off the DHCP services on the primary.

    Here is what I have setup. 80/20 rule

    Our primary DHCP server is on network - and I have 80% of the IP addresses setup to assign here.

    Secondary DHCP server is on a different network - Then I have the IP range at 20% here

    Is that a problem if my secondary server is on a different network? How does the DHCP request know to broadcast over to a different network or does it?

    We have over 225 users on our network.

    The network is our data center where our file servers are located. So no clients on this network that need it.

    Any ideas on this. I can't seem to find what I am doing wrong.

    Thanks for any help!

  • #2
    Re: Secondary DHCP Server is not Assigning Addresses

    The fact that the other DHCP server is on another network is a problem if the networks are separated by a router as router's won't normally forward the DHCP broadcast traffic. You need to set up what's is commonly referred to as a DHCP relay agent in order for the DHCP brodcasts to reach the other DHCP server.


    • #3
      Re: Secondary DHCP Server is not Assigning Addresses

      what joe said - basically, that DHCP server won't be reached by the clients.
      DHCP is a broadcast protocol and will not cross subnets.

      even if you add a relay, it will provide addresses in the 192.168 subnet - this may not be what you require.

      Consider the following:
      A DHCP lease is, by default, something like 8 days, depending on the OS.
      A DHCP workstation will try and renew it's lease at a half life of 50% - so, 4 days, for arguments sake.
      So by this concept, you could actually have your DHCP server off the network for up to 4 days, and you won't really notice. (Unless you plug new workstations in)

      of course, with all the leases ending at different times, this could be slightly problematic.
      Even after that 50% time though, DHCP will try and renew it's lease again, at 50% intervals from then on.. so another 2 days, then another 1 day...

      If you setup monitoring, then you should know if your DHCP service is fkd.
      A DHCP server is very quick and easy to knock up..
      Please do show your appreciation to those who assist you by leaving Rep Point


      • #4
        Re: Secondary DHCP Server is not Assigning Addresses

        Hey thanks guys. The big problem is we have contractors that come in the office all throughout the day and connect to our network.

        I think I'll just have to had another server at our site as a backup DHCP and a backup print server. This maybe the best way to go.

        Thanks for the information.