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On my network, I have 3 remote sites and one local that all receive DHCP through our central dhcp server.

all the sites have ASAs with dhcprelay and so on.

I have two domain controllers - is it possible to set the second dc as secondary dhcp server, add the information to the ASA - and use it as a failover incase the primary dhcp server is offline?

would this cause problems?

thanks

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  • possible duplicate of Two DHCP servers on the same network
    – GregD
    Apr 26, 2011 at 13:38
  • How long are your leases and why do you think you need a backup DHCP server?
    – GregD
    Apr 26, 2011 at 13:41
  • Sorry about the duplicate. Because all pcs on my network get there IP from the DHCP server which as the primary dc. If the primary dc would go offline for whatever reason for a long amount of time, i want the dc2 to be able to handle the dhcp as well as dns and a/d
    – Jeff
    Apr 26, 2011 at 13:50
  • possible duplicate of Can I have multiple DHCP servers on one network?
    – Rob Moir
    Sep 1, 2012 at 21:34

2 Answers 2

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Yes, this is possible and will not cause problems as long as it's configured properly. To setup the second DHCP server as a "failover" you will want to divide up the scopes DHCP 1 is serving. To do this you would configure the same scopes on DHCP 2 as there are on DHCP 1. You would then exclude a percentage of the scope on DHCP 1 and then exclude the opposite percentage of the scope on DHCP 2. This way together they would be serving the full scope.

Microsoft recommends using an 80% / 20% divide but there is debate on what works best.

Make sure that if you have any reservations set that they are setup on the secondary DHCP server (if they fall within the scope that will be served from that server). 

         DHCP 1                     DHCP 2

scope    192.168.1.0/24             192.168.1.0/24
exclude  192.168.205 - 254          192.168.1.1 - 204

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Yes, you can do this, probably the easiest way is just to split the ranges.

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