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Possible Duplicate:
Can I have multiple DHCP servers on one network?

Current Environment:

Windows Server 2003 (Primary Domain Controller) Primary DHCP Active Directory Print Server Exchange 2003

Windows Server 2008 (Secondary Domain Controller) Active Directory Hopefully secondary DHCP

So I am looking to setup DHCP on Windows Server 2008, as a safety net or if possible to run alongside the primary using the 50-50 rule. I am still very unsure on how its best to go about this.

Any guidance or links to further information would be greatly appreciated, or some examples of how you have this set up.

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Anicho
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  • Thanks mrdenny, I think I'll go with split scope option we do not have the need to move onto a different subnet at current and it would be a pain setting it up on all hardware in the office. Just found this will follow it: http://technet.microsoft.com/en-us/library/cc757346(WS.10).aspx – Anicho Sep 11 '09 at 11:00

4 Answers4

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Setup DHCP on the second server. Set it up to handle the same DHCP scope.

On the first server, block it from issuing IPs 1-128. On the new server, block it from issuing IPs 129-255. (adjust ranges as needed).

That or setup the second server to issue private IPs on a different subnet (you'll need to make sure that all your network equipment works on this subnet as well.

mrdenny
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DHCP by default backs itself up every 4 hours under c:\windows\system32\dhcp and dhcp-bak setup a copy file script to another server and in the event of a failure follow this article http://blogs.technet.com/b/teamdhcp/archive/2009/02/18/migration-of-dhcp-server-from-windows-server-2003-to-windows-server-2008.aspx

http://technet.microsoft.com/en-us/magazine/ff621490.aspx

Kevin E.
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I believe that mrdenny's answer is the best option for Windows networks.

The ISC dhcpd can do redundancy, where two servers both serve the same pool and keep track of the addresses issued, so that if one fails there is a much lower risk of duplicate leases being issued.

The bad part is that you'd need to run Linux, BSD, or Solaris to get access to this -- two servers, to get redundancy.

Google points you here as a how-to.

David Mackintosh
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  • Duplicate your full DHCP configuration on the second DC.
  • Stop and disable the DHCP service on it.
  • Monitor the DHCP service for availability on the first DC (e.g. poll it every hour with a script or something similar).

This won't give you fully automatic failover, but in your scenario I don't think that's going to be too big a deal. Firstly, your DHCP lease duration will prevent clients from abruptly dropping off the network. Secondly, if your first DC dies I think you're going to have far bigger problems that just not having DHCP, and that you will be aware of it well in advance of any issues with unavailability of DHCP taking effect.

Maximus Minimus
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  • Thanks for the advice, we are currently working on getting a fail-safe for exchange and getting exchange off our DC box, slowly but surely we will have much better redundancy the old system was horrible. – Anicho Sep 11 '09 at 11:11
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    This will not work as the second dhcp server will have no record of the leases assigned by the first, now dead, server. Sure, it could try pinging IPs before leases, but now that Windows firewalls deny ICMP echo requests by default that's unlikely to work. – David Mackintosh Sep 11 '09 at 17:44