Windows 8 DHCP Failover

by Marin Franković on 10 February, 2012

DHCP failover is one of the features that was supposed to be implemented in Windows Server 2008 but never saw the day of light. Although there is a IETF document that describes this possibility dating from 2003., Microsoft released this feature in Windows Server 8.

There are several prerequisites that must be met before you try this:

  • 2 Servers running the Windows 8 (Developer Preview in my case)
  • DHCP servers can be members of a domain or a workgroup
  • The DHCP Role installed on both servers
  • DHCP Servers must be authorized in Active Directory

During the configuration of DHCP failover as you will see in short video, you will have option to configure several failover features:

  • Relationship name: The name of the DHCP cluster
  • Maximum client lead time (MCLT): Controls the time beyond the expiration of a lease given to a client. The maximum client lead time is transmitted to the secondary server to be sure the failover mechanism keeps working when a DHCP server gives a lease to a client but fails to transmit the information about the given lease to it’s replication partner.
  • Load Balance Mode: When the cluster is configured in Load Balance mode, this results in an active-active setup of the two DHCP Servers.
  • Hot Standby Mode: When the cluster is configured in Hot Standby mode, only one DHCP server is used initially, if this server goes down, the Hot Standby is activated (Active-Passive).

As you can see, you can use this feature to set up DHCP failover od to set up load balancing between two DHCP server. IETF document gives detailed information on how to synchronize two DHCP databases to achieve this goal.

{ 2 comments… read them below or add one }

PrasadMSFT April 2, 2012 at 10:27

Thanks for the nice article, Marin!
Just wanted to point out that DHCP Failover has no dependency on one of the DHCP servers being a domain controller. In fact, DHCP Failover can be configured with workgroup DHCP servers also with no loss of functionality compared to a domain joined deployment.

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Marin Franković April 2, 2012 at 10:38

Hi PrasadMSFT,

you are correct. In this demo, DHCP servers are members of a domain, but it is not requirement (http://technet.microsoft.com/en-us/library/hh831493.aspx). I will make changes to the article to reflect that.

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