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How to Configure DHCP Failover in Windows Server 2012

DHCP Failover in Load Balance Mode

Reliable DHCP service is crucial to clients’ normal network connectivity. The requirements for this service evolved over the years. While the Split-Scope configuration has been a de facto standard for a long time, it’s been accompanied by two major short-comings.

  – Lack of IP addresses continuity in case of DHCP server failure.
  – Totally unsuitable for highly utilized scopes.

Another High Availability (HA) solution has been the DHCP cluster deployment. Naturally, this HA option has been available strictly to enterprises with the corresponding budget and expertise. Besides of its complex configuration and maintenance DHCP cluster solution comes with a single point of failure – the shared storage.

And now we have an elegant and superior HA solution, introduced with Server 2012 DHCP Failover. It can be configured in two modes:

  – Load Balance (Active-Active configuration)
  – Hot-Standby (Active-Passive configuration)

Here is the place to say that while the configuration and management of DHCP Failover is extremely simplified and user friendly in Server 2012, understanding the way DHCP Failover protocol is working in the background might be a challenge [DHCP Failover Protocol]. Trying to intuitively explain the behavior of DHCP servers when switching to different states and the corresponding lease durations usually leads to confusion. On the other hand, grasping the basic principles of DHCP Failover can be extremely helpful when choosing suitable parameters (ex. State Switchover Interval, Maximum Client Lead time/MCLT etc.) and troubleshooting your configuration.

In this screencast, we will start with discussing the basics of the Failover protocol (Step 1). Then we will go through some of the prerequisites, health checks and the actual configuration of DHCP Failover in Load Balance mode in Server 2012. Finally, you will see DHCP Failover in action when we simulate a partner down situation, and monitor the whole process of switching to Partner Down state and recovering back to Normal state.

Click to play 1 video
Step 1 In this step, we go through the basic principles of DHCP Failover protocol. You will see how the partner servers behave when switching through different states and what is the effect of parameters like MCLT (Maximum Client Lead Time) and State Switchover Interval upon the behavior of partners and the lease duration.

Click to play 2 video
Step 2 Next, we cover health checks and required prerequisites. After that we proceed with the configuration of DHCP Failover in Load Balance mode.

Click to play 3 video
Step 3 Finally, we validate our configuration. Then you will see DHCP failover in action. We simulate a partner failure and monitor what happens in the background while switching from Normal to Partner Down state; then we recover the failed partner and monitor switching back to Normal state.

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