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.