While replacing my 2 Domain Controllers today I also took the opportunity to clean up DHCP and DNS and DHCP which led me to one of my favorite new features in Windows server 2012 DHCP Failover. My only question is was there any reason beyond the lawsuits over giving away free software to end users that we didn’t have this years ago. If you haven’t used Windows Server 2012 with DHCP failover, you are missing out.. I know we had Split DHCP and DHCP Clusters with Windows Server 2008 R2 but this is much cooler.
DHCP failover: This feature provides the ability to have two DHCP servers serve IP addresses and option configuration to the same subnet or scope, providing for continuous availability of DHCP service to clients. The two DHCP servers replicate lease information between them, allowing one server to assume responsibility for servicing of clients for the entire subnet when the other server is unavailable. It is also possible to configure failover in a load-balancing configuration with client requests distributed between the two servers in a failover relationship. For more information about DHCP failover, see Step-by-Step: Configure DHCP for Failover
In Windows Server 2008 R2, there are two high availability options available for DHCP Server deployment. Each of these options is associated with some challenges.
1.DHCP in a Windows failover cluster. This option places the DHCP server in a cluster with an additional server configured with the DHCP service that assumes the load if the primary DHCP server fails. The clustering deployment option uses a single shared storage. This makes the storage a single point of failure, and requires additional investment in redundancy for storage. In addition, clustering involves relatively complex setup and maintenance.
2.Split scope DHCP. Split scope DHCP uses two independent DHCP servers that share responsibility for a scope. Typically 70% of the addresses in the scope are assigned to the primary server and the remaining 30% are assigned to the backup server. If clients cannot reach the primary server then they can get an IP configuration from the secondary server. Split scope deployment does not provide IP address continuity and is unusable in scenarios where the scope is already running at high utilization of address space, which is very common with Internet Protocol version 4 (IPv4).
DHCP failover in Windows Server 2012 enables administrators to deploy a highly resilient DHCP service to support a large enterprise without the challenges of the options discussed earlier. The main goals of the feature are the following:
Provide DHCP service availability at all times on the enterprise network.
- If a DHCP server is no longer reachable, the DHCP client is able to extend the lease on its current IP address by contacting another DHCP server on the enterprise network.
1. Right-Click on the Scope you want to enable failover from, Choose Configure Failover
2. Choose the Network that you want to provide Failover for or Select All, Click Next
3. Either enter the name of your Partner server or Click on Add Server to choose from other DHCP Servers on you network, Click OK, then Click Next
4. You can choose from 2options from the Mode Dropdown, we left the default “Load balance” but you can also choose the alternate “Hot standby”
5. You can also choose the interval between State Switch Failover Interval. Last, as mentioned earlier review the options available in the drop-down menu next to Mode. You can choose Load balance or Hot standby. By default, Load balance mode is chosen. Click Next verify your settings., and Click Finish
6. Once Completed Verify Success, and Click Close.
Note: When you choose the DHCP Fail Over Partner the partner should not have the Network you are going to be using to Fail over configured as part of any scope..