in this guide I will show you how to configure the DHCP service in high availability mode.
In previous Windows versions like Windows Server 2008 R2 and Windows Server 2003, you have two options to make DHCP highly available:
- 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.
- 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).
In Windows Server 2012 DHCP Failover enables administrators to deploy a highly resilient DHCP service to support your business without the challenges of the two options discussed above. It 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.
There are also two ways of making the DHCP role highly available. You can set it up your failover partners in hot standby mode or in load sharing mode.
- Hot standby mode
- Load sharing mode
Hot standby mode
In hot standby mode, an active server is responsible for providing IP addresses and configuration information to all clients in a scope or subnet and the secondary server assumes the responsibility if the primary server becomes unavailable.
Load sharing mode
In a load sharing mode, which is the default mode and the one we will setup in our lab, the two servers simultaneously serve IP addresses and options to clients on a given subnet. The client requests are load balanced and shared between the two servers.
- Test Machine
Add features and Next till the finish.
Wait for the installation process to complete, under the Notification area click Complete DHCP configuration.
In the DHCP Post-Install Configuration wizard, click Next in the Description page, Commit in the Authorization page and then Close to complete the installation. Differently from the previous version the DHCP authorization is done by the post-install wizard.
Then create a Scope and fill in all the item as required by the wizard.
Steps required to create reliability
1 – Add second DHCP server using DHCP manager
Follow the wizard adding the partner server, choosing in which mode you want to provide reliability and a shared secret for the comunication between them.
This should be the output. You can see both DHCP server with the same scopre replicated
This is an ipconfig on client side
You can find the same lease entry on both dhcp server, so even if a DHCP server fail you we don’t have the fault of the dhcp service but it can still work.