How to Set Up DHCP Failover On Windows Server

How to Set Up DHCP Failover On Windows Server

DHCP failover is a feature of the Microsoft DHCP server that allows you to configure two servers as a failover pair. When one server in the pair fails or becomes unavailable, it can automatically hand over DHCP lease management to its partner. This ensures that your network clients have uninterrupted access to network resources and services provided by DHCP servers.

Of course, you can only reap the benefits of DHCP failover if you know how to get it working in the first place. In this post, we’ll provide you with detailed instructions on how to set up DHCP failover on a Windows server.

Prerequisites

Before you get started, note the following to set up DHCP failover:

• You must be running Windows Server 2022 or later.
• You must have the DHCP server role installed on the primary or secondary server.

How to Install DHCP Server

To install the DHCP server role on Windows Server 2022, do the following:

• Click Add Roles and Features once you’re in the Server Manager.
• Select your server (or virtual machine) from the server pool list under Server Selection.
• In the Features page of Add Roles and Features Wizard, select DHCP Server.

The DHCP Server service is now installed on your computer as part of this wizard.

Configure DHCP Failover

To configure DHCP failover, you must first create a failover relationship. To do this:

• Add the server you want to be your primary DHCP server to the Failover Cluster Manager console.
• Add the server that will act as its partner in this relationship. This is called a secondary node and will run in standby mode until it’s needed by the primary node or another failure occurs in its cluster configuration (for example, if a network switch goes down). You can use any available quorum disk witness or file share witness for this step; make sure it’s accessible by both nodes on all networks where they’re connected before selecting it here.

Create a DHCP Scope

You will also need to create a DHCP scope on your server. To do so:

• In the DHCP console, right-click the IPv4 node and choose “New Scope…” from the context menu. Name this new scope with the same name as your primary DHCP server’s IP address (that is, if your primary DHCP server has an IP address of 192.168.0.1, then name your failover partner’s failover scope “192.168.0”). To use a different IP address for your failover partner (highly recommended), enter that hostname in this dialog box instead of manually configuring policies at each server individually—you’ll save yourself some time.
• Click Next through all remaining steps until reaching End now.

Activate the Scope

In Server Manager, select the DHCP server, right-click and select “Activate Scope.” This will activate the scope on your primary DHCP server. It will not start on your secondary DHCP server because you don’t want to use that one for failover.

Add a Primary Server to Failover Cluster Manager

To add a primary server to the failover cluster:

• Right-click the Failover Cluster Manager and select Add Server.
• Select the server you want to add. It can be physical or virtual or an existing Hyper-V failover cluster member (if you are using Hyper-V). You can also add multiple servers by selecting them in a single management console window. For example, if you have several Hyper-V hosts running Windows Server 2222 and need to create DHCP failover clusters on all of them, right-click each host in turn and then choose Add Server.
• Select the role you want to add on this new node (e.g., DHCP). If you’re unsure what roles are available for this type of server, click on the “Show Me More” button and then select relevant items from the drop-down list that appears below it (for example, “DHCP”). Click OK when done adding all necessary roles on this node (or Cancel if not).

Add a Secondary Server to Failover Cluster Manager

In Failover Cluster Manager, add the secondary server to the failover cluster.

Validate the Failover Relation

Once you’ve configured the failover relationship and tested it, you can evaluate the state of your DHCP servers. You should see that:

• The failover relation is working. The secondary server should receive requests from the primary server and respond to them as if they were the primary server.
• On another client computer with two interfaces connected via two different switches, you can see that both interfaces are getting their IP addresses from dhcp1; this tells you that both interfaces are connected directly to this node through separate cables as well as being able to communicate over TCP/IP via their VLANs on either switch.
• All traffic between nodes goes through at least one other node in addition to each node’s local subnet (or link). This means all traffic between hosts connected through different switches must go through another host somewhere else on your network.

Configure DHCP Policies for Split Scopes and Load Balance Scopes

Split scopes and load balance scopes come in handy when you have an extensive network. They allow you to split the range of IP addresses for DHCP into two or more ranges, each with its own settings. You can then define how these ranges interact with each other by assigning policies like “override” or “prefer” to one or more of them.

Load balance scopes are similar to split scopes but use a round-robin algorithm instead of a manual configuration. The round-robin algorithm ensures that each client gets an equal amount of time on the network so that none are left waiting in line when it comes time to get their IP address assigned.

Verify and Manage DHCP Failover Settings

After you’ve successfully configured DHCP failover, you can use the following commands to verify and manage your settings.

• To check the configuration of a DHCP failover scope: Get-DhcpServerv4Scope -ComputerName $Comp1, $Comp2 | Format-List ScopeState, IPAddress, PrimaryServerIdentifier
• To set up the primary or secondary server for a DHCP failover scope: Set-DhcpServerv4Scope -ComputerName $Comp1, $Comp2 -IsPrimary
• To check whether an IP address is assigned from one of the DHCP servers in your new or existing scope: Get-DhcpServerv4Lease -ComputerName $Comps | Where IPAddress = “10.0.0.5”| Select ServerAddress, ClientID, Flags

DHCP failover is a great way to ensure your network remains up and running despite server failures. When properly configured, DHCP servers can detect each other’s presence and automatically switch over to the secondary server if the first one fails.

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