DHCP Failover - Add Secondary DHCP

What is DHCP Failover?

DHCP Failover allows two DHCP servers to share responsibility for a scope. The two servers replicate lease information, so if one server fails, the other can take over. There are two modes of DHCP Failover:

Hot Standby Mode: One server actively serves IP addresses, while the other is on standby and takes over if the primary fails.
Load Balance Mode: Both servers actively serve IP addresses, sharing the load.

Prerequisites

Before configuring DHCP Failover, ensure the following:

Two Windows Servers: Both servers must have the DHCP Server role installed.
Static IP Addresses: Both servers must have static IP addresses.
Authorised DHCP Servers: Both servers must be authorised in Active Directory.
Identical Scopes: The primary DHCP server should have the scopes configured, and the secondary server should not have any conflicting scopes.

Step 1: Install the DHCP Server Role on Both Servers

If you haven’t already, install the DHCP Server role on both servers. Here’s how:

Open Server Manager.
Click Manage > Add Roles and Features.
In the Add Roles and Features Wizard, select the DHCP Server role.
Complete the installation on both servers.

Step 2: Configure Scopes on the Primary DHCP Server

Open DHCP Manager on the primary DHCP server:
- Go to Server Manager > Tools > DHCP.
In the left-hand pane, expand your server name and right-click IPv4.
Select New Scope and configure the scope (e.g., IP range, subnet mask, exclusions, lease duration, etc.).
Complete the scope configuration.

You can find more details here.

Step 3: Configure DHCP Failover

Open DHCP Manager on the primary DHCP server.
In the left-hand pane, expand your server name and right-click IPv4.
Select Configure Failover.

In the Configure Failover wizard, click Next.
Select the scopes you want to configure for failover (e.g., the scope you created earlier) and click Next.
On the Specify the partner server page, enter the name or IP address of the secondary DHCP server and click Next.
Configure the Failover Relationship settings:
- Relationship Name: Give the failover relationship a name (e.g., DHCP-Failover).
- Maximum Client Lead Time: Set the maximum time (in minutes) that one server can extend a lease for a client beyond the lease time known by the other server (default is 1 hour).
- Mode: Choose either Load Balance or Hot Standby.
  - For Load Balance, set the load distribution percentage (e.g., 50-50).
  - For Hot Standby, specify which server is the Active server and which is the Standbyserver.
- State Switchover Interval: Enable this option to allow automatic failover if one server becomes unavailable.
- Enable Message Authentication: Enable this option to secure communication between the two servers.

Click Next and then Finish.

Step 4: Verify DHCP Failover

Open DHCP Manager on both servers.
Right Click on IPv4 and check Display Statistics.

Verify that the failover relationship is active and working.

Step 5: Test DHCP Failover

Disconnect the primary DHCP server from the network (or stop the DHCP service).
On a client machine, release and renew the IP address:
- Open Command Prompt and run: ipconfig /release ipconfig /renew
Verify that the client receives an IP address from the secondary DHCP server.

Best Practices for DHCP Failover

Use Load Balance Mode for Equal Workload Distribution:
This mode is ideal for most environments where both servers are equally capable.
Use Hot Standby Mode for Redundancy:
This mode is ideal if one server is significantly more powerful than the other.
Monitor Failover Status:
Regularly check the failover status in DHCP Manager to ensure both servers are functioning correctly.
Backup DHCP Configuration:
Use the Export-DhcpServer PowerShell cmdlet to back up your DHCP configuration.

Happy Learning 🙂