Windows DHCP Server Configuration Guide

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Network nodes require an IP address configuration which typically includes the IP address, subnet mask, default gateway IP address for the router, name servers, and other values.

Administrators can manually set this information, resulting in a static configuration. A Dynamic Host Configuration Protocol (DHCP) server can also dynamically provide the information.

Usually servers, routers, network printers, and other such devices have a static configuration. End-user workstations, laptops, phones, tablets and other devices receive their configuration via DHCP.

Client devices lease their IP address configuration using the following four-step DORA process:

  1. Discover. The client broadcasts an attempt to discover a DHCP server.
  2. Offer. DHCP servers that receive the client broadcast offer an IP address configuration.
  3. Request. The client formally requests the IP configuration from the first DHCP server to respond.
  4. Acknowledge. The DHCP server recognizes the lease and does not offer this same address to another client.

The lease must be renewed periodically by the client.

Now that we’ve briefly gone through how IP addresses are allocated and the lease generation process, let’s take a closer look at how to configure Windows Server’s DHCP service.

1. Install DHCP on Windows Server 2019

The DHCP service is not automatically installed on Windows Server 2019. However, it is easy to add using Server Manager or Windows PowerShell.

To add DHCP using Server Manager, select Add roles and features, then select Dhcp in the Roles list.

To add the DHCP role using the command line, open Windows PowerShell (Admin) and enter the following:

Install-WindowsFeature DHCP -IncludeManagementTools
Install the DHCP role using Windows PowerShell.

Installation takes about a minute.

Once administrators have installed the DHCP service, they can manage it by selecting Tools> DHCP.

2. Allow DHCP in Active Directory

Windows DHCP servers must be registered with Active Directory (AD) before starting to offer IP address configurations to clients.

Right click on the server node in the DHCP console and select To allow to accomplish this authorization. You need enterprise administrator privileges to authorize DHCP.

3. Create a scope

Before creating the first pool of available IP addresses, it is essential to plan the deployment. Devices, such as servers, routers, and even printers, can have a static IP address configuration. Make sure you have identified these addresses and allow them in scope. Many administrators place all statically assigned IP addresses in the foreground of the scope.

Here is an example of a simple design:

  • Scope address range: 192.168.2.0/24
  • Static IP addresses: 192.168.2.1 to 192.168.2.25 (be sure to leave room for additional devices)
  • Dynamic IP addresses: 192.168.2.26 to 192.168.2.254

You should also gather additional configuration details, including:

  • Name and Description. The name of the scope and an optional description.
  • Default gateway value. The IP address of the network interface card in the router connected to this network.
  • Name resolution servers. The IP address of one or more DNS servers.
  • Reservations. All IP addresses that are dynamically allocated to specific clients, allowing those clients to acquire a consistent IP configuration from DHCP.
  • Lease term. Period of validity of the lease of the IP address. It must be renewed halfway through the lease. The Windows Server DHCP default is eight days.

4. Configure and activate the scope

Once you have documented the above values, you can configure the scope. Right click on the server node in the DHCP console and select New litter. A wizard prompts you to enter the information you collected above. These settings can be changed later.

New screenshot of DHCP scope
Create a new DHCP scope.

Once enabled, the DHCP server begins responding to discovery messages from the DHCP client by offering IP addresses. The scope can be disabled, the DHCP service can be stopped or restarted, and the DHCP server can be deauthorized in AD.

5. DNS registration

DNS combines easy-to-remember hostnames with hard-to-remember IP addresses. This database can be fed in several ways.

One method is to configure the DHCP server to create resource records for the client. The DHCP server can be configured to create A records (hostname to IP address), pointer (PTR) records (IP to hostname), or both.

By default, DHCP creates the PTR record, while the client itself registers its record with DNS.

screenshot of DNS configuration for DHCP
Configure the DNS options.

DHCP administration tasks

The DHCP service is easy to configure. But system administrators often find certain additional settings useful.

Create a reservation

In some cases, it is useful to allow a client machine to maintain a consistent IP address. Although you can set the IP address configuration statically, it is often best to reserve the IP address for the client in DHCP. The client goes through the DORA process to receive its settings, so values, such as router and name resolution servers, can always be updated through DHCP.

screenshot of IP address reservation
Reserve an IP address for the Dev-Computer.

DHCP failover

With Windows Server 2012, Microsoft introduced DHCP failover. It seems that many admins are unaware of this capability. The setup is simple and does not require any special software.

To configure DHCP failover, follow these steps:

  1. Make sure that the DHCP role is installed on both DHCP servers and that they have network connectivity between them.
  2. Configure a DHCP scope on one of the servers.
  3. Right-click on the staff and select DHCP failover from the context menu.
  4. Complete the wizard.
  5. Select the second DHCP server and observe that the new scope appears.
DHCP failover configuration screenshot
Configure DHCP failover.

Newspapers

Managing service log files is a standard feature for system administrators. DHCP writes messages to Event Viewer and to text files.

System administrators can check the system log for general DHCP and network messages. They can find DHCP entries by going to Applications and Services> Microsoft> Windows> DHCP-Server> Microsoft-Windows-DHCP-Server-Events> Operational.

DHCP also generates text log files stored in C: Windows System32 dhcp. These logs are extremely useful for troubleshooting. They can display information as to why the server was unable to lease configurations to clients.

dhcp text logs screenshot
DHCP Text Logs

Note that the text file logs are named after the days of the week and are overwritten every week. If you want to keep these logs, you must rename them before the next day of the week can overwrite them.

The DHCP role is not installed by default, so the first step is to add it. From there, create a new scope based on your plan.

Beware of conflicting fields of application

As more subnets – and therefore more DHCP scopes – are added to the network, it is imperative that system administrators accurately document IP address ranges. Overlapping scopes, where two DHCP servers offer the same IP addresses to clients, causes various network communication problems.

This is part of the reason Microsoft requires that DHCP servers be authorized in AD. This permission can only be implemented by enterprise administrators, who must have sufficient knowledge of network configuration to avoid scope conflicts.

Avoid duplicate IP address offers

One of the most serious configuration errors is a client computer configured with a static IP address that is within the scope of the DHCP server. In this case, the server can offer the IP address to a client because it does not know the static IP address. This results in an IP address conflict.

The Windows DHCP service can be configured to ping an IP address before offering it to a client. If the ping returns a response, the DHCP server knows that the address is already in use and should not be offered. The server offers a different address to the client.

screenshot of configuring conflict detection attempts
Configure conflict detection attempts.

The ping request occurs between the Discover and Offer stages of the lease generation process. This introduces a significant delay, so only configure this setting if you have a real problem with undocumented static IP addresses on client devices.

Conclusion

Microsoft has made it easy to set up a DHCP server. Make sure you understand the IP address configurations of the entire network before you begin, and plan your reach around dynamic and static IP address assignments.

The DHCP role is not installed by default, so the first step is to add it. From there, create a new scope based on your plan. Add options, such as DNS and reserved addresses. Check the log files regularly. DHCP is simple but essential for network communication.

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