How to Install a Simple DHCP Server on CentOS 7

A DHCP (Dynamic Host Configuration Protocol) server is a critical networking service used for the automatic assignment of IP addresses and other network parameters to devices on a local network.

This guide covers the absolute minimum steps required to install and configure a simple, secure DHCP server on enterprise-grade CentOS 7.

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1. Prerequisites & System Design

This walkthrough assumes a freshly installed CentOS 7 server with a configured static IP address.

For storage, this virtual machine has two separate disks provisioned. Disk 1 is dedicated to the OS, while Disk 2 will be used to host local yum repositories later.

Following the security recommendations from CIS Benchmarking Standards, the storage partitions are carved out using LVM as follows:

Disk 1 (80 GB) — Operating System

Disk 2 (60 GB) — Custom Repositories & Web Assets

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2. Base OS & Environment Setup

Enable EPEL Repository

Install the Extra Packages for Enterprise Linux (EPEL) repository. This repository provides additional debugging tools and security plugins we will use later:

yum install epel-release -y

Update the System

Bring all package dependencies up to date:

yum update -y

Disable SELinux

To ensure configuration changes apply cleanly, disable SELinux by editing the config file:

sed -i 's/^SELINUX=.*/SELINUX=disabled/g' /etc/selinux/config

Reboot the machine for changes to take effect:

reboot

Install Shell Helpers (Optional)

Install shell completion helpers and index databases so file searches are fast:

yum install bash-completion mlocate -y && updatedb
source /etc/profile.d/bash_completion.sh 

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3. Installing the DHCP Package

Now, install the core DHCP packages:

yum install dhcp.x86_64 -y

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4. Firewall & Service Configuration

Open Firewall Services

Allow incoming DHCP traffic in your local firewall:

firewall-cmd --add-service=dhcp --permanent
firewall-cmd --reload

Verify Opened Services

Confirm that the dhcp service is correctly listed and accessible:

firewall-cmd --list-all

Enable Service on Startup

Set the DHCP daemon to start automatically at boot:

systemctl enable dhcpd.service

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5. Setting Up the DHCP Configuration

Now, populate the configuration file /etc/dhcp/dhcpd.conf.

This configuration is set to be authoritative and uses an explicit whitelisting group. Clients whose MAC addresses are listed below will receive the same static IP addresses every time they ask for a lease:

cat > /etc/dhcp/dhcpd.conf <<EOF
#------------------------------------------------------
authoritative;
default-lease-time 600;
max-lease-time 7200;
option domain-name-servers 8.8.8.8, 8.8.4.4;
option domain-name "induslevel.com";
option ntp-servers lhr-ntp1.induslevel.com,lhr-ntp2.induslevel.com;
 
subnet 172.16.99.0 netmask 255.255.255.0 {
        option broadcast-address 172.16.99.255;
        option routers 172.16.99.1;
        filename "/pxelinux.0";
        pool {
                range 172.16.99.150 172.16.99.230;
        }
        group {
                next-server lhr-pxe1.induslevel.com;
                host tclient110 {
                        hardware ethernet    00:0c:29:d3:a1:d1;
                        fixed-address        172.16.99.110;
                        option host-name "tclient110.induslevel.local";
                }
                host tclient120 {
                        hardware ethernet    00:21:cc:6c:2e:42;
                        fixed-address        172.16.99.120;
                        option host-name "tclient120.induslevel.local";
                }
        }
}
deny unknown-clients;
EOF

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6. Explaining the Config Variables

Here is a brief description of the key keywords used in your new dhcpd.conf:

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7. Starting the Service

Now, start the DHCP service and confirm that it is running correctly:

systemctl start dhcpd.service && systemctl status dhcpd.service

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8. Testing Configuration Correctness

To test that your new server responds to DHCP requests and returns configured IP leases correctly, use Nagios' check_dhcp plugin (available in EPEL):

yum install nagios-plugins-dhcp.x86_64 -y

Assuming your DHCP server is running on the static IP 172.16.99.254, simulate a dynamic lease request from client interface ens192 with a whitelisted MAC:

/usr/lib64/nagios/plugins/check_dhcp -i ens192 -m 00:0c:29:d3:a1:d1 -s 172.16.99.254

If the query succeeds, the plugin returns a success message, indicating your server is correctly responding to queries and validating hardware profiles!

In my next article, I will cover how to set up and configure a TFTP server to serve the PXE boot files, enabling unattended OS installations and security hardening.