How to Set Up a DHCP Server with `isc-dhcp44-server` on FreeBSD

Introduction

Dynamic Host Configuration Protocol (DHCP) is essential for managing network configurations by automatically assigning IP addresses to clients. On FreeBSD, the isc-dhcp44-server package provides a reliable and flexible DHCP server implementation. This guide will walk you through installing, configuring, and managing a DHCP server using isc-dhcp44-server on FreeBSD.

Prerequisites

Before starting, ensure you have:

• A FreeBSD system with root or sudo access
• A static IP address configured on the network interface
• A basic understanding of networking concepts

Step 1: Installing isc-dhcp44-server

FreeBSD provides the isc-dhcp44-server package via the ports collection and binary package system. You can install it using either method.

Using pkg (Binary Package)

sudo pkg install isc-dhcp44-server

Using Ports Collection

If you prefer to build from source, use the ports collection:

cd /usr/ports/net/isc-dhcp44-server
sudo make install clean

Once installed, verify the installation:

pkg info isc-dhcp44-server

Step 2: Configuring the DHCP Server

The main configuration file is located at /usr/local/etc/dhcpd.conf. Open it using a text editor:

sudo vi /usr/local/etc/dhcpd.conf

Basic DHCP Configuration

Below is a simple DHCP configuration for a network 192.168.1.0/24:

default-lease-time 600;
max-lease-time 7200;
option domain-name "example.com";
option domain-name-servers 8.8.8.8, 8.8.4.4;

subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.100 192.168.1.200;
    option routers 192.168.1.1;
    option broadcast-address 192.168.1.255;
}

Assigning Static IP Addresses

To assign a static IP to a specific device, add an entry like this:

host mydevice {
    hardware ethernet AA:BB:CC:DD:EE:FF;
    fixed-address 192.168.1.50;
}

Replace AA:BB:CC:DD:EE:FF with the MAC address of the device.

Step 3: Configuring the DHCP Service

Specify the network interface that dhcpd will listen on by editing /etc/rc.conf:

sudo vi /etc/rc.conf

Add the following lines:

dhcpd_enable="YES"
dhcpd_ifaces="em0"

Replace em0 with your actual network interface. You can check available interfaces with:

ifconfig

Step 4: Starting and Managing the DHCP Service

Start the DHCP Server

sudo service isc-dhcpd start

Check Status

sudo service isc-dhcpd status

Enable DHCP Service at Boot

sudo sysrc dhcpd_enable=YES

Restart or Stop the Service

To restart:

sudo service isc-dhcpd restart

To stop:

sudo service isc-dhcpd stop

Step 5: Testing the DHCP Server

To test the server, connect a client device and check if it receives an IP address. You can verify DHCP leases on the server with:

cat /var/db/dhcpd.leases

For real-time logging:

tail -f /var/log/messages

Step 6: Troubleshooting Common Issues

DHCP Service Fails to Start

• Ensure there are no syntax errors in /usr/local/etc/dhcpd.conf by running:

  sudo dhcpd -t -cf /usr/local/etc/dhcpd.conf
  

• Confirm that the correct interface is set in /etc/rc.conf.

• Check logs for errors:

  sudo tail -f /var/log/messages
  

Clients Are Not Receiving IP Addresses

• Verify that the network interface has the correct IP configuration.

• Restart the DHCP service:

  sudo service isc-dhcpd restart
  

• Confirm that no other DHCP servers are running on the network.

Step 7: Advanced Configurations

Configuring Dynamic DNS Updates

If you want to integrate DHCP with a DNS server for dynamic updates, add the following to dhcpd.conf:

zone example.com. {
    primary 192.168.1.1;
    key DHCP_UPDATE_KEY;
}

You also need to configure the DNS server to accept updates from the DHCP server.

Configuring Multiple Subnets

For multiple subnets, define each subnet separately:

subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.100 192.168.1.200;
    option routers 192.168.1.1;
}

subnet 10.0.0.0 netmask 255.255.255.0 {
    range 10.0.0.100 10.0.0.200;
    option routers 10.0.0.1;
}

Conclusion

Setting up a DHCP server on FreeBSD using isc-dhcp44-server is a straightforward process. By following this guide, you should have a fully functional DHCP server that automatically assigns IP addresses to clients in your network. Regularly monitor logs and update configurations as needed to ensure optimal performance.