To set up a DHCP server on Ubuntu, first install the isc-dhcp-server package, which provides the ISC DHCP server daemon. Run the following commands to update the package repository and install the software:
sudo apt update && sudo apt install isc-dhcp-server -y
This installs the necessary binaries, configuration files, and dependencies for the DHCP server.
The main configuration file for the ISC DHCP server is /etc/dhcp/dhcpd.conf. You need to define global options (applied to all subnets) and subnet-specific settings (IP ranges, gateways, DNS servers).
Add these lines at the top of the file to set default values for all subnets:
default-lease-time 600; # Default lease time (10 minutes)
max-lease-time 7200; # Maximum lease time (2 hours)
option domain-name "example.com"; # Your domain name
option domain-name-servers 8.8.8.8, 8.8.4.4; # Public DNS servers
authoritative; # Declare this server as authoritative for the network
default-lease-time: Time (in seconds) a client can use an IP before renewal.max-lease-time: Maximum time a client can hold an IP (even if it requests a longer lease).authoritative: Ensures the server responds to all DHCP requests in its network (prevents rogue servers).Define a subnet block for your local network. Replace the example values with your actual network details (e.g., 192.168.1.0/24):
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.100 192.168.1.200; # Available IP range for dynamic allocation
option routers 192.168.1.1; # Default gateway (router) IP
option subnet-mask 255.255.255.0; # Subnet mask for the network
}
range: Defines the pool of IPs the server can assign to clients.option routers: The gateway IP clients use to access other networks (e.g., the internet).option subnet-mask: Identifies the network portion of IP addresses.The DHCP server must be configured to listen on the correct network interface (e.g., eth0, enp0s3). Edit the /etc/default/isc-dhcp-server file and modify the INTERFACESv4 line:
INTERFACESv4="eth0" # Replace 'eth0' with your actual interface name
To find your interface name, run ip a or ifconfig—look for the interface connected to your local network.
After configuring the files, start the DHCP server and enable it to launch at boot:
sudo systemctl start isc-dhcp-server # Start the service
sudo systemctl enable isc-dhcp-server # Enable auto-start on boot
Check the service status to ensure it’s running correctly:
sudo systemctl status isc-dhcp-server
A status of active (running) indicates the server is operational.
To confirm the server is assigning IPs, connect a client device (e.g., a laptop or another Ubuntu machine) to the same network and configure it to use DHCP:
/etc/netplan/01-netcfg.yaml (or the appropriate Netplan file) and set the interface to use DHCP:network:
version: 2
renderer: networkd
ethernets:
eth0: # Replace with your client interface name
dhcp4: yes
sudo netplan apply.ip addr show eth0 (replace eth0 with your interface). Look for an IP address within the range specified in the server’s subnet block (e.g., 192.168.1.100–192.168.1.200).To assign a fixed IP to a specific device (e.g., a printer or server), add a host block to the /etc/dhcp/dhcpd.conf file. Use the device’s MAC address (find it with ip link show on the client) and desired static IP:
host printer1 {
hardware ethernet 00:1a:2b:3c:4d:5e; # Replace with the client's MAC address
fixed-address 192.168.1.50; # Static IP to assign
}
Save the file and restart the DHCP server to apply changes:
sudo systemctl restart isc-dhcp-server
If clients aren’t receiving IPs, check the following:
sudo ufw allow 67/udp
sudo ufw allow 68/udp
dhcpd.conf file with sudo dhcpd -t (this checks for errors without starting the server).journalctl -u isc-dhcp-server.service -f
INTERFACESv4 value in /etc/default/isc-dhcp-server matches the interface connected to the network.By following these steps, you can set up a functional DHCP server on Ubuntu to automate IP address allocation for your local network.
