This tutorial will walk you through setting up an ISC DHCP server on Ubuntu 22.04 or 24.04 with support for multiple subnets and VLAN interfaces. You will learn how to:
- Install necessary packages
- Identify and configure network interfaces, including VLANs
- Configure Netplan for IP addressing and VLANs
- Configure ISC DHCP server with multiple scopes
- Enable and start the DHCP service
At the end, there is an interactive script that automates all these steps.
Prerequisites
- Ubuntu 22.04 or 24.04 system with root or sudo access
- Basic familiarity with Linux command line
- Network interfaces available (physical or virtual)
Step 1: Install required packages
Update your system and install the DHCP server and VLAN tools:
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sudo apt update
sudo apt install -y isc-dhcp-server vlan
Step 2: Identify network interfaces
Check available interfaces (excluding loopback):
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ip -o link show | awk -F': ' '{print $2}' | grep -v lo
Example output might be:
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eth0
eth1
eth2
Step 3: Plan your subnets
Decide how many subnets you want to configure. For each subnet, decide:
- Whether it will be on a physical interface or a VLAN
- IP address of the server interface
- Subnet mask
- Gateway IP
- DHCP IP range start and end
- CIDR prefix length
Step 4: Configure VLAN interfaces (optional)
If you want VLAN support:
- Choose a physical interface (e.g.,
eth0) as the VLAN parent. - Select a VLAN ID (e.g.,
10). - The VLAN interface name will be
<parent>.<vlan-id>, e.g.,eth0.10.
Step 5: Configure Netplan
Netplan configuration files are located in /etc/netplan/. To configure multiple interfaces and VLANs, create a file, e.g., /etc/netplan/01-multiscope-dhcp.yaml with content:
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network:
version: 2
ethernets:
eth0:
addresses: [192.168.1.1/24]
gateway4: 192.168.1.254
nameservers:
addresses: [8.8.8.8, 8.8.4.4]
vlans:
eth0.10:
id: 10
link: eth0
addresses: [192.168.10.1/24]
gateway4: 192.168.10.254
nameservers:
addresses: [8.8.8.8, 8.8.4.4]
Adjust addresses and interfaces according to your plan.
Apply the configuration:
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sudo netplan apply
Step 6: Configure ISC DHCP server
The main DHCP server configuration is in /etc/dhcp/dhcpd.conf.
Add subnet definitions like this for each subnet:
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default-lease-time 600;
max-lease-time 7200;
authoritative;
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.100 192.168.1.200;
option routers 192.168.1.254;
option subnet-mask 255.255.255.0;
option domain-name-servers 8.8.8.8, 8.8.4.4;
}
subnet 192.168.10.0 netmask 255.255.255.0 {
range 192.168.10.100 192.168.10.200;
option routers 192.168.10.254;
option subnet-mask 255.255.255.0;
option domain-name-servers 8.8.8.8, 8.8.4.4;
}
Step 7: Configure DHCP server to listen on interfaces
Edit /etc/default/isc-dhcp-server and set the INTERFACESv4 variable to include all your interfaces (physical and VLAN), e.g.:
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INTERFACESv4="eth0 eth0.10"
Step 8: Start and enable DHCP server
Restart the DHCP server to apply the configuration:
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sudo systemctl restart isc-dhcp-server
sudo systemctl enable isc-dhcp-server
Check status with:
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sudo systemctl status isc-dhcp-server
Summary
You have now set up a DHCP server on Ubuntu that supports multiple subnets including VLAN interfaces. This setup can be used in home labs, testing environments, or production with appropriate adjustments.
Optional: Automated Interactive Script
To simplify this whole process, you can use the following interactive Bash script. It will:
- Install needed packages
- Detect interfaces
- Let you configure multiple subnets (with or without VLANs)
- Automatically generate Netplan and DHCP configs
- Enable and start the DHCP server
Download and run:
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chmod +x setup-multiscope-dhcp-vlan.sh
sudo ./setup-multiscope-dhcp-vlan.sh
Script source:
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#!/bin/bash
set -e
echo "=== Interactive DHCP Installer (with VLAN support) for Ubuntu 22.04 / 24.04 ==="
if [[ $EUID -ne 0 ]]; then
echo "Please run this script as root (e.g., sudo $0)"
exit 1
fi
apt update && apt install -y isc-dhcp-server vlan
echo ""
echo "Available network interfaces:"
interfaces=$(ip -o link show | awk -F': ' '{print $2}' | grep -v lo)
echo "$interfaces"
echo ""
read -p "How many subnets do you want to configure? (e.g., 2): " SUBNET_COUNT
NETPLAN_CFG="network:\n version: 2\n ethernets:\n"
VLAN_CFG=""
DHCP_CONF="default-lease-time 600;\nmax-lease-time 7200;\nauthoritative;\n"
IFACE_LIST=()
for ((i=1; i<=SUBNET_COUNT; i++)); do
echo ""
echo "=== Configuration for subnet $i ==="
echo "Should this subnet use a VLAN interface? (y/n)"
read -n1 USE_VLAN
echo ""
if [[ "$USE_VLAN" == "y" || "$USE_VLAN" == "Y" ]]; then
echo "Select the parent (physical) interface for the VLAN:"
select PARENT_IFACE in $interfaces; do
[[ -n "$PARENT_IFACE" ]] && break
done
read -p "Enter VLAN ID (e.g., 10): " VLAN_ID
VLAN_IFACE="${PARENT_IFACE}.${VLAN_ID}"
IFACE_LIST+=("${VLAN_IFACE}")
VLAN_CFG+=" vlans:\n"
VLAN_CFG+=" ${VLAN_IFACE}:\n"
VLAN_CFG+=" id: ${VLAN_ID}\n"
VLAN_CFG+=" link: ${PARENT_IFACE}\n"
read -p "Enter the server IP address (e.g., 192.168.${VLAN_ID}.1): " SERVER_IP
read -p "Enter the subnet mask (e.g., 255.255.255.0): " NETMASK
read -p "Enter the default gateway (e.g., 192.168.${VLAN_ID}.254): " GATEWAY
read -p "Enter the DHCP range start (e.g., 192.168.${VLAN_ID}.100): " DHCP_START
read -p "Enter the DHCP range end (e.g., 192.168.${VLAN_ID}.200): " DHCP_END
read -p "Enter CIDR prefix length (e.g., 24): " CIDR
VLAN_CFG+=" addresses: [${SERVER_IP}/${CIDR}]\n"
VLAN_CFG+=" gateway4: ${GATEWAY}\n"
VLAN_CFG+=" nameservers:\n"
VLAN_CFG+=" addresses: [8.8.8.8,8.8.4.4]\n"
else
echo "Select a physical interface for this subnet:"
select IFACE in $interfaces; do
[[ -n "$IFACE" ]] && break
done
IFACE_LIST+=("$IFACE")
read -p "Enter the server IP address (e.g., 192.168.1.1): " SERVER_IP
read -p "Enter the subnet mask (e.g., 255.255.255.0): " NETMASK
read -p "Enter the default gateway (e.g., 192.168.1.254): " GATEWAY
read -p "Enter the DHCP range start (e.g., 192.168.1.100): " DHCP_START
read -p "Enter the DHCP range end (e.g., 192.168.1.200): " DHCP_END
read -p "Enter CIDR prefix length (e.g., 24): " CIDR
NETPLAN_CFG+=" ${IFACE}:\n"
NETPLAN_CFG+=" addresses: [${SERVER_IP}/${CIDR}]\n"
NETPLAN_CFG+=" gateway4: ${GATEWAY}\n"
NETPLAN_CFG+=" nameservers:\n"
NETPLAN_CFG+=" addresses: [8.8.8.8,8.8.4.4]\n"
fi
SUBNET_BASE=$(echo "$SERVER_IP" | awk -F'.' '{print $1"."$2"."$3".0"}')
DHCP_CONF+="\nsubnet ${SUBNET_BASE} netmask ${NETMASK} {\n"
DHCP_CONF+=" range ${DHCP_START} ${DHCP_END};\n"
DHCP_CONF+=" option routers ${GATEWAY};\n"
DHCP_CONF+=" option subnet-mask ${NETMASK};\n"
DHCP_CONF+=" option domain-name-servers 8.8.8.8, 8.8.4.4;\n"
DHCP_CONF+="}\n"
done
echo ""
echo "=== Generating configuration files ==="
# Finalize netplan config
NETPLAN_ALL="$NETPLAN_CFG"
if [[ -n "$VLAN_CFG" ]]; then
NETPLAN_ALL+="\n$VLAN_CFG"
fi
echo -e "$NETPLAN_ALL" > /etc/netplan/01-multiscope-dhcp.yaml
echo "Applying netplan..."
netplan apply
# Configure DHCP server interfaces
echo "INTERFACESv4=\"${IFACE_LIST[*]}\"" > /etc/default/isc-dhcp-server
echo -e "$DHCP_CONF" > /etc/dhcp/dhcpd.conf
systemctl restart isc-dhcp-server
systemctl enable isc-dhcp-server
echo ""
echo "✅ DHCP server is now running on interfaces: ${IFACE_LIST[*]}"
If you have any questions or want help extending this setup, feel free to reach out!