This error means Pi-hole’s DNS resolver is failing to get upstream DNS responses, preventing your network devices from accessing the internet.
1. Upstream DNS Server Unreachable
Diagnosis: Check connectivity to your configured upstream DNS servers from the Pi-hole host.
ping 8.8.8.8
ping 1.1.1.1
Cause: The Pi-hole host itself cannot reach the internet to query your chosen upstream DNS servers (e.g., Google DNS, Cloudflare DNS). This is often due to a network configuration issue on the Pi-hole’s host machine.
Fix: Ensure the Pi-hole host has a valid IP address, subnet mask, gateway, and DNS server configured. If you’re using DHCP on the Pi-hole host, check your router. If static, check /etc/dhcpcd.conf (Raspberry Pi OS) or /etc/network/interfaces (older Debian/Ubuntu).
Example for /etc/dhcpcd.conf (Raspberry Pi OS):
interface eth0
static ip_address=192.168.1.10/24
static routers=192.168.1.1
static domain_name_servers=1.1.1.1 8.8.8.8
Why it works: This provides the Pi-hole host with the necessary network information to communicate with the local network and the internet, allowing it to send DNS queries to upstream servers.
2. Incorrect Upstream DNS Server Configuration in Pi-hole
Diagnosis: Verify the upstream DNS servers listed in the Pi-hole web interface.
Navigate to Settings -> DNS in the Pi-hole web GUI.
Cause: The IP addresses of the upstream DNS servers entered into Pi-hole are incorrect, or the chosen servers are experiencing an outage.
Fix: Select a known-good public DNS provider like 1.1.1.1 (Cloudflare) or 8.8.8.8 (Google) from the list of common upstream providers. If you use custom servers, double-check their IP addresses.
Why it works: Pi-hole will then attempt to query these valid, reachable DNS servers for resolution.
3. Pi-hole Service Not Running or Crashed
Diagnosis: Check the status of the Pi-hole FTL (Faster Than Light) service.
sudo systemctl status pihole-FTL.service
Cause: The core Pi-hole DNS processing service has stopped or crashed, preventing it from listening for and processing DNS requests.
Fix: Restart the Pi-hole FTL service.
sudo systemctl restart pihole-FTL.service
Why it works: This re-initializes the DNS resolver and processing engine, allowing it to accept and handle DNS queries again.
4. Firewall Blocking DNS Traffic
Diagnosis: Check if a firewall on the Pi-hole host is blocking UDP/TCP port 53.
sudo ufw status # If using UFW
sudo iptables -L -n -v # If using iptables directly
Cause: A local firewall on the Pi-hole machine (or a network firewall) is preventing DNS queries (typically UDP port 53, sometimes TCP port 53 for larger responses) from being sent to or received from upstream servers.
Fix: Allow DNS traffic through the firewall.
Example for UFW:
sudo ufw allow 53/udp
sudo ufw allow 53/tcp
sudo ufw reload
Why it works: This explicitly permits DNS traffic, enabling Pi-hole to communicate with upstream servers and clients.
5. Router DNS Settings Pointing to Pi-hole Incorrectly
Diagnosis: Check your router’s DHCP and DNS settings.
Navigate to your router’s administration interface. Look for DHCP server settings and DNS server settings.
Cause: Your router’s DHCP server is configured to hand out IP addresses to clients, but the DNS server IP address it’s advertising is incorrect, unreachable, or not the Pi-hole’s IP address. This is common if you’ve recently changed your DNS setup or added Pi-hole.
Fix: Configure your router’s DHCP server to only advertise the Pi-hole’s IP address as the DNS server for your network. Ensure no other DNS servers are listed.
Example Router DHCP Settings:
- DHCP Server: Enabled
- Start IP Address: 192.168.1.100
- End IP Address: 192.168.1.200
- DNS Server 1:
192.168.1.10(Your Pi-hole’s IP) - DNS Server 2: (Leave blank or set to the same Pi-hole IP)
Then, renew the DHCP lease on your client devices (e.g., ipconfig /renew on Windows, reboot device, or disconnect/reconnect Wi-Fi).
Why it works: Clients on your network will then correctly point their DNS requests to Pi-hole, which can then forward them upstream.
6. Network Interface Down or Misconfigured
Diagnosis: Check the status of the network interface Pi-hole is using.
ip a
Cause: The network interface (e.g., eth0, wlan0) that Pi-hole is configured to listen on is down, disabled, or has an incorrect IP configuration.
Fix: Ensure the network interface is up and has a valid IP address. If static, verify /etc/dhcpcd.conf or equivalent. If it’s down, bring it up:
sudo ip link set eth0 up # Replace eth0 with your interface name
Why it works: Pi-hole needs an active network interface with a proper IP address to bind to and listen for DNS requests from clients.
The next error you’ll likely encounter if these are all resolved is a "Connection timed out" when trying to access a specific website, indicating a problem with the website’s server or a further network path issue.