How to fix dial tcp: connect: network is unreachable in Docker

First, confirm your host machine has internet access:

ping -c 3 8.8.8.8
curl -I https://registry-1.docker.io

If these fail, the problem is with your host's network configuration, not Docker. Check your network connection, router, and firewall settings.

If you previously configured Minikube, Docker Machine, or remote Docker, the DOCKER_HOST variable might point to an unreachable address:

echo $DOCKER_HOST

If it shows an IP address (like tcp://192.168.64.4:2376), unset it:

unset DOCKER_HOST
unset DOCKER_TLS_VERIFY
unset DOCKER_CERT_PATH

Also check and remove from your shell profile (~/.bashrc, ~/.zshrc) any lines like:

eval $(minikube docker-env)

A simple restart often resolves transient network issues:

# Linux with systemd
sudo systemctl restart docker

# macOS/Windows Docker Desktop
# Use the Docker Desktop menu to restart, or:
# macOS
killall Docker && open /Applications/Docker.app

# Verify Docker is running
docker info

Docker requires IP forwarding to be enabled for container networking. Check and enable it:

# Check current setting
sysctl net.ipv4.conf.all.forwarding

# Enable temporarily
sudo sysctl -w net.ipv4.conf.all.forwarding=1

# Enable permanently
echo "net.ipv4.conf.all.forwarding=1" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

Then restart Docker:

sudo systemctl restart docker

If Docker's network bridge is corrupted, reset it:

# Stop Docker
sudo systemctl stop docker

# Remove the existing bridge
sudo ip link set docker0 down
sudo ip link delete docker0

# Restart Docker (it will recreate docker0)
sudo systemctl start docker

# Verify the bridge exists
ip addr show docker0

Ensure Docker can reach DNS servers. Create or edit /etc/docker/daemon.json:

sudo nano /etc/docker/daemon.json

Add DNS configuration:

{
  "dns": ["8.8.8.8", "8.8.4.4"]
}

Restart Docker:

sudo systemctl restart docker

Note: Use your corporate DNS servers instead if public DNS is blocked.

Ensure iptables allows Docker traffic:

# Check if Docker's iptables rules exist
sudo iptables -L -n | grep -i docker

# Reset iptables NAT table (Docker will recreate rules on restart)
sudo iptables -t nat -F
sudo systemctl restart docker

# For firewalld (CentOS/RHEL/Fedora)
sudo firewall-cmd --permanent --zone=trusted --add-interface=docker0
sudo firewall-cmd --reload

If using UFW on Ubuntu:

sudo ufw allow in on docker0 from any to any

If your host only has IPv6 connectivity, Docker Hub's default registry may not be reachable. Use Docker's IPv6-enabled registry:

# Pull using IPv6 registry endpoint
docker pull registry.ipv6.docker.com/library/ubuntu:latest

Alternatively, enable IPv6 for Docker daemon in /etc/docker/daemon.json:

{
  "ipv6": true,
  "fixed-cidr-v6": "fd00::/80"
}

If you need IPv4 connectivity, contact your hosting provider to attach an IPv4 interface.

If running Docker inside a virtual machine:

1. Verify VM network adapter is connected and has the correct mode (NAT for internet access, or Bridged for direct network access)

2. For VirtualBox:
- Go to Settings > Network
- Ensure Adapter is attached to NAT or Bridged Adapter
- Check "Cable Connected" is enabled

3. For VMware:
- Check VM Settings > Network Adapter
- Set to NAT or Bridged mode

4. For cloud VMs (AWS, GCP, Azure):
- Verify security groups/firewall rules allow outbound HTTPS (port 443)
- Check that the instance has a public IP or NAT gateway configured

As a temporary workaround, bypass Docker's network isolation:

# Run container with host networking
docker run --network host your-image

# Or in Docker Compose
services:
  your-service:
    network_mode: host

Warning: This removes network isolation. Only use for debugging or when necessary.