✅ Quick Checklist

• Confirm your internet connection is working without VPN.
• Check your VPN credentials (username, password, certificates).
• Ensure the VPN server is online and reachable.
• Verify VPN software or client is up to date.
• Temporarily disable firewall or antivirus that may block VPN traffic.

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🛠 Step 1: Basic Troubleshooting

1. Restart your device and VPN client.
2. Try a different network to rule out ISP restrictions.
3. Use the VPN server’s IP instead of hostname if DNS resolution fails.
4. Check VPN client logs for error codes or messages.

🛠 Step 2: Verify VPN Protocols & Ports

• Common VPN protocols: OpenVPN, L2TP/IPSec, IKEv2, WireGuard.
• Ensure the correct protocol is selected in your client.
• Check router or firewall allows required ports (e.g., OpenVPN: UDP 1194, TCP 443; L2TP/IPSec: UDP 500 & 4500).
• Try switching between TCP and UDP if your VPN supports it.

🛠 Step 3: DNS & IP Configuration

• Flush local DNS cache:
  • Windows: ipconfig /flushdns
  • macOS: sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder
  • Linux: sudo systemd-resolve --flush-caches
• Check VPN-assigned DNS is working; sometimes you need to manually set DNS servers.
• Verify routing table changes after VPN connects using route print (Windows) or ip route (Linux/macOS).

🛠 Step 4: Firewall & Antivirus Settings

• Ensure your firewall allows the VPN client to connect to the required ports.
• Temporarily disable antivirus or security software to check for interference.
• Check for VPN “kill switch” or firewall rules that block traffic when disconnected.

🛠 Step 5: Advanced Troubleshooting

1. Check logs on VPN server (if accessible) for authentication or routing errors.
2. Update VPN client software and drivers (network adapters, TAP drivers for OpenVPN, etc.).
3. Test VPN connection using a different device to isolate client vs server issues.
4. Use traceroute or ping to verify reachability to VPN server.
5. Consider using alternative protocols if your ISP blocks VPN traffic.

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💡 Tips

• Keep VPN client and operating system up to date for security and compatibility.
• Document working configurations for multiple servers or devices.
• Consider splitting traffic (split tunneling) for better performance if VPN slows down all traffic.
• For persistent issues, contact your VPN provider with error logs for advanced troubleshooting.

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📊 Summary Table

Problem	Possible Cause	Solution	Difficulty
VPN fails to connect	Incorrect credentials, server offline, firewall block	Verify login, ping server, check firewall rules	Easy–Medium
Connection drops intermittently	Weak network, ISP interference, protocol issues	Switch protocol, use wired connection, check routing	Medium
Slow VPN performance	High latency, congested server, routing inefficiencies	Change server location, use split tunneling, test alternative protocols	Medium–Advanced