VPN Connection Errors
VPN errors can occur when authentication fails, network ports are blocked, or routing configurations conflict. This guide walks you through identifying, diagnosing, and fixing the most common connection issues.
Tip: Always ensure your VPN client is up to date. Older versions often fail after system or server updates.
Common VPN Error Codes
- Error 619: The connection failed after attempting to establish communication with the remote server.
- Error 720: The PPP configuration is invalid or corrupt. Try removing and re-adding the VPN connection.
- Error 809: The VPN tunnel failed to establish due to blocked ports, NAT issues, or firewall interference.
- SSL VPN Failure: Typically caused by expired certificates or TLS version mismatches.
Troubleshooting Steps
- Disable and re-enable your VPN adapter in Network Connections.
- Confirm your VPN credentials and correct server address.
- Check that UDP ports 500 and 4500 are allowed through your firewall for IPsec connections.
- Restart the IPsec Policy Agent and IKE and AuthIP IPsec Keying Modules services in Windows.
- If using SSL VPNs (FortiClient, OpenVPN, etc.), verify certificates and TLS compatibility.
Warning: Avoid disabling firewalls or antivirus entirely while testing connectivity. Instead, create temporary exceptions for your VPN client.
Advanced Options
- Disable split tunneling if internal corporate resources fail to load.
- Run
ipconfig /flushdnsafter disconnecting to clear cached DNS records. - Review client and server logs for authentication or certificate errors.
- Check DNS settings — VPNs may override local DNS or use internal resolvers.
Success Tip: Once your VPN connects successfully, test internal and external site access to verify proper routing.