When a Windows VPN connection fails with error 809, the message reads “The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g., firewalls, NAT, routers) between your computer and the remote server is not configured to allow VPN connections.” A firewall or NAT device between the PC and the server is blocking the VPN traffic.
The fix, in order
Try another network. Connect from a different Wi-Fi network or mobile data. If the VPN works there, the first network's firewall is blocking it, and the fix belongs to that network, not the PC.
Temporarily disable the local firewall. Turn the Windows Firewall or third-party firewall off briefly and test. If the VPN connects, add a rule to allow the VPN traffic instead of leaving the firewall off.
Check the required ports. L2TP/IPsec needs UDP ports 500 and 4500 open, and SSTP needs TCP port 443. If you manage the router or firewall, make sure those ports are allowed. The port numbers directory lists what each of these ports is used for.
Fix the NAT problem. Windows does not support L2TP/IPsec when the PC or the server sits behind a NAT device unless a registry setting is added. Microsoft documents the AssumeUDPEncapsulationContextOnSendRule value for this case. Back up the registry before changing it, and restart afterwards.
Check the VPN server address. A mistyped server name or address produces the same error, so confirm the address with the VPN administrator.
Try a different VPN protocol. If the server supports it, switching from L2TP/IPsec to IKEv2 or SSTP can avoid the blocked ports entirely.
Editing the registry to fix error 809 is an advanced step. Back up the registry first, and only add the documented AssumeUDPEncapsulationContextOnSendRule value. Never download a registry file from an untrusted site.
If it still happens
If the VPN fails with error 809 on every network, the server itself may be down or misconfigured, so check with the VPN administrator. If it fails only on one network, such as a hotel or office, that network is blocking VPN traffic, and the only fix is to use another network or ask the network owner.
Common questions
What does VPN error 809 mean? It means the PC could not reach the VPN server because something in between, usually a firewall or NAT device, blocked the VPN traffic. The server may be fine, but the traffic never gets to it.
Why does the VPN work at home but not at a hotel? Hotel and office networks often block VPN ports. The VPN is not broken, the network is filtering it. Switching to mobile data or asking the network owner are the practical options.