Skip to contentVPN kill switch on Windows: client settings and checks
Set up and test a Windows VPN kill switch. Understand WireGuard blocking, Defender rule precedence, DNS and IPv6 limits.
What a kill switch really is
An s4m VPN profile works with a compatible client; blocking is configured in that client. For WireGuard on Windows, open the tunnel editor and review its blocking option. The official client activates restrictive firewall semantics for one peer with a /0 AllowedIPs entry. Routes split into /1 ranges do not activate the same semantics. Check the general setup and tests and the official Windows behaviour: permitted exceptions include tunnel establishment, loopback, DHCP and IPv6 neighbour discovery. DNS restrictions depend on configured DNS servers. Keep the issued endpoint, keys and required routes; review changes before activation.
Inspect active Windows firewall policy
These PowerShell commands only inspect policy and routes; they do not enable a kill switch. Review existing allow rules and their address, port and interface filters.
Get-NetFirewallProfile -PolicyStore ActiveStore | Select-Object Name,Enabled,DefaultOutboundAction Get-NetFirewallRule -PolicyStore ActiveStore -Enabled True -Direction Outbound | Select-Object DisplayName,Action,Profile Get-NetRoute -AddressFamily IPv4 Get-NetRoute -AddressFamily IPv6
How it behaves, and its limits
Windows can enforce outbound restrictions, but existing allow rules can bypass a default block. An explicit block rule instead overrides conflicting allows. Use a documented client feature or a policy reviewed for the complete effective ruleset; test it before relying on it.
See Microsoft’s rule precedence. Test an unreachable endpoint while the tunnel stays active; manual deactivation is a different case and may remove blocking. Check DNS, IPv6 / WebRTC, new and existing connections using the leaks guide. Server policy does not establish VPN client behaviour.
Questions, answered
Can I make a VPN kill switch without extra software on Windows?
Windows can enforce outbound restrictions, but existing allow rules can bypass a default block. An explicit block rule instead overrides conflicting allows. Use a documented client feature or a policy reviewed for the complete effective ruleset; test it before relying on it.
Will a firewall kill switch stop all leaks?
Enable blocking when you need traffic to stay inside the VPN, then verify its scope and exceptions. Test failed handshakes, reconnects, sleep, startup and manual disconnect with IPv4, IPv6 and DNS. A successful IP check alone does not prove all traffic is protected.
Check protection before relying on it
Use the s4m profile with a compatible client, review its blocking settings, and test the traffic you need protected.
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