Viscosity will display a warning in the OpenVPN log if the "block-outside-dns" command is present in the advanced commands section or it has been pushed by the OpenVPN server. The use of this option is not required thanks to Viscosity's advanced DNS system.

OpenVPN 2.3.9 introduced the "block-outside-dns" command as a method to prevent DNS leaks under Windows by blocking access to VPN servers through normal network interfaces using Windows Filtering Platform (WFP) rules. In Viscosity, setting a connection's DNS to Full Mode (or Automatic where a connection will route all traffic over the VPN connection) will prevent DNS leaks outside the VPN Interface. You can find more information about network traffic and DNS leaks in the Preventing Network and DNS Traffic Leaks article, and information about the available DNS settings in the Configuring DNS and WINS settings article.

As the "block-outside-dns" command may interfere with Viscosity's DNS support, causes known performance issues, and offers no additional security, its use is disabled in Viscosity.