Windows: updating the DNS cache

A frequently recurring question on the openvpn-users mailing lists is related to the DNS name resolution on Windows after the VPN connection is established. If the OpenVPN server pushes out a new DNS server, then this is automatically picked up by the OpenVPN client, yet name resolution does not always work right after establishing the connection. This has little to do with OpenVPN and more to do with the way the Windows DNS caching service works. As this question comes up quite regularly, a new directive register-dns was added in OpenVPN 2.1.3. When this directive is specified, OpenVPN updates the Windows DNS cache and registers the VPN IP address in the Windows DNS tables. As this feature appeared only recently, this recipe will also show how the Windows DNS cache can be updated using a script when the VPN connection is established. Some users disable the DNS caching service altogether, which seems to have a little impact on the operating system, except...