VPN changes your Internet Protocol address aka IP address. When you connect to a web server, you are sending your web browser a request over the network. Your web browser then requests an IP address from your ISP (Internet Service Provider), McDonald's server in this instance. The ISP provides the web browser with one of their IP addresses. This is called your "IP address" or your "local IP". A local IP is used to identify your computer on the network. Since VPN overrides the IP address of Mcdonald's free wifi server, you can not get past the ISP server using a VPN.