A virtual private network (VPN) extends a private network across a public network such as the internet. A VPN enables a computer to send and receive data across public networks as if it were directly connected to the private network. Neutron provides a set of APIs to allow users to create IPSec-based VPN tunnels from Neutron routers to remote gateways when using the open source reference implementation. The use of VPN as a Service is outside the scope of this book.