VPN being leaked

Tunnels A tunnel is a means of forwarding data across a network from one node to another, as if the two nodes were directly connected.  This is achieved by encapsulating the data – an extra header is added to data sent by the transmitting end of the tunnel, and the data is forwarded by intermediate nodes based on an this outer header without looking at the contents of the original packet. This is illustrated in the diagram below, which shows data going from A to B being sent through a tunnel between X and Z.  The intermediate tunnel node, node Y, does not need to be aware of the final destination, B, but just forwards the data along the tunnel to Z.  (In this scenario, X is known as the ingress to the tunnel and Z as the egress.) A X Y Z BSend to ZSend to BDataSend to ZSend to BDataSend to BDataSend to BDataTunnel from X to ZThis tunneling of data means that the P devices do not need to be aware of the VPNs, but just need to be able to forward tunneled data.  This is important as it reduces the network resources consumed by the VPN and the amount of configuration required to set it up.   In addition, by sending data between VPN sites using tunnels, it is possible to maintain separation of data between different VPNs, and to prevent data from a VPN being leaked into the provider network or global internet.  It also means that the addresses of devices within the VPN sites are hidden in the data transported over the tunnel, so they do not need to be changed to allow them to communicate over the Internet. There are a number of protocols that may be used to establish these tunnels, and the properties of the tunnel have a significant effect on the overall properties of the VPN using that tunnel.  However, many of the VPN solutions that we will describe do not rely on a particular tunneling technology and will work with one of several types.  For this reason, we do not cover the details of the tunnels when describing the different VPN solutions (except where necessary), but instead we give an overview of the main types of VPN tunnels in chapter 7, Tunnel Technologies.