Virtual private networking, or VPN, is a technology that allows you to create a secure connection to another network from a remote site. The technology relies on a VPN server, which is a special server designed to create the secure tunnel to your computer and pass information to and from your computer and the private network. VPN connections are usually characterised by a decrease in bandwidth and an increased latency (or the time it takes to fulfil requests) because all data has to pass through an extra server (the VPN server). Fortunately, there is an easy way to quantify the quality of a VPN connection by testing the speed of a VPN.
Determine the speed of your Internet connection without using a VPN server. The easiest way to do this is to use an Internet bandwidth test such as those available freely from the Federal Communications Commission (see Resources). Your bandwidth test will have three key components--download speed, upload speed and latency. Upload and download speeds quantify how fast you transfer data to and from Internet servers, respectively. Latency is the time it takes to fulfil an Internet request.
Connect to the VPN server using your choice of VPN clients. Many VPN servers require specific types of clients, so use your support documentation or IT department to determine the best client to use.
Repeat the speed test and get new values for download speed, upload speed, and latency while using the VPN connection.
Subtract your download and upload speeds using the VPN connection from the corresponding values without using the VPN connection. This will tell you how much speed is lost from connecting through a VPN server. Subtract the latency without using the VPN connection from that when you are using a VPN connection to determine the increase in latency when using a VPN connection.