If the VPN server is behind a firewall, packet filters must be configured for both an Internet interface and a perimeter network interface. In this scenario, the firewall is connected to the Internet, and the VPN server is an intranet resource that is connected to the perimeter network. The VPN server has an interface on both the perimeter network and the Internet.

VPNs can be either remote-access (connecting a computer to a network) or site-to-site (connecting two networks). In a corporate setting, remote-access VPNs allow employees to access their company's intranet from home or while travelling outside the office, and site-to-site VPNs allow employees in geographically disparate offices to share one cohesive virtual network. A VPN can also be used to interconnect two similar networks over a dissimilar middle network; for example, two IPv6 networks over an IPv4 network.[6]

Because a TCP connection is not used, L2TP uses message sequencing to ensure delivery of L2TP messages. Within the L2TP control message, the Next-Received field (similar to the TCP Acknowledgment field) and the Next-Sent field (similar to the TCP Sequence Number field) are used to maintain the sequence of control messages. Out-of-sequence packets are dropped. The Next-Sent and Next-Received fields can also be used for sequenced delivery and flow control for tunneled data.
Servers – IVPN offers 51 servers located in 23 countries. IVPN offers a multi-hop feature for in all of these servers, which basically scatters the traffic of users by moving it through different servers before finally reaching its true destination. This serves to enhance the security and helps protect the identity of the user. It is this feature that sets the VPN’s network apart from its competitors, something I found really good during IVPN review.
When you're away from home or the office and you connect to the internet, you'll most often be doing so via Wi-Fi provided by your hotel or the restaurant, library, or coffee shop you're working out of in that moment. Sometimes, the Wi-Fi has a password. Other times, it will be completely open. In either case, you have no idea who else is accessing that network, and therefore, you have no idea who might be snooping on your traffic.
Are you so used to your data traveling over Wi-Fi that you've stopped worrying about the security of that data—and about who else might be spying on it, or even stealing it for nefarious purposes? If so, you are—sadly—in the majority, and you ought to consider using a viritual private network, or VPN. In fact, when PCMag conducted a survey on VPN usage, we found that a dismal 71 percent of the 1,000 respondents had never used a VPN. Even among those who support net neutrality—who you might think would tend to be well informed on technology and privacy issues—only 45 percent had used a VPN.