## 2 Related Works  
Many works exist that propose security systems at different protocol stack layers and in different network typologies, showing cryptography performance analysis such as in [10] where authors provide a MAC layer security study on Wireless Sensor Networks (WSNs) also with the use of new technology as Elliptic Curve Cryptography (ECC) [11] proposingdifferent solution at different network attacks such as denial of services attack [12; 13]. Many studies are proposed that deal with the VPN issues showing performance evaluation in terms of throughput and delay in different testbed environments. In this section, we show a brief state-of-the-art summary of the VPN literature in order to present a brief overview about this important topic. In [7] a general VPN study approach is provided. The work focuses on the concept that VPN technology can only be meaningfully analyzed by referring to the values and motivations of the people who make up companies. A key finding reports the observed differences in \"how\" the terms \"VPN\" \"security,\" and \"privacy\" are perceived and understood in the corporate employee population. In [14], network layer-based VPN is evaluated. VPN provides secure encrypted communications between remote LANs around the world using Internet Protocol (IP) tunnels and a shared medium such as the Internet. The document focuses in particular on showing the strength of each VPN, through several studies on state-of-the-art and then analyzing the protocol Wireguard. A series of comparisons between deployments based on IPsec and GRE [15] and Wireguard is discussed in [15]. SSL VPN works at secure sockets layer. Again in this work [16], it is highlighted how an SSL-VPN is used extensively to guarantee authentication and confidentiality of data between the client (Web browser) and the server (SSL Server). In [17] an approach to using VPN technologies for secure encryption of traffic in untrusted networks, such as bars, lounges, conferences, free hotspots, free wifi at the airport, and generically during any trip are discussed. In [18; 19] VPN technology is discussed in depth. In particular, this work focuses on the weaknesses and poor performance in the presence of a high load of a web browser-based SSL VPN, which among other things, only supports Windows [16] operating systems. In paper [20] the choice of the IPSEC-IKEv2 suite is justified against other (SSL/TLS VPN, SSH Tunnel) possible implementations to ensure the security of the IP communication layer. The motivation lies in the ownership of \"transparency\" for the layers higher than the IP of IPSEC-IKEv2, as well as allowing a quick update of the encryption in case of data channel compromise. In this work [21] we evaluate the use of IPSEC to create VPNs suitable for \"e-business\" needs. A router Linksys, with the functionality of both an access point and a VPN concentrator and OpenSWAN as a system daemon, is used. This router supports the IKEv1-L2 TP tunnel type (authentication/traffic via L2 TP and encryption guaranteed by IPSEC). The IPSec stack consists of three subcomponents: Encapsulating Security Payload (ESP), Authentication Header (AH), and Internet Key Exchange Protocol (IKE). The AH protocol is also discussed in [22] the security and quality of service aspects of VPNs are considered. The IKE protocol allows the various VPN endpoints to produce session keys for secure communications through a series of message exchanges. IKE currently consists of two versions, IKEv1 [23; 24] and IKEv2 [16]. IKEv1 is very flexible and allows different configuration options, but it has a great architectural complexity that makes it increasingly difficult to deploy in modern networks. IKEv2 collects the legacy of the previous version and overcomes its limits, also providing more modern and performing encryption systems for network traffic. An important feature of IKEv2 is native support on current platforms (OS X 10.11+, iOS 9.1+, Linux 3.x + and Windows 8+).