VPN systems use non-TCP/UDP

VPN systems use non-TCP/UDP protocol, or use privileged low (< 1024) ports (e.g. ISAKMP used by IPSEC uses port 500) that are often blocked by firewalls. This means that VPN clients can be unusable from many places like public hotspots, hotels and many GPRS connections. User mobility and remote access often do not work with a VPN model. The above limitations of the current VPN systems have been the driving force for the authors for the design of N2N. In a nutshell we ask: "Is it possible to have decentralised, network-administrator-free, secure and permanent network access with a single/uniform address regardless of the current user's location, local IP address and network type?".The authors  designed N2N  to give N2N users the ability to create dynamic private networks. As happens with community networks, users should be able to create their own overlay network which other users are invited to join. With VPN the network administrator chooses who may join the VPN and what interactions will be tolerated. N2N is somewhat similar to Hamachi [12], a popular application mostly used for creating private networks on which to play games. With N2N users can choose their IP address and the encryption keys, whereas with Hamachi this is not possible and all the security is delegated to Hamachi, making the whole solution weak from a security point of view.