WHAT IS VPN?

(VPN) extends a private network across a public network, and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running on a computing device, e.g., a laptop, desktop, smartphone, across a VPN may, therefore, benefit from the functionality, security, and management of the private network. Encryption is a common, though not an inherent, part of a VPN connection.

• confidentiality such that even if the network traffic is sniffed at the packet level (see network sniffer and deep packet inspection), an attacker would see only encrypted data
• sender authentication to prevent unauthorized users from accessing the VPN
• message integrity to detect any instances of tampering with transmitted messages.

Secure VPN protocols include the following:

• Internet Protocol Security (IPsec) was initially developed by the Internet Engineering Task Force (IETF) for IPv6, which was required in all standards-compliant implementations of IPv6 before RFC 6434 made it only a recommendation. This standards-based security protocol is also widely used with IPv4 and the Layer 2 Tunneling Protocol. Its design meets most security goals: availability, integrity, and confidentiality. IPsec uses encryption, encapsulating an IP packet inside an IPsec packet. De-encapsulation happens at the end of the tunnel, where the original IP packet is decrypted and forwarded to its intended destination.
• Transport Layer Security (SSL/TLS) can tunnel an entire network's traffic (as it does in the OpenVPN project and SoftEther VPN project) or secure an individual connection. A number of vendors provide remote-access VPN capabilities through SSL. An SSL VPN can connect from locations where IPsec runs into trouble with Network Address Translation and firewall rules.
• Datagram Transport Layer Security (DTLS) – used in Cisco AnyConnect VPN and in OpenConnect VPN to solve the issues SSL/TLS has with tunneling over TCP (tunneling TCP over TCP can lead to big delays and connection aborts).
• Microsoft Point-to-Point Encryption (MPPE) works with the Point-to-Point Tunneling Protocol and in several compatible implementations on other platforms.
• Microsoft Secure Socket Tunneling Protocol (SSTP) tunnels Point-to-Point Protocol (PPP) or Layer 2 Tunneling Protocol traffic through an SSL 3.0 channel (SSTP was introduced in Windows Server 2008 and in Windows Vista Service Pack 1).
• Multi-Path Virtual Private Network (MPVPN). Ragula Systems Development Company owns the registered trademark "MPVPN".
• Secure Shell (SSH) VPN – OpenSSH offers VPN tunneling (distinct from port forwarding) to secure remote connections to a network or to inter-network links. OpenSSH server provides a limited number of concurrent tunnels. The VPN feature itself does not support personal authentication.