virtual private network (VPN)

What is a virtual private network (VPN)?

A virtual private network (VPN) is a network that uses a public telecommunication infrastructure, such as the Internet, to provide remote offices or individual users with secure access to their organization's network. A virtual private network can be contrasted with an expensive system of owned or leased lines that can only be used by one organization. The goal of a VPN is to provide the organization with the same capabilities, but at a much lower cost.

A VPN works by using the shared public infrastructure while maintaining privacy through security procedures and tunneling protocols such as the Layer Two Tunneling Protocol (L2TP). In effect, the protocols, by encrypting data at the sending end and decrypting it at the receiving end, send the data through a "tunnel" that cannot be "entered" by data that is not properly encrypted. An additional level of security involves encrypting not only the data, but also the originating and receiving network addresses.

Secure VPNs use cryptographic tunneling protocols to provide confidentiality by blocking intercepts and packet sniffing, allowing sender authentication to block identity spoofing, and provide message integrity by preventing message alteration.


Secure VPN protocols include the following:

IPsec (Internet Protocol Security) was originally developed for IPv6, which requires it. This standards-based security protocol is also widely used with IPv4. Layer 2 Tunneling Protocol frequently runs over IPsec.

Transport Layer Security (SSL/TLS) can tunnel an entire network's traffic, as it does in the OpenVPN 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), is used in Cisco's next-generation VPN product, Cisco AnyConnect VPN, to solve the issues SSL/TLS has with tunneling over TCP.

Microsoft Point-to-Point Encryption (MPPE) works with their Point-to-Point Tunneling Protocol and in several compatible implementations on other platforms.

Microsoft introduced Secure Socket Tunneling Protocol (SSTP) in Windows Server 2008 and Windows Vista Service Pack 1. SSTP tunnels Point-to-Point Protocol (PPP) or Layer 2 Tunneling Protocol traffic through an SSL 3.0 channel.

MPVPN (Multi Path Virtual Private Network). Ragula Systems Development Company owns the registered trademark "MPVPN".^[2]

Secure Shell (SSH) VPN -- OpenSSH offers VPN tunneling to secure remote connections to a network or inter-network links. This should not be confused with port forwarding. OpenSSH server provides limited number of concurrent tunnels and the VPN feature itself does not support personal authentication.