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A virtual private Network (VPN) extends a private network across a public network, such as the Internet. It enables a computer to send and receive data across shared or public networks as if it were directly connected to the private network, while benefiting from the functionality, security and management policies of the private network.[1] This is done by establishing a virtual point-to-point connection through the use of dedicated connections, encryption, or a combination of the two.

A virtual private network connection across the Internet is similar to a wide area network (WAN) link between the sites. From a user perspective, the extended network resources are accessed in the same way as resources available from the private network.[2]

VPNs allow employees to securely access their company's intranet while traveling outside the office. Similarly, VPNs securely and cost-effectively connect geographically disparate offices of an organization, creating one cohesive virtual network. VPN technology is also used by ordinary Internet users to connect to proxy servers for the purpose of protecting one's identity.

Types[edit]

Early data networks allowed VPN-style remote connectivity through dial-up modems or through leased line connections utilizing Frame Relay and Asynchronous Transfer Mode (ATM) virtual circuits, provisioned through a network owned and operated by telecommunication carriers. These networks are not considered true VPNs because they passively secure the data being transmitted by the creation of logical data streams.[3] They have given way to VPNs based on IP and IP/Multiprotocol Label Switching Networks (MPLS), due to significant cost-reductions and increased bandwidth[4] provided by new technologies such as Digital Subscriber Line (DSL)[5] and fiber-optic networks.

VPNs can be either remote-access (connecting an individual computer to a network) or site-to-site (connecting two networks together). In a corporate setting, remote-access VPNs allow employees to access their company's intranet from home or while traveling 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]

VPN systems may be classified by:

the protocols used to tunnel the traffic.

the tunnel's termination point location, e.g., on the customer edge or network-provider edge.

whether they offer site-to-site or remote-access connectivity.

the levels of security provided.

the OSI layer they present to the connecting network, such as Layer 2 circuits or Layer 3 network connectivity.

Security mechanisms[edit]

To prevent disclosure of private information, VPNs typically allow only authenticated remote access and make use of encryption techniques.

VPNs provide security by the use of tunneling protocols and through security procedures[7] such as encryption. The VPN security model provides:

confidentiality such that even if the network traffic is sniffed at the packet level (see network sniffer and Deep packet inspection), an attacker would only see 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) as 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.[8] This standards-based security protocol is also widely used with IPv4 and the Layer 2 Tunneling Protocol. Its design meets most security goals: authentication, 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[9]) 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[10] to solve the issues SSL/TLS has with tunneling over UDP.

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".[11]

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.[12][13][14]

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