Расширение частной сети через публичную сеть.

Extension of a private network across a public one

A virtual private network (VPN) is a mechanism for creating a secure connection between a computing device and a computer network, or between two networks, using an insecure communication medium such as the public Internet. A VPN can extend access to a private network (one that disallows or restricts public access) to users who do not have direct access to it, such as an office network allowing secure access from off site over the Internet. The benefits of a VPN include security, reduced costs for dedicated communication lines, and greater flexibility for remote workers. A VPN is created by establishing a virtual point to point connection through the use of tunneling protocols over existing networks. A VPN available from the public Internet can provide some of the benefits of a private wide area network (WAN).

Tunnel endpoints must be authenticated before secure VPN tunnels can be established. User created remote access VPNs may use passwords, biometrics, two factor authentication, or other cryptographic methods. Network to network tunnels often use passwords or digital certificates. Depending on the VPN protocol, they may store the key to allow the VPN tunnel to establish automatically, without intervention from the administrator. Data packets are secured by tamper proofing via a message authentication code (MAC), which prevents the message from being altered or tampered without being rejected due to the MAC not matching with the altered data packet.

Tunneling protocols can operate in a point to point network topology however, this would theoretically not be considered a VPN because a VPN by definition is expected to support arbitrary and changing sets of network nodes. But since most router implementations support a virtual, software defined tunnel interface, customer provisioned VPNs often are simply defined tunnels running conventional routing protocols.

VLAN is a Layer 2 technique that allows for the coexistence of multiple local area network (LAN) broadcast domains interconnected via trunks using the IEEE 802.1Q trunking protocol. Other trunking protocols have been used but have become obsolete, including Inter Switch Link (ISL), IEEE 802.10 (originally a security protocol but a subset was introduced for trunking), and ATM LAN Emulation (LANE).

Developed by Institute of Electrical and Electronics Engineers, VLANs allow multiple tagged LANs to share common trunking. VLANs frequently comprise only customer owned facilities. Whereas VPLS as described in the above section (OSI Layer 1 services) supports emulation of both point to point and point to multipoint topologies, the method discussed here extends Layer 2 technologies such as 802.1d and 802.1q LAN trunking to run over transports such as metro Ethernet. As used in this context, a VPLS is a Layer 2 PPVPN, emulating the full functionality of a traditional LAN. From a user standpoint, a VPLS makes it possible to interconnect several LAN segments in a way that is transparent to the user, making the separate LAN segments behave as one single LAN. In a VPLS, the provider network emulates a learning bridge, which may include VLAN service optionally.

PW is similar to VPLS but can provide different L2 protocols at both ends. Typically, its interface is a WAN protocol such as Asynchronous Transfer Mode or Frame Relay. In contrast, when aiming to provide the appearance of a LAN contiguous between two or more locations, the Virtual Private LAN service or IPLS would be appropriate.

EtherIP is an Ethernet over IP tunneling protocol specification. EtherIP has only a packet encapsulation mechanism. It has no confidentiality or message integrity protection. EtherIP was introduced in the FreeBSD network stack and the SoftEther VPN server program.

A subset of VPLS, the CE devices must have Layer 3 capabilities; the IPLS presents packets rather than frames. It may support IPv4 or IPv6.

Ethernet VPN (EVPN) is an advanced solution for providing Ethernet services over IP MPLS networks. In contrast to the VPLS architectures, EVPN enables control plane based MAC (and MAC,IP) learning in the network. PEs participating in the EVPN instances learn the customer's MAC (MAC,IP) routes in control plane using MP BGP protocol. Control plane MAC learning brings a number of benefits that allow EVPN to address the VPLS shortcomings, including support for multi homing with per flow load balancing and avoidance of unnecessary flooding over the MPLS core network to multiple PEs participating in the P2MP/MP2MP L2VPN (in the occurrence, for instance, of ARP query). It is defined .

Some virtual networks use tunneling protocols without encryption to protect the privacy of data. While VPNs often provide security, an unencrypted overlay network does not fit within the secure or trusted categorization. For example, a tunnel set up between two hosts with Generic Routing Encapsulation (GRE) is a virtual private network but is neither secure nor trusted. Native plaintext tunneling protocols include Layer 2 Tunneling Protocol (L2TP) when it is set up without IPsec and Point to Point Tunneling Protocol (PPTP) or Microsoft Point to Point Encryption (MPPE).

Trusted VPNs do not use cryptographic tunneling; instead, they rely on the security of a single provider's network to protect the traffic. Multiprotocol Label Switching (MPLS) often overlays VPNs, often with quality of service control over a trusted delivery network. L2TP which is a standards based replacement, and a compromise taking the good features from each, for two proprietary VPN protocols: Cisco's Layer 2 Forwarding (L2F) (obsolete ) and Microsoft's Point to Point Tunneling Protocol (PPTP). From a security standpoint, a VPN must either trust the underlying delivery network or enforce security with a mechanism in the VPN itself. Unless the trusted delivery network runs among physically secure sites only, both trusted and secure models need an authentication mechanism for users to gain access to the VPN.

Mobile virtual private networks are used in settings where an endpoint of the VPN is not fixed to a single IP address, but instead roams across various networks such as data networks from cellular carriers or between multiple Wi Fi access points without dropping the secure VPN session or losing application sessions. Mobile VPNs are widely used in public safety where they give law enforcement officers access to applications such as computer assisted dispatch and criminal databases, and in other organizations with similar requirements such as field service management and healthcare.

A limitation of traditional VPNs is that they are point to point connections and do not tend to support broadcast domains; therefore, communication, software, and networking, which are based on layer 2 and broadcast packets, such as NetBIOS used in Windows networking, may not be fully supported as on a local area network. Variants on VPN such as Virtual Private LAN Service (VPLS) and layer 2 tunneling protocols are designed to overcome this limitation.