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2019-03-27T06:34:24Z

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A '''virtual private network''' ('''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 across the VPN may therefore benefit from the functionality, security, and management of the private network.

VPNs may allow employees to securely access a corporate [[intranet]] while located outside the office. They are used to securely connect geographically separated offices of an organization, creating one cohesive network. Individual Internet users may secure their [[wireless]] transactions with a VPN, to circumvent [[Geo-blocking|geo-restrictions]] and censorship, or to connect to [[proxy server]]s for the purpose of protecting personal identity and location. However, some Internet sites block access to known VPN technology to prevent the circumvention of their geo-restrictions.

A VPN is created by establishing a virtual [[point-to-point (network topology)|point-to-point]] connection through the use of dedicated connections, virtual [[tunneling protocols]], or traffic [[encryption]]. A VPN available from the public Internet can provide some of the benefits of a [[wide area network]] (WAN). From a user perspective, the resources available within the private network can be accessed remotely.

Traditional VPNs are characterized by a point-to-point topology, and they do not tend to support or connect [[broadcast domain]]s, so services such as [[Microsoft Windows]] [[NetBIOS]] may not be fully supported or work as they would on a [[local area network]] (LAN). Designers have developed VPN variants, such as [[Virtual Private LAN Service]] (VPLS), and [[Layer 2 Tunneling Protocol|layer-2 tunneling protoco]]ls, to overcome this limitation.

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 They have been replaced by VPNs based on IP and IP/[[Multiprotocol Label Switching|Multi-protocol Label Switching]] (MPLS) Networks, due to significant cost-reductions and increased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

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

VPN systems may be classified by:
* The [[tunneling protocol|protocols]] used to [[IP tunnel|tunnel]] the traffic
* The tunnel's termination point location, e.g., on the customer [[Edge device|edge]] or network-provider edge
* The type of topology of connections, such as site-to-site or network-to-network
* The levels of security provided
* The [[OSI model|OSI layer]] they present to the connecting network, such as Layer 2 circuits or Layer 3 network connectivity
* The number of simultaneous connections

==Security mechanisms==
VPNs cannot make online connections completely anonymous, but they can usually increase privacy and security. To prevent disclosure of private information, VPNs typically allow only authenticated remote access using [[tunneling protocols]] and [[Encryption software|encryption]] techniques.

The VPN security model provides:
* [[Information security#Confidentiality|Confidentiality]] such that even if the network traffic is sniffed at the packet level (see [[Packet analyzer|network sniffer]] and [[deep packet inspection]]), an attacker would only see [[Encryption|encrypted data]]
* Sender [[authentication]] to prevent unauthorized users from accessing the VPN
* Message [[Data integrity|integrity]] to detect any instances of tampering with transmitted messages

Secure VPN protocols include the following:
* [[Internet Protocol Security]] ([[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: 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]] ([[Transport Layer Security|SSL/TLS]]) can [[tunneling protocol|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]] ([[Datagram Transport Layer Security|DTLS]]) – used in [[Cisco Systems#Cisco AnyConnect VPN Client|Cisco AnyConnect VPN]] and in [[OpenConnect]] VPN to solve the issues [[Transport Layer Security|SSL/TLS]] has with tunneling over [[User Datagram Protocol|UDP]].
* [[Microsoft Point-to-Point Encryption]] ([[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]] ([[Secure Socket Tunneling Protocol|SSTP]]) tunnels [[Point-to-Point Protocol]] (PPP) or [[Layer 2 Tunneling Protocol]] traffic through an [[Transport Layer Security|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.

===Authentication===
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]]. They permanently store the key to allow the tunnel to establish automatically, without intervention from the administrator.

==Routing==
[[Tunneling protocol]]s can operate in a [[Point-to-point (telecommunications)|point-to-point]] [[network topology]] that would theoretically not be considered as a VPN, because a VPN by definition is expected to support arbitrary and changing sets of network nodes. But since most [[Router (computing)|router]] implementations support a software-defined tunnel interface, customer-provisioned VPNs often are simply defined tunnels running conventional routing protocols.

===Provider-provisioned VPN building-blocks===
Depending on whether a provider-provisioned VPN (PPVPN) operates in layer 2 or layer 3, the building blocks described below may be L2 only, L3 only, or combine them both. [[Multiprotocol label switching|Multi-protocol label switching]] (MPLS) functionality blurs the L2-L3 identity.

RFC 4026 generalized the following terms to cover L2 and L3 VPNs, but they were introduced in RFC 2547. More information on the devices below can also be found in Lewis, Cisco Press.

; Customer (C) devices
A device that is within a customer's network and not directly connected to the service provider's network. C devices are not aware of the VPN.

; Customer Edge device (CE)
A device at the edge of the customer's network which provides access to the PPVPN. Sometimes it's just a demarcation point between provider and customer responsibility. Other providers allow customers to configure it.

; Provider edge device (PE)
A PE is a device, or set of devices, at the edge of the provider network which connects to customer networks through CE devices and presents the provider's view of the customer site. PEs are aware of the VPNs that connect through them, and maintain VPN state.

; Provider device (P)
A P device operates inside the provider's core network and does not directly interface to any customer endpoint. It might, for example, provide routing for many provider-operated tunnels that belong to different customers' PPVPNs. While the P device is a key part of implementing PPVPNs, it is not itself VPN-aware and does not maintain VPN state. Its principal role is allowing the service provider to scale its PPVPN offerings, for example, by acting as an aggregation point for multiple PEs. P-to-P connections, in such a role, often are high-capacity optical links between major locations of providers.'''

==User-visible PPVPN services==
===OSI Layer 2 services===

;[[Virtual LAN]]
A Layer 2 technique that allow for the coexistence of multiple 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).

;Virtual private LAN service (VPLS)
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, rather than a private line, emulating the full functionality of a traditional [[local area network]] (LAN). From a user standpoint, a VPLS makes it possible to interconnect several LAN segments over a packet-switched, or optical, provider core; a core transparent to the user, making the remote LAN segments behave as one single LAN.

In a VPLS, the provider network emulates a learning bridge, which optionally may include VLAN service.

;Pseudo wire (PW)
PW is similar to [[VPLS]], but it 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.

; Ethernet over IP tunneling
[http://tools.ietf.org/search/rfc3378 EtherIP (RFC 3378)] is an Ethernet over IP tunneling protocol specification. EtherIP has only packet encapsulation mechanism. It has no confidentiality nor message integrity protection. EtherIP was introduced in the [[FreeBSD]] network stack and the [[SoftEther VPN]] server program.

;IP-only LAN-like service (IPLS)
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.

===OSI Layer 3 PPVPN architectures===
This section discusses the main architectures for PPVPNs, one where the PE disambiguates duplicate addresses in a single routing instance, and the other, virtual router, in which the PE contains a virtual router instance per VPN. The former approach, and its variants, have gained the most attention.

One of the challenges of PPVPNs involves different customers using the same address space, especially the IPv4 private address space. The provider must be able to disambiguate overlapping addresses in the multiple customers' PPVPNs.

;BGP/MPLS PPVPN
In the method defined by RFC 2547, BGP extensions advertise routes in the IPv4 VPN address family, which are of the form of 12-byte strings, beginning with an 8-byte [[route distinguisher|Route Distinguisher]] (RD) and ending with a 4-byte IPv4 address. RDs disambiguate otherwise duplicate addresses in the same PE.

PEs understand the topology of each VPN, which are interconnected with MPLS tunnels, either directly or via P routers. In MPLS terminology, the P routers are [[Label Switch Router]]s without awareness of VPNs.

;Virtual router PPVPN
The virtual router architecture, as opposed to BGP/MPLS techniques, requires no modification to existing routing protocols such as BGP. By the provisioning of logically independent routing domains, the customer operating a VPN is completely responsible for the address space. In the various MPLS tunnels, the different PPVPNs are disambiguated by their label, but do not need routing distinguishers.

===Unencrypted tunnels===
Some virtual networks use [[tunneling protocol]]s without encryption for protecting the privacy of data. While VPNs often do provide security, an unencrypted [[overlay network]] does not neatly 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 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 delivery networks==
Trusted VPNs do not use cryptographic [[tunneling protocol|tunneling]], and instead rely on the security of a single provider's network to protect the traffic.
* [[Multi-Protocol Label Switching]] (MPLS) often overlays VPNs, often with quality-of-service control over a trusted delivery network.
* [[Layer 2 Tunneling Protocol]] (L2TP) which is a standards-based replacement, and a compromise taking the good features from each, for two proprietary VPN protocols: Cisco's [[L2F|Layer 2 Forwarding (L2F)]] (obsolete ) and Microsoft's Point-to-Point Tunneling Protocol ([[PPTP]]).

From the security standpoint, VPNs either trust the underlying delivery network, or must enforce security with mechanisms 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.

==VPNs in mobile environments==
[[Mobile virtual private network]]s are used in settings where an endpoint of the VPN is not fixed to a single [[IP address spoofing|IP address]], but instead roams across various networks such as data networks from cellular carriers or between multiple [[Wi-Fi]] access points. Mobile VPNs have been widely used in [[public safety]], where they give law enforcement officers access to mission-critical applications, such as [[computer-assisted dispatch]] and criminal databases, while they travel between different subnets of a mobile network. They are also used in [[field service management]] and by healthcare organizations, among other industries.

Increasingly, mobile VPNs are being adopted by mobile professionals who need reliable connections. Setting up VPN support on a router and establishing a VPN allows any networked device to have access to the entire network—all devices look like local devices with local addresses. Supported devices are not restricted to those capable of running a VPN client.

Many router manufacturers supply routers with built-in VPN clients. Some use open-source firmware such as [[DD-WRT]], [[OpenWRT]] and [[Tomato (firmware)|Tomato]], in order to support additional protocols such as [[OpenVPN]].

Setting up VPN services on a router requires a deep knowledge of network security and careful installation. Minor misconfiguration of VPN connections can leave the network vulnerable. Performance will vary depending on the ISP.

==Networking limitations==
One major limitation of traditional VPNs is that they are point-to-point, and do not tend to support or connect [[broadcast domain]]s. Therefore, communication, software, and networking, which are based on [[OSI layer|layer 2]] and broadcast [[Network packet|packet]]s, such as [[NetBIOS]] used in [[My Network Places|Windows networking]], may not be fully supported or work exactly as they would on a real [[Local area network|LAN]]. Variants on VPN, such as [[Virtual Private LAN Service]] (VPLS), and [[layer 2]] [[tunneling protocol]]s, are designed to overcome this limitation.

==Source==

[http://wikipedia.org/ http://wikipedia.org/]

[[de:Virtuelles privates Netzwerk]]

[[Category:Services]]
[[Category:Anonymity and security]]
==See Also on BitcoinWiki==
* [[Bitcoinker]]
* [[Enumerator polynomial]]
* [[IHT Real Estate Protocol]]
* [[BTC Trader]]
* [[Gladiacoin]]

Virtual private network - Revision history

Admin: Created page with "A '''virtual private network''' ('''VPN''') extends a private network across a public network, and enables users to send and receive data across shared or public networks..."