VPN

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Virtual private network

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"VPN" redirects here. For other uses, see VPN (disambiguation).

VPN connectivity overview

A virtual private network (VPN) extends aprivate 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.^[1]

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 transactions with a VPN, to circumventgeo-restrictions and censorship, or to connect to proxy servers for the purpose of protecting personal identity and location in order to stay anonymous on the internet. However, some Internet sites block access to known VPN technology to prevent the circumvention of their geo-restrictions. Therefore, many personal use VPN providers have been developing technologies to bypass the blocking of proxies.

A VPN is created by establishing a virtualpoint-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.^[2]

Traditional VPNs are characterized by a point-to-point topology, and they do not tend to support or connect broadcast domains, so services such as Microsoft Windows NetBIOSmay 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), andLayer 2 Tunneling Protocols (L2TP), to overcome this limitation.

TypesEdit

Early data networks allowed VPN-style remote connections through dial-up modem or through leased line connections utilizingFrame Relay and Asynchronous Transfer Mode (ATM) virtual circuits, provided through networks owned and operated bytelecommunication 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 been replaced by VPNs based on IP and IP/Multi-protocol Label Switching(MPLS) Networks, 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 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 intranetfrom 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.^[6]

VPN systems may be classified by:

• The tunneling protocol used to tunnel the traffic
• The tunnel's termination point location, e.g., on the customer 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 layer they present to the connecting network, such as Layer 2 circuits or Layer 3 network connectivity
• The number of simultaneous connections

Security mechanismsEdit

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 andencryption techniques.

The VPN security model provides:

• Confidentiality such that even if the network traffic is sniffed at the packet level (seenetwork sniffer and deep packet inspection), an attacker would see onlyencrypted 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 beforeRFC 6434 made it only a recommendation.^[7] This standards-based security protocol is also widely used withIPv4 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 VPNproject^[8]) 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 withNetwork Address Translation and firewall rules.
• Datagram Transport Layer Security (DTLS) – used in Cisco AnyConnect VPN and inOpenConnect VPN^[9] to solve the issuesSSL/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".^[10]
• 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.^[11][12][13]

AuthenticationEdit

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 cryptographicmethods. 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.

RoutingEdit

Tunneling protocols can operate in a 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 routerimplementations support a software-defined tunnel interface, customer-provisioned VPNs often are simply defined tunnels running conventional routing protocols.

Provider-provisioned VPN building-blocksEdit

Depending on whether a provider-provisioned VPN (PPVPN)^{[clarification needed]} operates in layer 2 or layer 3, the building blocks described below may be L2 only, L3 only, or combine them both. Multi-protocol label switching (MPLS) functionality blurs the L2-L3 identity.^{[citation needed][original research?]}

RFC 4026 generalized the following terms to cover L2 and L3 VPNs, but they were introduced in RFC 2547.^[14] More information on the devices below can also be found in Lewis, Cisco Press.^[15]

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 is 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 servicesEdit

OSI Layer 2 servicesEdit

Virtual LAN

Virtual LAN (VLAN) is a Layer 2 technique that allow 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).

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 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.^[16]

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 asAsynchronous 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

EtherIP (RFC 3378)^[17] 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 theFreeBSD network stack^[18] and the SoftEther VPN^[19] 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 architecturesEdit

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.^[20] 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 (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 Routers without awareness of VPNs.

Virtual router PPVPN

The virtual router architecture,^[21][22] 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 tunnelsEdit

Some virtual networks use tunneling protocols 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.^{[citation needed]} For example, a tunnel set up between two hosts with Generic Routing Encapsulation (GRE) is a virtual private network, but neither secure nor trusted.^[23][24]

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).^[25]