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. The benefits of a VPN include increases in functionality, security, and management of the private network. It provides access to resources that are inaccessible on the public network and is typically used for remote workers. Encryption is common, although not an inherent part of a VPN connection.
A VPN is created by establishing a virtual point-to-point connection through the use of dedicated circuits or with tunneling protocols over existing networks. 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.
Virtual private networks may be classified by several categories:
Typically, individuals interact with remote access VPNs, whereas businesses tend to make use of site-to-site connections for business-to-business, cloud computing, and branch office scenarios. Despite this, these technologies are not mutually exclusive and, in a significantly complex business network, may be combined to enable remote access to resources located at any given site, such as an ordering system that resides in a datacenter.
VPN systems also may be classified by:
VPNs cannot make online connections completely anonymous, but they can increase privacy and security. To prevent disclosure of private information or data sniffing, VPNs typically allow only authenticated remote access using tunneling protocols and secure encryption techniques.
The VPN security model provides:
Secure VPN protocols include the following:
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 that 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 software-defined tunnel interface, customer-provisioned VPNs often are simply defined tunnels running conventional routing protocols.
Depending on whether a provider-provisioned VPN (PPVPN) operates in Layer 2 (L2) or Layer 3 (L3), the building blocks described below may be L2 only, L3 only, or a combination of both. Multi-protocol label switching (MPLS) functionality blurs the L2-L3 identity.[original research?]
RFC 4026 generalized the following terms to cover L2 MPLS VPNs and L3 (BGP) VPNs, but they were introduced in RFC 2547.
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.
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.
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.
A device that 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.
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 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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.[need quotation to verify].
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.
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OpenConnect is a client for Cisco's AnyConnect SSL VPN [...] OpenConnect is not officially supported by, or associated in any way with, Cisco Systems. It just happens to interoperate with their equipment.
[...] VPNs using dedicated circuits, such as Frame Relay [...] are sometimes called trusted VPNs, because customers trust that the network facilities operated by the service providers will not be compromised.