Virtual private network
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 a VPN may therefore benefit from the functionality, security, and management of the private network.
A VPN is created by establishing a virtual 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.
VPN technology was developed to allow remote users and branch offices to access corporate applications and resources. To ensure security, the private network connection is established using an encrypted layered tunneling protocol and VPN users use authentication methods, including passwords or certificates, to gain access to the VPN. In other applications, Internet users may secure their transactions with a VPN, to circumvent geo-restrictions and censorship, or to connect to proxy servers to protect personal identity and location to stay anonymous on the Internet.
VPNs can be either remote-access (connecting a computer to a network) or site-to-site (connecting two networks). A VPN can also be used to interconnect two similar networks over a dissimilar middle network;
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.
Early data networks allowed VPN-style connections to remote sites through dial-up modem or through leased line connections utilizing Frame Relay and Asynchronous Transfer Mode (ATM) virtual circuits, provided through networks owned and operated by telecommunication carriers.
VPNs cannot make online connections completely anonymous, but they can usually increase privacy and security.
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 see only 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:
. Datagram Transport Layer Security (DTLS) – used in Cisco AnyConnect VPN and in OpenConnect VPN to solve the issues SSL/TLS has with tunneling over TCP (tunneling TCP over TCP can lead to big delays and connection aborts .
. 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”.
. 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.
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.
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.
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. Multi-protocol label switching (MPLS) functionality blurs the L2-L3 identity.[original research?]
RFC 4026 generalized the following terms to cover L2 and L3 VPNs, but they were introduced in RFC 2547.
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.
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.
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.
User-visible PPVPN services
OSI Layer 2 services:
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, Virtual LANs (VLANs) allow multiple tagged LANs to share common trunking. VLANs frequently comprise only customer-owned facilities.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.
Ethernet over IP tunneling:
EtherIP (RFC 3378) is an Ethernet over IP tunneling protocol specification. EtherIP has only packet encapsulation mechanism.
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.
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.
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).
Increasingly, mobile professionals who need reliable connections are adopting mobile VPNs.[need quotation to verify] They are used for roaming seamlessly across networks and in and out of wireless coverage areas without losing application sessions or dropping the secure VPN session. A conventional VPN can not withstand such events because the network tunnel is disrupted, causing applications to disconnect, time out,or fail, or even cause the computing device itself to crash.
Users utilize mobile virtual private networks 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. 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.
Many router manufacturers supply routers with built-in VPN clients. Some use open-source firmware such as DD-WRT, OpenWRT and Tomato, in order to support additional protocols such as OpenVPN.
With the increasing use of VPNs, many have started deploying VPN connectivity on routers for additional security and encryption of data transmission by using various cryptographic techniques. Home users usually deploy VPNs on their routers to protect devices, such as smart TVs or gaming consoles, which are not supported by native VPN clients. Supported devices are not restricted to those capable of running a VPN client.
One major limitation of traditional VPNs is that they are point-to-point, and do not tend to support or connect 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 or work exactly as they would on a real LAN. Variants on VPN, such as Virtual Private LAN Service (VPLS), and layer 2 tunneling protocols, are designed to overcome this limitation.
A VPN connection may not be as robust as a direct connection to a network. A VPN connection depends on the VPN provider and the ISP. If either fails, the connection fails.
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