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A Virtual Private Network, or VPN, is a private communications network usually used within a company, or by several different companies or
organisations, communicating over a public network. VPN message traffic is carried on public networking infrastructure (ie, the
Internet) using standard (possibly unsecure) protocols.
VPNs use cryptographic tunneling protocols to provide the necessary confidentiality (preventing snooping), sender authentication
(preventing identity spoofing), and message integrity (preventing message alteration) to achieve the privacy intended. When
properly chosen, implemented, and used, such techniques can indeed provide secure communications over unsecure networks.
Note that such choice, implementation, and use are not trivial and there are many unsecure VPN schemes on the market. Users
are cautioned to investigate products they propose to use very carefully. 'VPN' is a label which, by itself, provides little
except a marketing tag.
VPN technologies may also be used to enhance security as a 'security overlay' within dedicated networking infrastructures.
VPN protocols include:
- IPSec (IP security), an obligatory part of IPv6.
- PPTP (point-to-point tunneling protocol), developed by Microsoft.
- L2F (Layer 2 Forwarding), developed by
Cisco.
- L2TP (Layer 2 Tunnelling Protocol), including work by both Microsoft and Cisco.
Multi-protocol label switching can
be used to build VPNs.
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