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Virtual Private Network

A virtual private network (VPN) is a private network that uses a public network, such as the Internet, to provide remote sites or users with secure access to their organisation’s network by establish ‘virtual’ encrypted links. Privacy on these networks is ensured through the use of security procedures and tunnelling protocols.


Security procedures include:

  • Firewalls: These provide a barrier between the VPN and the Internet. They help to keep intruders out of the networks, especially when the VPN sessions are ended.

  • Encryption: Data sent between the computers in the network are encrypted using either symmetric key encryption or public-key encryption.

    With symmetric key encryption, each computer on the network is assigned a secret key or code which is used to encrypt the data before it is sent over the network. The keys are then distributed to all on the computers. When the data is received by the destined computer, it uses the code of the sender computer to decode the data.

    Public key encryption uses a private key and public key that is assigned to which computer on the network. The private key is known by only the computer that it is has been assigned to. The computer uses this private key to encrypt data before it sends it over the network. The data is decrypted by the receiving using the public key of the pair, which is made available to all computers on the network.
  • IPSec (Internet Protocol Security Protocol) – IPSec provides its users with strong encryption algorithms and a comprehensive authentication procedure.

  • AAA Server – An AAA (authentication, authorization and accounting) server is used to provide secure access in a remote access environment. When individual users request a connection the network, the AAA server verifies who the user is (authentication), what the user is allowed to do (authorization) and what the user does on gaining access to the network (accounting).

Tunnelling protocols are used to encrypt data, along with the originating and destination network addresses, at the sending end. The protocols are also used to send the data through a ‘tunnel’ that cannot be entered by any data unless it has been properly encrypted and then decrypt the sent data at the receiving end.

Tunnelling protocols are essential in creating a private network over the Internet and they include L2TP (Layer 2 Tunnelling Protocol), PPTP (Port-to-Port Tunnelling Protocol), L2F (Layer 2 Forwarding) and GRE (Generic routing encapsulation).

There are two main types of VPNs available:

  • Remote Access VPN: also known as Virtual private dial-up network (VPDN). This is used for establishing secure connections between remotely located employees and a central office.

  • Site-to-Site VPN: is used for establishing connections between multiple fixed sites over a public network such as the Internet, using dedicated equipment and large scale encryption. Site-to-site VPNs could be set-up as intranets or extranet. One of the best known examples of a site-to-site VPN is the NHSnet maintained by the National Health Service (NHS in the United Kingdom.



International Medical Informatics Association
American Medical Informatics Association
UK Health Informatics Society
Healthcare Information and Management Systems Society

Knowledge Center
Biomedical Informatics
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Computer Networks Topics
Client/Server Networks
Intranets and Extranets
Peer-to-Peer Networks
Thin Client Server Technology
Virtual Private Networks
Wireless Technology

Last Updated: 10 August 2006.

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