A virtual private network extends a private network across a public network, such as the Internet. It enables a computer to send and receive data across shared or public networks as if it were directly connected to the private network, while benefiting from the functionality, security and management policies of the private network.

1. SARMAD ALI
Source:
- http://computer.howstuffworks.com/vpn4.htm
- Wikipedia

2. What is Virtual private network (VPN) ?
A virtual private network extends a private network across a public network, such as the Internet. It
enables a computer to send and receive data across shared or public networks as if it were directly
connected to the private network, while benefiting from the functionality, security and management
policies of the private network. This is done by establishing a virtual point-to-point connection through
the use of dedicated connections, encryption, or a combination of the two.
A VPN connection across the Internet is similar to a wide area network (WAN) link between the sites.
From a user perspective, the extended network resources are accessed in the same way as resources
available from the private network.

3. TYPES OF VPN
1) Site-to-VPN
A site-to-site VPN allows offices in multiple fixed locations to establish secure connections with each
other over a public network such as the Internet. Site-to-site VPN extends the company's network,
making computer resources from one location available to employees at other locations. An
example of a company that needs a site-to-site VPN is a growing corporation with dozens of branch
offices around the world.

4. There are two types of site-to-site VPNs:
Intranet-based: If a company has one or more remote locations that they wish to join in a single private
network, they can create an intranet VPN to connect each separate LAN to a single WAN.
Extranet-based: When a company has a close relationship with another company (such as a partner,
supplier or customer), it can build an extranet VPN that connects those companies' LANs. This extranet
VPN allows the companies to work together in a secure, shared network environment while preventing
access to their separate intranets.

5. 1) Remote-Access VPN
A remote-access VPN allows individual users to establish secure connections with a remote computer
network. Those users can access the secure resources on that network as if they were directly plugged in
to the network's servers. An example of a company that needs a remote-access VPN is a large firm with
hundreds of salespeople in the field. Another name for this type of VPN is virtual private dial-up
network (VPDN), acknowledging that in its earliest form, a remote-access VPN required dialing in to a
server using an analog telephone system.

6. There are two components required in a remote-access VPN. The first is a network access server (NAS,
usually pronounced "nazz" conversationally), also called a media gateway or a remote-access server
(RAS). (Note: IT professionals also use NAS to mean network-attached storage.) A NAS might be a
dedicated server, or it might be one of multiple software applications running on a shared server. It's a NAS
that a user connects to from the Internet in order to use a VPN. The NAS requires that user to provide valid
credentials to sign in to the VPN. To authenticate the user's credentials, the NAS uses either its own
authentication process or a separate authentication server running on the network.