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Private: the resources of VPN are unavailable to unauthorized VPN users on the internet;
VPN can ensure and protect its internal information from external intrusion.
Virtual: the communication among VPN users is realized via public network which,
meanwhile can be used by unauthorized VPN users so that what VPN users obtained is
only a logistic private network. This public network is regarded as VPN Backbone.
Build a credible and secure link by connecting remote users, company branches, partners to the
network of the headquarters via VPN so as to realize secure transmission of data.
It is shown in the figure below:
Enterprise
Headquarter
Embranchment
Cooperative
Partner
VP
N
VP
N
VPN
Remote Access
Fundamental Principle of VPN
The fundamental principle of VPN indicates to enclose VPN message into tunnel with tunneling
technology and to establish a private data transmission channel utilizing VPN Backbone so as to
realize the transparent message transmission.
Tunneling technology encloses the other protocol message with one protocol. Also, encapsulation
protocol itself can be enclosed or carried by other encapsulation protocols. To the users, tunnel is
logical extension of PSTN/link of ISDN, which is similar to the operation of actual physical link.
3.5.1 IPSec Settings
A majority of data contents are Plaintext Transmission on the Internet, which has many potential
