There are different technologies available for Wide Area Network (WAN) connectivity. But the main drawback of many Wide Area Network (WAN) connectivity solutions is "Cost". Think about an organization which has 100 offices all over the world. Providing Wide Area Network (WAN) connectivity using Leased Lines, for all these offices will be too costly.
If broadband internet access is available at all these 100 offices, linking all these offices using broadband internet is the most budget friendly Wide Area Network (WAN) connectivity solution. But we have a very serious problem related with security if we use public internet to connect all our 100 offices using broadband internet. Security!!!!.
Internet is a public network consisting of thousands of service providers and your organization's private Data is not much secure in a public network. We need protection for our private data against eavesdropping, tampering and we must make sure we are sending the data to exact recipient (mutual authentication).
A Virtual Private Network (VPN) is a Network Security Technology, which is used to secure private network traffic over a public network such as the Internet. A VPN ensures Data Confidentiality (privacy) and Data Integrity for network data in its journey from the source device to destination device using network security protocols like IPSec (Internet Protocol Security). IPSec (Internet Protocol Security) VPN provide Data Confidentiality by encrypting the data at the sending device and decrypting the data at receiving end. IPSec (Internet Protocol Security) VPN also provides Data Integrity (making sure that the Data is not changed while its journey) by using Hashing Algorithms like MD5 (Message Digest) and SHA (Secure Hashing Algorithm).