The Internet is a worldwide, publicly accessible IP network. Due to its vast global proliferation, it has become a viable method of interconnecting remote sites. However, the fact that it is a public infrastructure has deterred most enterprises from adopting it as a viable remote access method for branch and SOHO sites.

A virtual private network (VPN) is a concept that describes how to create a private network over a public network infrastructure while maintaining confidentiality   and   security. VPNs use cryptographic tunneling protocols to provide sender authentication, message integrity, and confidentiality by protecting against packet sniffing. VPNs can be implemented at Layers 2, 3, and 4 of the Open Systems Interconnection (OSI) model. Figure illustrates a typical VPN topology. Components required to establish a VPN include:

  • An existing network with servers and workstations
  • Connection to the Internet
  • VPN gateways (i.e., routers, PIX, ASA, VPN concentrators) that act as endpoints to establish, manage, and control VPN connections
  • Software to create and manage tunnels

The key to VPN technology is security. VPNs secure data by encapsulating the data, encrypting the data, or both encapsulating the data and then encrypting it:

  • Encapsulation is also referred to as tunneling because encapsulation transmits data transparently from network to network through a shared network infrastructure.
  • Encryption codes data into a different Decryption decodes encrypted data into the data’s original unencrypted format.



                            Fig:(a) A leased-line private network. (b) A virtual private network.

Basically, a VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as a leased line, a VPN uses "virtual" connections routed through the Internet from the company's private network to the remote site or employee.

A well-designed VPN can greatly benefit a company. For example, it can:

  • Extend geographic connectivity
  • improve security
  • Reduce operational costs versus traditional WAN
  • Reduce transit time and transportation costs for remote users
  • Improve productivity
  • Simplify network topology
  • Provide global networking opportunities
  • Provide telecommuter support
  • Provide broadband networking compatibility
  • Provide faster ROI (return on investment) than traditional WAN

What features are needed in a well-designed VPN?

It should incorporate:

  • Security
  • Reliability
  • Scalability
  • Network management
  • Policy management