VPN allows for secure communication over public networks through tunneling protocols like PPTP, L2TP, and IPsec. There are three main types of VPN implementations: intranet within an organization, extranet between an organization and outside users, and remote access for mobile users. VPNs provide advantages like reducing costs of long-distance lines and charges while allowing flexibility and efficiency. However, they also have disadvantages like requiring expertise in security issues and performance depending on external factors. Industries like healthcare, manufacturing, retail, and banking commonly use VPNs to securely transfer private information between locations.

1. BY : WAQAS ANWAR

5. VPN Encapsulation of Packets 1-18

7. VPN Basic Architecture 1-18

11. Site-to-Site VPNs 1-18

17. 1:Feilner, Markus. "Chapter 1 - VPN—Virtual Private Network". OpenVPN: Building and Integrating Virtual Private Networks: Learn How to Build Secure VPNs Using this Powerful Open Source Application. Packt Publishing. 2: Address Allocation for Private Internets, RFC 1918, Y. Rekhter et al. 3: RFC 2917, A Core MPLS IP VPN Architecture 4: Layer Two Tunneling Protocol "L2TP", RFC 2661, W. Townsley et al. 5: IP Based Virtual Private Networks, RFC 2341, A. Valencia et al 6: Point-to-Point Tunneling Protocol (PPTP), RFC 2637, K. Hamzeh et al. 7: Http://en.wikipedia.org/wiki/vpn