This document explains the concepts and configuration of virtual private networks (VPNs), including gateway-to gateway and hub-and-spoke configurations, dynamic DNS, dial-up and IKE-mode clients, Internet browsing configuration, redundant VPN, transparent mode VPN, manual key, IPv6 IPsec, L2TP IPsec, protecting OSFP with IPsec, and phase 1 and phase 2 parameters.