VPN concepts
It is important that you have at least a basic knowledge of standard VPN technologies before you implement a VPN connection.
Virtual private networking (VPN) uses several important TCP/IP protocols to protect data traffic. To better understand how any VPN connection works, familiarize yourself with these protocols and concepts and how VPN uses them:
- IP Security protocols
IP Security (IPSec) provides a stable, long lasting base for providing network layer security. - Key management
A dynamic VPN provides additional security for your communications by using the Internet Key Exchange (IKE) protocol for key management. IKE allows the VPN servers on each end of the connection to negotiate new keys at specified intervals. 
IKE version 2
IKE version 2 is an enhancement to the Internet key exchange protocol.- Layer 2 Tunnel Protocol
Layer 2 Tunneling Protocol (L2TP) connections, which are also called virtual lines, provide cost-effective access for remote users by allowing a corporate network systems to manage the IP addresses assigned to its remote users. Further, L2TP connections provide secure access to your system or network when you use them in conjunction with IP Security (IPSec). - Network address translation for VPN
VPN provides a means for performing network address translation, called VPN NAT. VPN NAT differs from traditional NAT in that it translates addresses before applying the IKE and IPSec protocols. Refer to this topic to learn more. - NAT compatible IPSec with UDP
UDP encapsulation allows IPSec traffic to pass through a conventional NAT device. Review this topic for more information about what it is and why you should use it for your VPN connections. - IP Compression
The IP Payload Compression protocol (IPComp) reduces the size of IP datagrams by compressing the datagrams to increase the communication performance between two partners. - VPN and IP filtering
IP filtering and VPN are closely related. In fact, most VPN connections require filter rules to work properly. This topic provides you information about what filters VPN requires, as well as other filtering concepts related to VPN.
Parent topic: Virtual Private Networking