ZyXEL Communications P660HN-Fx User Manual

ADSL Series User’s Guide

A virtual private network (VPN) provides secure communications between sites without the expense 
of leased site-to-site lines. A secure VPN is a combination of tunneling, encryption, authentication, 
access control and auditing. It is used to transport traffic over the Internet or any insecure network 
that uses TCP/IP for communication.

Internet Protocol Security (IPSec) is a standards-based VPN that offers flexible solutions for secure 
data communications across a public network like the Internet. IPSec is built around a number of 
standardized cryptographic techniques to provide confidentiality, data integrity and authentication 
at the IP layer. The following figure is an example of an IPSec VPN tunnel.

VPN: Example

• Use  the  Setup screen (

) to view the configured VPN policies and add, 

edit or remove a VPN policy.

• Use  the  Monitor screen (

) to display and manage the current active 

VPN connections.

A VPN tunnel is usually established in two phases. Each phase establishes a security association 
(SA), a contract indicating what security parameters the ZyXEL Device and the remote IPSec router 
will use. The first phase establishes an Internet Key Exchange (IKE) SA between the ZyXEL Device 
and remote IPSec router. The second phase uses the IKE SA to securely establish an IPSec SA 
through which the ZyXEL Device and remote IPSec router can send data between computers on the 
local network and remote network. The following figure illustrates this.