Chapter 21 Ipsec Vpn; Virtual Private Networks (Vpn) Overview - ZyXEL Communications ZyWall USG20-VPN User Manual

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IPSec VPN

21.1 Virtual Private Networks (VPN) Overview

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.
IPSec VPN
Internet Protocol Security (IPSec) VPN connects IPSec routers or remote users using IPSec client
software. This standards-based VPN offers flexible solutions for secure data communications across
a public network. IPSec is built around a number of standardized cryptographic techniques to
provide confidentiality, data integrity and authentication at the IP layer. The USG can also combine
multiple IPSec VPN connections into one secure network. Here local USG X uses an IPSec VPN
tunnel to remote (peer) USG Y to connect the local (A) and remote (B) networks.
Figure 221 IPSec VPN Example
Internet Key Exchange (IKE): IKEv1 and IKEv2
The USG supports IKEv1 and IKEv2 for IPv4 and IPv6 traffic. IKE (Internet Key Exchange) is a
protocol used in setting up security associations that allows two parties to send data securely.
IKE uses certificates or pre-shared keys for authentication and a Diffie–Hellman key exchange to
set up a shared session secret from which encryption keys are derived. A security policy for each
peer must be manually created.
IPSec VPN consists of two phases: Phase 1 and Phase 2. Phase 1's purpose is to establish a secure
authenticated communication channel by using the Diffie–Hellman key exchange algorithm to
generate a shared secret key to encrypt IKE communications. This negotiation results in one single
bi-directional ISAKMP Security Association (SA). The authentication can be performed using either
pre-shared key (shared secret), signatures, or public key encryption. Phase 1 operates in either
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