ZyXEL Communications Unified Security Gateway ZyWALL 300, User Manual

Page: 474 / 1156

Chapter 25 IPSec VPN
ZyWALL USG 300 User’s Guide
474
• Use the
VPN Gateway
screens (see Section 25.2.1 on page 478 ) to manage
the ZyWALL’s VPN gateways. A VPN gateway specifies the IPSec routers at
either end of a VPN tunnel and the IKE SA settings (phase 1 settings). You can
also activate and deactivate each VPN gateway.
• Use the
VPN Concentrator
screens (see Section 25.4 on page 497 ) to combine
several IPSec VPN connections into a single secure network.
25.1.2 What You Need to Know
An IPSec VPN tunnel is usually established in two phases. Each phase establishes
a security association (SA), a contract indicating what security parameters the
ZyWALL and the remote IPSec router will use. The first phase establishes an
Internet Key Exchange (IKE) SA between the ZyWALL and remote IPSec router.
The second phase uses the IKE SA to securely establish an IPSec SA through
which the ZyWALL and remote IPSec router can send data between computers on
the local network and remote network. This is illustrated in the following figure.
Figure 353 VPN: IKE SA and IPSec SA
In this example, a computer in network
A
is exchanging data with a computer in
network B . Inside networks A and B , the data is transmitted the same way data is
normally transmitted in the networks. Between routers
X
and
Y
, the data is
protected by tunneling, encryption, authentication, and other security features of
the IPSec SA. The IPSec SA is secure because routers
X and Y established the IKE
SA first.