Chapter 21 IPSec VPN
USG20(W)-VPN Series User’s Guide
336
21.1.2 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 USG and the remote IPSec
router will use. The first phase establishes an Internet Key Exchange (IKE) SA between the USG
and remote IPSec router. The second phase uses the IKE SA to securely establish an IPSec SA
through which the USG and remote IPSec router can send data between computers on the local
network and remote network. This is illustrated in the following figure.
Figure 224
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.
Summary of Contents for ZyWall USG20-VPN
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