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Chapter 20 IPSec VPN
ZyWALL 110/310/1100 Series User’s Guide
283
20.1.2 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 177 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.