ZyXEL Communications G.SHDSL.bis 4-port Security Gateway P-793H - Manual (Page 156)

P-793H User’s Guide
156 Chapter 11 IPSec VPN
Figure 72 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 the tunneling, encryption, and
authentication of the IPSec SA. The IPSec SA is established securely using the IKE SA that
routers X and Y established first.
The rest of this section discusses IKE SA and IPSec SA in more detail.
11.1.1 IKE SA Overview
The IKE SA provides a secure connection between the ZyXEL Device and remote IPSec
router.
It takes several steps to establish an IKE SA. The negotiation mode determines how many
steps are required. There are two negotiation modes: main mode and aggressive mode. Main
mode provides better security, while aggressive mode is faster.
Note: Both routers must use the same negotiation mode.
These modes are discussed in more detail in Section 11.1.2.1 on page 159 . The examples in
this section use main mode.
11.1.1.1 IP Addresses of the ZyXEL Device and Remote IPSec Router
In the ZyXEL Device, you have to specify the IP addresses of the ZyXEL Device and the
remote IPSec router to establish an IKE SA.
You can usually provide a static IP address or a domain name for the ZyXEL Device.
Sometimes, your ZyXEL Device might also offer another alternative, such as using the IP
address of a port or interface.
You can usually provide a static IP address or a domain name for the remote IPSec router as
well. Sometimes, you might not know the IP address of the remote IPSec router (for example,
telecommuters). In this case, you can still set up the IKE SA, but only the remote IPSec router
can initiate an IKE SA.