Additional Topics For Ipsec Sa - ZyXEL Communications Unified Security Gateway ZyWALL 300 User Manual

Chapter 20 IPSec VPN
If you enable PFS, the ZyWALL and remote IPSec router perform a DH key exchange every
time an IPSec SA is established, changing the root key from which encryption keys are
generated. As a result, if one encryption key is compromised, other encryption keys remain
secure.
If you do not enable PFS, the ZyWALL and remote IPSec router use the same root key that
was generated when the IKE SA was established to generate encryption keys.
The DH key exchange is time-consuming and may be unnecessary for data that does not
require such security.

20.1.2 Additional Topics for IPSec SA

This section provides more information about IPSec SA in your ZyWALL.
20.1.2.1 IPSec SA using Manual Keys
You might set up an IPSec SA using manual keys when you want to establish a VPN tunnel
quickly, for example, for troubleshooting. You should only do this as a temporary solution,
however, because it is not as secure as a regular IPSec SA.
In IPSec SAs using manual keys, the ZyWALL and remote IPSec router do not establish an
IKE SA. They only establish an IPSec SA. As a result, an IPSec SA using manual keys has
some characteristics of IKE SA and some characteristics of IPSec SA. There are also some
differences between IPSec SA using manual keys and other types of SA.
20.1.2.1.1 IPSec SA Proposal using Manual Keys
In IPSec SA using manual keys, you can only specify one encryption algorithm and one
authentication algorithm. You cannot specify several proposals. There is no DH key exchange,
so you have to provide the encryption key and the authentication key the ZyWALL and remote
IPSec router use.
The ZyWALL and remote IPSec router must use the same encryption key and
authentication key.
20.1.2.1.2 Authentication and the Security Parameter Index (SPI)
For authentication, the ZyWALL and remote IPSec router use the SPI, instead of pre-shared
keys, ID type and content. The SPI is an identification number.
The ZyWALL and remote IPSec router must use the same SPI.
20.1.2.2 NAT for Inbound and Outbound Traffic
The ZyWALL can translate the following types of network addresses in IPSec SA.
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