ZyXEL Communications ZyWALL USG 200 Series User Manual page 508

Chapter 25 IPSec VPN
Additional Topics for IPSec SA
This section provides more information about IPSec SA in your ZyWALL.
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.
IPSec SA Proposal using Manual Keys
In an 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.
Note: The ZyWALL and remote IPSec router must use the same encryption key and
authentication key.
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.
Note: The ZyWALL and remote IPSec router must use the same SPI.
NAT for Inbound and Outbound Traffic
The ZyWALL can translate the following types of network addresses in IPSec SA.
• Source address in outbound packets - this translation is necessary if you want
the ZyWALL to route packets from computers outside the local network through
the IPSec SA.
• Source address in inbound packets - this translation hides the source address of
computers in the remote network.
• Destination address in inbound packets - this translation is used if you want to
forward packets (for example, mail) from the remote network to a specific
computer (like the mail server) in the local network.
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