ZyXEL Communications ZyXEL ZyAIR 100 - Manual (Page 227)

ZyWALL 10~100 Series Internet Security Gateway
VPN Screens 15-21
Table 15-8 VPN IKE: Advanced
LABEL DESCRIPTION
SA Life Time
(seconds)
Define the length of time before an IKE SA automatically renegotiates in this field. It
may range from 60 to 3,000,000 seconds (almost 35 days).
A short SA Life Time increases security by forcing the two VPN gateways to update
the encryption and authentication keys. However, every time the VPN tunnel
renegotiates, all users accessing remote resources are temporarily disconnected.
Encapsulation Select Tunnel mode or Transport mode from the drop-down list box.
Perfect Forward
Secrecy (PFS)
Perfect Forward Secrecy (PFS) is disabled (NONE) by default in phase 2 IPSec SA
setup. This allows faster IPSec setup, but is not so secure. Choose DH1 or DH2 from
the drop-down list box to enable PFS. DH1 refers to Diffie-Hellman Group 1 a 768 bit
random number. DH2 refers to Diffie-Hellman Group 2 a 1024 bit (1Kb) random
number (more secure, yet slower).
OK Click OK to save your changes back to the ZyWALL and return to the Configure-IKE
screen.
CANCEL Click CANCEL to return to the Configure-IKE screen without saving your changes.
15.13 Manual Key Setup
Manual key management is useful if you have problems with IKE key management.
15.13.1 Security Parameter Index (SPI)
An SPI is used to distinguish different SAs terminating at the same destination and using the same IPSec
protocol. This data allows for the multiplexing of SAs to a single gateway. The SPI (Security Parameter
Index) along with a destination IP address uniquely identify a particular Security Association (SA). The SPI
is transmitted from the remote VPN gateway to the local VPN gateway. The local VPN gateway then uses
the network, encryption and key values that the administrator associated with the SPI to establish the tunnel.
Current ZyXEL implementation assumes identical outgoing and incoming SPIs.
15.14 Configuring Manual Key
You only configure VPN Manual Key when you select Manual in the Key Management field on the VPN
IKE screen. This is the VPN Manual Key screen as shown next.