ZyXEL Communications P-334W - Manual (Page 235)

Prestige 334W User’s Guide
VPN Screens 16-25
Table 16-8 VPN IKE: Advanced
LABEL DESCRIPTION
Authentication
Algorithm
Select SHA1 or MD5 from the drop-down list box. MD5 (Message Digest 5) and
SHA1 (Secure Hash Algorithm) are hash algorithms used to authenticate packet
data. The SHA1 algorithm is generally considered stronger than MD5, but is
slower. Select MD5 for minimal security and SHA-1 for maximum security.
SA Life Time
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.
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 from DH1
or DH2 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).
Basic Select Basic to go to the previous VPN configuration screen.
Apply Click Apply to save your changes.
Reset Click Reset to begin configuring this screen afresh.
16.13 Manual Key Setup
Manual key management is useful if you have problems with IKE key management.
16.13.1 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.