ZyXEL Communications P-661H Series, User Manual, Page: 221 / 383

P-661H/HW Series User’s Guide
Chapter 13 VPN Screens 221
13.14 Manual Key Setup
Manual key management is useful if you have problems with IKE key management.
13.14.1 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.
13.15 Configuring Manual Key
You only configure VPN Manual Key when you select Manual in the IPSec Key Mode field
on the VPN IKE screen. This is the VPN Manual Key screen as shown next.
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 SHA1 for maximum security.
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).
Apply Click Apply to save your changes back to the ZyXEL Device and return to the
VPN-IKE screen.
Cancel Click Cancel to return to the VPN-IKE screen without saving your changes.
Table 85 Advanced VPN Policies (continued)
LABEL DESCRIPTION