ZyXEL Communications HW-D Series User Manual

P-662H/HW-D Series User’s Guide

Chapter 16 VPN Screens

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Manual key management is useful if you have problems with IKE key management.

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.

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 SHA-1 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 95   Advanced VPN Policies