ZyXEL 202H 91-003-194003B User Manual

P-202H Plus v2 User’s Guide

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Chapter 11 VPN Screens

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.

Note: Current ZyXEL implementation assumes identical outgoing and incoming SPIs.

Encryption Algorithm 

The encryption algorithm for the ZyXEL Device and the secure remote 

gateway should be identical. 
When DES is used for data communications, both sender and receiver must 

know the same secret key, which can be used to encrypt and decrypt the 

message or to generate and verify a message authentication code. The DES 

encryption algorithm uses a 56-bit key. Triple DES (3DES) is a variation on 

DES that uses a 168-bit key. As a result, 3DES is more secure than DES. It 

also requires more processing power, resulting in increased latency and 

decreased throughput. Select NULL to set up a tunnel without encryption. 

When you select NULL, you do not enter an encryption key.

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. 

Encapsulation 

Select Tunnel mode or Transport mode from the drop down list-box. The 

ZyXEL Device's encapsulation mode should be identical to the secure remote 

gateway. 

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). 

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 ZyXEL 

Device.

Table 38   Advanced Rule Setup (continued)