ZyXEL Communications HW-D Series User Manual

P-662H/HW-D Series User’s Guide

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Chapter 16 VPN Screens

Negotiation Mode Select Main or Aggressive from the drop-down list box. Multiple SAs connecting 

through a secure gateway must have the same negotiation mode. 

Pre-Shared Key Type your pre-shared key in this field. A pre-shared key identifies a 

communicating party during a phase 1 IKE negotiation. It is called "pre-shared" 

because you have to share it with another party before you can communicate with 

them over a secure connection. 
Type from 8 to 31 case-sensitive ASCII characters or from 16 to 62 hexadecimal 

("0-9", "A-F") characters. You must precede a hexadecimal key with a "0x” (zero 

x), which is not counted as part of the 16 to 62-character range for the key. For 

example, in "0x0123456789ABCDEF", “0x” denotes that the key is hexadecimal 

and “0123456789ABCDEF” is the key itself.
Both ends of the VPN tunnel must use the same pre-shared key. You will receive 

a “PYLD_MALFORMED” (payload malformed) packet if the same pre-shared key 

is not used on both ends.

Encryption

Algorithm

Select DES, 3DES or AES from the drop-down list box. 
When you use one of these encryption algorithms for data communications, both 

the sending device and the receiving device must use 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. This implementation of AES uses 

a 128-bit key. AES is faster than 3DES. 

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. 

Key Group You must choose a key group for phase 1 IKE setup. DH1 (default) refers to 

Diffie-Hellman Group 1 a 768 bit random number. DH2 refers to Diffie-Hellman 

Group 2 a 1024 bit (1Kb) random number. 

Phase 2

Active Protocol Use the drop-down list box to choose from ESP or AH. 

Encryption

Algorithm

This field is available when you select ESP in the Active Protocol field.
Select DES, 3DES, AES or NULL from the drop-down list box. 
When you use one of these encryption algorithms for data communications, both 

the sending device and the receiving device must use 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. This implementation of AES uses 

a 128-bit key. AES is faster than 3DES. 
Select NULL to set up a tunnel without encryption. When you select NULL, you 

do not enter an encryption key.

Table 95   Advanced VPN Policies