ZyXEL 2WG Guida Utente

Chapter 3 Wizard Setup

ZyWALL 2WG User’s Guide

The following table describes the labels in this screen.

This read-only screen shows the status of the current VPN setting. Use the summary table to 
check whether what you have configured is correct.

Table 19   VPN Wizard: IPSec Setting

Encapsulation Mode Tunnel is compatible with NAT, Transport is not.

Tunnel mode encapsulates the entire IP packet to transmit it securely. A Tunnel 

mode is required for gateway services to provide access to internal systems. 

Tunnel mode is fundamentally an IP tunnel with authentication and encryption. 

Transport mode is used to protect upper layer protocols and only affects the 

data in the IP packet. In Transport mode, the IP packet contains the security 

protocol (AH or ESP) located after the original IP header and options, but before 

any upper layer protocols contained in the packet (such as TCP and UDP). 

IPSec Protocol

Select the security protocols used for an SA. 
Both AH and ESP increase ZyWALL processing requirements and 

communications latency (delay).

Encryption Algorithm 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. 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.

Authentication 

Algorithm

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. The minimum value is 180 seconds.
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. 
Select DH1, DH2 or DH5 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). DH5 refers to Diffie-Hellman Group 

5 a 1536-bit random number.

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