ZyXEL ZyWALL 5 User Guide - Page 101
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Figure 37 VPN Wizard: IPSec Setting Chapter 4 Wizard Setup The following table describes the labels in this screen. Table 20 VPN Wizard: IPSec Setting LABEL DESCRIPTION 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. ZyWALL 5/35/70 Series User's Guide 101