ZyXEL Communications P-793H User Manual

Chapter 11 IPSec VPN

P-793H User’s Guide

The following table describes the fields in this screen.

Table 53   VPN > Setup > Edit > Advanced

VPN - IKE - 

Advanced Setup

Protocol

Enter the IP protocol number whose traffic is allowed to use the VPN tunnel. 

Enter 0 to allow all IP protocols to use the VPN tunnel. See 

 for some common IP protocols.

Enable Replay 

Detection

Select this to enable replay detection. As a VPN setup is processing intensive, 

the system is vulnerable to Denial of Service (DoS) attacks. The IPSec receiver 

can detect and reject old or duplicate packets to protect against replay attacks.

Local Start Port
End

Enter the port number or range of port numbers in the local network whose traffic 

is allowed to use the VPN tunnel. Enter 0 in both fields to allow all port numbers in 

the local network to use the VPN tunnel. See 

common port numbers.

Remote Start Port
End

Enter the port number or range of port numbers in the remote network whose 

traffic is allowed to use the VPN tunnel. Enter 0 in both fields to allow all port 

numbers in the remote network to use the VPN tunnel. See 

 for some common port numbers.

Phase 1

Negotiation Mode

Select the negotiation mode for the IKE SA. Main is more secure than 

Aggressive. The ZyXEL Device and remote IPSec router must use the same 

negotiation mode.

Pre-Shared Key

Type the pre-shared key the IKE SA uses. The ZyXEL Device and remote IPSec 

router must use the same pre-shared key. If the keys are different, the ZyXEL 

Device receives a “PYLD_MALFORMED” (payload malformed) packet.
You can use 8-31 ASCII characters or 16-62 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 16-62 characters. For example, in 

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

“0123456789ABCDEF” is the key itself.

Encryption 

Algorithm

Select one of the following encryption algorithms for the IKE SA. The algorithms 

are listed in order from weakest to strongest.
Data Encryption Standard (DES) is a widely used (but breakable) method of data 

encryption. It applies a 56-bit key to each 64-bit block of data.
Triple DES (3DES) is a variant of DES. It iterates three times with three separate 

keys, effectively tripling the strength of DES.
Advanced Encryption Standard (AES) is a newer method of data encryption that 

also uses a secret key. AES applies a 128-bit key to 128-bit blocks of data.
Select NULL to set up a VPN tunnel without encryption.

Authentication 

Algorithm

Select one of the following authentication algorithms for the IKE SA. The 

algorithms are listed in order from weakest to strongest.
Message Digest 5 (MD5) produces a 128-bit digest to authenticate packets.
Secure Hash Algorithm (SHA1) produces a 160-bit digest to authenticate 

packets.

SA Life Time 

(Seconds)

Enter the length of time before the ZyXEL Device automatically renegotiates the 

IKE SA. It may range from 60 to 3,000,000 seconds (almost 35 days).
A low value increases security by forcing the two VPN gateways to update the 

encryption and authentication keys. However, if every time the IKE SA is 

renegotiated, any users trying to establish IPSec SA experience delays. (Existing 

IPSec SA are not affected.)