ZyXEL 2WG Guida Utente

ZyWALL 2WG User’s Guide

A firewall is a system that enforces an access-control policy between two networks. It is 
generally a mechanism used to protect a trusted network from an untrusted network. 
The ZyWALL physically separates the LAN, DMZ, WLAN and the WAN and acts as a secure 
gateway for all data passing between the networks. The ZyWALL protects against Denial of 
Service (DoS) attacks, prevents theft, destruction and modification of data, and logs events.
Enable the firewall to protect your LAN computers from attacks by hackers on the Internet and 
control access between the LAN, DMZ, WLAN and WAN. By default the firewall:

• allows traffic that originates from your LAN computers to go to all of the networks. 
• blocks traffic that originates on the other networks from going to the LAN. 
• allows traffic that originates on the WLAN to go to the WAN. 
• allows traffic that originates on the WAN to go to the DMZ and protects your DMZ 

computers against DoS attacks.

• allows VPN traffic between any of the networks.

The following figure illustrates the default firewall action. User A can initiate an IM (Instant 
Messaging) session from the LAN to the WAN (1). Return traffic for this session is also 
allowed (2). However other traffic initiated from the WAN is blocked (3 and 4).

Figure 148   Default Firewall Action

Your customized rules take precedence and override the ZyWALL’s default settings. The 
ZyWALL checks the source IP address, destination IP address and IP protocol type of network 
traffic against the firewall rules (in the order you list them). When the traffic matches a rule, 
the ZyWALL takes the action specified in the rule.