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ZyWALL 2 Plus User’s Guide
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CHAPTER 11
Firewall
This chapter shows you how to configure your ZyWALL’s firewall.
11.1 Firewall Overview
The networking term firewall is a system or group of systems 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 113 Default Firewall Action