Firewall; Chapter 9 Firewall; Firewall Overview; Figure 79 Default Firewall Action - ZyXEL Communications ZYWALL P1 User Manual

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H A P T E R
This chapter shows you how to configure your ZyWALL's firewall.

9.1 Firewall Overview

In networking, the term "firewall" refers to 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 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 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 VPN traffic between 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 79 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.
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