User's Guide

LTE Series User’s Guide
126
CHAPTER 12
Firewall
12.1 Overview
This chapter shows you how to enable the Zyxel Device firewall. Use the firewall to protect your Zyxel
Device and network from attacks by hackers on the Internet and control access to it. The firewall:
• allows traffic that originates from your LAN computers to go to all other networks.
• blocks traffic that originates on other networks from going to the LAN.
By default, the Zyxel Device blocks DoS attacks whether the firewall is enabled or disabled.
The following figure illustrates the 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 93 Default Firewall Action
12.1.1 What You Need to Know About Firewall
DoS
Denials of Service (DoS) attacks are aimed at devices and networks with a connection to the Internet.
Their goal is not to steal information, but to disable a device or network so users no longer have access
to network resources. The Zyxel Device is pre-configured to automatically detect and thwart all known
DoS attacks.
ICMP
Internet Control Message Protocol (ICMP) is a message control and error-reporting protocol between a
host server and a gateway to the Internet. ICMP uses Internet Protocol (IP) datagrams, but the messages
are processed by the TCP/IP software and directly apparent to the application user.