User's Manual Part 1

AMG1202-T10A User’s Guide 139
CHAPTER 10
Firewall
10.1 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. By
default 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.
• blocks SYN and port scanner attacks.
By default, the ZyXEL Device blocks DDOS, LAND and Ping of Death attacks whether the firewall is
enabled or disabled.
10.1.1 What You Can Do in the Firewall Screens
Use the Firewall screen (Section 10.2 on page 141) to enable firewall on the ZyXEL Device.
10.1.2 What You Need to Know About Firewall
SYN Attack
A SYN attack floods a targeted system with a series of SYN packets. Each packet causes the
targeted system to issue a SYN-ACK response. While the targeted system waits for the ACK that
follows the SYN-ACK, it queues up all outstanding SYN-ACK responses on a backlog queue. SYN-
ACKs are moved off the queue only when an ACK comes back or when an internal timer terminates
the three-way handshake. Once the queue is full, the system will ignore all incoming SYN requests,
making the system unavailable for legitimate users.
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.
DDoS
A DDoS attack is one in which multiple compromised systems attack a single target, thereby
causing denial of service for users of the targeted system.