ZyXEL Communications P-660RU-T1 v3, Руководство пользователя, Страница: 109 / 230

P-660RU-Tx v3 User’s Guide
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H A P T E R
13
Firewall
13.1 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.
13.1.1 What You Can Do in the Firewall Screens
Use the Firewall screen ( Section 13.2 on page 110 ) to enable firewall and/or SPI on the
ZyXEL Device.
13.1.2 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.