ZyXEL Communications P-2612HW-F1 -, Руководство пользователя

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Chapter 12 Firewall
P-2612HW Series User’s Guide
230
• Use the Threshold screen ( Section 12.4 on page 241 ) to set the thresholds that
the ZyXEL Device uses to determine when to start dropping sessions that do not
become fully established (half-open sessions).
12.1.2 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.
Anti-Probing
If an outside user attempts to probe an unsupported port on your ZyXEL Device,
an ICMP response packet is automatically returned. This allows the outside user to
know the ZyXEL Device exists. The ZyXEL Device supports anti-probing, which
prevents the ICMP response packet from being sent. This keeps outsiders from
discovering your ZyXEL Device when unsupported ports are probed.
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.
DoS Thresholds
For DoS attacks, the ZyXEL Device uses thresholds to determine when to drop
sessions that do not become fully established. These thresholds apply globally to
all sessions. You can use the default threshold values, or you can change them to
values more suitable to your security requirements.
Finding Out More
• See Section 12.1.3 on page 230 for an example of setting up a firewall.
• See Section 12.5 on page 245 for advanced technical information on firewall.
12.1.3 Firewall Rule Setup Example
The following Internet firewall rule example allows a hypothetical “MyService”
connection from the Internet.