ZyXEL P-793H v2 User Guide - Page 134
What You Need to Know About Firewall
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Chapter 9 Firewalls • Use the Threshold screen (Section 9.4 on page 145) to set the thresholds that the P-793H v2 uses to determine when to start dropping sessions that do not become fully established (half-open sessions). 9.1.2 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 P-793H v2, an ICMP response packet is automatically returned. This allows the outside user to know the P-793H v2 exists. The P-793H v2 supports anti-probing, which prevents the ICMP response packet from being sent. This keeps outsiders from discovering your P-793H v2 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 P-793H v2 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 9.1.3 on page 135 for an example of setting up a firewall. • See Section 9.5 on page 149 for advanced technical information on firewall. 134 P-793H v2 User's Guide