ZyXEL ZyWALL 2 Plus User Guide - Page 208
The Threshold Screen
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Chapter 11 Firewall Screens The following table describes the labels in this screen. Table 52 SECURITY > FIREWALL > Anti-Probing LABEL DESCRIPTION Respond to PING on Select the check boxes of the interfaces that you want to reply to incoming Ping requests. Clear an interface's check box to have the ZyWALL not respond to any Ping requests that come into that interface. Do not respond to requests for unauthorized services. Select this option to prevent hackers from finding the ZyWALL by probing for unused ports. If you select this option, the ZyWALL will not respond to port request(s) for unused ports, thus leaving the unused ports and the ZyWALL unseen. If this option is not selected, the ZyWALL will reply with an ICMP port unreachable packet for a port probe on its unused UDP ports and a TCP reset packet for a port probe on its unused TCP ports. Note that the probing packets must first traverse the ZyWALL's firewall rule checks before reaching this anti-probing mechanism. Therefore if a firewall rule stops a probing packet, the ZyWALL reacts based on the firewall rule to either send a TCP reset packet for a blocked TCP packet (or an ICMP port-unreachable packet for a blocked UDP packets) or just drop the packets without sending a response packet. Apply Click Apply to save your changes back to the ZyWALL. Reset Click Reset to begin configuring this screen afresh. 11.7 The Threshold Screen For DoS attacks, the ZyWALL uses thresholds to determine when to start dropping sessions that do not become fully established (half-open sessions). These thresholds apply globally to all sessions. Click SECURITY > FIREWALL > Threshold to bring up the next screen. The global values specified for the threshold and timeout apply to all TCP connections. Figure 135 SECURITY > FIREWALL > Threshold 208 ZyWALL 2 Plus User's Guide
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