ZyXEL Communications ZyXEL ZyWALL P1, User Manual

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ZyWALL P1 User’s Guide
Chapter 7 Firewall Screens 119
Figure 46 Firewall: Anti-Probing
The following table describes the labels in this screen.
7.10 Configuring Attack Alert
Attack alerts are the first defense against DoS attacks. In the Threshold screen, shown later,
you may choose to generate an alert whenever an attack is detected. For DoS attacks, the
ZyWALL 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.
Table 35 Firewall: Anti-Probing
LABEL DESCRIPTION
Respond to PING
on
The ZyWALL does not respond to any incoming Ping requests when Disable is
selected. Select LAN to reply to incoming LAN Ping requests. Select WAN to reply
to incoming WAN Ping requests. Select LAN & WAN to reply to incoming Ping
requests on the LAN and WAN.
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. By default this option is not selected and 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 mechanism
before reaching this anti-probing mechanism. Therefore if the firewall mechanism
blocks a probing packet, the ZyWALL reacts based on the firewall policy, which by
default, is to send a TCP reset packet for a blocked TCP packet. You can use the
command "sys firewall tcprst rst [on|off]" to change this policy. When the firewall
mechanism blocks a UDP packet, it drops the packet 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.