ZyXEL Communications ZyXEL ZyWALL 5 - Manual (Page 184)

ZyWALL 5 User’s Guide
Chapter 10 Firewall Screens 183
Click FIREWALL, then the Anti-Probing tab to open the screen.
Figure 75 Anti-Probing
The following table describes the labels in this screen.
10.10 DoS Thresholds
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 54 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 DMZ to reply to incoming DMZ Ping
requests. Otherwise select LAN & WAN & DMZ to reply to both incoming LAN and
WAN and DMZ Ping requests.
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.