ZyXEL Communications Internet Security Appliance ZyWALL5UTM 4.0 - Manual (Page 222)

ZyWALL 5/35/70 Series User’s Guide
Chapter 11 Firewall Screens 222
11.9 Anti-Probing
If an outside user attempts to probe an unsupported port on your ZyWALL, an ICMP response
packet is automatically returned. This allows the outside user to know the ZyWALL exists.
The ZyWALL supports anti-probing, which prevents the ICMP response packet from being
sent. This keeps outsiders from discovering your ZyWALL when unsupported ports are
probed.
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.
Click SECURITY, FIREWALL, then the Anti-Probing tab to open the screen.
Figure 100 Anti-Probing
The following table describes the labels in this screen.
Table 71 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. Select WLAN to reply to incoming WLAN Ping requests. Otherwise
select ALL to reply to both incoming LAN and WAN and DMZ and WLAN 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 corresponding firewall
policy to 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.