ZyWALL 5/35/70 Series User’s Guide

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-Probingtab 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

The ZyWALL does not respond to any incoming Ping requests when Disable is

on

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

Select this option to prevent hackers from finding the ZyWALL by probing for

requests for

unused ports. If you select this option, the ZyWALL will not respond to port

unauthorized

request(s) for unused ports, thus leaving the unused ports and the ZyWALL

services.

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.

 

 

Chapter 11 Firewall Screens

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