P-661H/HW Series User’s Guide

If an outside user attempts to probe an unsupported port on your ZyXEL Device, an ICMP response packet is automatically returned. This allows the outside user to know the ZyXEL Device exists. Your ZyXEL Device supports anti-probing, which prevents the ICMP response packet from being sent. This keeps outsiders from discovering your ZyXEL Device when unsupported ports are probed.

Figure 148 Remote Management: ICMP

The following table describes the labels in this screen.

Table 111 Remote Management: ICMP

LABEL

DESCRIPTION

 

 

ICMP

Internet Control Message Protocol 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.

Respond to Ping

The ZyXEL Device will 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. Otherwise, select LAN & WAN to reply to both

 

incoming LAN and WAN Ping requests.

Do not respond to

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

requests for

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

unauthorized

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

services

unseen. By default this option is not selected and the ZyXEL Device 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 ZyXEL Device's firewall

 

mechanism before reaching this anti-probing mechanism. Therefore if the firewall

 

mechanism blocks a probing packet, the ZyXEL Device 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 [onoff]" 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 customized settings and exit this screen.

 

 

Cancel

Click Cancel to begin configuring this screen afresh.

 

 

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Chapter 17 Remote Management Configuration