Figure 171 Remote Management: Icmp; Table 131 Remote Management: Icmp - ZyXEL Communications 802.11g ADSL 2+ 4-Port Security Gateway HW-D Series User Manual

P-662H/HW-D 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 171 Remote Management: ICMP

The following table describes the labels in this screen.

Table 131 Remote Management: ICMP

LABEL
ICMP
Respond to Ping
on
Do not respond to
requests for
unauthorized
services
Apply
Cancel
318
DESCRIPTION
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.
The ZyXEL Device will 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. Otherwise select LAN & WAN to reply to both
incoming LAN and WAN Ping requests.
Select this option to prevent hackers from finding the ZyXEL Device by probing for
unused ports. If you select this option, the ZyXEL Device will not respond to port
request(s) for unused ports, thus leaving the unused ports and the ZyXEL Device
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 "
change this policy. When the firewall mechanism blocks a UDP packet, it drops the
packet without sending a response packet.
Click Apply to save your customized settings and exit this screen.
Click Cancel to begin configuring this screen afresh.
sys firewall tcprst rst [on|off]
Chapter 21 Remote Management Configuration
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