ZyXEL Communications NBG-417N - V1.0 Manual page 137

Click Security > Firewall > Services. The screen appears as shown next.
Figure 75 Security > Firewall > Services l
The following table describes the labels in this screen.
Table 48 Security > Firewall > Services
LABEL
ICMP
Respond to Ping
on
Do not respond
to requests for
unauthorized
services
Apply
Reset
NBG-417N User's Guide
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 NBG-417N 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 all incoming LAN and WAN Ping requests.
Select this option to prevent hackers from finding the NBG-417N by
probing for unused ports. If you select this option, the NBG-417N will
not respond to port request(s) for unused ports, thus leaving the
unused ports and the NBG-417N unseen. By default this option is not
selected and the NBG-417N 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 NBG-417N's
firewall mechanism before reaching this anti-probing mechanism.
Therefore if the firewall mechanism blocks a probing packet, the NBG-
417N 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.
Click Apply to save the settings.
Click Reset to start configuring this screen again.
Chapter 13 Firewall
137