ZyXEL Communications NBG-417N manual 138, Icmp

Chapter 13 Firewall

Click Security > Firewall > Services. The screen appears as shown next.

Figure 77 Security > Firewall > Services

The following table describes the labels in this screen.

Table 51 Security > Firewall > Services

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 NBG-417N will not respond to any incoming Ping requests when
on	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.
Do not respond	Select this option to prevent hackers from finding the NBG-417N by
to requests for	probing for unused ports. If you select this option, the NBG-417N will
unauthorized	not respond to port request(s) for unused ports, thus leaving the
services	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 [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 the settings.
Reset	Click Reset to start configuring this screen again.

138

NBG-417N User’s Guide