ZyXEL p-334wh Mode D'Emploi

P-334WH User’s Guide

140 

Chapter 12 Firewall

Do not respond to 

requests for 

unauthorized 

services

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 "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.

Enable Services 

Blocking

Select this check box to enable this feature.

Available Services This is a list of pre-defined services (ports) you may prohibit your LAN computers 

from using. Select the port you want to block using the drop-down list and click 

Add to add the port to the Blocked Services field.

Blocked Services

This is a list of services (ports) that will be inaccessible to computers on your LAN 

once you enable service blocking. 

Custom Port

A custom port is a service that is not available in the pre-defined Available 

Services list and you must define using the next two fields.

Type

Choose the IP port (TCP or UDP) that defines your customized port from the drop 

down list box.

Port Number

Enter the port number range that defines the service. For example, if you want to 

define the Gnutella service, then select TCP type and enter a port range from 6345 

to 6349.

Add

Select a service from the Available Services drop-down list and then click Add to 

add a service to the Blocked Services

Delete

Select a service from the Blocked Services list and then click Delete to remove 

this service from the list.

Clear All

Click Clear All to empty the Blocked Services.

Day to Block:

Select a check box to configure which days of the week (or everyday) you want 

service blocking to be active. 

Time of Day to 

Block (24-Hour 

Format)

Select the time of day you want service blocking to take effect. Configure blocking 

to take effect all day by selecting All Day. You can also configure specific times by 

selecting From and entering the start time in the Start (hour) and Start (min) 

fields and the end time in the End (hour) and End (min) fields. Enter times in 24-

hour format, for example, "3:00pm" should be entered as "15:00".

Bypass Triangle 

Route

Select this check box to have the ZyXEL Device firewall ignore the use of triangle 

route topology on the network. 

Max NAT/Firewall 

Session Per User

Type a number ranging from 1 to 2048 to limit the number of NAT/firewall sessions 

that a host can create.

Apply

Click Apply to save the settings. 

Reset

Click Reset to start configuring this screen again. 

Table 54   Firewall Services