ZyXEL Communications NBG334S User Manual page 132

Chapter 12 Firewall
Table 51 Security > Firewall > Services
LABEL
Do not respond to
requests for
unauthorized
services
Service Setup
Enable Services
Blocking
Available
Services
Blocked Services
Custom Port
Type
Port Number
Add
Delete
Clear All
Schedule to Block
Day to Block:
Time of Day to
Block (24-Hour
Format)
Misc setting
Bypass Triangle
Route
Max NAT/Firewall
Session Per User
Apply
Reset
132
DESCRIPTION
Select this option to prevent hackers from finding the NBG334S by probing for
unused ports. If you select this option, the NBG334S will not respond to port
request(s) for unused ports, thus leaving the unused ports and the NBG334S
unseen. By default this option is not selected and the NBG334S 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 NBG334S's firewall
mechanism before reaching this anti-probing mechanism. Therefore if the firewall
mechanism blocks a probing packet, the NBG334S 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.
Select this check box to enable this feature.
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.
This is a list of services (ports) that will be inaccessible to computers on your LAN
once you enable service blocking.
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.
Choose the IP port (TCP or UDP) that defines your customized port from the drop
down list box.
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.
Select a service from the Available Services drop-down list and then click Add to
add a service to the Blocked Services
Select a service from the Blocked Services list and then click Delete to remove
this service from the list.
Click Clear All to empty the Blocked Services.
Select a check box to configure which days of the week (or everyday) you want
service blocking to be active.
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".
Select this check box to have the NBG334S firewall ignore the use of triangle
route topology on the network.
Type a number ranging from 1 to 2048 to limit the number of NAT/firewall sessions
that a host can create.
Click Apply to save the settings.
Click Reset to start configuring this screen again.
NBG334S User's Guide