ZyXEL Communications P-660HW-DX, User Manual

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Chapter 10 Firewall Configuration
P-660HW-Dx User’s Guide
172
The following table describes the labels in this screen.
10.10 DoS Thresholds
For DoS attacks, the ZyXEL Device uses thresholds to determine when to drop sessions that
do not become fully established. These thresholds apply globally to all sessions.
You can use the default threshold values, or you can change them to values more suitable to
your security requirements.
Refer to
Section 10.10.3 on page 173 to configure thresholds.
10.10.1 Threshold Values
Tune these parameters when something is not working and after you have checked the firewall
counters. These default values should work fine for most small offices. Factors influencing
choices for threshold values are:
• The maximum number of opened sessions.
• The minimum capacity of server backlog in your LAN network.
• The CPU power of servers in your LAN network.
• Network bandwidth.
• Type of traffic for certain servers.
If your network is slower than average for any of these factors (especially if you have servers
that are slow or handle many tasks and are often busy), then the default values should be
reduced.
You should make any changes to the threshold values before you continue configuring
firewall rules.
Table 62 Firewall: Anti Probing
LABEL DESCRIPTION
Respond to PING
on
The ZyXEL Device does 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.
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
corresponding firewall policy to send a TCP reset packet for a blocked TCP
packet or an ICMP port-unreachable packet for a blocked UDP packets or just
drop the packets without sending a response packet.
Apply Click Apply to save your changes to the ZyXEL Device.
Cancel Click Cancel to begin configuring this screen afresh.