P-662H/HW-D Series User’s Guide

The following table describes the labels in this screen.

Table 70 Firewall: Anti Probing

LABEL

DESCRIPTION

 

 

Respond to PING

The ZyXEL Device does not respond to any incoming ping requests when Disable

on

is selected. Select the interface which you want to reply to incoming ping requests.

Do Not Respond to

Select this option to prevent hackers from finding the ZyXEL Device by probing for

Requests for

unused ports. If you select this option, the ZyXEL Device will not respond to port

Unauthorized

request(s) for unused ports, thus leaving the unused ports and the ZyXEL Device

Services.

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 back to the ZyXEL Device.

 

 

Cancel

Click Cancel to begin configuring this screen afresh.

 

 

11.10 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 11.10.3 on page 200 to configure thresholds.

11.10.1 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.

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Chapter 11 Firewall Configuration