Chapter 11 Firewall

The following table describes the labels in this screen.

Table 73 SECURITY > FIREWALL > Threshold

LABEL

DESCRIPTION

Disable DoS Attack

Select the check boxes of any interfaces (or all VPN tunnels) for which you want

Protection on

the ZyWALL to not use the Denial of Service protection thresholds. This disables

 

DoS protection on the selected interface (or all VPN tunnels).

 

You may want to disable DoS protection for an interface if the ZyWALL is treating

 

valid traffic as DoS attacks. Another option would be to raise the thresholds.

 

 

Denial of Service

The ZyWALL measures both the total number of existing half-open sessions and

Thresholds

the rate of session establishment attempts. Both TCP and UDP half-open

 

sessions are counted in the total number and rate measurements. Measurements

 

are made once a minute.

 

 

One Minute Low

This is the rate of new half-open sessions per minute that causes the firewall to

 

stop deleting half-open sessions. The ZyWALL continues to delete half-open

 

sessions as necessary, until the rate of new connection attempts drops below this

 

number.

 

 

One Minute High

This is the rate of new half-open sessions per minute that causes the firewall to

 

start deleting half-open sessions. When the rate of new connection attempts rises

 

above this number, the ZyWALL deletes half-open sessions as required to

 

accommodate new connection attempts.

 

For example, if you set the one minute high to 100, the ZyWALL starts deleting

 

half-open sessions when more than 100 session establishment attempts have

 

been detected in the last minute. It stops deleting half-open sessions when the

 

number of session establishment attempts detected in a minute goes below the

 

number set as the one minute low.

 

 

Maximum

This is the number of existing half-open sessions that causes the firewall to stop

Incomplete Low

deleting half-open sessions. The ZyWALL continues to delete half-open requests

 

as necessary, until the number of existing half-open sessions drops below this

 

number.

 

 

Maximum

This is the number of existing half-open sessions that causes the firewall to start

Incomplete High

deleting half-open sessions. When the number of existing half-open sessions

 

rises above this number, the ZyWALL deletes half-open sessions as required to

 

accommodate new connection requests. Do not set Maximum Incomplete High

 

to lower than the current Maximum Incomplete Low number.

 

For example, if you set the maximum incomplete high to 100, the ZyWALL starts

 

deleting half-open sessions when the number of existing half-open sessions rises

 

above 100. It stops deleting half-open sessions when the number of existing half-

 

open sessions drops below the number set as the maximum incomplete low.

 

 

TCP Maximum

An unusually high number of half-open sessions with the same destination host

Incomplete

address could indicate that a DoS attack is being launched against the host.

 

Specify the number of existing half-open TCP sessions with the same destination

 

host IP address that causes the firewall to start dropping half-open sessions to

 

that same destination host IP address. Enter a number between 1 and 256. As a

 

general rule, you should choose a smaller number for a smaller network, a slower

 

system or limited bandwidth. The ZyWALL sends alerts whenever the TCP

 

Maximum Incomplete is exceeded.

Action taken when

Select the action that ZyWALL should take when the TCP maximum incomplete

TCP Maximum

threshold is reached. You can have the ZyWALL either:

Incomplete

Delete the oldest half open session when a new connection request comes.

reached threshold

or

 

 

Deny new connection requests for the number of minutes that you specify

 

(between 1 and 256).

 

 

Apply

Click Apply to save your changes back to the ZyWALL.

 

 

Reset

Click Reset to begin configuring this screen afresh.

 

 

 

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ZyWALL 2WG User’s Guide