ZyXEL Communications ZyWALL5UTM 4.0 User Manual

ZyWALL 5/35/70 Series User’s Guide

Chapter 11 Firewall Screens

226

Click SECURITY, FIREWALL, then the Service tab to open the screen as shown next. Use 
this screen to configure custom services for use in firewall rules or view the services that are 
predefined in the ZyWALL.

Maximum 

Incomplete High

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

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.
The above values, say 80 in the Maximum Incomplete Low field and 100 in this 

field, cause the ZyWALL to start deleting half-open sessions when the number of 

existing half-open sessions rises above 100, and to stop deleting half-open 

sessions with the number of existing half-open sessions drops below 80.

TCP Maximum 

Incomplete 

This is 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.

Action taken when 

the TCP Maximum 

Incomplete 

threshold is 

reached.

Delete the oldest 

half open session 

when new 

connection request 

comes

Select this radio button to clear the oldest half open session when a new 

connection request comes.

Deny new 

connection request 

for

Select this radio button and specify for how long the ZyWALL should block new 

connection requests when TCP Maximum Incomplete is reached. 
Enter the length of blocking time in minutes (between 1 and 256).

Apply

Click Apply to save your changes back to the ZyWALL.

Reset 

Click Reset to begin configuring this screen afresh.

Table 72   Firewall Threshold (continued)