ZyXEL Communications ZyWALL 2 Series Attack Alert, Blocking Period, Blocking Period, Blocking Period, TCP Maximum Incomplete, TCP Maximum Incomplete, Figure 11-12Attack Alert

ZyWALL 2 Series User’s Guide

Whenever the number of half-open sessions with the same destination host address rises above a threshold (TCP Maximum Incomplete), the ZyWALL starts deleting half-open sessions according to one of the following methods:

1.If the Blocking Period timeout is 0 (the default), then the ZyWALL deletes the oldest existing half-open session for the host for every new connection request to the host. This ensures that the number of half- open sessions to a given host will never exceed the threshold.

2.If the Blocking Period timeout is greater than 0, then the ZyWALL blocks all new connection requests to the host giving the server time to handle the present connections. The ZyWALL continues to block all new connection requests until the Blocking Period expires.

The ZyWALL also sends alerts whenever TCP Maximum Incomplete is exceeded. The global values specified for the threshold and timeout apply to all TCP connections. Click the Attack Alert tab to bring up the next screen.

Figure 11-12 Attack Alert

The following table describes the fields in this screen.

11-22 Firewall Screens