ZyXEL Communications Internet Security Gateway ZyWALL 2 Series - Manual (Page 178)

ZyWALL 2 Series User’s Guide
11-22 Firewall Screens
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.