Figure 79 Firewall Threshold; Table 61 Firewall Threshold - ZyXEL Communications ZyWall 70 User Manual

Internet security appliance

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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 Time 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

2 If the Blocking Time 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 Time

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

FIREWALL link and then the Threshold tab to bring up the next screen.

Figure 79 Firewall Threshold

The following table describes the labels in this screen.

Denial of Service

One Minute Low

Chapter 10 Firewall Screens

This is the rate of new half-open sessions 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.

ZyWALL 70 User's Guide