ZyXEL Communications P-660R-F1 series, Руководство пользователя

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Chapter 7 Firewalls
P-660R-F1 Series User’s Guide
98
The following table describes the labels in this screen.
Table 36
Security > Firewall > Threshold
LABEL DESCRIPTION
Denial of Service
Thresholds The ZyXEL Device measures both the total number of existing half-open
sessions and 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 ZyXEL Device 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 ZyXEL Device deletes half-open sessions as
required to accommodate new connection attempts.
For example, if you set the one minute high to 100, the ZyXEL Device 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
Incomplete Low This is the number of existing half-open sessions that causes the firewall to stop
deleting half-open sessions. The ZyXEL Device continues to delete half-open
requests as necessary, until the number of existing half-open sessions drops
below this number.
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 ZyXEL Device 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 ZyXEL Device
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
Incomplete An unusually high number of half-open sessions with the same destination host
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 ZyXEL Device sends alerts
whenever the
TCP Maximum Incomplete is exceeded.
Action taken when
TCP Maximum
Incomplete
reached threshold Select the action that ZyXEL Device should take when the TCP maximum
incomplete threshold is reached. You can have the ZyXEL Device either:
Delete the oldest half open session when a new connection request comes.
or
Deny new connection requests for the number of minutes that you specify
(between 1 and 255).
Apply Click this to save your changes.
Cancel Click this to restore your previously saved settings.