IP Configuration Configuring IP
page 18-24 OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008
• Port scan penalty value threshold.The switch is given a port scan penalty value threshold. This
number is the maximum value the running penalty total can achieve before triggering an SNMP trap.
• Decay value. A decay value is set. The running penalty total is divided by the decay value every
minute.
• Trap generation. If the total penalty value exceeds the set port scan penalty value threshold, a trap is
generated to alert the administrator that a port scan may be in progress.
For example, imagine that a switch is set so that TCP and UDP packets destined for closed ports are given
a penalty of 10, TCP packets destined for open ports are given a penalty of 5, and UDP packets destined
for open ports are given a penalty of 20. The decay is set to 2, and the switch port scan penalty value
threshold is set to 2000:
.
In one minute, 10 TCP closed port packets and 10 UDP closed port packets are received. This would bring
the total penalty value to 200, as shown using the following equation:
(10 TCP X 10 penalty) + (10 UDP X 10 penalty) = 200
This value would be divided by 2 (due to the decay) and decreased to 100. The switch would not record a
port scan:
DoS Settings
UDP/TCP closed = 10
UDP open = 20
TCP open = 5
Threshold = 2000
Decay = 2
Penalty Total = 0
DoS Settings
UDP/TCP closed = 10
UDP open = 20
TCP open = 5
Threshold = 2000
Decay = 2
Minute 1 Penalty Total = 100
Do Not
Generate DoS
Attack Warning
Trap
10 TCP closed port packets
10 UDP closed port packets
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