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DES-3200-10/18/28/28F Layer 2 Ethernet Managed Switch User Manual
In Exhausted mode, two modes can be implemented to limit the bandwidth assigned to ARP packets, “Strict” and
“Fuzzy”.
In Strict mode, the Switch will drop all ARP packets. The Switch will reluctantly process any packets not destined for
the Switch and broadcast packets, no matter what is causing the high utilization rate on the CPU, which may not be an
ARP storm.
In Fuzzy mode, the Switch uses an algorithm to assign different bandwidth levels for ARP packets. In Fuzzy mode, the
Switch will analyze the rate of received ARP traffic to adjust the bandwidth dynamically. Once in Exhausted mode, the
packet flow will decrease by half of the level that caused the Switch to enter Exhausted mode. After the packet flow
has stabilized, the rate will initially increase by a small amount of processed packets and then return to a normal
packet flow
In both Strict mode and Fuzzy mode the Safeguard Engine will check for packet flooding issues at regular intervals.
For every consecutive checking interval that reveals a packet flooding issue, the Switch will double the time it will
accept a few ingress ARP packets. In the example above, the Switch doubled the time for dropping ARP packets
when consecutive flooding issues were detected at 5-second intervals. (First stop = 5 seconds, second stop = 10
seconds, third stop = 20 seconds) Once the flooding is no longer detected, the wait period for limiting ARP packets will
return to 5 seconds and the process will resume.
To configure the Safeguard Engine for the Switch, click Security > Safeguard Engine, which will open the following
window:
Figure 5 - 2. Safeguard Engine window
To configure the Switch’s Safeguard Engine, change the State to Enabled when the Safeguard Engine is enabled a
green light will show on the gray bar at the top of this window, next to Safeguard. To set the Safeguard Engine for the
Switch, complete the following fields:
Parameter Description
Rising Threshold
Used to configure the acceptable level of CPU utilization before the Safeguard Engine
mechanism is enabled. Once the CPU utilization reaches this percentage level, the Switch
will move into the Exhausted state.
Falling Threshold
Used to configure the acceptable level of CPU utilization as a percentage, where the Switch
leaves the Exhausted state and returns to normal mode.
Trap/log
Use the pull-down menu to enable or disable the sending of messages to the device’s SNMP
agent and switch log once the Safeguard Engine has been activated by a high CPU utilization
rate.
Mode
Toggle the State field to either Strict or Fuzzy for the Safeguard Engine of the Switch.
Click Apply to implement the settings made.
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