D-Link xStack Reference Manual page 138

xStack® DES-3200 Series Layer 2 Ethernet Managed Switch WEB UI Reference Guide
Figure 5 - 1. Safeguard Engine Checking Interval Example on the Switch
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
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