D-Link xStack Reference Manual page 276

xStack® DGS-3120 Series Layer 2 Stackable Managed Switch Web UI Reference Guide
many packets flooding the Switch. If the threshold has been crossed, the Switch will initially stop all ingress ARP and
IP broadcast packets and packets from un-trusted IP addresses for five seconds. After another five-second checking
interval arrives, the Switch will again check the ingress flow of packets. If the flooding has stopped, the Switch will
again begin accepting all packets. Yet, if the checking shows that there continues to be too many packets flooding the
Switch, it will stop accepting all ARP and IP broadcast packets and packets from un-trusted IP addresses for double
the time of the previous stop period. This doubling of time for stopping these packets will continue until the maximum
time has been reached, which is 320 seconds and every stop from this point until a return to normal ingress flow would
be 320 seconds. For a better understanding, please examine the following example of the Safeguard Engine.
For every consecutive checking interval that reveals a packet flooding issue, the Switch will double the time it will
discard ingress ARP and IP broadcast packets and packets from the illegal IP addresses. In the example above, the
Switch doubled the time for dropping ARP and IP broadcast 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 dropping ARP and IP broadcast packets will return to 5 seconds and the
process will resume.
In Fuzzy mode, once the Safeguard Engine has entered the Exhausted mode, the Safeguard Engine will decrease the
packet flow by half. After returning to Normal mode, the packet flow will be increased by 25%. The switch will then
return to its interval checking and dynamically adjust the packet flow to avoid overload of the Switch.
NOTICE: When Safeguard Engine is enabled, the Switch will allot bandwidth to various traffic flows (ARP,
IP) using the FFP (Fast Filter Processor) metering table to control the CPU utilization and limit
traffic. This may limit the speed of routing traffic over the network.
Users can enable the Safeguard Engine or configure advanced Safeguard Engine settings for the Switch.
To view this window, click Security > Safeguard Engine Settings as shown below:
Figure 8-71 Mapping QoS on the Switch
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