Configuring dampening on an Ethernet interface
The interface dampening feature uses an exponential decay mechanism to suppress the effects of
excessive interface flapping events on routing protocols and routing tables in the network. Suppressing
interface state change events protects the system processing resources.
If an interface is not dampened, its state changes are reported. For each state change, the system also
generates an SNMP notification and log message.
After a flapping interface is dampened, it does not report its state changes to the CPU. For state change
events, the interface only generates SNMP notifications and log messages.
Parameters
• Penalty—The interface has a initiate penalty of 0. When the interface flaps, it is assigned a penalty
of 1000 for each down even, and does not increase for up events.
• Ceiling—The penalty stops increasing after it reaches the ceiling.
• Suppress-limit—The accumulated penalty that triggers the device to dampen the interface. In
dampened state, the interface does not report its state changes to the CPU. For state change events,
the interface only generates SNMP notifications and log messages
• Reuse-limit—When the accumulated penalty decreases to this reuse threshold, the interface is not
dampened. Interface state changes are reported to the higher layers. For each state change, the
system also generates an SNMP notification and log message.
• Decay—The amount of time (in seconds) after which a penalty is decreased.
• Max-suppress-time—The maximum amount of time the interface can be dampened. If the penalty
is still higher than the reuse threshold when this timer expires, the penalty stops increasing for down
events.
The maximum penalty is equal to 2
(Max-suppress-time/Decay)
× reuse-limit. It is not user configurable.
Figure 1 shows the change rule of the penalty value. t
0
and t
2
indicate the start time and end time of the
suppression, respectively. The period from t
0
to t
2
indicates the suppression period, t
0
to t
1
indicates the
max-suppress-time, and t
1
to t
2
indicates the complete decay period.
7
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