Interface State Change Events; Suppress Threshold; Half-Life Period; Reuse Threshold - Cisco Nexus 3548 Configuration Manual

Interface State Change Events

consume substantial amounts of system processing resources and cause routing protocols to lose synchronization
with the state of the flapping interface.
The IP Event Dampening feature introduces a configurable exponential decay mechanism to suppress the
effects of excessive interface flapping events on routing protocols and routing tables in the network. This
feature allows the network operator to configure a router to automatically identify and selectively dampen a
local interface that is flapping. Dampening an interface removes the interface from the network until the
interface stops flapping and becomes stable. Configuring the IP Event Dampening feature improves convergence
times and stability throughout the network by isolating failures so that disturbances are not propagated. This,
in turn, reduces the utilization of system processing resources by other devices in the network and improves
overall network stability.
Interface State Change Events
This section describes the interface state change events of the IP Event Dampening feature. This feature
employs a configurable exponential decay mechanism that is used to suppress the effects of excessive interface
flapping or state changes. When the IP Event Dampening feature is enabled, flapping interfaces are dampened
from the perspective of the routing protocol by filtering excessive route updates. Flapping interfaces are
identified, assigned penalties, suppressed if necessary, and made available to the network when the interface
stabilizes. Figure 1 displays interface state events as they are perceived by routing protocols.

Suppress Threshold

The suppress threshold is the value of the accumulated penalty that triggers the router to dampen a flapping
interface. The flapping interface is identified by the router and assigned a penalty for each up and down state
change, but the interface is not automatically dampened. The router tracks the penalties that a flapping interface
accumulates. When the accumulated penalty reaches the default or preconfigured suppress threshold, the
interface is placed in a dampened state.

Half-Life Period

The half-life period determines how fast the accumulated penalty can decay exponentially. When an interface
is placed in a dampened state, the router monitors the interface for additional up and down state changes. If
the interface continues to accumulate penalties and the interface remains in the suppress threshold range, the
interface will remain dampened. If the interface stabilizes and stops flapping, the penalty is reduced by half
after each half-life period expires. The accumulated penalty will be reduced until the penalty drops to the
reuse threshold. The configurable range of the half-life period timer is from 1 to 30 seconds. The default
half-life period timer is 5 seconds.

Reuse Threshold

When the accumulated penalty decreases until the penalty drops to the reuse threshold, the route is unsuppressed
and made available to other devices in the network. The range of the reuse value is from 1 to 20000 penalties.
The default value is 1000 penalties.

Maximum Suppress Time

The maximum suppress time represents the maximum time an interface can remain dampened when a penalty
is assigned to an interface. The maximum suppress time can be configured from 1 to 255 seconds. The
maximum penalty is truncated to maximum 20000 unit. The maximum value of the accumulated penalty is
calculated based on the maximum suppress time, reuse threshold, and half-life period.
Cisco Nexus 3548 Switch NX-OS Interfaces Configuration Guide, Release 9x
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Configuring IP Event Dampening