Port Dampening (Stack Ports)

The Port Dampening feature enables link dampening on stacking ports by default. Whenever stacking ports are configured and stacking is enabled, link dampening is automatically applied to those stacking ports.

Link dampening prevents every hardware link‑scan event from being forwarded immediately to higher‑level applications. Instead, link events are processed using a sampling window. In the current implementation, a one‑second sampling window is used together with a 250‑millisecond background task, resulting in a total effective sampling window of 1.250 seconds. This mechanism allows very short port up/down transitions (micro‑flaps) to be collapsed into fewer, delayed notifications. These notifications follow the normal port‑event processing path but are time‑controlled.

On stacking ports, brief cable movements or PHY‑level events can generate multiple link callbacks within a very short time. If all such events are propagated immediately, the stacking control plane may interpret them as continuous flapping, potentially triggering unnecessary stack elections or control‑plane churn. Link dampening reduces this noise by filtering transient link events while still ensuring that genuine link state changes are eventually reported. As a result, only valid and sustained port flap events are forwarded to the stacking application, improving stack stability without masking real link failures.

Previously, the link dampening feature was not available on stacking ports. Link dampening was supported only on uplink (data) ports and had to be enabled explicitly using CLI commands.

To enable link dampening on data ports, the following command sequence is used:

device# configure terminal 
device(config)# linkdampen 4 ethernet 1/1/4
 ***CAUTION Link-Dampening may cause momentary traffic loss,
may cause status convergence issues and other side effects.
Use Link-Dampening only when required.
Recommended usage Link-Dampening interval 4 - 1 second.