A route flap is a change in the state of a route, from up to down or down to up. A route state change causes changes in the route tables of the devices that support the route.
Frequent changes in route states can cause Internet instability and add processing overhead to the devices that support the route. Route flap dampening helps reduce the impact of route flap by changing the way a BGP4 device responds to route state changes. When route flap dampening is configured, the device suppresses unstable routes until the number of route state changes drops enough to meet an acceptable degree of stability.
The route flap dampening mechanism is based on penalties. When a route exceeds a configured penalty value, the device stops using that route and stops advertising it to other devices. The mechanism also allows route penalties to reduce over time if route stability improves.
The dampening command offers several parameters that you can use to enable and fine-tune the route dampening feature.
| half-life | The number of minutes after which the route penalty becomes half its value. The default is 15. |
| reuse | Minimum penalty below which the route becomes usable again. The default is 750. |
| suppress | Maximum penalty above which the route is suppressed by the device. The default is 2000. |
| max-suppress-time | Maximum number of minutes that a route can be suppressed by the device. The default is 40. |