Configuring BGP Route Dampening

The main cause of route instability is route flapping. A route is considered to be flapping when it repeatedly appears and then disappears in the routing table. BGP is generally applied to complex networks where routes change frequently. Frequent route flapping consumes lots of bandwidth and CPU resources and even seriously affects network operations.

BGP route dampening prevents frequent route flapping by using a penalty value to measure route stability. When a route flaps for the first time, a penalty value is assigned to the route. Later, each time the route flaps, the penalty value of the route increases by a specific value. The greater the penalty value, the less stable the route. If the penalty value of a route exceeds the pre-defined threshold, the route will not be advertised until the penalty value of the route reduces to the reuse threshold.

Route dampening applies only to EBGP routes. IBGP routes, however, cannot be dampened. Generally, IBGP routes include routes from the local AS, requiring that the forwarding tables be the same. In addition, IGP fast convergence aims to achieve information synchronization. If IBGP routes are dampened, dampening parameters vary on different devices, and the forwarding tables are inconsistent.