BGP Dynamics during Route Flap Damping

The BGP routing protocol uses a mechanism called Route Flap Damping [13] to limit the impact of connectivity instability to any individual sites. Although it is believed that this damping mechanism contributes to the stability of global Internet routing, the exact effects of damping has not been thoroughly examined in a large scale network setting. Previous work [8] has shown that damping can be falsely triggered by BGP’s path exploration and significantly extends the routing convergence time after even a single route flap. In this paper we examine the impact of damping under a range of connectivity flapping patterns and different damping parameters. Our results show that damping can confine global routing dynamics to follow a predictable analytical model when connectivity to a destination flaps persistently. However when the number of flaps is small, the global routing behavior deviates from the intended analytical model and damping leads to higher dynamics as measured by both message overhead and network convergence. Such dynamics are largely shaped by the interaction between route reuse timers at different routers; route suppression and reuse at one router can affect the number of routing updates received by other routers, and in turn, others’ damping behavior. We show how this reuse timer interaction, when combined with BGP path exploration, can lead to a staged behavior of routing updates consisting of charging, suppression, releasing, and possible additional rounds of secondary charging phases. We also examine the effects of flapping interval, damping parameters, and network topology on both message overhead and network convergence.