Destination Reachability and BGP Convergence Time

One important performance measure for routing protocols is packet delivery. An ideal routing protocol should quickly adapt to topological changes and deliver packets as long as any path to the destination exists. In this paper, we examine the packet delivery performance in a network running the BGP routing protocol when a destination may be disconnected from time to time. We develop two metrics, extra downtime and false uptime, to capture the time difference between actual loss of connectivity and perceived unreachability. Our results show that extra downtime closely matches Tup convergence delay, and false uptime closely matches Tdown convergence delay. Furthermore, our results show that, for transient connectivity failures, a shorter Tdown convergence time can have negative impact on packet delivery.