Taking Routers Off Their Meds: Unstable Routers and the Buggy BGP Implementations That Cause Them

Abstract

Both academic research and historical incidents have shown the impact of unstable BGP speakers on network performance and reliability. A large amount of time and energy has been invested improving router stability. In this paper, we show how an adversary in control of a BGP speaker in a transit AS can cause a victim router in an arbitrary location on the Internet to become unstable. Through experimentation with both hardware and software routers, we examine the behavior of routers under abnormal conditions and come to four conclusions. First, routers placed in certain states behave in anything but a stable manner. Second, unexpected but perfectly legal BGP messages can place routers into those states with disconcerting ease. Third, an adversary can use these messages to disrupt a victim router to which he is not directly connected. Fourth, modern best practices do little to prevent these attacks. These conclusions lead us to recommend more rigorous testing of BGP implementations, focusing as much on protocol correctness as software correctness.