Hunting BGP zombies in the wild

ABSTRACTAs the key component of Internet's inter-domain routing, BGP is expected to work flawlessly. However, a recent study has revealed the presence of BGP zombies: Withdrawn prefixes that are still active in routing tables and that can cause routing issues. That study used experimental prefixes with scheduled withdrawals (BGP beacons). In this study we aim at detecting BGP zombies for any prefixes announced on the Internet. To that end we study characteristics of withdrawn messages, and devise a method to differentiate withdraw messages corresponding to local topological changes to those standing for prefixes withdrawn by their origin AS. Based on this classification we study the occurrence of zombies in the wild in six years of BGP data. We find over 6.5 millions zombies, among those we confirm that 94% report incoherent states and caused 468 potential routing loops. Our study also reveals that noisy prefixes, long AS paths, and ASes announcing a large number of prefixes are more prone to zombies.