Quantifying Violations of Destination-based Forwarding on the Internet

摘要

Initially, packet forwarding in the Internet was destination-based -that is, a router would forward all packets with the same destination address to the same next hop. In this paper, we use active probing methods to quantify and characterize deviations from destination-based forwarding in today's Internet. From over a quarter million probes, we analyze the forwarding behavior of almost 40,000 intermediate routers. We find that, for 29% of the targeted routers, the router forwards traffic going to a single destination via different next hops, and 1.3% of the routers even select next hops in different ASes. Load balancers are unlikely to explain these AS-level variations, and in fact we uncover causes including routers inside MPLS tunnels that otherwise employ default routes. We also find that these violations can significantly affect the results of measurement tools that rely on destination-based forwarding, and we discuss some ideas for making these tools more robust against these violations.