Dont Forget to Lock the Front Door! Inferring the Deployment of Source Address Validation of Inbound Traffic This paper concerns the problem of the absence of ingress filtering at the network edge, one of the main causes of important network security issues. Numerous network operators do not deploy the best current practice  Source Address Validation (SAV) that aims at mitigating these issues. We perform the first Internetwide active measurement study to enumerate networks not filtering incoming packets by their source address. The measurement method consists of identifying closed and open DNS resolvers handling requests coming from the outside of the network with the source address from the range assigned inside the network under the test. The proposed method provides the most complete picture of the inbound SAV deployment state at network providers. We reveal that 32 673 Autonomous Systems (ASes) and 197 641 Border Gateway Protocol (BGP) prefixes are vulnerable to spoofing of inbound traffic. Finally, using the data from the Spoofer project and performing an open resolver scan, we compare the filtering policies in both directions.

Practical Verifiable Innetwork Filtering for DDoS defense In light of everincreasing scale and sophistication of modern DDoS attacks, it is time to revisit innetwork filtering or the idea of empowering DDoS victims to install innetwork traffic filters in the upstream transit networks. Recent proposals show that filtering DDoS traffic at a handful of large transit networks can handle volumetric DDoS attacks effectively. However, the innetwork filtering primitive can also be misused. Transit networks can use the innetwork filtering service as an excuse for any arbitrary packet drops made for their own benefit. For example, transit networks may intentionally execute filtering services poorly or unfairly to discriminate their competing neighbor ASes while claiming that they drop packets for the sake of DDoS defense. We argue that it is due to the lack of verifiable filtering  i.e., no one can check if a transit network executes the filter rules correctly as requested by the DDoS victims. To make innetwork filtering a more robust defense primitive, in this paper, we propose a verifiable innetwork filtering, called VIF, that exploits emerging hardwarebased trusted execution environments (TEEs) and offers filtering verifiability to DDoS victims and neighbor ASes. Our proof of concept demonstrates that a VIF filter implementation on commodity servers with TEE support can handle traffic at line rate (e.g., 10 Gbs) and execute up to 3,000 filter rules. We show that VIF can easily scale to handle larger traffic volume (e.g., 500 Gbs) and more complex filtering operations (e.g., 150,000 filter rules) by parallelizing the TEEbased filters. As a practical deployment model, we suggest that Internet exchange points (IXPs) are the ideal candidates for the early adopters of our verifiable filters due to their central locations and flexible softwaredefined architecture.