Toward Comprehensive Network Verification: Practices, Challenges and Beyond Guaranteeing that large scale networks are always operated as policy goals dictate is critical for network availability, security, and performance. The problem is challenging, as it should not only assure the correctness of policy configurations across various network devices, but also guarantee the faithfulness of policy enforcement on actual packet forwarding behaviors. In this article, we provide a systematic overview of the direction of network verification, which covers both verification of network configurations and assurance of device actual behaviors. In particular, we summarize stateoftheart designs with focuses from early stateless data planes with switchesrouters to more recent stateful ones containing middleboxes. After analyzing and comparing these works, we also specify future directions in the verification of stateful networks.

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.