  IoT networks are increasingly becoming target of sophisticated new
cyber-attacks. Anomaly-based detection methods are promising in finding new
attacks, but there are certain practical challenges like false-positive alarms,
hard to explain, and difficult to scale cost-effectively. The IETF recent
standard called Manufacturer Usage Description (MUD) seems promising to limit
the attack surface on IoT devices by formally specifying their intended network
behavior. In this paper, we use SDN to enforce and monitor the expected
behaviors of each IoT device, and train one-class classifier models to detect
volumetric attacks.
  Our specific contributions are fourfold. (1) We develop a multi-level
inferencing model to dynamically detect anomalous patterns in network activity
of MUD-compliant traffic flows via SDN telemetry, followed by packet inspection
of anomalous flows. This provides enhanced fine-grained visibility into
distributed and direct attacks, allowing us to precisely isolate volumetric
attacks with microflow (5-tuple) resolution. (2) We collect traffic traces
(benign and a variety of volumetric attacks) from network behavior of IoT
devices in our lab, generate labeled datasets, and make them available to the
public. (3) We prototype a full working system (modules are released as
open-source), demonstrates its efficacy in detecting volumetric attacks on
several consumer IoT devices with high accuracy while maintaining low false
positives, and provides insights into cost and performance of our system. (4)
We demonstrate how our models scale in environments with a large number of
connected IoTs (with datasets collected from a network of IP cameras in our
university campus) by considering various training strategies (per device unit
versus per device type), and balancing the accuracy of prediction against the
cost of models in terms of size and training time.
