1. NetCheck: Network Diagnoses from Blackbox Traces Yanyan Zhuang, Eleni Gessiou NYU Poly, University of British Columbia

2. Motivation Ping – Only reachability Wireshark – Applicationor network-specific knowledge Network Config Analysis – Detailed network knowledge – HW + config …

3. Goal Diagnose network problems in large and complex applications Without modifying the original application

4. Syscall trace from strace

5. Challenges Accuracy: ambiguity in order reconstruction Efficiency: exploring an exponential space of possible orderings Network complexity: diagnosing issues in real networks

6. NetCheck Overview Finding deviations from the model of the network (Deutsch’s Fallacies) network is reliable, latency is zero, etc.

7. Priority & Dependency of syscalls

8. e.g.

9. Fault diagnoses

10. Rules summary Example of rule (1): when a client is behind a NAT, (i) the client uses a private IP, (ii) the peer socket address in server’s accept is not the client’s IP

11. Evaluation Reproduce reported bugs from bug trackers (Python, Apache, Ruby, Firefox, etc.) – A total of 71 bugs – Correct analysis of 95.7% bugs Twenty faults observed in practice on a live network(Seattle Testbed) – 90% of cases correctly detected

12. Runtime performance overhead Best: O(l) Worst: O(nl)

13. Conclusion Derives a plausible global traces ordering as a proxy for the ground truth Uses a model of expected and simple network behavior to identify and diagnose unexpected behavior