Debugging faults in complex networks often requires capturing and analyzing traffic at the packet level. In this paper, DataCenter Networks (DCNs) present unique challenges with their scale, traffic volume and diversity of faults. To troubleshoot faults in a timely manner, DCN administrators must identify affected packets inside large volume of traffic; track them across multiple network components; analyze traffic traces for fault patterns; and test or confirm potential causes. To the authors’ knowledge, no tool today can achieve both the specificity and scale required for this task.