A variety of schemes based on the technique of Probabilistic Packet Marking (PPM) have been proposed to identify Distributed Denial of Service (DDoS) attack traffic sources by IP traceback. These PPM-based schemes provide a way to reconstruct the attack graph - the network path taken by the attack traffic - hence identifying its sources. Despite the large amount of research in this area, the influence of the underlying topology on the performance of PPM-based schemes remains an open issue. In this paper, we identify three network-dependent factors that affect different PPM-based schemes uniquely giving rise to a variation in and discrepancy between scheme performance from one network to another. Using simulation, we also show the collective effect of these factors on the performance of selected schemes in an extensive set of 60 Internet-like networks. We find that scheme performance is dependent on the network on which it is implemented. We show how each of these factors contributes to a discrepancy in scheme performance in large scale networks. This discrepancy is exhibited independent of similarities or differences in the underlying models of the networks.