MULTOPS needs to see traffic in both directions to detect disproportional packet rates--this requires symmetric routes. However, Paxson demonstrated that many routes on the Internet are asymmetric [Pax97]. To circumvent this problem, MULTOPS should be placed on the edges of the network--in a data center, for example. If such a site is multi-homed, then packet rate statistics from all on-site routers need to be combined. This requires (preferably out of band) communication between several MULTOPS-equipped routers. The details of such a setup are beyond the scope of this paper.