Diagnosing performance faults on Internet paths is a difficult and time-consuming task for which there is little operational support, especially when the paths cross multiple ISPs. Standard tools such as traceroute test connectivity but do not pinpoint the lossy or congested segments of the path; performance tools such as pathchar are often bandwidth-intensive or inaccurate over long paths.

In this talk, we describe tulip, a new tool to diagnose performance problems on Internet paths from the host running the tool to arbitrary IP destinations. Like traceroute, tulip requires no special privileges at the routers along the path. It uses two prevalent but little exploited router features: ICMP timestamps and IP identifiers. ICMP timestamps yield remote timing information that enables the location of congestion to be estimated. IP identifiers yield remote ordering information that enables the location of loss and reordering to be estimated. On most paths we have measured tulip can narrow the region of loss and reordering to within three hops and congestion to within four hops.

We are particularly interested in better understanding the operational needs for diagnostic support and the utility of tools such as tulip to ISPs. As an example of the possibilities in this space, we will describe simple, backwards-compatible changes to routers that enable more efficient and more accurate diagnostic tools that our work on tulip helped to identify.

The tulip tool and a research paper describing our work can be found at http://www.cs.washington.edu/research/networking/tulip/.

About the Presenter
Ratul Mahajan received a B.Tech. degree from the Indian Institute of Technology, Delhi, India, and an M.S. degree from the University of Washington. He is currently pursuing a Ph.D. degree at the University of Washington. His research interests span the entire range of internetworking-related topics. His past work includes a study of global routing configuration errors and discovering Internet topology and routing policies.