1. Imperfect of “End-to-End Routing Behavior in the Internet” Yao Zhao

2. Bad Resolution of Traceroute In D 1, mean interval of 1-2 days –Each NDP make a traceroute measurement once every two hours In D 2, 60% with mean interval of 2 hours and 40% with mean interval of 2.75 days Underestimate the prevalence of network connectivity problem

3. How Representative Are the Observations? 37 hosts of known 50,000 hosts in NSFNET Do routers in the same AS have similar characteristics? –Different roles of routers –Different relationship to other ASes 8% of 1000 routers involved in the measurement

4. Not Smart Experiment Design Centralized design –Underestimation of network problems –Can be improved by using batch jobs Simple traceroute –Do not work smartly, only do traceroute as requested –Cannot repeat traceroute or adjust interval based on the current situation

5. Underestimate Routing Asymmetry Paxon studied asymmetry in the level of city and AS –Why city? –Why not routers?

6. Conclusions are Out of Date Paxon’s data were collected in 1994 and 1995 Now it is year 2006 –Internet grows 20 times larger. More than 20,000 ASes so far. –Do the conclusion drawn in 1996 still hold today? –De the routing problems disappear or become severer?