IPwatch: A Tool for Monitoring Network Locality

Mark J. Lorence and M. Satyanarayanan


In this paper we introduce the concepts of Logical and Physical Network Locality and point out their importance to the performance of distributed systems. We then describe the design of IPwatch, a simple and inexpensive tool for monitoring logical network locality. IPwatch exploits short-term locality to enable monitoring of medium- and long-term locality of large networks using modest computational resources. We describe experiments at Carnegie Mellon University to validate our ideas and to calibrate IPwatch. The results confirm the existence of substantial short-term locality in this environment. Less than 5 percent of the possible host pairs account for 75 percent of the traffic, and less than 15 percent of them account for 90 percent. Comparative measurements on another network in our environment show even stronger short-term locality.