Routing instability has been one of the most interesting topics for both network operators and researchers for years. While many efforts have focused on inter-domain routing instability, studies of intra-domain routing are quite limited. Most network operators still do not have enough knowledge about how frequently intra-domain routing instability can occur on their networks, and how the instability can affect the networks.

This presentation aims to help network operators get a clearer understanding of intra-domain routing instability. Firstly, we present the results of two case studies. By analyzing routing messages collected on two networks, the WIDE Internet and the APAN Tokyo-XP, over a three-year period, we will show that although network operators hardly notice, intra-domain routing instability can occur, sometimes frequently, on service networks. Following the statistical results, we estimate the impact that such instability brings to the network and summarize the causes found to account for the observed instability. We will also show a self-developed monitoring system (will be released in May 2004) which can be used for detecting routing instability in real-time.

The second part of this talk focuses on troubleshooting routing instability problems. As most routing flaps occur intermittently, finding the right causes has been a hard task for network operators. We propose a method of collecting data for troubleshooting which is based on an event-driven model. We will show what kind of data is useful for troubleshooting and how to use the collected data to isolate root causes of the detected instability.

We answer the following questions in this presentation.

1. What is intra-domain routing instability like?
2. How frequently can intra-domain routing instability occur on a service network and affect the network?
3. How can one efficiently detect routing instability with our monitoring system?
4. What are the most likely causes of routing instability?
5. How can one troubleshoot routing instability problems?

About the Presenter
Zhang Shu is a researcher at the National Institute of Information and Communications Technology, Japan. He received a B.E. degree from Waseda University in 1996, and M.E. and Ph.D. degrees from Nara Institute of Science and Technology in 1999 and 2003, respectively. His research interests include routing, MPLS, and network management. He used to be one of the operators of the WIDE Internet and now is contributing to the operation of the APAN Tokyo-XP network. He is a member of the WIDE Project.