Monitoring and analyzing dynamics of routing protocols have become active areas of research of late. Route monitoring systems have started to appear in the market-place from networking startups, such as Packet Design [4] and Ipsum Networks [5]. However, the products offered by these companies have appeared in the market after our OSPF Monitor was designed. Moreover, details about the architecture and implementation of these products are not available in the public domain. The IP monitoring project at Sprint [6] consists of an IS-IS listener and a BGP listener that collects IS-IS and BGP data from the Sprint network. Although a number of studies have appeared based on the data collected by these listeners, the actual architecture of the monitoring system has not received attention. Our prior work [7] and Watson et al. [8] presented case studies of OSPF dynamics in real networks. Although [7] used the OSPF Monitor described in this paper to collect and analyze the OSPF data for the case study, the paper did not focus on the design and implementation of the monitor itself. Neither did [8] focus on the design of the monitor. Route-Views [9] and RIPE [10] collect and archive BGP updates from several vantage-points; a number of research studies have benefited from this data. However, both Route-Views and RIPE merely collect BGP updates; they do not provide software for monitoring or analyzing the updates.
Recall that one of the design goals of the OSPF Monitor is to track the OSPF topology. Several studies have dealt with the discovery and tracking of the network topology. For instance, our prior work [3] described SNMP and LSA-based approaches for designing an OSPF topology server, and evaluation of these approaches in terms of operational complexity, reliability and timeliness of information. The evaluation showed the superiority of the LSA-based approach in terms of reliability and robustness over the SNMP-based approach. This paper extends the LSA-based approach for monitoring OSPF. The Rocketfuel project [11,12,13] tackled the problem of inferring ISP topologies and weight settings through end-to-end measurements. Feldmann et al. [14] described the approach of periodically dumping router configuration files of routers. This approach provides a static view of the topology. One can make it more dynamic by increasing the dumping frequency, but it is hard to go beyond certain limits because of the size of IP networks today. Lakshman et al. [15] mentioned approaches for real-time discovery of topology in their work on the RATES System for MPLS traffic engineering. But topology discovery was just one of the modules of their system and they did not go into details. Siamwalla et al. [16] and Govindan [17] discussed topology discovery methods that do not require cooperation from the network service providers, relying on a variety of probes, including pings and traceroutes. Such methods provide indications of interface up/down status and router connectivity. However, these methods do not deal directly with OSPF topology tracking or monitoring, the topic of this paper.