Efficient physical topology discovery for large OSPF networks

Accurate network topology information can play very important role in a network management system. Discovering network topology is a prerequisite for many critical network management tasks including reactive and proactive resource management, fault management, and root-cause analysis. Unfortunately, the equipment managed in an NMS includes switches as well as routers, so a network management system must discover physical links/connections between a router and a switch and between a switch and a switch. Most previous methods of discovering network topology via SNMP use ipRouteTable MIB, which has big routing information. Many network operators repeat the saying, ldquoDo not burn your house to rid it of the mouse.rdquo reffering to the concern of overloading the capacity of the router. Most previous methods were not concerned with this simple maxim, and in fact, there is no need to worry about managing overhead in a small test-bed. In this paper, the problems of previous works using ipRouteTable are presented. We focus on large OSPF backbone networks that have hundreds of routers and switches, and discover physical topology with minimal overhead. Our approach finds adjacencies between router and router / router and switch using ospfNbrIpAddr MIB which is much smaller than ipRouteTable. The experimental results clearly validate that our approach is an efficient algorithm for discovering network topology in time that is mathematically quadratic to the number of routers, as compared to cubic when ipRouteTable is used.