An Efficient Algorithm for Ethernet Topology Discovery in Large Multi-subnet Networks

Topology discovery is a crucial requirement for a number of network management and troubleshooting tasks. Major portion of our today´s networks comprises of Ethernet LANs. In this paper we have devised, developed and implemented a topology discovery algorithm for Ethernet LANs. Our topology discovery algorithm makes minimum use of information available through switches in the form of Address Forwarding Tables. We have devised a necessary and sufficient condition under which our topology discovery algorithm discovers accurate layer 2 topology, while only single MAC Address from each switch for each subnet needs to be present in the Address Forwarding Table (AFT) of switches. We have used the concept of direction awareness by exploiting the property of switches, by which they populate their Address forwarding tables. We demonstrate that our topology discovery algorithm works equally well in case of multi-subnet switched domains and for all practical purposes our topology discovery algorithm can discover accurate topology.