Traffic Engineering with OSPF Multi-Topology Routing

The Open Shortest Path First (OSPF) routing protocol for IP networks uses destination-based, single shortest path routing to compute routes. A side effect of this computation is that traffic cannot be easily load balanced across multiple paths with unequal cost paths. We explore the potential for an extension of OSPF, known as Multi-Topology Routing (MTR), to provide more load balancing choices within the OSPF framework. MTR works by overlaying multiple logical OSPF topologies on a single physical topology, and by consistently mapping packets (based on header bits, for example) to a logical topology at each hop. By assigning link costs on a per-topology basis, traffic to the same destination can be routed over different paths. We describe an MTR Route Manager and Analyzer that automates the process of configuring OSPF MTR metrics in response to measured or pre-planned traffic patterns and dynamic sampling of the network topology. We also describe how MTR can be emulated using route maps, for routers that only implement standard OSPF. We explore the performance benefits and scaling trends of MTR traffic management in a small scale network setting.