Optimal OSPF traffic engineering using legacy Equal Cost Multipath load balancing

In this paper, an optimal traffic engineering technique is proposed that uses only unmodified OSPF shortest path routing with stock ECMP (Equal-Cost MultiPath) load-balancing. The main problem with OSPF ECMP is that it can only divide the traffic in equal proportion among the least-cost paths. Our proposal works around this limitation by setting up virtual links alongside existing physical ones, this way adjusting the effective splitting ratio. In this paper, we study the special case of full-mesh MPLS overlays, which already promises with important practical applications yet turns out rather untrivial to solve. We formulate the problem of how to provision the virtual links to approximate the desired traffic splitting ratio, thereby minimizing congestion, we solve this problem under various restrictions arising from present OSPF practice, and finally we present extensive numerical evaluations suggesting that our technique effectively emulates optimal traffic engineering using only off-the-shelf IP routing technology.