On the Interaction between Dynamic Routing in the Native and Overlay Layers

Overlay networks have recently gained attention as a viable alternative to overcome functionality limitations of the Internet. We are concerned with scenarios where a dynamic routing protocol is employed in the overlay network to adapt overlay routing tables to changing network conditions. At the same time, the native network over which the overlay is built also runs its own set of dynamic routing protocols. We are interested in investigating the behavior of this mixed routing environment and in particular the characteristics of the interaction between these two routing layers. In this paper, we focus on the specific problem of rerouting around failed links. We first study a Dual Rerouting scenario in which the two routing layers run completely independent of each other. Our goal is to understand the effect of the various settings of routing protocol parameters on the packet loss, number of route flaps, and the optimality of the adopted overlay path. We show that Dual Rerouting provides relatively fast path recovery. But, it tends to be sub-optimal in terms of the number of route flaps and the overlay path cost inflation. This is due to the overlap of functionality between the two layers, unawareness of the other layer’s decisions, and lack of flexibility. We next investigate schemes that increase awareness of the native routing protocol and its parameters at the overlay layer. We consider three such approaches: Probabilistically Suppressed Overlay Rerouting, Deferred Overlay Rerouting and Follow-on Suppressed Overlay Rerouting. We show that with such schemes one can trade off longer path recovery times with improvements in route flapping and path cost inflation. However, there is a fundamental limit on the amount of achievable gain if we receive no support from the native layer. To counter that, we propose a novel approach towards the tuning of native layer parameters to suit the functioning of the overlay layer.