A Simple and General Operational Framework to Deploy Optimal Routes With Source Routing

Source Routing, currently facilitated by Segment Routing (SR), enables routers to add forwarding instructions to the packet to follow a particular path that deviates from the typical IGP path. These instructions form a list of detours (called segments). However, the number of segments that can be imposed at line-rate is tightly constrained by the hardware. Hence, the main challenge consists in incorporating this constraint into a path computation algorithm. The goal is to be able to solve many existing problems, including finding multi-constrained paths and re-routing packets after a failure, in a way that is deployeable in existing networks using Segment Routing. Existing solutions either lack generality, correctness, optimality, or practical computing efficiency – in particular for sparse realistic networks. In this paper, we address all such challenges with GOFOR-SR. Our framework extends usual path computation algorithms by integrating the SR constraint within the path computation itself and modifying the distance comparison method. GOFOR allows algorithm with various optimization objectives to efficiently compute optimal segment lists. Despite the loss of substructure optimality induced by SR, GOFOR proves particularly efficient, inducing only a linear overhead at worst. It also offers different strategies and path diversity options for intricate load-balancing. We formally prove the correctness and optimality of GOFOR, implement our framework for various practical use-cases, and demonstrate its performance and benefits on both real and challenging topologies.