Robust LFA Protection for Software-Defined Networks (RoLPS)

In software-defined networks, forwarding entries on switches are configured by a controller. In case of an unreachable next-hop, traffic is dropped until forwarding entries are updated, which takes significant time. Therefore, fast reroute (FRR) mechanisms are needed to forward affected traffic over alternate paths in the meantime. Loop-free alternates (LFAs) and remote LFAs (rLFAs) have been proposed for FRR in IP networks. However, they cannot protect traffic for all destinations and some LFAs may create loops under challenging conditions. This paper proposes robust LFA protection for software-defined networks (RoLPS). RoLPS augments the coverage of (r)LFAs with novel explicit LFAs (eLFAs). RoLPS ranks available LFAs according to protection quality and complexity for selection of the best available LFA. Furthermore, we introduce advanced loop detection (ALD) so that RoLPS stops loops caused by LFAs. We evaluate RoLPS-based protection variants on a large set of representative networks with unit and non-unit link costs. We study their protection coverage, additional forwarding entries, and path extensions for rerouted traffic, and compare them with MPLS facility backup. Results show that RoLPS can protect traffic against all single link or node failures, and against most double failures while inducing only little overhead. We implement FRR on the P4-programmable switch ASIC Tofino and provide a control plane logic based on RoLPS. Measurement results show that the prototype achieves a throughput of 100 Gb/s, reroutes traffic within less than a millisecond, and reliably detects and drops looping traffic.