Towards a Highly-Available SD-WAN: Rapid Failover based on BFD Protocol

As SD-WAN is more and more employed by enterprises embracing digital transformation, ensuring seamless failover and tunnel handoff between WAN links becomes critical for maintaining uninterrupted network connectivity. To achieve high availability in SD-WANs, the continuous monitoring of the WAN links is necessary, as it enables proactive detection of link failures or degradation. This paper investigates the use of Bidirectional Forwarding Detection (BFD) protocol for tunnel handoff in SD-WAN through an experimental study. Furthermore, an automatic tuning mechanism of BFD parameters is proposed to enhance the failure detection ability of the protocol as well as the detection time over different WAN types. The experiments are conducted using an emulated network topology in Cisco Modeling Labs, consisting of two SD-WAN sites interconnected via two Edge Routers by means of different kinds of WANs. This paper highlights that a fixed configuration of the BFD algorithm does not guarantee optimal performance due to its sensitivity to WAN types and conditions, that affect detection time and precision. In contrast, the proposed methodology enhances the performance of the protocol by exploring various configurations and observing the output.