RFC 9866: Root Node Failure Detector (RNFD): Fast Detection of Border Router Crashes in the Routing Protocol for Low-Power and Lossy Networks (RPL)

By and large, correct operation of a network running the Routing Protocol for Low-Power and Lossy Networks (RPL) requires border routers to be up. In many applications, it is beneficial for the nodes to detect a failure of a border router as soon as possible to trigger fallback actions. This document specifies the Root Node Failure Detector (RNFD), an extension to RPL that expedites detection of border router crashes by having nodes collaboratively monitor the status of a given border router. The extension introduces an additional state at each node, a new type of RPL Control Message Option for synchronizing this state among different nodes, and the coordination algorithm itself.