One use case of the Empty path type lies in the context of link-failure detection. To this end, SCION uses the Bidirectional Forwarding Detection (BFD) protocol ([RFC5880] and [RFC5881]). BFD is a protocol intended to detect faults in the bidirectional path between two forwarding engines, with typically very low latency. It operates independently of media, data protocols, and routing protocols. SCION uses the Empty path type, together with OneHopPath path type, to bootstrap BFD within SCION. (For more information on the OneHopPath path type, see Section 2.2.3.3.)
However, we don't say much about how it works.
How much should be in the draft? (is it necessary to add details, or could we leave it open)?
Why do routers have to use something like BFD? What do they do with signals from BFD?
We currently mention BFD in 2.2.3.1. Empty Path Type:
However, we don't say much about how it works.