RFC 3021 (/31 networks) appear to be unsupported
RFC 3021 introduced the concept of using /31 networks for point-to-point links. This works in most major OSs, but it doesn't seem to work in DFly.
In DFly, the interface comes up with the correct netmask (0xfffffffe), however the kernel complaints about the other side attempting to change the permanent arp entry for the remote IP, with the arp entry according to "arp -a" being ff:ff:ff:ff:ff:ff (eg, broadcast). Ping doesn't work, even though the interface is up.
So it appears that DFly doesn't seem to understand that for a /31 PtP link, there is no "network" and "broadcast".