This document describes the Depth-First Forwarding (DFF) protocol for IPv6 networks based on the LoWPAN adaptation layer as specified in RFC4944. The protocol is a mesh-under data forwarding mechanism that increases reliability of data delivery. DFF forwards data frames using a network-wide "depth-first search" for the Final Destination of the frame. DFF may be used in conjunction with a routing protocol, which provides "hints" for DFF in which order to try to send the frame to the neighbors discovered by the neighborhood discovery mechanism. In that case, DFF can be used as local repair mechanism.