Multiple Hop Unaffiliate BFD

The Bidirectional Forwarding Detection (BFD) is a fault detection protocol designed to rapidly identify communication failure between two forwarding engines. This document suggests utilizing BFD Echo when the local system supports BFD, but the neighboring system does not. BFD Control packets and their processing procedures can be executed over the BFD Echo port, where the neighboring system solely loops packets back to the local system. This document serves as an update to RFC 5880 and draft-ietf-bfd- unaffiliate-echo-10.