Cisco Systems UniDirectional Link Detection (UDLD) Protocol
RFC 5171

Received changes through RFC Editor sync (changed abstract to 'This document describes a Cisco Systems protocol that can be used to detect and disable unidirectional Ethernet fiber or copper links caused, for instance, by mis-wiring of fiber strands, interface malfunctions, media converters' faults, etc. It operates at Layer 2 in conjunction with IEEE 802.3's existing Layer 1 fault detection mechanisms.

This document explains the protocol objectives and applications, illustrates the specific premises the protocol was based upon, and describes the protocol architecture and related deployment issues to serve as a possible base for future standardization. This memo provides information for the Internet community.')