17CFD configurationThis chapter includes these sections:• Overview• CFD configuration task list• Displaying and maintaining CFD• CFD configuration exampleOverviewConnectivity Fault Detection (CFD), which conforms to IEEE 802.1ag Connectivity Fault Management(CFM) and ITU-T Y.1731, is an end-to-end per-VLAN link layer Operations, Administration andMaintenance (OAM) mechanism used for link connectivity detection, fault verification, and fault location.Basic concepts in CFDMaintenance domainA maintenance domain (MD) defines the network where CFD plays its role. The MD boundary is definedby some maintenance association end points (MEPs) configured on the ports. An MD is identified by anMD name.To accurately locate faults, CFD assigns eight levels (from 0 to 7) to MDs. The bigger the number, thehigher the level and the larger the area covered. Domains can touch or nest (if the outer domain has ahigher level than the nested one) but cannot intersect or overlap.MD levels facilitate fault location and make fault location more accurate. As shown in Figure 3, MD_Ain light blue nests MD_B in dark blue. If a connectivity fault is detected at the boundary of MD_A, anyof the devices in MD_A, including Device A through Device E, may fail. If a connectivity fault is alsodetected at the boundary of MD_B, the failure points may be any of Device B through Device D. If thedevices in MD_B can operate properly, at least Device C is operational.Figure 3 Two nested MDs
