1-4CFD FunctionsCFD works effectively only in properly-configured networks. Its functions, which are implementedthrough the MPs, include:z Continuity check (CC)z Loopback (LB)z Linktrace (LT)Continuity checkContinuity check is responsible for checking the connectivity between MEPs. Connectivity faults areusually caused by device faults or configuration errors. This function is implemented through periodicsending of continuity check messages (CCMs) by the MEPs. As a multicast message, a CCM sent byone MEP is intended to be received by all the other MEPs in the same MA. If a MEP fails to receive theCCMs within 3.5 sending periods, the link is considered as faulty and a corresponding log is generated.When multiple MEPs send CCMs at the same time, the multipoint-to-multipoint link check is achieved.LoopbackSimilar to ping at the IP layer, loopback is responsible for verifying the connectivity between a localdevice and a remote device. To implement this function, the local MEP sends loopback messages(LBMs) to the remote MEP. Depending on whether the local MEP can receive a loopback replymessage (LBR) from the remote MEP, the link state between the two can be verified. LBMs and LBRsare unicast messages.LinktraceLinktrace is responsible for identifying the path between the source MEP and the destination MEP. Thisfunction is implemented in the following way: the source MEP multicasts linktrace messages (LTMs) tothe destination MEP. After receiving the messages, the destination MEP and the MIPs that the LTMspass send back linktrace reply messages (LTRs) to the source MEP. Based on the reply messages, thesource MEP can identify the path to the destination MEP. Note that LTMs are multicast frames whileLTRs are unicast frames.Protocols and StandardsThe CFD function is implemented in accordance with IEEE 802.1ag: Virtual Bridged Local AreaNetworks Amendment 5: Connectivity Fault Management.CFD Configuration Task ListFor CFD to work effectively, you should first design the network by performing the following tasks:z Grade the MDs in the entire network, and define the boundary of each MD.z Assign a name for each MD. Make sure that the same MD has the same name on different devices.z Define the MA in each MD according to the VLAN you want to monitor.z Assign a name for each MA. Make sure that the same MA in the same MD has the same name ondifferent devices.z At the edges of MD and MA, MPs should be designed at the device port. MEPs can be designed ondevices or ports that are not at the edges.Complete the following tasks to configure CFD:
