H3C Technologies H3C S12500-X Series Switches - Manual (Page 22)

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CFD functions
CFD works effectively only in networks that are configured correctly. Its functions, which are implemented
through the MPs, include:
• Continuity check (CC)
• Loopback (LB)
• Linktrace (LT)
Continuity check
Connectivity faults are usually caused by device faults or configuration errors. Continuity check checks
the connectivity between MEPs. This function is implemented through periodic sending of CCMs by the
MEPs. A CCM sent by one MEP is intended to be received by all the other MEPs in the same MA. If a MEP
fails to receive the CCMs within 3.5 times the sending interval, the link is considered as faulty and a log
is generated. When multiple MEPs send CCMs at the same time, the multipoint-to-multipoint link check
is achieved. CCM frames are multicast frames.
Loopback
Similar to ping at the IP layer, loopback verifies the connectivity between a source device and a target
device. To implement this function, the source MEP sends loopback messages (LBMs) to the target MEP.
Depending on whether the source MEP can receive a loopback reply message (LBR) from the target MEP,
the link state between the two can be verified. LBM frames and LBR frames are unicast frames.
Linktrace
Linktrace is similar to traceroute. It identifies the path between the source MEP and the target MP. The
source MEP sends the linktrace messages (LTMs) to the target MP. After receiving the messages, the target
MP and the MIPs that the LTM frames pass send back linktrace reply messages (LTRs) to the source MEP.
Based on the reply messages, the source MEP can identify the path to the target MP. LTM frames are
multicast frames and LTRs are unicast frames.
Protocols and standards
IEEE 802.1ag, Virtual Bridged Local Area Networks Amendment 5: Connectivity Fault Management
CFD configuration task list
For CFD to work correctly, design the network by performing the following tasks:
• Grade the MDs in the entire network, and define the boundary of each MD.
• Assign a name for each MD. Make sure that the devices in the same MD use the same MD name.
• Define the MA in each MD according to the VLAN you want to monitor.
• Assign a name for each MA. Make sure that the devices in the same MA in the same MD use the
same MA name.
• Determine the MEP list of each MA in each MD. Make sure that devices in the same MA maintain
the same MEP list.
• At the edges of MD and MA, MEPs should be designed at the device port. MIPs can be designed
on devices or ports that are not at the edges.
To configure CFD, perform the following tasks: