Basic Functions Of Cfd - 3Com 4210G Series Configuration Manual

Figure 6-4 Levels of MPs

Basic Functions of CFD

CFD works effectively only in properly-configured networks. Its functions, which are implemented
through the MPs, include:
Continuity check (CC);
Loopback (LB)
Linktrace (LT)
Continuity check
Continuity check is responsible for checking the connectivity between MEPs. Connectivity faults are
usually caused by device faults or configuration errors. This function is implemented through periodic
sending of continuity check messages (CCMs) by the MEPs. As a multicast message, 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 sending periods, the link is regarded 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.
Loopback
Similar to ping at the IP layer, loopback is responsible for verifying the connectivity between a local
device 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 reply
message (LBR) from the remote MEP, the link state between the two can be verified. LBMs and LBRs
are unicast messages. They are used to verify the connectivity between two points.
Linktrace
Linktrace is responsible for identifying the path between the source MEP and the destination MEP. This
function is implemented in the following way: the source MEP multicasts linktrace messages (LTMs) to
the destination MEP. After receiving the messages, the destination MEP and the MIPs that the LTMs
pass send back linktrace reply messages (LTRs) to the source MEP. Based on the reply messages,
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