H3C Technologies H3C S12500 Series Switches - Manual (Page 33)

22
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 MEP. This
function is implemented in the following way—the source MEP sends the linktrace messages (LTMs) to the
target MEP. After receiving the messages, the target MEP 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 MEP. LTM frames are multicast frames and LTRs are unicast frames.
AIS
The AIS function suppresses the number of error alarms reported by MEPs. If a local MEP receives no
CCM frames from its peer MEP within 3.5 times the CCM transmission interval, it immediately starts to
send AIS frames periodically in the opposite direction of CCM frames. Upon receiving the AIS frames,
the peer MEP suppresses the error alarms locally, and continues to send the AIS frames. If the local MEP
receives CCM frames within 3.5 times the CCM transmission interval, it stops sending AIS frames and
restores the error alarm function. AIS frames are multicast frames.
TST
The TST function tests the bit errors between two MEPs. The source MEP sends a TST frame, which carries
the test pattern, such as pseudo random bit sequence (PRBS) or all-zero, to the target MEP. Upon receiving
the TST frame, the target MEP determines the bit errors by calculating and comparing the content of the
TST frame. TST frames are unicast frames.
Protocols and standards
• IEEE 802.1ag, Virtual Bridged Local Area Networks Amendment 5: Connectivity Fault
Management
• ITU-T Y.1731, OAM functions and mechanisms for Ethernet based networks
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 to each MD. Make sure that the same MD has the same name on different devices.
• Define the MA in each MD according to the VLAN you want to monitor.
• Assign a name to each MA. Make sure that the same MA in the same MD has the same name on
different devices.
• 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.
Complete the following tasks to configure CFD: