This section describes how to configure continuity check (CC) and connectivity verification (CV) for an LSP.
CC detects LOC on a link between any MEPs in a MEG. A MEP sends continuity check messages (CCMs) to its remote MEP (RMEP) at a specified interval. If the RMEP does not receive CCMs within a period of 3.5 times as long as the specified interval, the RMEP considers that the connectivity between the MEPs has errors, reports an alarm, and enters the Down state. After that, automatic protection switching (APS) is triggered on both MEPs. Upon receipt of a CCM from the MEP, the RMEP clears the alarm and exits from the Down state.
CV enables a MEP to report alarms when receiving unexpected packets. For example, if a CV-enabled device receives a packet from an LSP and finds that this packet is incorrectly transmitted through the LSP, the device will report an alarm indicating a forwarding error.
Transport networks have strict requirements on the correctness of data forwarding. In addition, MPLS-TP requires that the data plane should be able to work without IP support, which means that packet forwarding is based on label switching only. Therefore, the correctness of label-based forwarding must be ensured.
In practice, CC and CV are used together in the NetEngine 8000 F. The configurations for CC and CV are the same. Perform the following steps on a MEP and its RMEP:
The system view is displayed.
A MEG is created, and the MEG view is displayed.
Ensure that the same value is set on the MEP and RMEP; otherwise, an alarm will be generated.
To configure an interval at which CCMs are sent, run the cc interval interval-value command.
To configure a priority for CCMs, run the cc exp exp-value command.
If the MPLS-TP network is severely congested and the priority of CCMs is low, CCMs fail to be sent. Therefore, configure an appropriate priority for CCMs according to network conditions.
RDI is disabled.
RDI is enabled by default.
If an MEP detects a defect or fault, the RDI flag is set to 1 in CCMs. The MEP then sends the CCMs to the RMEP to notify it of the defect or fault.