CFD levels
MD levels
To accurately locate faults, CFD introduces eight levels (from 0 to 7) to MDs. The bigger the number, the higher the level and the larger the area covered. Domains can touch or nest (if the outer domain has a higher level than the nested one) but cannot intersect or overlap.
MD levels facilitate fault location and make fault location more accurate. As shown in Figure 2, MD_A in light blue nests MD_B in dark blue. If a connectivity fault is detected at the boundary of MD_A, any of the devices in MD_A, including Device A through Device E, might fail. If a connectivity fault is also detected at the boundary of MD_B, the failure points can be any of Device B through Device D. If the devices in MD_B can operate correctly, at least Device C is operational.
Figure 2: Two nested MDs
CFD exchanges messages and performs operations on a per-domain basis. By planning MDs correctly in a network, you can use CFD to rapidly locate failure points.
MA and MP levels
The level of an MA equals the level of the MD to which the MA belongs.
The level of a MEP equals the level of the MD to which the MEP belongs.
The level of a MIP is defined by its generation rule and the MD to which the MIP belongs. MIPs are generated on each port automatically according to the following MIP generation rules:
Default rule—If no lower-level MIP exists on an interface, a MIP is created on the current level. A MIP can be created even if no MEP is configured on the interface.
Explicit rule—If no lower-level MIP exists and a lower-level MEP exists on an interface, a MIP is created on the current level. A MIP can be created only when a lower-level MEP is created on the interface.
If a port has no MIP, the system will check the MAs in each MD (from low to high levels), and follow the procedure as described in Figure 3 to create or not to create MIPs at the current level.
Figure 3: Procedure of creating MIPs
CFD grading example
Figure 4 demonstrates a grading example of the CFD module. Four levels of MDs (0, 2, 3, and 5) are designed. The bigger the number, the higher the level and the larger the area covered. MPs are configured on the ports of Device A through Device F. Port A of Device B is configured with the following MPs:
A level 5 MIP.
A level 3 inward-facing MEP.
A level 2 inward-facing MEP.
A level 0 outward-facing MEP.
Figure 4: CFD grading example
