15
Configuring CFD
Overview
Connectivity Fault Detection (CFD) is an end-to-end per-VLAN link layer OAM mechanism used for link
connectivity detection, fault verification, and fault location. It conforms to IEEE 802.1ag CFM and ITU-T
Y.1731.
Basic CFD concepts
This section explains the concepts of CFD.
MD
A maintenance domain (MD) defines the network or part of the network where CFD plays its role. An MD
is identified by its MD name.
To accurately locate faults, CFD assigns eight levels ranging from 0 to 7 to MDs. The bigger the number,
the higher the level, and the larger the area covered. If the outer domain has a higher level than the
nested one, domains can touch or nest, but they cannot intersect or overlap.
MD levels facilitate fault location and its accuracy. As shown in Figure 3, MD_A in li
ght 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, may fail. If a connectivity fault is also detected at the boundary of
MD_B, the failure points may be any of Device B through Device D. If the devices in MD_B can operate
properly, at least Device C is operational.
Figure 3 Two nested MDs
CFD exchanges messages and performs operations on a per-domain basis. By planning MDs properly
in a network, you can use CFD to rapidly locate failure points.
MA
A maintenance association (MA) is a part of an MD. You can configure multiple MAs in an MD as
needed. An MA is identified by the "MD name + MA name".
Device A Device B Device C Device D
Device E
MD_A
MD_B
VLAN 100
Port
Port2
Port1 Port3
Port2
Port1 Port3
Port2
Port1 Port3
Port2
Port1 Port3
Port2
Port1 Port3
Port4 Port4 Port4 Port4
Port4
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