Ethernet Connectivity Fault Management is defined in IEEE 802.1ag standard. It provides the capability useful for detecting, verifying and isolating connectivity failures in Ethernet Networks and can be used in networks operated by multiple independent organizations which are restricted only access to each other's equipments.
The Layer 2 network that is managed will be divided into different Maintenance Domains. A maintenance domain (MD) is an administrative domain for managing and administering a network. The Maintenance Domain provides management and hierarchy. A domain is assigned a unique maintenance level (up to 8) by the administrator.
The figure below is an example of the application of CFM. Four switches SW1 to SW4 are directly connected in a linear topology. SW3 and SW4 devices from Operator and SW1 and SW2 are devices from Operator who provide service to Provider.