A maintenance domain is a management space for managing and administering a network. A domain is owned and operated by a single
entity and defined by the set of ports internal to the domain and at its boundary. A maintenance association identifies a
service that can be uniquely identified within the maintenance domain. The CFM protocol runs within a maintenance association.
A maintenance end point (MEP) is a demarcation point on an interface that participates in CFM within a maintenance domain.
MEPs drop all lower-level frames and forward all higher-level frames. MEPs are defined per maintenance domain (level) and
service (S-VLAN or ethernet virtual circuit (EVC)). They are at the edge of a domain and define the boundary and confine CFM
messages within that boundary. MEPs can proactively transmit CFM continuity check messages (CCMs) and at the request of an
administrator, transmit traceroute, and loopback messages.
A down MEP sends and receives CFM frames through the wire connected to the port on which the MEP is configured. For CFM frames
coming from the relay side, the down MEP drops all lower-level frames and those that are at its level. For CFM frames coming
from the wire side, the down MEP processes all frames at its level and drops lower-level frames, except for traffic going
to the other lower level down MEP. The MEP transparently forwards all CFM frames at a higher level, regardless of whether
they are received from the relay or through the wire.
In order to deploy down MEP per subinterface, you must first create a EVC+VLAN maintenance association, configure the VLAN
id under the subinterface, and then configure down MEP under the parent interface of that subinterface.
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