41-3
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 41 Configuring Ethernet OAM, CFM, and E-LMI
Understanding Ethernet CFM
Figure 41-1 CFM Maintenance Domains
Figure 41-2 Allowed Domain Relationships
Maintenance Points
A maintenance point is a demarcation point on an interface that participates in CFM within a
maintenance domain. Maintenance points drop all lower-level frames and forward all higher-level
frames. There are two types of maintenance points:
• Maintenance end points (MEPs) are inward-facing points at the edge of the domain that define the
boundary and confine CFM messages within these boundaries. Inward facing means that they
communicate through the relay function side, not the wire side (connected to the port). A MEP sends
and receives CFM frames through the relay function. It drops all CFM frames of its level or lower
that come from the wire side. For CFM frames from the relay side, it processes the frames at its level
and drops frames at a lower level. The MEP transparently forwards all CFM frames at a higher level,
regardless of whether they are received from the relay or wire side. CFM runs at the provider
maintenance level (UPE-to-UPE), specifically with inward-facing MEPs at the user network
interface (UNI).
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Operator Domains
Service Provider Domain Level 6
Operator 1
PE 1CE 1 CE 2PE 2 PE 3 PE 4
Operator 2
MEP
Level 4 Level 4
Level 3
Level 2
MEP MEP
MIP
MIP MIP
MEP MEPMIP MIP
MIP MEP
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Scenario A:
Touching Domains OK
Scenario B:
Nested Domains OK
Scenario C:
Intersecting Domains Not
Allowed
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