Installation and User Manual
EtherHaul
1200™
EH-INST-02, Issue 4.0
Page 87
7.2.1
CFM Overview
Connectivity Fault Management (CFM) is an Ethernet layer operation, administration,
and management (OAM) protocol designed to monitor and troubleshoot networks. CFM
enables you to detect, verify, and isolate connectivity failures in virtual bridged local
area networks.
A Maintenance Domain (MD) is a part of a network that is controlled by a single
operator and used to support the connectivity between service access points. There are
eight hierarchical Maintenance Domain Levels (MD Level). Each CFM layer supports
OAM capabilities independently, with the customer at the highest level, the provider in
the middle, and the operator at the lowest level.
CFM is designed to be transparent to the customer data transported by the network and
to provide maximum fault coverage. These capabilities are used in networks operated
by multiple independent organizations, each with restricted management access to each
other’s equipment.
CFM entities support an individual service instance as Maintenance Association End
Points (MEPs) are configured to create a Maintenance Association (MA). The MA
monitors connectivity provided by that instance through the Maintenance Domain.
Maintenance Association Intermediate Points (MIPs) are the intermediate points in a
specific MA or MD.
The major features of CFM are fault detection, path discovery, fault verification, fault
isolation, and fault recovery.
7.2.1.1
Fault Detection
A Continuity Check protocol detects both connectivity failures and unintended
connectivity between service instances (heartbeat). Each MEP can periodically transmit
a multicast Connectivity Check Message (CCM) announcing the identity of the MEP and
its MA, and tracks the CCMs received from the other MEPs.
7.2.1.2
Path Discovery
The path is determined by the linktrace (L2 Trace Route). Linktrace messages (LTM) are
multicast from the originating MEP to the target MAC (MIP or MEP)/MEP ID. Linktrace
replies (LTR) are unicast from the target (or MIPs on route) to the orig inating MEP.
7.2.1.3
Fault Verification and Isolation
A Loopback protocol performs fault verification, typically after fault detection. An MEP
can be ordered to transmit a unicast Loopback Message (LBM) to an MEP or MIP in the
MA. The receiving MP responds by transforming the LBM into a unicast Loopback Reply
(LBR) sent back to the originating MEP.
