Ethernet Operation, Administration and Management 802.1ag CFM
CFM MEP Monitoring and Analysis Tools
ML devices support several EFM mechanisms used for locating the source and cause of
network failures. These mechanisms operate using the capabilities provided by VLAN
endpoints configured as MEPs (on page 11-8) (required part of the provisioning procedure).
MEPs are able to originate ping (loopback) trace packets, and support continuity-check and
cross-check functionalities. These Layer-2 mechanisms are used for troubleshooting faults of
a customer service level.
The continuity-check mechanism can be used to determine which EVCs are impacted so the
service provider can identify the downed customer services. The operator can verify the loss
of connectivity using CFM loopback (on page 11-12) (ping), and locate the connection
failure using CFM link trace (on page 11-14). The problem can then be further diagnosed and
remedied. Finally, CFM loopback may be used to verify that the remedial action has
succeeded and that the service has been re-established.
The test options are available on the MEP Pane (on page 11-11). This section describes the
802.1ag analysis tools. Note the list of limitations that should be taken into account for
various types of MLs.
802.1ag supports the following analysis tools
NOTE: CFM MIB SNMP notifications are sent in a regular “SNMPv2 over UDP over IP over ETH”
way, a new transport “SNMP over ETH”, defined in IEEE802.1ag, is unsupported.
Continuity Check Messages (CCM) - these are Multicast heartbeat message(s) that are
exchanged periodically between MEPs. CCM enables MEP to discover other (remote)
MEPs within a (CFM) domain. In addition, CCMs allow detection of configuration
mismatch in an MA (802.1ag) or MEG (Y.1731) and remote MEP defect indication
(RDI).
An RDI signal is sent by MEPs that do not receive a CCM from a discovered Remote
MEP during "RMEP self-defined interval" x 3.5. The RDI signal received from the
Remote MEP is immediately reported (by the ML) as a RDI alarm on MEP AID via TL1
or as dot1cfmFaultAlarm trap via SNMP.
Linktrace messages (on page 11-14)
Loopback Messages (on page 11-12)
Limitations
ML aggregated switch specific: CFM Traffic is dropped when passing through Ethernet
Ports configured with stacked membership. In such deployments, in order to pass the
ML230/ML2300 device transparently, no CFM domains shall be configured on the NE.
ML50 specific: When configured as CPE, ML50 passes transparently CFM PDU
received on the port only if Stacked VLAN is configured on this port. In all other
configurations CFM PDU received on a port will be dropped if found as not matching to
ETH type configured by ED-BRIDGE on ML50.
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