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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 32 Configuring Ethernet OAM, CFM, and E-LMI
Understanding Ethernet CFM
The default continuity check message (CCM) interval on the switch is 10 seconds. You can set it to
be 100 ms, 1 second, 1 minute, or 10 minutes by entering the continuity-check interval Ethernet
service mode command. Because faster CCM rates are more CPU intensive, we do not recommend
configuring a large number of MEPs running at 100 ms intervals.
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Loopback messages—unicast or multicast frames transmitted by a MEP at administrator request to
verify connectivity to a particular maintenance point, indicating if a destination is reachable. A
loopback message is similar to an Internet Control Message Protocol (ICMP) ping message. Refer
to the ping ethernet privileged EXEC command.
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Traceroute messages—multicast frames transmitted by a MEP at administrator request to track the
path (hop-by-hop) to a destination MEP. Traceroute messages are similar in concept to UDP
traceroute messages. Refer to the traceroute ethernet privileged EXEC command.
Crosscheck Function and Static Remote MEPs
The crosscheck function is a timer-driven post-provisioning service verification between dynamically
configured MEPs (using crosscheck messages) and expected MEPs (by configuration) for a service. It
verifies that all endpoints of a multipoint service are operational. The crosscheck function is performed
only one time and is initiated from the command-line interface (CLI).
CFM 802.1ag also supports static remote MEPs or static RMEP check. Unlike the crosscheck function,
which is performed only once, configured static RMEP checks run continuously. To configure static
RMEP check, enter the continuity-check static rmep Ethernet CFM service mode command.
SNMP Traps and Fault Alarms
The MEPs generate two types of SNMP traps: CC traps and crosscheck traps. Supported CC traps are
MEP up, MEP down, cross-connect (a service ID does not match the VLAN), loop, and configuration
error. The crosscheck traps are service up, MEP missing (an expected MEP is down), and unknown MEP.
Fault alarms are unsolicited notifications sent to alert the system administrator when CFM detects a
fault. You can configure the priority level of alarms that trigger an SNMP trap or syslog message. You
can also configure a delay period before a fault alarm is sent and the time before the alarm is reset.
Configuration Error List
CFM configuration errors in CFM 802.1ag can be misconfigurations or extra configuration commands
detected during MEP configuration. They can be caused by overlapping maintenance associations. For
example, if you create a maintenance association with a VLAN list and a MEP on an interface, a potential
leak error could occur if other maintenance associations associated with the same VLAN exist at a higher
level without any MEPs configured. You can display the configuration error list, which is informational
only, by entering the show ethernet cfm errors configuration privileged EXEC command.
