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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 75 Configuring Ethernet OAM and CFM
About Ethernet CFM
If port on which the MEP is configured is blocked by Spanning-Tree Protocol (STP), the MIP can receive
and might respond to CFM messages from both the wire and relay side, but cannot forward any CFM
messages. This differs from CFM draft 1, where STP blocked ports could not send or receive CFM
messages.
CFM Messages
CFM uses standard Ethernet frames distinguished by EtherType or (for multicast messages) by MAC
address. All CFM messages are confined to a maintenance domain and to a service-provider VLAN
(S-VLAN). These CFM messages are supported:
• Continuity Check (CC) messages—multicast heartbeat messages exchanged periodically between
MEPs that allow MEPs to discover other MEPs within a domain and allow MIPs to discover MEPs.
CC messages are configured to a domain or VLAN. Enter the continuity-check Ethernet service
configuration command to enable CCM.
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.
• 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.
• 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 verifies a post-provisioning timer-driven service 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. In CFM draft 1, fault alarms were sent instantaneously when detected. In CFM 802.1ag, 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.
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