+ <p>
+ Indicates a connectivity fault triggered by an inability to receive
+ heartbeats from any remote endpoint. When a fault is triggered on
+ <ref table="Interface"/>s participating in bonds, they will be
+ disabled.
+ </p>
+ <p>
+ Faults can be triggered for several reasons. Most importantly they
+ are triggered when no CCMs are received for a period of 3.5 times the
+ transmission interval. Faults are also triggered when any CCMs
+ indicate that a Remote Maintenance Point is not receiving CCMs but
+ able to send them. Finally, a fault is triggered if a CCM is
+ received which indicates unexpected configuration. Notably, this
+ case arises when a CCM is received which advertises the local MPID.
+ </p>
+ </column>
+
+ <column name="cfm_fault_status" key="recv">
+ Indicates a CFM fault was triggered due to a lack of CCMs received on
+ the <ref table="Interface"/>.
+ </column>
+
+ <column name="cfm_fault_status" key="rdi">
+ Indicates a CFM fault was triggered due to the reception of a CCM with
+ the RDI bit flagged. Endpoints set the RDI bit in their CCMs when they
+ are not receiving CCMs themselves. This typically indicates a
+ unidirectional connectivity failure.
+ </column>
+
+ <column name="cfm_fault_status" key="maid">
+ Indicates a CFM fault was triggered due to the reception of a CCM with
+ a MAID other than the one Open vSwitch uses. CFM broadcasts are tagged
+ with an identification number in addition to the MPID called the MAID.
+ Open vSwitch only supports receiving CCM broadcasts tagged with the
+ MAID it uses internally.
+ </column>
+
+ <column name="cfm_fault_status" key="loopback">
+ Indicates a CFM fault was triggered due to the reception of a CCM
+ advertising the same MPID configured in the <ref column="cfm_mpid"/>
+ column of this <ref table="Interface"/>. This may indicate a loop in
+ the network.
+ </column>
+
+ <column name="cfm_fault_status" key="overflow">
+ Indicates a CFM fault was triggered because the CFM module received
+ CCMs from more remote endpoints than it can keep track of.
+ </column>
+
+ <column name="cfm_fault_status" key="override">
+ Indicates a CFM fault was manually triggered by an administrator using
+ an <code>ovs-appctl</code> command.
+ </column>
+
+ <column name="cfm_fault_status" key="interval">
+ Indicates a CFM fault was triggered due to the reception of a CCM
+ frame having an invalid interval.
+ </column>
+
+ <column name="cfm_remote_opstate">
+ <p>When in extended mode, indicates the operational state of the
+ remote endpoint as either <code>up</code> or <code>down</code>. See
+ <ref column="other_config" key="cfm_opstate"/>.
+ </p>
+ </column>
+
+ <column name="cfm_health">
+ <p>
+ Indicates the health of the interface as a percentage of CCM frames
+ received over 21 <ref column="other_config" key="cfm_interval"/>s.
+ The health of an interface is undefined if it is communicating with
+ more than one <ref column="cfm_remote_mpids"/>. It reduces if
+ healthy heartbeats are not received at the expected rate, and
+ gradually improves as healthy heartbeats are received at the desired
+ rate. Every 21 <ref column="other_config" key="cfm_interval"/>s, the
+ health of the interface is refreshed.
+ </p>
+ <p>
+ As mentioned above, the faults can be triggered for several reasons.
+ The link health will deteriorate even if heartbeats are received but
+ they are reported to be unhealthy. An unhealthy heartbeat in this
+ context is a heartbeat for which either some fault is set or is out
+ of sequence. The interface health can be 100 only on receiving
+ healthy heartbeats at the desired rate.
+ </p>
+ </column>
+
+ <column name="cfm_remote_mpids">
+ When CFM is properly configured, Open vSwitch will occasionally
+ receive CCM broadcasts. These broadcasts contain the MPID of the
+ sending Maintenance Point. The list of MPIDs from which this
+ <ref table="Interface"/> is receiving broadcasts from is regularly
+ collected and written to this column.
+ </column>
+
+ <column name="other_config" key="cfm_interval"
+ type='{"type": "integer"}'>
+ <p>
+ The interval, in milliseconds, between transmissions of CFM
+ heartbeats. Three missed heartbeat receptions indicate a
+ connectivity fault.
+ </p>
+
+ <p>
+ In standard operation only intervals of 3, 10, 100, 1,000, 10,000,
+ 60,000, or 600,000 ms are supported. Other values will be rounded
+ down to the nearest value on the list. Extended mode (see <ref
+ column="other_config" key="cfm_extended"/>) supports any interval up
+ to 65,535 ms. In either mode, the default is 1000 ms.
+ </p>
+
+ <p>We do not recommend using intervals less than 100 ms.</p>
+ </column>
+
+ <column name="other_config" key="cfm_extended"
+ type='{"type": "boolean"}'>
+ When <code>true</code>, the CFM module operates in extended mode. This
+ causes it to use a nonstandard destination address to avoid conflicting
+ with compliant implementations which may be running concurrently on the
+ network. Furthermore, extended mode increases the accuracy of the
+ <code>cfm_interval</code> configuration parameter by breaking wire
+ compatibility with 802.1ag compliant implementations. And extended
+ mode allows eight byte MPIDs. Defaults to <code>false</code>.
+ </column>
+
+ <column name="other_config" key="cfm_demand" type='{"type": "boolean"}'>
+ <p>
+ When <code>true</code>, and
+ <ref column="other_config" key="cfm_extended"/> is true, the CFM
+ module operates in demand mode. When in demand mode, traffic
+ received on the <ref table="Interface"/> is used to indicate
+ liveness. CCMs are still transmitted and received. At least one
+ CCM must be received every 100 * <ref column="other_config"
+ key="cfm_interval"/> amount of time. Otherwise, even if traffic
+ are received, the CFM module will raise the connectivity fault.
+ </p>
+
+ <p>
+ Demand mode has a couple of caveats:
+ <ul>
+ <li>
+ To ensure that ovs-vswitchd has enough time to pull statistics
+ from the datapath, the fault detection interval is set to
+ 3.5 * MAX(<ref column="other_config" key="cfm_interval"/>, 500)
+ ms.
+ </li>
+
+ <li>
+ To avoid ambiguity, demand mode disables itself when there are
+ multiple remote maintenance points.
+ </li>
+
+ <li>
+ If the <ref table="Interface"/> is heavily congested, CCMs
+ containing the <ref column="other_config" key="cfm_opstate"/>
+ status may be dropped causing changes in the operational state to
+ be delayed. Similarly, if CCMs containing the RDI bit are not
+ received, unidirectional link failures may not be detected.
+ </li>
+ </ul>
+ </p>