In some cases, the requirement exists to prevent a MEP from entering the defRemoteCCM defect, remote peer timeout, for more time than the standard 3.5 times the ccm-interval. Both the IEEE 802.1ag standard and ITU-T Y.1731 recommendation provide a non-configurable 3.5 times the CCM interval to determine a peer time out. However, when sub-second CCM timers (10 ms/100 ms) are enabled, the carrier may want to provide additional time for different network segments to converge before declaring a peer lost because of a timeout. To maintain compliance with the specifications, the ccm-hold-timer down delay-down option artificially increases the amount of time it takes for a MEP to enter a failed state if the peer times out. This timer is only additive to CCM timeout conditions. All other CCM defect conditions, like defMACStatus, defXconCCM, and so on, maintain their existing behavior of transitioning the MEP to a failed state and raising the correct defect condition without delay.
When the ccm-hold-timer down delay-down option is configured, the following calculation is used to determine the remote peer time out: 3.5 ✕ ccm-interval + ccm-hold-timer down delay-down.
This command is configured under the association. Only sub-second CCM-enabled MEPs support this hold timer. Ethernet tunnel paths use a similar but slightly different approach and continue to use the existing method. Ethernet tunnels are blocked from using this new hold timer.
It is possible to change this command on the fly without deleting it first. Entering the command with the new values change the values without having to first delete the command.
It is possible to change the ccm-interval of a MEP on the fly without first deleting it. This means it is possible to change a sub-second CCM-enabled MEP to 1 second or more. The operator is prevented from changing an association from a sub second CCM interval to a non-sub second CCM interval when a ccm-hold-timer is configured in that association. The ccm-hold-timer must be removed using the no option before allowing the transition from sub second to non-sub second CCM interval.