This notification is generated when a tunnel running over an interface as specified in the mplsFrrConstraintsTable is initially protected by the backup tunnel also specified in the mplsFrrConstraintsTable. In some implementations, there may be a difference between when the control plane triggers this notification and when the hardware is programmed to utilize the protection path. Due to the urgency of this operation, it is acceptable for the control plane to issue this notification either before or after it programs the hardware. In cases where it is the latter approach, the notification MUST be sent immediately after the data plane has been altered. This notification should not be generated for each subsequent tunnel that is backed up by the FRR feature on this LSR, as this may result in potential scaling issues with regard to LSR performance and network load. Note also that notifications MUST be generated in accordance with the mplsFrrNotificationsMaxRate.