If a DLDP interface in Active, Advertisement, or Probe state receives a Port-Down event, the interface enters Inactive state and clears the neighbor information. In some cases, the interface is Down for a short time. For example, failure of the Tx fiber on an interface may cause jitter of optical signals on the Rx fiber, which makes the interface Down and then Up again. To prevent the neighbor information from being deleted immediately in this case, the DLDP interface first enters the DelayDown state and starts the DelayDown timer. Before the DelayDown timer times out, the interface retains the neighbor information and responds to only Port-Up events.
If the DLDP interface does not receive any Port-Up event when the DelayDown timer times out, the interface enters the Inactive state and deletes the neighbor entry.
If the DLDP interface receives the Port-Up event before the DelayDown timer times out, the interface returns to the previous state.