DLDP Timers

DLDP uses the following timers.

**Table 1** DLDP timers
Timer	Description
Active timer	After DLDP is enabled and the link is Up or neighbor entries are cleared, the interface enters the Active state and starts the Active timer to send Advertisement packets with RSY tags. The default value of the Active timer is 1 second. The interface sends an Advertisement packet with an RSY tag every 1 second, and sends a maximum of five Advertisement packets. If no response packet is received after the interface sends five Advertisement packets with RSY tags, the Active timer times out and the interface enters the Advertisement state.
Advertisement timer	When an interface enters the Advertisement state, the interface starts the Advertisement timer and sends Advertisement packets. This timer determines the interval for sending Advertisement packets, which can be set using a command. The default value of the Advertisement timer is 5 seconds.
Probe timer	When receiving a packet from an unknown neighbor, the interface enters the Probe state and sends a probe packet to check for the unidirectional link. The interface in Probe state starts the Probe timer. This timer determines the interval for sending Probe packets (the default value is 1 second). A DLDP interface in Probe state sends two Probe packets every second.
Echo timer	This timer is triggered when DLDP transitions to the Probe state. The default value is 10 seconds. If an interface in Probe state does not receive any echo packet from a neighbor when the Echo timer times out, the interface status is set to unidirectional and the DLDP state machine transitions to the Disable state. In this case, the system records logs and alarms information and sends flush packets. In addition, the system shuts down or promotes the user to shut down the interface according to the DLDP Down mode, and deletes the neighbor entry.
Entry aging timer	When a new neighbor joins, a neighbor entry is created and the entry aging timer is triggered for the entry. When a DLDP packet is received from a neighbor, DLDP updates the corresponding neighbor entry and resets the entry aging timer depending on the following modes: In normal mode, if no DLDP packet is received from a neighbor when the corresponding entry aging timer times out, the local device sends Advertisement packets with RSY tags and deletes the neighbor entry. In enhanced mode, the enhanced timer is triggered if no DLDP packet is received from a neighbor when the entry aging timer times out. The value of the entry aging timer is three times the value of the Advertisement timer.
Enhanced timer	In enhanced mode, the enhanced timer is triggered if no DLDP packet is received from a neighbor when the entry aging timer times out. The local device consecutively sends eight probe packets to the neighbor, at the rate of 1 pps. If no echo packet is received from the neighbor when the enhanced timer times out, DLDP enters the Disable state. The value of the enhanced timer is 10 seconds.
DelayDown timer	In enhanced mode, when DLDP in Active, Advertisement, or Probe state detects a Port-Down event, it transitions to the DelayDown state instead of deleting the neighbor entry and transitioning to the Inactive state. At this time, the system reserves DLDP neighbor information and only responds to Port-Up events. If DLDP does not receive any Port-Up event when the DelayDown timer times out, DLDP deletes the neighbor entry and enters the Inactive state. If DLDP receives a Port-Up event before the DelayDown timer times out, DLDP returns to the previous state.
RecoverProbe timer	An interface in Disable state sends one RecoverProbe packet every 2 seconds to detect whether the unidirectional link fault is rectified. Upon receiving a RecoverEcho packet from the remote end, the local interface checks whether the neighbor information in the RecoverEcho packet is the same as that on the local interface. If they are the same, the link between the local interface and the neighbor has recovered. The local interface transitions from the Disable state to the Active state and reestablishes the neighbor relationship.