An interface that is manually shut down cannot automatically go Up using the link auto-recovery mechanism.
An interface that is automatically shut down can automatically go Up using the link auto-recovery mechanism.
In automatic shutdown mode, DLDP sets the interface state to DLDP Down when detecting a unidirectional link. A DLDP Down interface receives and forwards only BPDUs, not user traffic. A DLDP Down interface can be recovered upon link recovery. The DLDP Down interface periodically sends RecoverProbe packets. If the interface receives correct RecoverEcho packets, the unidirectional link becomes a bidirectional link and the interface becomes Up.
The link auto-recovery process is as follows:
The DLDP Down interface sends one RecoverProbe packet every 2 seconds. A RecoverProbe packet carries only information about the local interface.
Upon receiving a RecoverProbe packet, the remote end returns a RecoverEcho packet.
When receiving the RecoverEcho packet, 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 Active state and re-establishes the neighbor relationship.