About DLDP
Physical layer detection mechanisms, such as auto-negotiation, can detect physical signals and faults. However, they cannot detect communication failures for unidirectional links where the physical layer is in connected state.
As a data link layer protocol, the Device Link Detection Protocol (DLDP) can do the following:
Monitor status of the fiber link or twisted-pair link at the link layer.
Cooperate with physical layer protocols to detect whether the link is correctly connected and whether the two ends of the link can exchange packets correctly.
When DLDP detects unidirectional links, it can automatically shut down the faulty port to avoid network problems. Alternatively, a user can manually shut down the faulty port.